One of the many wonders of nature that we hardly ever think about is the amazing variation in the size and shape of the beaks of birds. Even though some birds are famous for their use of primitive tools made from twigs, their main tool is their beak. Beaks reflect the necessity of reaping the primary food source of each species and Darwin was one of the first to point out the remarkable evolutionary changes that can occur in the forms of beaks over time even when derived from a common source. His work on the so-called Darwin’s finches in the Galapagos Islands is a classic demonstration of how beaks change in response to adaptation.
We can look around us every day and discover the amazing variety of beak shape and think about how each beak is suitable for a certain range of foods and forging methods. I am attaching a series of photographs of birds that illustrate some of this variety.
The blue-gray gnatcatcher has a very tiny beak and when you observe its behavior it spends a lot of time foraging for tiny insects in foliage. In contrast the blue grosbeak has a massive beak which is well adapted for eating large seeds; this is a typical beak for finches that eat seeds with a tough outer shell. One of the most bizarre beaks in the world is that of the crossbill which is adapted for prying open the scales of the cones of conifer trees to reach the seeds. Given the variety of the cones, it is perhaps predictable that there would be considerable variation among red crossbills in their bills that reflect the predominant food type found in different locations.
One of the most familiar but in some ways the strangest bill is that of the duck, which is broad and flat. This is suitable for dabbling for plants and small animal prey; in a case of convergent evolution the bizarre platypus of Australia has developed a similar means of catching invertebrates underwater.
The classic bill for fishing is illustrated by the tri-colored heron which has a long straight beak for grasping fish which it spots while wading in shallow water. In contrast, the familiar but strange pelican has a massive bill with a flexible pouch underneath which opens as the pelican dives into a school of fish and engulfs the prey. The wood stork also feeds on fish and other aquatic life but has a fundamentally different method of prey capture; it holds its beak open while walking and shuffling its pink feet in shallow water and the bill snaps shut very rapidly whenever anything touches it.
The bald eagle has a short hooked beak typical of different types of raptors; this form is efficient in grasping and killing prey, and in ripping off chunks to eat.
So let’s vow to pay more attention to some of the details we see all about us in nature and think about the patterns we observe and the reasons for them. The glories of the natural world can be appreciated at many different levels, but greater knowledge often leads to a heightened appreciation of the wonders of nature.
Thanks to Stan Bentley (grosbeak and crossbill) and Paula Kaye (eagle) for some outstanding photos.
Bill Dunson, Englewood, FL & Galax, VA