Cowbirds

Over the past few weeks, I've been noticing the brown-headed cowbirds hanging around elk and deer in the valley. More than just another dark bird, they are one of the most unusual of our feathered residents.

The cowbirds name comes from its curious habit of hanging around cattle and horses in order to collect the various insects attracted to our hoofed friends. Around Canmore, they're also attracted to the other ungulates; hoofed animals like elk, deer, sheep and goats. Rarely over the last few weeks have I come across an elk that has not been surrounded by several cowbirds.

The males are easier to identify as their bodies are black with brown heads. The dark feathers are somewhat iridescent and the colours tend to change slightly with the lighting; much like starlings. Often confused with another blackbird, the Brewer's, the cowbird's brown head, along with its brown eyes (the Brewer's eyes are yellow), easily distinguish it. Female cowbirds are much more earthy in colouration. This is typical in many bird species as they must remain hidden while on the nest. As we shall soon find, this colouration is for a much different reason on the cowbird.

Cowbirds often seem to be completely unaware of humans. A few days ago I had two males contentedly sitting on a railing right beside me. Unlike the gray jays which tend to swoop in and quickly disappear with your lunch, cowbirds often seem completely unconcerned with you. Apparently female cowbirds are even more cheeky than the males. They've been known to alight on people, just to get closer to the mosquitoes buzzing about. I guess they can't tell the difference between cotton and elk fur.

Since they tend to move about with the local ungulates, they don't have the opportunity to build a nest and raise their young as do most of their feathered relatives. Instead, the female sneaks into the nest of other birds and lays a single egg. In many cases, this egg will hatch and the unwitting adoptive parent will raise it as her own. Over 250 species of birds may fall victim to this strategy, but song sparrows are the preferred lot.

This parasitic behaviour is well planned out. Over the course of a summer, the female cowbird will lay 10-12 eggs, one at a time, in various nests. They say birds can't count, but the cowbird doesn't take any chances. Generally she removes one of the residents eggs by throwing it out of the nest or eating it (just in case).

This ploy doesn't always work and about half of the host species have figured out ways of taking care of unwanted adoptees. This may be as simple as removing the offending egg (robins) or even building a new nest on top of the cowbird egg.

The eggs hatch rather quickly, in 11 or 12 days and the hatchling is often larger than its nest mates. In the nest, its often the largest nestling that claims the most food and so the natural nestlings may end up starving as the cowbird gets larger. It leaves the nest after about 11 days but hangs around for another few weeks for hand outs.