Wednesday, November 7, 2012

Holy Crows

Posted by Jess dePiano. Jess is a junior ENVS major/Ecological Agriculture minor in the College of Arts and Sciences, and is very interested in ecology and wildlife conservation.

What: Centennial Woods is a great place to observe some pretty dramatic phenological changes that are occurring as we approach the winter months. By now, pretty much all of the deciduous trees have lost their leaves (save the reluctant Norway maples), insects are few and far between, and animals are preparing for the long, cold months ahead. One amazing event that is occurring right now is a mass migration of crows flying over the Burlington area. This daily migration was first pointed out to me by one of my professors at UVM, Teage O'Connor. Seeing this migration over the past few days made me wonder: Where are the crows going? Where are they coming from? Why are they traveling in such large groups (sometimes in the thousands!)? I decided to do some research to look into these questions.

The American crow (Corvus brachyrhynchos) generally migrates short-distance during the winter months. The crows that we are seeing flying over Burlington are traveling to a communal roost (possibly near Red Rocks) where thousands of birds can be found roosting each night. This type of behavior is typical of American crows at this time of year, although to the observer, the sight of hundreds or even thousands of birds flying overhead is extraordinary.

Crow behavior is fascinating. These birds are extremely intelligent creatures, although some regard them as nuisances. Crows travel and forage for food in family groups year-round. When winter approaches, however, massive flocks form and migrate together to roosting sites, like the one here in Burlington. Over the past 60 years crow roosts have become increasingly urban and increasingly large (the largest recorded was estimated around 2 million crows). The sheer number of crows roosting together provides them with protection from predation (strength in numbers!), warmth, and the chance for adolescents to meet potential mates. Also, since crows forage in groups, belonging to such a large group may increase their chances of finding food in the winter. In an urban area like Burlington, the crows have a much better chance at finding food to scavenge and are less likely to encounter large predatory birds (compared to more 'wild' areas).

The migration is a daily one for crows, some traveling well over 10-20 miles to get to Burlington. They arrive in the evenings in a steady stream from around 3-5pm. As winter progresses, we should expect to see more of these birds migrating in the late afternoon into Burlington in search of shelter. If this winter proves to be especially harsh, crow populations may reach over five thousand. If you get a chance, take some time out of your day to watch this incredible event. I personally have never seen anything like it!

Where: Burlington, VT

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