Saturday 19 March 2016

How Crossbills Feed

Crossbills use their specially adapted bills to pry open cones and extract the seeds. They always use their lower mandible such that it points towards the axis/centre of the cone. This means that only part of the seeds can be reached easily depending on the birds position or if the cone can't be removed from the tree and turned around.

Check out how this bird pries open the cone scale with its bill. Click on the picture to see a much bigger version :)

In the next picture you'll see that the same bird has its LOWER mandible pointed towards its LEFT. 
Review the above photo and you'll see that the lower mandible is pointing towards the axis of the cone.

But only 50% of crossbills have their bills crossed in this way. The other half have their bills in the opposite orientation. This bird has its lower mandible pointing towards its RIGHT:

Studies have shown that there is an equal frequency of left-to-right mandible crossings within the crossbill populations. This minimizes overlap in the use of cones and maximizes foraging efficiency.

This adult male is a lefty:

While this adult male is a righty:

Crossbills are an exciting species to observe. They descend upon spruce trees in chattering flocks of a dozen or more, and are often very approachable while they busily pry the seeds out of the cones creating a light flurry of little winged spruce seeds that float to the ground around you.

There is often a wide array of colours visible in a single flock from bright yellow young males to the deep pinks and roses of adult males. The young males can be a blend of yellow and red, while the females are rather greenish-yellow. Juveniles tend to have bolder streaking on the flanks.

Check out this close-up video of a WWCR feeding on a cone to get an idea of how they pry open those cones!

Another interesting tidbit about White-winged Crossbills is that they breed very early in the year to take advantage of maximal cone supplies. With the high numbers of crossbills in Newfoundland this winter I've been expecting to see breeding evidence. So far I haven't found any signs yet - maybe someone will beat me to it?

Compare these two maps of White-winged Crossbill sightings from winter 2014-2015:

And winter 2015 - 2016: