Saturday, March 9, 2013

White-winged Crossbills Feeding on Alder

I did a quick tour of some of the area around Guelph this morning with Dave Bell and Josh Vandermeulen. The general theme was gorgeous weather and Horned Larks constantly flying north. A few migrant Red-winged Blackbirds were around, but it looks like tomorrow should provide the first push of migrants this spring, with species like blackbirds, robins, Killdeer and so on. From now on, even when the weather turns wintry again, there should be some spring birds around to keep things interesting. For now though, here's one last gasp of winter birding from a few weeks ago.

On February 18 I teamed up with Todd Hagedorn to see what we could find along the waterfront in Etobicoke and Mississauga. There were a number of interesting birds around like Northern Pintails, Pied-billed Grebes and a Glaucous Gull, but the undoubted highlight was a group of four incredibly tame White-winged Crossbills at Humber Bay Park East. The birds were feeding on the cones (technically the female catkins) of alders right next to a busy pathway, and seemed utterly unconcerned about having people only feet away. The pictures are mostly mediocre, but I found the behaviour extremely interesting.

White-winged Crossbills normally feed on conifer cones, particularly spruce and tamarack, but may exploit other food sources when available. These crossbills were certainly exploiting the alders to the best of their ability, clambering all over the branches like parrots, as well as occasionally coming down to the ground for snow.

Although sometimes the cones would be conveniently positioned, the birds also had to break off some cones and manipulate them in their feet to feed.

Crossbills have a very special way of extracting seeds from cones. By pushing the two mandibles sideways, they can pry apart the scales on the cone to expose the seed within. Next, the bird uses it long flexible tongue to remove the seed. I was extremely lucky to catch this shot of one of the crossbills with its tongue extended.  If you zoom in you can see seeds and bit of debris stuck to the tongue.

While looking through the pictures afterwards, I noticed that there were birds with bills crossed in both directions:

The proportion of right-crossing and left-crossing bills is generally even in a population, and this probably evolved because each morph can exploit conifer cones in certain orientations better than the other morph. The consequence of this is that a flock of White-winged Crossbills can more fully utilise one tree before moving on. See this article for more details.

We certainly enjoyed the time we spent watching one of Ontario's coolest birds!

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