Signs of Summer 6: A Good (Bad?”) Year For Ticks

Photo by D. Sillman

Ticks are a recurring topic on the pages of this blog. We are exploring the ecology of Western Pennsylvania, after all, and Pennsylvania has been experiencing a population explosion of black legged ticks and is also the epicenter of the national Lyme disease epidemic. So ticks and their symbionts have to be a part of our discussions!

A quick review of what we know about black legged ticks and the bacterium that causes Lyme disease:

The black-legged tick (Ixodes scapularis) (formerly called the “deer tick”) is a small, common tick found throughout the northeastern and north-central parts of the United States. It is the transmission vector for a number of bacterial and viral pathogens including the bacterium that causes Lyme disease, Borrelia burgdoferi. For the last five years, Pennsylvania has led the nation in the number of human cases of Lyme disease and the number of cases is growing each year (From the Center for Disease Control, human Lyme disease cases in Pennsylvania: preliminary 2016 (12,092 cases), 2015 (9000 cases), 2014 (7400 cases), 2013 (5900 cases)).

The life cycle of the black-legged can involve combinations of over one hundred different potential hosts (fifty-two different species of mammals, sixty species of birds, and eight species of reptiles) and can stretch out over a two or even a three year period with staggered emergences of different instar stages during different months of the year. Also, early instars of this tick are extremely small and difficult to see!  Below is an idealized version of the life cycle that I described in a blog a few years ago:

Photo by California department of Public Health (Flickr)

Eggs deposited in the fall in low, grassy or scrubby vegetation hatch the next summer into the very small, six-legged larva life forms. These tiny ticks typically seek out small hosts (white-footed mice (Peromyscus leucopus) seem to be the preferred host for this life stage) but are able opportunistically to attach to larger mammals, too, including humans. These larva, though, are not born with any of the pathogens associated with Ioxdes scapularis and are, thus, unable to transmit any of its diseases (a small piece of good news!). If these larvae feed on a host that is carrying one of I. scapularis’ bacterial or viral pathogens, though, that tick will become infected with that disease causing agent and will carry it and be able to transmit it throughout the rest of its life cycle.

After the larva has taken its blood meal it molts into the larger, eight-legged nymph life form. This molt often is delayed until the following spring. These nymphs, then, seek a host for their blood meal. These hosts are usually mammals ranging in size from white-footed mice to dogs to cats to deer to humans. Because of the timing of this nymph emergence the spring (May and June here in Western Pennsylvania) is a time of great risk for ticks bites (and disease transmission) for humans!

Photo by D. Sillman

After the nymphs have taken their blood meals they molt into adults. These adults are especially abundant in the fall. These much larger ticks (like the one in the picture to the left) typically attach to large mammals. The female adult ticks take a large blood meal from their hosts and then use the energy from this feeding to make eggs. The adult male ticks attach to the same hosts, but do not feed (and, therefore, do not transmit pathogens at this stage). They are there to find a female and to mate! The males die shortly after mating and the females die after dropping off of their hosts to lay their eggs in the grassy and scrubby vegetation. Those eggs then overwinter and hatch in the summer to start the life cycle all over again.

So why have the number of Lyme disease cases increased in recent years? Media reports stress the “common sense” inference that our increasingly warm winters (possibly due to climate change) are leading to increased survival of the ticks and increased spring and summer populations. Unfortunately, scientific research does not support this logical connection. A study published in 2012 in the Journal of Medical Entomology clearly showed that in spite of “common knowledge” to the contrary, cold winters (and they used Upstate New York as their cold winter site!) do not reduce the numbers of overwintering black-legged ticks. The ticks just have too many adaptations for cold tolerance and too many protected microhabitats available for even the brutal winter temperatures of New York State to have any effect on them at all.

Most researchers looking at these ticks attribute their increases to increases in the most critical host in the black-legged tick’s life cycle: the white-footed mouse. Fragmentation of forest habitats and the optimal conditions of suburban ecosystems for these mice along with significant declines in their natural predators have led to great increases in their numbers. Black legged ticks, then, in their larval and nymphal life stages are increasingly likely to find a white-footed mouse on which to feed and are, therefore, increasingly likely to survive to the next instar level. White-footed mice are also significant reservoirs for the Lyme disease bacterium, so the ticks have a higher probability of assimilating and then passing on these bacteria.

Weather and climate factors can have an impact on populations of white-footed mice, but it is not temperature that is the most important weather/climate feature but precipitation. Wet and humid conditions favor the growth of the plants upon which white-footed mice feed and thus can lead to increased population sizes. More white-footed mice means that nymphal black-legged ticks have an increased chance of finding its ideal “blood meal” host thus increasing the numbers of later instar stages.  Further, right after a black-legged tick has taken its blood meal its ability to control its body water concentration is greatly impaired. A tick, then, right after a blood meal is very likely to die if it encounters a dry environment. Increased precipitation and higher relative humidity, then, also favors survival of the tick!

Photo by Jamaine Wikimedia Commons

An article in the Wall Street Journal this past April (sent to me by my WSJ watcher, Larry in California!) warned of a “bad summer for ticks” because of the mild winter (probably not) and because of the 2015 “bumper crop” of acorns in the Northeast! These acorns fed more white-footed mice which in turn sustained (and infected) more black-legged ticks! The adults of the tick explosion are out there this year searching for their last blood meal!

Your best defense against Lyme disease is a “tick check” after any potential tick exposure. Remember, the ticks may be anywhere that white-footed mice might live (yards, fields, woods, etc.). The ticks have to be attached to you for 36 hours before they can begin to transfer the Lyme bacterium. Use a tick puller and dispose of the tick in a creative manner (drown them in alcohol or flush them down the toilet). Don’t let the threat of ticks keep you from the woods or hiking trails!

The story of the Lyme disease vaccines is very interesting, by the way! I will talk about that in a future blog!

 

 

 

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Signs of Summer 5: Leaf Shapes (and great questions!)

Photo by D. Sillman

A couple of weeks ago I got an email from a Seventh Grade student named Gordon. Gordon was doing a Life Science project that involved coming up with a question that could not be answered by simply doing a Google search. Gordon’s question was, “What determines each tree’s type of leaf and their structure?”  Gordon found my essay out on the Virtual Nature Trail about leaf shapes and strategies and thought that I would be a good person to possibly answer his question. Here is my answer! My compliments to Gordon for coming up with such an interesting question and also to Gordon’s science teacher for coming up with such a creative and meaningful project!

 

Gordon:

What a great question!

Leaves are incredibly important to any plant since they are the organs where photosynthesis occur. Since the shape of a leaf is controlled by a number of very specific genes most scientists feel that natural selection and evolution must have played a role in determining leaf shape. It is not clear, though, what exact factors in a tree species’ ecological and evolutionary environment were the determining, natural selection variables for leaf shape.

Looking at the extremes of leaf shapes (needle shaped leaves vs. broad, flat leaves) (and this is what I wrote about in the on-line essay that you found), it is pretty clear what evolutionary factors were in play: needles can withstand the very dry and very cold conditions of winter and, thus, persist for many years on a tree. Broad leaves cannot handle the dryness and freezing conditions of winter, but they are more efficient photosynthesizing organs! So a tree balancing its energy demands either makes a leaf (a needle) that lasts for several photosynthesizing seasons but generates, each season, less sugar from photosynthesis, or it makes a single season leaf (the broad leaf) which generates a lot of sugar in one season and then “throws the leaf away” in the Fall! You would expect in colder or drier environments the “needle leaf” solution would work best for a tree!

Looking at overall leaf size, it is also pretty clear which selection factors are at work: in any type of stressful environment (very cold, very hot, very dry, low nutrient, or high salt conditions) trees tend to make very small leaves. These leaves, while less efficient in photosynthesis than large leaves, match the energy balances required for the tree to survive under these very stressful conditions.

All of the more subtle differences in leaf shape, though, are much harder to explain! There are a few really interesting hypotheses, though.

First of all, when a leaf develops on a tree its tissues (where the cells are that contain the chlorophyll that accomplish photosynthesis) develop and grow around the leaf’s vascular tissues (its “veins”). These leaf veins bring water to the photosynthetic cells and take away the sugars that they make in photosynthesis. Overall leaf shape seems to be correlated to the energy efficiency of this water delivery/sugar transport system! Each photosynthetic cell has to be close to a leaf vein! Lots of different shapes can “solve” this energy requirement successfully!

Also, when sunlight hits a leaf LOTS of heat is generated! So the leaf, when it photosynthesizes must dissipate this excess heat out to its environment. Some of the sculpting of the leaf edges (the serrations and deep invaginations into the leaf mass) may be related to solving the problem of efficient heat dissipation.

Here are a couple of types of oak leaves that illustrate these ideas: (the images are from Wikivisual and are listed under Creative Commons usage rights):

Chestnut oak leaf

You see the leaf veins in each type of leaf, and you can imagine the leaf forming by growing the leaf tissue around those veins. The close proximity of the leaf tissue to the veins sets up a very efficient water delivery/sugar exporting system! The deep invaginations of the pin oak leaf, though, means that although there is less leaf tissue for photosynthesis, there is more efficient heat dissipation from the leaf! The balance between overall photosynthesis rates and heat dissipation may be the factors determining the subtle differences in the shapes of a particular

Pin oak leaf

tree species’ leaves! Not surprisingly, chestnut oaks tend to grow in colder environments, and pin oaks tend to grow in warmer environments!

Thank you for your wonderful question! I plan to use some of my answer in my weekly ecology blog sometime this summer! I will be sure to give you credit for the question! You can find my blog at http://sites.psu.edu/ecologistsnotebook/

Keep enjoying science!

Dr. Hamilton

Department of Biology

Penn State New Kensington

There are a few other possible variables that might be important in some leaf shape natural selection systems. Plants growing in environments with low light levels might show evolutionary patterns for shapes that optimize light reception. Other plants under intense herbivore pressures might show selection patterns for shapes that resist that herbivory. Leaf shape might also be subject to the complex constraints of biomechanical factors and overall structural integrity of the leaf. There are also a number of hypotheses that consider leaf shape the consequence of selection for genes that code for completely different features of the tree (like flower shape, for example). The impact of these genes on the development and shape of the leaves, then, is just an inadvertent tie-in to the actual selection for that different factor!

I can imagine some experiments that should be conducted to explore this question. For example, do the leaves of a northern red oak (which have very subtle edge invaginations) photosynthesize better than the leaves of a scarlet oak (which have very pronounced edge invaginations) in cooler environments? Or, do those scarlet oak leaves photosynthesize better that northern red oak in warmer environments? Or, do these very different leaf shapes have no effect on their efficiency of photosynthesis? Experiments like these could help to focus the evolutionary discussion of leaf shape and help to define the significance of its possible natural selection variables.

 

 

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Signs of Summer 4: Fledglings in the Yard

Photo by D. Sillman

Watching the fledglings around my yard:

A robin with a juvenile speckled breast follows an adult around my concrete slab basketball court. You assume the adult is teaching the fledgling how to find food, but the fledgling seems to be staring off into space rather than watching what the adult is doing. The adult frequently finds worms and larvae and insects in the slab cracks of the court and instantly the fledgling pops out of its mental fog and rushes up to the adult. She flutters her wings and chirps and puts her open beak an inch away from the adult. The adult stuffs whatever she found into the fledgling’s mouth and then goes back to hunting. The fledgling does not seem aware of the process, only the end result.

Photo by I. Taylor. Wikimedia Commons

The front yard crows made their nest up in the red pines of my street-side woodlot. I watched them back in early April flying in and out of the pines with great beaks full of sticks and grass. A couple of weeks ago a fledgling (as large as the adult she was following but not quite as glossy black) showed up at the morning peanut and shelled corn feast out under my sunflower feeders. The fledgling watched the adult crow closely and raised her wings and shook her head when the adult picked up a peanut or a piece of corn. That went on for several days until finally all of the morning crows were independently gathering their breakfast bits. The fledgling still shows himself through the day by lingering in the yard even when I step off the porch, or by not immediately flying to the high, safe perches when cars or dogs or cats cruise by. Breakfast was an easy lesson, there are many harder things that a young crow needs more days (and weeks) to learn. Two adult crows frantically chased off a sharp-shinned hawk yesterday afternoon. The crow fledgling just sat out in the middle of the field agitated by all of noise but uncertain as what to do.

This morning when I went out to fill the bird feeders a house finch fledgling kept her spot on the perch of my hopper feeder even after I opened the top and began to pour in a scoop of sunflower seeds. She only flew when the noise (or vibration?) of the falling seeds rattled her perch.

Photo by K. Thomas, USFWS Public Domain

Also this morning a cardinal fledgling was standing on the sidewalk and let me walk right past her as I went in and out of the porch door. No fear. No flight. As I sit at my writing desk, I am watching an adult male cardinal jumping down into the leaf compost pile out in the backyard.  He grabs the odd wiggler or tidbit from the compost and then jumps back up on the surrounding wire fence to give the morsel to his fluttering fledgling. When he hops back into the compost the fledgling freezes in place. When he hops back up she flutters like mad and chirps. This goes on for fifteen minutes and then they both fly away.

A Carolina wren and her fledgling are chirping loudly in the lower branches of the arbor vitae. They are being incredibly conspicuous in a zone frequently prowled by the neighborhood cats! The fledgling, though, can’t seem to keep her volume down when the parental bird is in sight! I

Photo by D. Sillman

have watched the adult stick her beak into the open beak of the fledgling. I can only imagine the tasty mix of branch-gleaned insects and larvae that she is sharing! The adult immediately moves up to higher branches to keep hunting. The fledgling sits down low, in the danger zone, waiting for more. Later the wren and the fledgling join us on the deck. The fledgling sits on the surrounding fence like a Christmas ornament while the adult frets and fusses.

The mortality rate of these fledglings is incredible. Probably half of them won’t make it to their one or two month birthday. Predators can just walk up to them (or swoop down on them) and grab a quick snack, and the learning curves for self-sustained food gathering are incredibly steep. Many of them have only just figured out the basic physics of flying, but they are having difficulties avoiding obstacles like branches or buildings. Windows especially are something that takes a long time to understand. Some of the fledglings will be eaten, others will starve, some will break their necks or wings in collisions, and then their parents (the creme-de-la-crème from their own generations!) will start all over again.

Photo by Neonorange, Wikimedia Commons

I mentioned the geese down on Roaring Run a few weeks ago. I was on a bike ride and saw two adult Canada geese with six brand new, feather-fuzzy goslings. The parent’s both hissed at me as I biked past (bringing back some really vivid memories of being chased by goose when I was a kid (I climbed up into an apple tree to get away!)). Well, the next week there were only four goslings. Today, there were only three. The parents still hissed when I rode past, but they don’t seem to have the same energy they did when they had their full family.

The fledglings are born without fear and without any innate hunting behaviors. Both must be learned very quickly if they are to go to the head of their generation and have the chance to mate and pass along their DNA. The slaughter of the young, though, like Malthus inferred and Darwin described, sculpts the population (and the species) into its wild, functional form. If all of these baby birds survived, the population would be full of inept buffoons who had no idea of what it really meant to be a bird!

Good news! The robin fledgling is by herself on the basketball court. She is hopping from crack to crack and probing the weeds with her sharp beak. I haven’t seen her catch anything yet, but she is making all of the right moves! She will graduate from her juvinile spots soon, I am sure!

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Signs of Summer 3: The Bluebirds of Harrison Hills Park

Photo by D. Sillman

The Cavity Nesting Team is back for its third consecutive season in Harrison Hills Park in northern Allegheny County! The team (which includes Mardelle and Patrick Kopnicky, Sharon Svitek, Odessa Garlitz, Chris Urik, Paul Dudek, Kathy and Dave Brooke, and Deborah and I) monitor and maintain the 28 “bluebird boxes” scattered around the park and record weekly data on the nests, eggs, and hatchlings in each box. In 2015 and 2016 the team made some important observations on nest box location preferences for our cavity nesting species (including bluebirds, tree swallows, chickadees, and house wrens) and on seasonal timing of their reproduction and the influences of environmental variables on reproductive rates for each of our species. I summarized these data in my “Signs of Fall 2” (September 22, 2016).

The experimental objectives this year involve two ideas: 1. Can we orient the nest boxes in a way to reduce their use by house wrens? (House wrens are very active nest predators and nest box usurpers and have significant impacts on both bluebird and tree swallow reproduction). And 2. Are there any of our cavity nesting species utilizing natural tree cavities for their nests?

Photo by dfaulder, Wikimedia Commons

Our plan for Objective #1 involves active removal of house wren “dummy nests” from our nesting boxes. These dummy nests are built by male house wrens as displays designed to attract females. Since these nests do not have any eggs, we can legally remove them from the boxes and thus, hopefully, keep the males busy making their displays without getting down to actual reproduction. We also have oriented the openings of our field-placed nest boxes away from the surrounding tree/shrub ecotone. The house wrens inhabit these ecotones preferentially and are known to respond to the movement of other birds in and out of their nests by actively invading and preying on those nests. All of our boxes, then, have been turned to face the centers of their fields and meadows.

Our plan for Objective #2 involves close observation of the standing trees on the edges of our fields and meadows. Some of these trees may be of sufficient size and age to house cavity nesting birds. Many of these trees have also been worked on by pileated woodpeckers and have significant numbers of rectangular holes in their trunks. These observations will be on-going through the breeding season.

We are two months into our 2017 observations (time goes by so quickly!). What have we seen so far?

K. Thomas, Public Domain

We are coming to the end of the early spring bluebird reproduction cycle. This April/May burst of reproduction (which we also observed in 2015 and 2016) has involved bluebird’s nesting in eleven of our twenty-eight boxes with the production of forty-nine eggs and, so far, forty hatchlings (which are just now beginning to fledge). We have seen some nest predation (five hatchlings were killed in one of our boxes), but, overall, the rate of reproduction and success rate (percentage of eggs maturing into hatchlings and fledglings) is higher this year than in either of the previous years. We expect the bluebirds to take a reproductive pause as summer sets in (maybe because of food availability or maybe because of competition with other cavity nesting species?) but then carry out a late summer nesting cycle in July and August.

Photo by D. Sillman

Tree swallows have just begun their seasonal nesting. This timing also fits into our previous years’ observations. The swallows rely on aquatic insects to feed their nestlings and time their nesting to the June emergence of large numbers of these insects. The very dry conditions of June 2016 may have resulted in reduced insect numbers, and the swallows, which have been described in the literature as a resource-dependent nesting species, then, reduced their numbers of nests and numbers of eggs significantly from 2015 (which was a much wetter summer). We will watch with great interest how the reproductive rate of the tree swallows is influenced by this, so far anyway, wet spring and summer. We have thus far counted five swallow nests in our boxes.

The house wrens made nests in nine of our boxes in 2016 (there were no house wren nests in 2015). A total of thirty-four house wren eggs and twenty-three fledges were observed in 2016. The house wrens, like the bluebirds, nested and reproduced in an early spring and then a late summer timing cycle. So far, we have seen seven house wren nests and twenty-nine eggs! Four of the seven nests are in boxes located in the ”bat house meadow” in the northern section of the park. One wren nest was in a nesting box in a small meadow near the pond that had not had any birds’ nests at all throughout our three years of observation! Initially, it does not seem that our orientation of the nest boxes to point away from the surrounding trees and shrubs and toward the open spaces of the fields and meadows has been effective in reducing house wren activity.

Photo by A. Wolf, Wikimedia Commons

Last year we observed three chickadee nests in which fifteen eggs were deposited (there were, however, only four confirmed fledges from these eggs). The nesting timing of the chickadees in 2016 was in late May and early June. So far this year we have only seen one chickadee nest and that nest was usurped by a house wren. The next few weeks may be critical for successful 2017, chickadee nesting in Harrison Hills Park.

When I went out on my nest box circuit yesterday afternoon I also walked the edges of our three northern meadows (the bat house meadow, the high meadow and the purple martin field) where fifteen of our twenty-eight nesting boxes are located. I was looking for sufficiently large trees that may serve as natural, nest cavity locations for any of our cavity nesting bird species. I need to get out to these meadows in the morning to see if these is any evidence of cavity nesting activity. Right now all parental bluebirds, for example, are actively feeding their growing nestlings. If these are nests in the tree holes, I should see the comings and goings of the parental birds!

So, our 2017 season is going along well! The bluebirds are booming, and the tree swallows are following closely behind. The house wrens have made significant inroads into our nesting resources, though. Maybe we have to just take them along with the bluebirds and swallows!

More soon!

 

 

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Signs of Summer 2: Whites’ Woods

Photo by D. Sillman

Last Monday Deborah and I went over to Indiana, Pennsylvania and went for a hike in a small, recreational area called Whites’ Woods. We read about the trails on a blog site (http://whiteswoodsindianapa.blogspot.com/) and were excited to go and see some new trails and scenery.

Whites’ Wood is a 250 acre recreational park situated in White Township just north of Indiana, PA. The land was once owned by a railroad company (Pennsylvania Railroad?) and then in the 1950’s was sold to a real estate company (that was owned by someone named “White,” I think). Finally, in the 1960’s this 250 acre piece of land was donated by the White heirs to the township for use as a recreational park.

Whites’ Woods is a publicly owned land resource that has been beset over its 50 plus years of existence by many of the problems facing much larger, more resource rich sites throughout the United States. Competing and often conflicting interests and goals (quiet, wooded trails for hiking vs. income from timber harvesting or natural gas development, areas set aside for wildlife vs. areas opened up for hunting, etc.) openly contend with each other for the use and fate of Whites’ Woods. Township supervisors proposed as recently as 2007 to open significant areas of White’s Woods up for logging. This proposal was resisted by a “Friends of Whites’ Woods” (FWW) organization. The initial timber removal plan was recognized as flawed by the Pennsylvania Department of Conservation and Natural Resources (DCNR) for both environmental and also possible legal reasons (based on the terms of the original land donation), but several areas within the woods were logged anyway

Photo by D. Sillman

The trails were broad and clear but not well marked. Blazes were few and far between and often the colors of the trail markers did not match up with the trail color code of the maps. There was, though, very little chance of getting lost in this small area (even for us!).

The trees were primarily yellow poplar, red maple, yellow birch and black cherry. The black cherry trees were in states of some age-related decay (and extensive woodpecker damage). This forest is, then, a predictable mix of sun-loving, fast growing trees that quickly grow in a site after clear cutting. Many of the poplars, strictly based on size, were between 60 and 80 years old (which would fit the recent history of the site). This could be a secondary growth forest but it is more likely to be tertiary. Heavy use of timber for building construction and for the railroad (fuel and track ties) in the early to mid Nineteenth Century probably took down first the virgin forest and then the secondary re-growth 60 or 70 years later. What we see is the probably the next re-growth stage. Interestingly, there were also some relatively large big-toothed aspens (probably 40 or 50 years old) planted in fairly regular intervals along one side of the trail. Big-toothed aspens are often planted on reclaimed or intentionally re-forested sites. They may represent some human involvement in the reforestation of Whites’ Woods..

Photo by D. Sillman

As we walked up the curving trail we came across an increasing number of red oaks growing in the “double trunk” configuration suggestive of stump sprouting following logging. I estimated that the largest red oaks, based on size, were between 80 and 100 years old.  There was also a great deal of downed wood throughout the surrounding forests. Fallen trees, broken trunks, and scattered limbs littered the spaces between the standing trees and suggested an actively re-sculpting forest that was thinning and pruning itself.

In the under-story New York fern, hay-scented fern, Christmas fern, garlic mustard and wild geranium (also called “crane’s bill”) were abundant. Along the edge of the trail were milkweed plants and small patches of multifloral rose.

Photo by D. Sillman

Off of the trail were several areas with thick stands of yellow birch and sugar maple saplings. These dense copses suggest relatively recent removal of the older, established trees and may be the sites of the 2007 logging referred to above. Throughout the poplar/birch/red maple forest there were also abundant sugar maple saplings growing. There had been some discussion on the Whites’ Woods blog about tree damage caused by excessive numbers of white-tailed deer, but our observations were that these woods are a robustly regenerating forest with a rich population of potentially long-lived sugar maples steadily growing up into the canopy.

We saw large numbers of robins noisily digging through the leaf litter, we heard (but did not see) wood thrushes all along our hike. We also heard northern flickers and saw abundant evidence of pileated woodpecker activity (large, rectangular holes in the black cherry trunks). I also saw a pair of flycatchers vigorously interacting up in the branches of some middle canopy trees.

We walked around the “Old Quarry” and then took a trail that led down a shallow, wooded ravine. The multifora rose was very abundant along the small stream that the trail followed. Maidenhair fern and interrupted fern were also along this part of the trail.

Photo by D. Sillman

Laying on the trail were several, golf ball sized, green balls that were incredibly, almost insubstantially light in weight. We opened one of them and saw that it was filled with an array of white fibers that converged on its center. These were “empty oak apple galls” made by the parasitic wasp Amphibolips quercusinanis.  The female wasp lays her eggs in the leaf buds of oak trees (usually scarlet or red oaks) and hormones associated with the eggs drive the growing tissues of the emerging leaf to make this spherical chamber for the wasp larva. Deborah put one of the galls in her pocket, but by the time we got home it had dried out and collapsed.

Photo by D. Sillman

We also saw squawroot (Conopholis americana) (also called “cancer root” or “bear cone” growing in both large and relatively small clusters all over White’s Woods. Squawroot is more common in older forests, and its presence and relative abundance in a site may be significant indicators of forest age and stability. In areas where oak forests are being replaced by secondary forests that are dominated by maples or other non-oak tree species, squawroot is an increasingly uncommon and possibly threatened plant. Here is Whites’ Woods, though, the density of red oaks seems adequate for its sustained existence.

It is not clear in the literature if squawroot seriously compromises the health of its host tree. It is likely that it, by itself, may exist in a very stable parasite host symbiosis with its much larger and longer lived host oak or beech tree. But, if other stresses combine with squawroot’s presence, the health and vitality of the host tree may be reduced.

Photo by D. Sillman

Up on the top of the Whites’ Woods hill we came across a stunning flower blooming at the top of a spindly, eight foot tall, woody trunk. Based on the extreme length of the flower stamens, we tentatively identified it as pink azalea (Rhododendron periclymenoides). It is supposed to have very little fragrance, but it was too high up to check!

Photo by D. Sillman

And finally, we found a plant that we have been looking for over the past few weeks: fire pink (Silene virginica). Fire pink has a stunningly intense, five petalled, red flower and almost always grows in the crumbling soil of an eroding soil bank.  It blooms in late spring/early summer. We followed its blooming season very closely on our northward hike on the Baker Trail back in the spring of 2010. Fire pink’s flowers are long and tubular with nectaries and ova housed deep inside. Only organisms with long tongues (like hummingbirds and large butterflies) are able to reach its sweet nectar and, thus, deliver pollen to the ova. Ruby-throated hummingbirds are the principle pollinators of fire pink. June is very near if fire pink is blooming!

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Signs of Summer 1: Plant Chemicals and Dragon’s Blood

Mayapple plant with flower bud circled

Photo by D. Sillman

Fourteen years ago I wrote an essay entitled “Do We Need Nature.” In it I talked about one very important aspect of wild plants and animals: their incredible array of genes, proteins and other chemicals that might be able to be used to fight human disease. I called this the “tool box” of Nature. Recently I have come across several journal and news articles that have added to this “tool box” idea.

In “Do We Need Nature?” I used the story of the May apple (Podophyllum peltatum) (pictured above (with flower circled!)) as an example of unexpected benefits from a wild species.  May apple is currently dominating the understory vegetation of many of our local forests, and its abundance and commonness belies its rich history and ethnobotanical significance.

Native Americans recognized the chemical importance of the May apple. They used dilute preparations of its rhizome to treat a wide array of maladies (from constipation to liver and kidney disease). They also used a concentrated preparation of the rhizome as a poison. European settlers learned of the properties of May apple from the native peoples and similarly utilized these oral preparations.

In 1835 the drug “podophyllin”  was isolated from the May apple rhizome and by 1850 concentrated forms of podophyllin were available commercially. Podophyllin was used as a laxative, a “duct opener,” a de-worming treatment (it killed both nematodes and flatworms), and as promoter of bile synthesis and release. It also had many serious side effects and was quite toxic. A topical form of podophyllin was manufactured in 1942 and was found to be very effective in treating the genital warts caused by the human papillomavirus (HPV). HPV generated genital warts are the most common sexually transmitted disease in the world, and untreated HPV infections can lead to cervical cancers. Podophyllin, then, the secondary chemical of the abundant and unassuming May apple, plays a role in the prevention of cervical cancer!

In the April 1, 2017 issue of The Scientist, Jef Akst wrote about a scientist who helped to facilitate a large number of cancer therapy breakthroughs. Jonathan Hartwell joined the National Cancer Institute (NCI) in 1938 (and stayed there until his retirement in 1975). He set up a “natural products division” at NCI whose task was to explore natural plant chemicals for possible anti-cancer properties. Hartwell worked with fellow scientists in the Agriculture Department and at many major universities and over his 37 year career described over 3000 plant chemicals that had potential impacts on cancerous growths.  Hartwell published a book (Plants Against Cancer) in 1981 in which he summarized his research. This is a very difficult book to find in a print edition, but now, fortunately, it is available in an electronic form via Google Books. Hartwell was also the author of over one hundred scientific articles and books over his long career. Summaries of Dr. Hartwell’s career can be found at http://www.altcancer.com/hartwell.htm and  http://www.encognitive.com/node/4384 .

Xi Shu tree. Photo by Daderot, Wikiimedia Commons

In addition to his laboratory work, Hartwell studied the herbal and medical lore of the ancient Chinese, Egyptians, Greeks and Romans for possible clues as to which plants to analyze. Any plant that was described to have efficacy against cancer in these pre-scientific cultures was carefully evaluated by Hartwell’s lab or by one of his university affiliates.

Some notable successes from these research efforts were extracts from Chinese “happy tree” (Xi Shu tree, also known as Camptothica acuminata). Anti-cancer, chemotherapy drugs developed from this plant include camptothecin whose synthetic derivatives are still being used to treat metastatic colon and rectal cancers. Also extracts from the Pacific yew tree (Taxus brevifollia) led to isolation of the drug “taxol” which is used to treat breast, ovarian, lung, bladder, prostate and esophageal

Rosy periwinkle Photo by Ramshug Wikimedia Commons

cancers along with melanoma.  Chemicals from the rosy periwinkle (Catharanthus roseus) led to the development of vinblastine which is used to treat both Hodgkin’s and non-Hodgkin’s lymphomas and vincristine which is used to treat both of these types of lymphomas and also childhood leukemia along with several other types of cancer.

The specific actions of these drugs in cells often involves disruption of the microtubules of the mitotic spindle or enzymes involved in DNA synthesis or repair. Thus, rapidly dividing cells (i.e. cancer cells) are particularly disrupted by these drugs (although even normal cells will be affected, too). As my oncologist once told me, chemotherapy is poison, but it is poison we try to control.

It has been estimated that 60% of the current cancer chemotherapy drugs are either chemicals isolated from plants or derivatives of those plant chemicals.  We should all plant periwinkles (and May apples and Happy Trees!) in our gardens!

Photo by M. Dumont, Wikimedia Commons

Another part of the biological “tool box” are chemicals found in animals. A recent article in the New York Times (April 17, 2017) described a new type of antibiotic that was isolated from the blood of a Komodo dragon (Varanus komodoensis) by Monique Van Hoek and Barney Bishop of George Mason University. This antibiotic (named “DRGN-1”) killed both Gram negative and Gram positive bacteria and also dissolved their protective biofilms. It sped up wound healing in lab mice, too. The mouth of a Komodo dragon contains a rich, toxic microbiome of bacteria. When a dragon bites a large prey species (like a deer or a buffalo) it injects the bite wound with bacteria and also a recently described venom. The infection and the venom slowly disable the prey animal and the dragon, who follows the bitten prey closely, eventually can feed on the stricken animal. Researchers assumed that for a dragon to house such a toxic oral microflora, it must have mechanisms to protect itself from both self-infection and also infections from the frequent bites from their fellow, often aggressively interacting dragons. Hence the discovery of DRGN-1! Researchers report that there are forty other substances in their dragon blood that may also have antibiotic properties!

The public health fight against antibiotic resistant bacteria may depend upon the blood of dragons (and other types of monitor lizards, crocodiles and even sharks!). There are more things in heaven and earth, Horatio, than are dreamt of in our philosophies!

Happy Summer, everyone!

 

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Signs of Spring 13: Gene Drives

Photo by D.G.E.Robertson, Wikimedia Commons

Earlier this year I read an article in The New Yorker (January 2, 2017) in which a program designed to change the genome of the white-footed mouse was discussed. This change would make these mice (which are the principle biotic reservoir for Borrelia burgdorferi (the bacterium that causes Lyme disease)) unsuitable hosts for that bacterium. If this could be accomplished, the passage of B. burgdorferi from white-footed mice to and from black-legged ticks (Ixodes scapularis) could be stopped and the ticks’ transmission of this bacterium to hundreds of different vertebrate hosts (including humans) would be severely disrupted. This could result in the ecological control of Lyme disease.

For the last several years, Pennsylvania has led the nation in the number of human cases of Lyme disease (in 2014 there were 7487 conformed human Lyme disease cases in Pennsylvania up from 5904 cases in 2013). Further, the Center for Disease Control (CDC) states that the number of reported Lyme cases in the United States (30,000 in 2014) represents only 10% of the actual number of infections.

Borrelia bacteria, CDC, Public Domain

Dogs can also develop Lyme disease. Most dogs (95%) that receive the Borrelia bacterium via a tick bite show no symptoms at all. The dogs that do react to the bacterial infection often develop lameness in one of their legs that typically lasts for a few days. The lameness can then shift to another leg and can be quite debilitating. In some dogs the Lyme infection can also lead to kidney disease and even kidney failure. The actual number of dogs infected each year by B. burgdorferi is not known. Informal reporting from local veterinarians, though, indicates that the number is large (and increasing each year!).

Any plan that focuses on an ecological solution to this epidemic disease should be given serious consideration. The control project described in The New Yorker article has two very straightforward and technologically elegant phases that are based on some very significant, cutting-edge molecular biological developments.

CRISPR, J. Atmos, Wikimedia Commons

In the first phase of the project, CRISPR is used to insert a gene directly into the white-footed mouse’s DNA. CRISPR is a technology that employs specifically engineered RNA sequences and a protein that cuts (and pastes) DNA in order to line up a sequence of DNA at a specific gene locus and then insert it into the DNA strand.

The second phase of the project utilizes a recognized interaction between an organism’s homologous chromosomes (the two coding strands of DNA (plus proteins) that carry the organism’s two different versions of all of its genes). In this interaction one of the homologous chromosomes contains a specific DNA sequence that makes an enzyme that spontaneously cuts the DNA sequence of the other chromosome. This is very similar to CRISPR except that in this system the “cutting” gene sticks a copy of itself into the severed DNA sequence. This second system is called a “gene drive,” and it results in the amplification of a gene passing through generations in a population.

CRISPR was first observed in bacteria and is used by these types of cells to store and pass along to subsequent generations the immunological memories of virus exposures. The Broad Institute of M.I.T has an excellent “question and answer” web posting about CRISPR if you would like to read more about it.

Gene drives occur in many natural genetic systems and are mechanism by which genes, even if they are not beneficial to the species, can rapidly build up in a population. . If you would like to read more about gene drives please see the “FAQ’s about gene drives” posed by the Wyss Institute of Harvard.

The essential idea of this Lyme disease control project is to make a DNA sequence that codes for an anti-Lyme antibody protein and then insert it into the white-footed mouse’s DNA along with a gene drive! These genetically altered mice would be “immune” to the Lyme bacterium and, when released into a wild population, they will spread the gene-driven antibody gene very rapidly through the entire white-footed mouse population. Eventually, these white-footed mice would be free of  Borrelia burgdorferi and Lyme disease would no longer be transmitted or amplified by them!

The scientists of the Lyme control program are looking for a small island on which the controlled release of the altered mice could be closely monitored. A number of island communities here in the East (where Lyme disease has become an exponentially expanding problem in human (and dog) populations) have already volunteered to be the anti-Lyme test site. Unease and uncertainty about the unintended consequences that might arise from the release of genetically altered organisms into our ecosystems, though, represent significant ethical and ecological concerns that need to be thoroughly evaluated before this experiment is carried out.

Other pathogens dispersed by targetable vectors are also being considered for similar types of genetic modifications and gene drive insertions. Control systems for malaria, for example, were discussed in an article by Tony Nolan and Andrea Cristanti in  The Scientist earlier this year (January 1, 2017).

Anopheles mosquito, CDC, Public Domain

For years, Nolan and Crisanti report, scientists have been working to sequence the complete genome of the various Anopheles mosquito species that are responsible for most of the transmission of the protozoan parasites (Plasmodium spp.) that cause malaria. With the complete Anopheles genome now in hand, researchers can begin to identify the specific genes that allow Plasmodium to live and reproduce inside of the Anopheles mosquito. They are also

Mature Plasmodium in blood, CDC, Public Domain

looking for those genes needed to transmit the Plasmodium life stages to bite victims through the mosquito’s saliva. Once these genes are identified, altered versions that act to block the Plasmosium life cycle or prevent transmission could be engineered and inserted (with gene drives) into the mosquito’s DNA.  Release of these gene-driven mosquitoes into a wild population of malaria carrying mosquitoes, then, could disrupt the transmission of Plamodium and, possibly control the disease.

Other ideas for mosquito control (and, thus, malaria (or Zika or Denge or encephalitis or West Nile virus) control) involve inserting genes (with gene drives) that disrupt mosquito reproduction or sex ratios. These genetic modifications could result not just in disease control but possibly the extinction of an entire mosquito species! When you consider the “good” things that mosquitoes do in an ecosystem (Signs of Spring 13, May 19, 2016) this plan for extinction is very disturbing.

We are the verge of having some very powerful new tools to fight disease. We must be careful, though, to see beyond our short-term goals of disease control and be sure that we understand the long-term ecological and even evolutionary impacts that the use of these tools may trigger! Ecosystems much more complex than they appear, and some changes can have completely unanticipated consequences!

 

 

 

 

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Signs of Spring 12: The Forest and the Trees!

Photo by D. Sillman

The woods around us are changing almost daily due to their relative abundances and leafing orders of their trees. These passing days let us see the trees for the forests! They also remind us of a century and a half of ecological history!

A month ago the ridges throughout Western Pennsylvania had a reddish glow from all of the flowers of the incredibly abundant red maple trees. Those flowers have now faded and fallen, and the leaf buds of all of the species of maples are opening up. The red maple’ new leaves will live up to their common name and have, initially, a distinctly reddish tint. This red, though, will be quickly covered up by the deepening green of their rapidly synthesizing chlorophyll molecules. We won’t see their red color again until fall.

Photo by D. Sillman

The red maples next to my house started to leaf out a few days ago, and the silver maple at the bottom of my field set its leaves last week. I have seen sugar maples all over the area that are already covered with large, deep green leaves. I have seen some others, though, that are still mostly bare. There is a lot of individual variation in sugar maples as to when they unfurl (or when they shed) their leaves!

Along Roaring Run the yellow poplars started to leaf out a couple of weeks ago and are now covered in their distinctive, tulip-shaped leaves. The abundance of poplars on the hillsides is really apparent now, too, as Deborah’s picture (at the top of page) of the hillside on the south bank of the Kiski River shows you. Most of the spaces in between the green of the poplars have a faint, reddish tint. These are all of those red maples just starting to roll out their leaves.

Photo by D. Sillman

The apple, crab apple, pear and cherry trees have all leafed out and are in or have been in flower. The grass beneath them has been speckled with shed, white flower petals. Fields, roadsides and hillsides are flushing green especially with the abundance of black cherry trees that characterize this southern edge of the “Allegheny Hardwood” forest mix. The sun-loving black cherries (along with all of those red maples and yellow poplars!) were among the first species to recolonize the clear-cut forest sites all across Western Pennsylvania in the early years of the Twentieth Century. This forest mix grew rapidly but is made up of relatively short-lived tree species. The first black cherries that grew in this forest succession sequence will be reaching the end of their expected life spans within the next couple of decades.

What will these forests look like when all of those trees are gone? The deer have eaten most of the seedlings that tried to grow under the mature canopy. The deer leave behind the ferns, of course, and the multiflora rose. Maybe all of these Pennsylvania forests will turn into vast fern and rose thickets.

Another major tree of our forests is the red oak. It responded to the clear-cut forest destruction by sprouting new trunks from the stumps and roots of the downed trees. Often the re-sprouting red oak trunks grow in pairs, so when you see a double trunked red oak you are looking at a tree that rebounded from the ecological devastation of the late nineteenth and early twentieth centuries, the devastation that Gifford Pinchot called “an orgy of forest destruction.”  Red oaks are just starting to unfold their leaves. Many are covered with tiny, light green versions of their familiar looking leves.

Photo by D. Sillman

The young red oaks in my back yard grew up protected from the deer under the cover of my now departed spruces. They are fine looking pole trees between twelve and twenty-five feet tall. The shorter trees, sheltered from the winter winds, held onto last year’s leaves until very recently. I wonder if these old leaves that cling on these trees help to protect the new leaf buds? Or, do these tough, old, oak leaves weather down a bit while they up hanging in the wind and weather and then decompose more rapidly when they finally get added to litter layer of the forest floor in the spring? Beech trees (another very tough leaved species!) keep their leaves through the winter, too. It would be interesting to look at this more closely!

That we have forests around us at all after that century-plus ago, uncontrolled assault on our ecosystems is a credit to the nutrient richness of our soils, the abundance of our rainfall, and to the ecological reservoirs of plant species (especially trees!) to fuel a robust successional recovery. The forest we see now, though, is very different than the forest that had evolved here over the millennia after the retreat of the last Ice Age’s glaciers. These forests are an unprecedented, broad scale experiment whose ultimate fate is not at all known.

And finally, along many waterways and in many tended yards, willow trees have been in light green leaf for a couple of weeks now. I have been watching set of willows that grow along my driving route to campus from my home. They are starting to fill in their dropping branches with denser and denser arrays of leaves, and are slowly becoming more and more solid to the eye.

Photo by D. Sillman

Looking out the window over my writing desk I still see the dark, bare branches of the black locust trees and the oaks. Spring is just getting started! Deborah saw a pair of pileated woodpeckers out on our old cherry stump this afternoon. They must have their nest somewhere close. I thought that I heard a Baltimore oriole down on Roaring Run this morning, and I did hear a wood thrush up on campus last week! The spring migrants are returning in numbers! The rose-breasted grosbeaks and scarlet tanagers should be filling in the forest gaps on the trails down along the river soon, and the indigo buntings should be flitting in and out of the shrubby cover further up river toward Edmund.  The whole summer ensemble will be here soon!

 

 

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Signs of Spring 11: Invaders All Around Us!

Photo by D. Sillman

(This is an update of a 2013 posting)

Deborah and I have been out hiking on quite a few woodland trails this spring. One of the generalized observations we have made concerns the preponderance of alien, invasive plant species that make their ecological presence known long before most of the native species. Early leafing and early flowering are excellent strategies for an invasive plant to gain a “foothold” in our deciduous forest ecosystems. Add the ability to make abundant seeds and an absence of co-evolved biological controls and these exotic, invasive plant species can truly come to dominate an ecosystem!

Most of the trails we have been walking on have been lined by multiflora rose (Rosa multiflora). Multiflora rose is one of the first understory plants to sprout leaves in the early spring, and its fresh leafed appearance makes entire wooded hillsides glow green. I had mentioned previously seeing this plant’s just unfolding leaf buds out at Harrison Hills Park a few weeks ago. This is time of year to appreciate how much multiflora rose there is in our Western Pennsylvania ecosystems! Unfortunately, the story about this plant is both good and bad. It is an extremely aggressive and rapidly growing exotic invasive (from Asia, brought to this country as an ornamental plant) that has choked out many native plant species. It also, though, generates very favorable habitats for many species of small mammals and birds.

Public Domain

I have a large, dome-shaped multiflora rose thicket down at the far end of my field. I remember consciously mowing around a spindly rose stem twenty-five years ago and watching over the next decade as the multiflora rose spread and grew into a eight feet high and twenty feet diameter thicket. There is a large woodchuck burrow in the middle of this thicket and almost always a rabbit or two hiding out in the low tangles of thorny branches. Cardinals and house finches perch and nest in the upper branches. Nothing is growing under the thicket, though. The constant spring and summer shading prevents the survival of any other plants.

Photo by D. Sillman

Small low growing leaves of garlic mustard (another invasive plant brought in from Europe) dot almost every forest floor we walk past. Garlic mustard (Alliaria petiolata) is also an “early riser” in the spring and is also doing a great deal of damage to native plant species. Along with its ability to make abundant seeds and grow in a wide variety of soil and habitat conditions, garlic mustard also releases poisonous, allelopathic chemicals that negatively affect the soil fungi (“mycorrhizal fungi”) upon which most trees and many other plants depend for nutrient absorption. It has also been noted that white-tailed deer seldom feed on garlic mustard (but, as we know, they do eat almost everything else!). The expansion of this alien plant species has been extensive and rapid.

Photo by A. Salo, Wikimedia Commons

Japanese knotweed (Fallopia japonica) is not a particularly early spring sprouter, but its tall, dry stalks dominate sections of trails that are near roads or rivers or railroad tracks. Under these dense, old stalks we are just now, almost exclusively seeing new, green sprouts of knotweed.  Almost no other plant species are able to grow in these thickets. Knotweed has an amazing ability to spread vegetatively. The tiniest piece of a stalk or leaf is able to grow into a new plant. When I see trail workers in the summer using power trimmers to cut down knotweed, all I can think of is that they are broadcasting new propagules of the species far and wide along the trails.

We have also mentioned several other alien plants in a much more positive, “signs of spring-like” sense. Forsythia (Forsythia suspensa) is a species from China that has been widely planted in European and American gardens. It has also “escaped” into the wild and has formed dense thickets of feral plants. Daffodils (Narcissus spp.)  are native plants of Europe, Asia, and northern Africa. They have been widely bred and planted throughout North America and have also “escaped” into wild habitats. Both of these plant species are beautiful harbingers of the spring season, but we have to remember that they are exotic invaders!

Photo by Fcb981, Wikimedia Commons

There is such a long list of these exotic flowers, shrubs and trees! Dandelions, privet, tree of heaven, burning bush, Norway maple, poison hemlock, Queen Anne’s lace, English ivy, several honeysuckles, Russian olive, and Kudzu are just a few of the better known species. The U.S Fish and Wildlife Service estimates that there are 50,000 non-native species in the United States and that over 4000 of these are dangerous invasives!

Are alien species always “bad?” The impacts of many exotics would suggest so. The loss of less aggressive or less fecund native species that are unable to compete with these very robust invaders is a serious blow to local biodiversity and may have extensive, reverberating impacts throughout an affected ecosystem. There are suggestions, though, that in some cases and in some ecosystems alien species may actually increase the biodiversity and “quality” of an ecosystem. It is very logical that the answer to the question about the impacts of invasive species should not be as simple as we once thought. Many animals, as we saw above, use multiflora rose thickets for protective habitats, many birds eat honeysuckle berries, and the honey made in the fall from knotweed nectar and pollen is dark and delicious!

In his book “1493,” Charles Mann visualizes the European discovery of the New World as a moment that began the reversal of the breakup of the supercontinent Pangea that occurred some 250 million years before. The human generated movement of plant and animal species, both domesticated and agriculturally focused and also wild and uncontrolled, between the now widely separated continents is generating an increasingly homogenous Earth-wide biome  dominated by a small set of aggressive, generalist species.  Mann even defines this as a new geological epoch, the Homogenocene. Invasive species, then, may be the defining features of our future world.

 

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Signs of Spring 10: Watching Some Birds

Photo by D. Sillman

A couple of weeks ago I was sitting in my car up in the parking lot of the Environmental Learning Center at Harrison Hills Park just next to the purple martin houses. I had just walked my bluebird circuit to check our nesting boxes and was waiting for Deborah to return from an early season wildflower walk. It was a cool, cloudy day, and I had to keep the car windows rolled down to prevent fogging them up with my breath. I spent my car time looking at birds.

The purple martin houses were recently uncovered, but the martins had not yet returned from their over-wintering ranges (they are back now, though!). The large, communal houses remind me of my old neighborhood in Houston. It seemed like every other house on my street had one of these purple martin apartment complexes prominently displayed on a tall pole. I can’t remember how many of them actually had birds in them, though.

A northern flicker landed in a circle of low grass and started very purposefully pecking the ground. I assumed he was eating ants (a flicker’s favorite food!) and I glanced at my watch to make a note of how long he would stay in that spot anting. He hardly moved a half a meter in the hour and a half! His hunting style was as stationary as could be! Find a place with ants, stay put and eat the ants! Sometimes life is a simple equation!

Photo by D. Sillman

About twenty meters from the flicker five robins were also looking for food. I assumed that they were looking for earthworms that might be lingering on the surface of the wet soil. The robins moved in a beautifully choreographed dance across the grassy field: each bird stayed about five meters away from their closest neighbors. When one bird moved the others reacted, and the small flock methodically worked their way across field. Their movements were sudden and saltatory: five or six quick steps, a head turn to focus one of their eyes on the ground (they usually used their right eye) and very occasionally a peck and grab, and even more occasionally a head shake and a swallow. Once or twice a new robin landed among the hunting cohort. This threw all of the established birds into a cackling furor. The robins flapped their wings and lifted up a foot or so about the ground, and then re-settled into their familiar spacing with their additional flock member and continued to work the field.

Bluebirds (early arriving males) were also out in the field. They flew from clump of tall grass to clump of tall grass grabbing onto the upper portion of the grass stems to survey the section of the field in front of them. They seemed to avoid the part of the field being worked by the robins and flew many tens of meters at a time from grass clump to grass clump. I could see the bluebirds turning their heads through an acute angle as they scanned the ground area immediately in front of them. Even rarer than one of the robins pecking up a worm, though, was one of the bluebirds crashing down to the grass surface in front of them to snag an insect (or worm?). Any success by one bluebird was immediately noticed by the others, and they flew in close to see if there were more morsels in that spot to consume.

Photo by D. Sillman

Off on shrubby edges of the field I could hear a familiar “cheeritt” call. Towhees were calling and hunting in the leaf litter. The towhees have only very recently returned to the park after overwintering in nearby valleys and sheltered areas. They are short-distance migrators that seek out sources of food (berries etc.) to sustain them through the winter. They then return early in the spring to their summer breeding ranges. Towhees have a different way of hunting for their food. They attack a layer of leaf litter with their feet and send leaves and soil flying in a cloud of disturbance. They then jump back and explore the wreckage of their efforts in the hope of having stirred up some worms or insects or almost any other type of small invertebrate or vertebrate. In the summer you often hear this ground and litter scraping and come to recognize it as a sign of nearby towhees.

Photo by D. Sillman

A foraging group of crows flew overhead. They wheeled and turned and filled the air with their raucous calls. You never need to wonder if crows are around! They announce themselves with volume and energy! When I fill my bird feeders in the morning, my local crows are almost always perched in the surrounding circle of tall trees fifty or hundred meters away. Sometimes they watch silently as I fill the feeders and spread their morning favorite, peanuts in the shell! Sometimes they get so excited by the sight of the peanuts that they start bobbing and calling in anticipation. They won’t fly toward the yard until I go back into the house, though. They are loud, but cautious hunters. This hesitation on their part  gives the waiting blue jays (who have been perched out of sight in my line of arbor vitae) enough time to swoop in and grab a few of the crow peanuts for themselves.

Just on the edge of the parking lot a small chipping sparrow hopped from weed clump to weed clump pecking and rubbing at the plant stems with its beak. The sparrow seemed to be hunting purely by feel. Its eyes were open, but they almost looked like they were focused on some faraway object. Its beak did all of the probing and work. I didn’t see any obvious hunting success, but the sparrow’s prey might have been too small for me to see at distance.

Photo by D. Sillman

Finally, a pileated woodpecker flew over the parking lot and landed on the side of a distant tree. The woodpecker immediately started banging on the tree, and I saw some bark and woody debris float to the ground beneath him. It was hard to tell if this woodpecker was hunting and feeding on the insects in this tree or if he was drumming to get the attention of a female. It is a bit late in the spring to start looking for a mate, but hope springs eternal. Woodpecker holes in large, old trees are an important natural nest cavity site for bluebirds (and tree swallows, and chickadees, wrens and nuthatches!). Our bluebird boxes are an artificial substitute for these once abundant, tree trunk and branch cavity sites. As our forest matures, I hope that we let the older, larger trees remain in place so that the woodpeckers can make them into cavity nester’s nest sites!

An hour and a half has gone by. The flicker is still in the same spot eating his ants. The robins and bluebirds are cruising the field in their own ways and at their own paces. The towhees are still calling, but the crows, woodpeckers and chipping sparrow are gone.

Deborah returns from her walk. It is too early for very many spring wildflowers and too cold for the few that are in flower to be open. While we are talking two turkey vultures circle over the car and then wobble away on the light breeze and disappear from sight.

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