Saturday, September 8, 2012

Midair Feeding Strata?

One of the great things about birding in the forest is how easy it is to pick out each bird's ecological niche. For example, on the bottom, you have Ovenbirds and Thrushes, in the middle you have all sorts of warblers, tanagers, flycatchers, tree-clinging birds, etc., and on top you have vireos and certain other flycatchers. And this is just Eastern Woodland birds. All forests have developed these "feeding strata", or levels wherein different kinds of organisms feed on the different food items that are found there. These strata are unique for every forest, and they show how forests evolve and develop relationships as a system, and when one cog in the master machine falls out, the machine can no longer function as a whole.

Another classic example of feeding strata is underwater, in coral reefs or elsewhere. Different fishes feed at different levels. But what about in midair? We all know and love swallows, swifts, and other aerialists whose energy and agility are an infinite source of free entertainment. Do they have different preferred levels at which they feed too? Most of the time, we see these so-called aerialists separately, some swallows at a pond, some swifts of a neighborhood, some nighthawks over a parking lot, etc. But when they come together, it becomes obvious that there are in fact feeding strat in the sky. One morning, not to long ago, a cloud of swallows--multiple species--had gathered over a local marsh. The swallows remained relatively close to the marsh without going more than say 50 feet above the cattails. Below them, in some taller shrubs and small trees, a flock of Cedar Waxwings was displaying their aerial abilities--something they're often not given credit for--by sallying out and then back to catch flying insects, but never in the level of the swallows. Up above the 50 feet of hirundinid madness, Chimney Swifts had gathered to feed on insects higher than the swallows would push for. So clearly some aerial strata have developed: waxwings on the bottom, swallows in the middle, and swifts on top. And what does this tell us? It tells us that each group of birds is adapted to hunting in different altitudes (their niches are different), and in doing this, they avoid direct competition between species.

 This just comes to show that even the littlest, seemingly insignificant observation can tell us a lot about nature, so get out there, keep your eyes and ears open, and who knows what discoveries you'll make!

To top this post off, here's an amazing video of Tree Swallows gathering for migration:

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