A lot of animals have very specialized methods of feeding, and today’s bird is no exception. They’ve developed a unique way of utilizing a food source that is often well protected. Crossbills are a group of birds that feed on the seeds of coniferous trees. Those big pinecones don’t look too easy to get at, but crossbills have found a way. The name crossbill refers to the shape of the bird’s beak, which is crossed over to aid in feeding. The crossbill inserts its beak into a pinecone and then bites down with its strange bill, which pries the pinecone open, while the bird sticks its tongue out to grab the seed. Here’s a picture of the beak:
Pretty ridiculous, right? It gets even better. Each species of crossbill has different sized and shaped beaks to open a specific type of pinecone. Even more astounding, birds within the same species have a preference for different cones. For example, western red crossbills have big bills, and feed on Engelmann’s spruce and ponderosa pine, while eastern red crossbills eat Newfoundland black spruce seeds. Each of these distinct groups of birds have their own calls, which differ from crossbills of the same species that feed on different trees. You’d think that would mean each population has developed into separate species, but according to DNA studies there is no evidence of this.
Crossbills are monogamous, and stay with their mate throughout the year. They can breed at almost any month of the year when food is available, often breeding in winter to take advantage of conifer cone crops. Once the chicks have hatched, the females incubate the young while the male guards their territory and brings food to the nest. Unlike adult crossbills which produce their own distinct calls, the young birds all have similar calls. Once they grow up enough to leave the nest, however, the young birds develop the same calls as their parents.
When they feed, crossbills flock together, a behaviour that not only helps protect against predators but also optimizes their foraging strategy. When some birds find a tasty meal they call up all their friends to come join the feast. Once a fair number are at the party, the noise increases until eventually the cops come and the birds have to disperse. Well, not actually, but as the birds’ song comes to a crescendo, this seems to be a signal that food is no longer abundant, and the flock leaves to find another feeding site. Interestingly, these calls do not attract crossbills of a different call type, supporting the theory that call type is related to the specific trees the birds feed on.
Crossbills are an amazing example of a species that has evolved to utilize a food source that other seed eating birds cannot use. Plus, they look pretty silly. Which is always a point in my books, for any animal.
Cover image By Elaine R. Wilson, http://www.naturespicsonline.com – CC BY-SA 3.0