Signs of Spring (March 4, 2007)
I have made a number of observations over the past week that, in spite of the fresh snow cover we all woke up to this morning, point very strongly to nearness of spring.
Last Monday morning, Deborah and I were driving to campus along Pine Run Road and saw in a low, wet field near an overflowing stream at least 200 robins evenly spaced out over three or four acres of ground.
The birds were scratching and probing into the wet soil for worms and insects. They were moving in what seemed to be an orchestrated, almost organism-like search pattern across the field. Bird flock (and fish school) behaviors are interesting areas of research. When a flock behaves in some coordinated way (like banking and turning en mass while in flight, for example, or by efficiently gleaning a field of available worms and grubs) how are the commands for this group behavior transmitted? Does a leader among the flock signal “hard right rudder” or some other suitable order? Watching the complexity and speed of flock (or school) movements, you might, in fact, come to believe that the animals must be communicating telepathically in order to accomplish such rapid and highly coordinated tasks! No evidence of bird or fish ESP, though, has ever been found. Instead, researchers utilizing high speed photography have come up some very simple explanations to these complex questions of group control. Each individual in the flock or school simply pays extremely close attention to those other individuals immediately around them. Then, if one bird turns (say in response to a predator sighting or to recognition of a possible source of food), the ten, or so, birds immediately around him also turn, and then the ten around each of these ten turning birds turns, etc. Their individual reaction time is so quick that it appears that the entire flock is turning and wheeling in perfect unison, but it is, in fact, just a rapid, amplifying cascade of action and reaction. Watching the search patterns of the robins moving across the field, we could see the effect of one bird even slightly encroaching in on an adjacent bird’s foraging space and the domino-like ripples of movement that this bird’s reaction caused as it rolled through first dozens and then hundreds of other birds.
This flock, by the way, is not the first Penn State New Kensington robin sighting of the season. Lori Hensel, back on Valentines Day, saw 40 to 50 robins in her back yardi n and around her holly hedge. They disappeared after the 14th, though, possibly heading to a more sheltered habitat or possibly returning back a bit south to wait for the coming thaw.
Another sign of spring occurred in my dining room this week. My box turtle (formerly my daughter’s box turtle, but as everyone who has had children head off for college knows pet ownership is an extremely transferable kind of obligation) had his first meal since November! He ate a nice piece of banana and has been active in his terrarium ever since, probably searching for strawberries (which are his favorite food). But, since strawberries are $4 a package, he will have to make do with bananas for a little while at least.
At the bottom of my field is a large silver maple tree. During the first two weeks of January when we were all wondering where in the world winter was (and, boy, did we find out!), I noticed that the branches of this tree were getting increasingly granular looking. These reddish, twig granules were the tree’s leaf and flower buds that were swelling with the rising tree sap and the warm day-time temperatures. These buds seemed, two months ago, to be getting dangerously close (relative to the season) to opening up! Temperatures, unfortunately for us but maybe fortunately for the trees, became more seasonal and the rate of bud swelling slowed down considerably. Within the next few weeks, though, both the silver maple and the similar and much more common red maple will flower. They are among the first trees to flower in the spring.
The buds with which these trees encase and protect their embryonic flowers and leaves are very interesting structures. The outer part of the bud is made of tough scales which form an overlapping, shingle-like structure around the delicate leaf or flower growth tip. These bud scales keep out destructive insects and also insulate the inner tissues. These scales are really tiny, very tough, modified leaves. Buds are typically classified as to whether they encase flowers (“floral” buds) or leaves (“vegetative” or, simply, “leaf” buds). Some tree species have buds that contain both floral and leaf embryonic tissues (“mixed” buds). The positions of the buds on a twig are also important with “terminal” buds found at the end of a twig and “lateral” buds found along the sides. On silver and red maple trees most buds are either floral or vegetative. The floral buds are larger and spherical and the leaf buds are smaller and more oblong. The floral buds are also typically clustered together in bunches on the twig.
Soon (may only two weeks from now!), the floral buds on the silver and red maples will open and the delicate clusters of red and yellow flowers will cover the reddish twigs. The tiny pollen grains from these flowers will be spread by the wind and some will encounter ova in the ovaries of other flowers and accomplish the fertilization phase of the reproductive life cycle. The pollen is produced in prodigious amounts by these trees, and you can easily understand why. The probability of a given pollen grain, randomly being dispersed through the atmosphere by the wind, finding an appropriate ovum is infinitesimally small! To insure that fertilization occurs at all, the trees must fill the air with pollen. Human interactions with this pollen mass can generate allergic reactions in sensitized individuals. Hardwood tree pollen, in general, is a major spring allergy concern.
Once an ovum is fertilized it will develop into the silver and red maple’s distinctive winged seeds (their “samara”). These “maple keys” will, by early May or so, form great, fluttering clouds as they drop from the trees and become scattered by the wind across lawns and woodlots. Some of these seeds will germinate immediately while others may lay dormant in the soil until the following year. But these seeds and seedlings are topics for a summer essay (and (great news!) summer is not that far away!)