Naturespeak A naturalist's view of the world

November 1, 2010

A Murderous Migration

Filed under: Uncategorized — wykes @ 8:23 pm

The sight of hundreds of crows filling the gray morning sky on Sunday morning should not have surprised me. It was Hallowe’en day, after all, when all manner of dark and suspicious things are supposed to occur (and Crows are both dark and suspicious birds). A “murder” of crows would be a natural part of the script. But, I was mildly surprised. Having already witnessed the very same thing only two days before, I was delighted to be privy to a repeat performance. Yes, there are many dark and suspicious birds on the move in S.E. Michigan.

Crows are unusual in that they are both migratory and non-migratory in nature. Typically they are cold hardy birds which do not shy away from winter conditions. In fact, as scavengers and intelligent opportunists, they actually thrive in the harsh northern climes of winter. The Lower Detroit River region is a winter gathering point for crows. But, local populations – especially those from the Canadian Shield area – do seek slightly warmer climes (with an emphasis on the word “slightly”). They engage in a population shift ranging form a few hundred to a few thousand miles. Southern crows are much more laid back and so they don’t bother to migrate at all.

That these migrating birds were Canadians was evidenced not only from their Northeastern flight origin but also by their slight accent (“Caw Caw-eh”). For the most part the flyover was silent, however. On both days, the crows streamed overhead like a living river. The flow direction of the flock changed course like a rivulet running down a windshield, but it rarely broke up. At the Detroit River crossing the flocks often appeared on the horizon like a haphazard cluster of blown autumn leaves before narrowing to a column. Fifteen miles south, over my yard in Monroe County, the birds stuck to a tighter riverine pattern.

I did attempt some type of quantification. I mean, saying that there was a “bunch” of crows just wouldn’t cut it. “Lots,” “Scads,” or a “Butt Load” wouldn’t cut it either (the latter statement depends on the size of the butt involved and therefore is very inexact). A “murder” is an old fashioned way to refer to a crow grouping, and only by extending this to “a serial murder of crows” could I come to a proper description of the flocks that flew overhead. This, however, would be even more confusing. So, I did attempt to block out portions of the sky for a time and count the individuals flying past. On two occasions I came up with 200 plus birds per minute. At times the combination of distant birds and those flying over at tree top height made it difficult to focus (see below, here, & here). This explains why my other attempts were abandoned in a flurry of Old English phrasing.

It is probably impossible to put a figure on these migration events, but it is easily involved tens of thousands of birds. In other words, a butt load!  Hawk counters at the Detroit River Hawkwatch sight, although focusing primarily on birds of prey, noted the first day’s flight as exceeding 15,000 birds. The Hallowe’en flight was certainly larger than this by a factor of 100 or so.  It is interesting to note that crows have proven themselves able to count. If we knew the language, and the proper French-Canadian inflection, we could probably ask them to account for themselves. Unfortunately, because their kind often proves smarter than we are, we dare not ask out of jealousy.

Whether you like crows or dislike them, the sight of so many of them at one time was an awe inspiring sight. They are native birds who have suffered from the effects of West Nile virus in the recent past. It is good to see at least one component of their population thriving. Oh, by the way, for those of you who are irritated by my spelling of Hallowe’en in this piece I am simply using the old style spelling – the kind found in the type of books which refer to a grouping of crows as a “murder”.

1 Comment »

  1. It’s reassuring to know that large flights of birds still exist, even if they are not passenger pigeons or Carolina parakeets. I haven’t seen a cloud of birds of any truly significant size since, oh, the late-80s or mid-90s. It’s been a while.

    Comment by Ellen — November 2, 2010 @ 11:09 pm

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