Signs of Spring 5: Harrison Hills Walk and Cavity Nesting Team (3.0)

Photo by D. Sillman

Last Thursday Deborah and I headed up to Harrison Hills Park in northern Allegheny County to take advantage of a few hours of sunny, spring weather before the next cold front (and set of snowstorms) blew in. We wanted to get at least one hike in during our Spring Break!

It was a beautiful morning: sunny, in the fifties (with a slight change of warming up close to sixty!). Only the wind made us think of the coming storms. There was an article in this week’s New York Times in which data on “first leaf” emergence from observers all over North America were compiled into an animated map. The wave of “first leaves” surged up the breadth of the country a full three weeks ahead of the thirty year average! It is an early spring this year, a VERY early spring!

We parked near the Environmental Learning Center and headed out across some open, grassy areas to find the first group of our nest boxes. The soil was wet and oozing underfoot and there was flowing surface water running from a number of seeps and springs. The water supported a thick growth of moss (in many places there was much more moss than grass). Small, black Pardosa spiders ran about on the soil and plant surfaces. We hoped that they were getting out of the way of our footfalls!

Photo by D. Sillman

Our boxes were in good shape and had weathered the winter very well. We were especially interested, though, in the direction that their access holes pointed. Last year, 9 of our 28 nesting boxes had house wren nests (no boxes from our 2015 study had had house wren nests). Six of the 9 house wren nesting boxes had been previously nested in by bluebirds (4 boxes) and chickadees (2 boxes). House wrens and bluebirds have many similar nesting characteristics: they tend to nest in two seasonal cohorts (early spring (May) and late summer (July/August), and they tend to select nesting sites no more than 50 to 100 feet from a wooded edge. Possibly our 2016 box relocation project moved a significant number of our boxes into nesting sites also preferred by house wrens.

The problem is house wrens are one of the most common causes of nest failure in bluebirds, tree swallows and chickadees. House wrens destroy eggs, kill nestlings, and even kill adult birds so that they can then start their own nests in the usurped box. Also, male house wrens attempt to attract females by building numerous “dummy nests” (piles of sticks sometimes piled on top of the active nests of other birds!). These dummy nests are an important sign of house wren activity and can be used to thwart house wren nest invasion. Since these dummy nests contain no eggs, they can be removed from the nest boxes without violating the Migratory Bird Treaty’s protections of native bird species. Prompt removal of these stick piles may keep a male house wren occupied in re-building the displays rather than getting down to actual reproduction.

Photo by dfraulder, Wikimedia Commons

Also, the literature on “wren guards” (various nest box modifications that are designed to repel house wren nest box invaders) stresses that it is the visual cues of the nesting birds entering and leaving a nest box that are the critical stimulations that then trigger the house wrens to attack the active nest.  Possibly, turning all house wren utilized nest boxes to point their openings away from the surrounding woods (where the house wrens spend much of their time foraging for food and hiding in the covering vegetation) would make the visualization of the nesting birds entering and leaving the nest box less apparent and decrease the rate of house wren infestation. Re-orienting the boxes was one of the tasks that Deborah and I hoped to accomplish today.

We looped through the meadow near the purple martin houses and then hiked up into meadow on top of the nearby hill. I walked up to the “High Meadow” on a narrow path that cut through the woods while Deborah took the longer (but less likely to have ticks) route back down to the access road than ran from the Learning Center. I scared up a bird  from the dense vegetation along the path as I walked along. The sudden rise of the bird was noisy and very exciting!  I think it was a grouse but it moved so rapidly that I did not get a good look at it. I also picked up a black-legged tick (which Deborah found working its way up my pant leg when we stopped to do a tick-check up in the High Meadow). It is the time of year to be very watchful!

We finished the High Meadow and the nearby Bat House Meadow loop doing some small repairs on the seventeen boxes and their poles and turning each box so that it faced away from its surrounding trees. One box in the Bat House Meadow had a metal, predator guard on its pole. We remembered that that box was the one that had the black snake inside of it when Sharon (one of the Cavity Nesting Team) open up the box to check on a swallow nest. The snake had eaten the swallow nestlings and was napping inside of the box. Good adrenaline rush, I am sure! The guard should keep that from happening again.

Photo by D. Sillman

Five male bluebirds followed us around in the Bat House Meadow. They are the first bluebird arrivals (or, maybe, the hardy, overwintering individuals?) and are checking out and competing for optimal locations for their breeding territories. Plenty of boxes for everyone, boys! The females should arrive in a couple of weeks

We then drove to the park entrance and checked the two boxes set on a fence line just to the south of  Y-intersection of the two park roads. Both of these boxes had predator guards and both had old nest materials in them. Possibly some overwintering bluebirds had built some nests, or some late fall swallows had done some practice nest building. The dry grasses were not tightly woven together and there were few feathers and very little feces in either box. There was no evidence of any recent activity. We cleaned them out and packed away the debris.

Photo by D. Sillman

The road to the soccer fields was closed so we had a long walk from the upper parking lot down to the cluster of boxes set around the field edges. We turned each box to face away from the surrounding trees. The wet soil of the soccer fields were blooming with the tiny white flowers of Pennsylvania bitter cress (Cardamine pensylvanica), and in the even wetter areas along the flowing drainage ditches and streams, the mottled purple, tear-dropped shaped spathes of skunk cabbage (Symplocarpus foetidus) grew in dense clusters.

Photo by D. Sillman

One of our nest boxes was missing! “Box V” that had been set next to the pond just up from the soccer fields was gone. This had been an important tree swallow box in both 2015 and 2016. We will have to locate it or replace it before swallow breeding season starts in late May.

We hiked back up the hill to the parking area through the woods that bordered our two nest boxes that had no nesting activity either in 2015 or in 2016. We left the boxes in place, though, because these two meadows seem so perfect for bluebirds (or chickadees or nuthatches or swallows). There is something, though, about these two sites that birds don’t like. We will have to figure out what it is!

The shrubs and trees on the pond side of the uphill climb were covered with American bittersweet vines (Celastrus scandeus). A few of the vines still had some of their distinctive, orange, pea-sized berries on them. These berries are poisonous to people but are a very popular winter food for birds. January before last we were hiking on this path and were amazed by all of the overwintering robins that were there. They must have been living on these very abundant, bittersweet berries.

Bluebird season will start the third or fourth week of March! The boxes are ready, and the Cavity Nesting Team will be there to watch and report!

Happy Spring, everyone!

This entry was posted in Bill's Notes. Bookmark the permalink.

One Response to Signs of Spring 5: Harrison Hills Walk and Cavity Nesting Team (3.0)

  1. Patrick says:

    In the event that I forget to tell you at our Cavity Nester meeting tomorrow, the 3RBC several meadowlarks were spotted in the batt box meadow. Also woodcocks have been flushed out by some of our Friends while chasing photo ops this spring.

Leave a Reply

Your email address will not be published. Required fields are marked *