A Bouquet of Crows

by Sharon McInnes

During a Cornell Lab webinair called The Secret Lives of Crows, our instructor, Dr. Kevin McGowan, urged us to avoid the term “a murder of crows” on the basis that it’s unscientific and perjorative.  He’d prefer, he said, “a bouquet of crows. ” So, in honour of McGowan’s more than 25 years studying the social and reproductive behaviour of the American Crow (Corvus brachyrhynchos), a bouquet it is.

American Crow
Wikipedia image

McGowan does his research in Ithaca New York, home of Sapsucker Woods and the Cornell Lab of Ornithology. Here on Gabriola, we have the Northwestern Crow (Corvus caurinus) which is slightly smaller than the American Crow and has a more nasal call but “is so similar that the two may in fact be the same species.” (http://www.allaboutbirds.org/guide/Northwestern_Crow/id) Given the similarities, I think it’s fair to assume that his findings apply to our local crows too.

Three Northwestern Crows conferring.
Photo by Junior Libby - CC license. 

For decades now, crows have been making headlines when they roost, in the tens of thousands, in cities. A 2010 article in The Vancouver Sun refers to that city, my home town, as “The City of Crows”. Certainly when I stay at my daughter’s in the West End, I’m regularly awakened by the raucous calling of crows, and cannot take a walk along the seawall without crossing paths with dozens of them. But it hasn’t always been like this. Crows only started moving into cities, in large numbers, in the 1980s. During the webinair McGowan explained that this press into urban environments had multiple causes but was due in part to the fact that hunting is banned in cities. Crows have been hunted – by farmers and “sport” hunters – since the dawn of time, and still are, as this 2009 post by a Pennsylvania hunter, Bob Aronsohn, attests:

Then my friend … and I shot an additional 6,932 crows from November to February.  Our largest shoot last season was 543 crows in one day. We had several over 400 and quite a few in the two and three hundred range. The main reason I love to hunt crows so much is because you just don't setup just anywhere and expect to have a good shoot. It takes plenty of scouting in order to line up a good shoot. I don't get good shooting all the time, sometimes I just don't get in the right spot.  (http://www.gofoxpro.com/site/crow-hunting)

So, who can blame the crows, intelligent, social, family-oriented beings that they are, for choosing to leave the country?  Besides safety from hunters, city living offers the advantages of readily-available food (since crows have adapted to scavenging our leftovers) and fewer predators such as raccoons, jays, squirrels, owls, and hawks, an asset that is especially important during nesting season. McGowan’s research shows that city and suburban nests are subject to less predation than rural nests. In total, 57% of city nests compared to 48% of rural nests are successful.  

There are also disadvantages, though, to leaving one’s home in the country. For one thing, that city ‘fast food’ is less easily digestible than the crow’s natural diet: invertebrates, fish, snakes, frogs, small birds and mammals, bird eggs, nestlings, fruit and seeds.  Besides being less nutritious, the garbage that crows ingest in cities also carries the risk of contamination. This may not be a big deal for an adult crow but it can be deadly for a nestling.

In the end, though, the advantages and disadvantages of the two habitats appear to cancel each other out, in terms of nesting success, and they end up with the same number of fledglings.  Even though fewer rural babies survive, the ones that do are bigger than their city counterparts.  They’re heavier by 40-50 grams, have longer legs and bills, and possibly (although this not yet proven) larger brains.  McGowan and his team wondered: what makes the difference?  Turns out it’s all that good old country food. Researchers discovered this by feeding their city crows the kind of food mama crows would feed their babies in the wild. The result? Bigger nestlings.  It seems that crows, like humans, will eat junk food, to their detriment, just because it’s there.

This article was first published (with fewer images)
in the Flying Shingle on March 10 2014.