Brian L. Sullivan
While flipping through any field guide, you’ll immediately see that birds occur in all shapes, sizes and colors. This is not surprising since they occupy nearly all of the earth’s habitats, prey on a wide variety of food resources and have adapted to be most suitable to the niches that they occupy.
As birders, we immediately notice the patterns of color in a bird’s plumage, and we often use these to identify species. We also can use other general patterns when looking at birds.
The general shape and structure of a bird can help us, but it also can tell us something about the birds themselves. Features such as wing shape and tail length relate to how a bird lives in its environment.
We can learn a lot about a bird by looking at the shape of its wings. On birds that spend a lot of time in the air, wing shape is relatively easy to determine. It is more subtle on smaller birds, yet important differences remain.
If you study the shape of a soaring bird’s wings, you’ll see that they are typically long and broad, with fairly rounded "hands.” Soaring birds like Red-tailed Hawks, Sandhill Cranes and American White Pelicans use thermals — rising columns of warm air generated by the sun — for migration, and they have adapted similar wing shapes for efficient soaring.
Other species share different wing shapes based on their migrations. For example, falcons, swifts, swallows and terns have narrower wings with more pointed "hands.” On these long-distance migrants, their wings are built more for efficient powered flight than for soaring — an adaptation comes in handy when making long water crossings where thermal productivity is reduced.
As short to medium-distance migrants, Red-tailed Hawks have broader and more rounded wings.
Looking more closely within any of these groups reveals even more about how each particular species behaves. In the large soaring hawks, wing shapes differ depending on each species’ natural history. As short to medium-distance migrants, Red-tailed Hawks have broader and more rounded wings. Swainson’s and Broad-winged Hawks, on the other hand, are long-distance migrants moving as far as southern South America to winter. Although they have broad wings compared with many birds, within the genus Buteo they are among the narrower-winged species, and both share relatively pointed wingtips.
Migration is just one evolutionary process that shapes the features of a bird’s wings. Other factors suchas foraging technique come into play and can have important implications for the wing shape of more sedentary birds.
One of the most obvious features, the tail is easy to describe. Is it long or short relative to the body? Is it narrow or wide? These simple observations can tell us something about the species in question.
If you spend a lot of time on the ground, it makes sense to have a short tail like this Western Meadowlark. A long tail would brush up against the ground and hamper maneuverability.
Long tails add increased maneuverability in flight, acting as a rudder and promoting faster direction changes. Looking at hawks again, we see that the woodland hawks of the genus Accipiter share long tails. Sharp-shinned Hawks, Cooper’s Hawks and Northern Goshawks use their long tails to effectively chase prey through dense tangles and woods.
It is certainly an amazing sight to see a massive Northern Goshawk disappear into a dense thicket without moving a twig. Other species of hawks with long tails include Northern Harriers, which use a combination of long wings and tail to float effortlessly above a marsh before radically changing direction to pounce on prey.
Conversely, birds with exceptionally short tails often are ground-dwellers. Many species of grassland birds, such as Western Meadowlark and the sparrows of the genus Ammodramus, share generally short tails. So do many tropical ground-dwellers such as antpittas in Central and South America. If you spend a lot of time on the ground, it makes sense to have a short tail; a long tail would brush up against the ground and hamper maneuverability. Having adapted to have very short tails, these birds are relatively poor fliers.
There are many exceptions to the rule, however. Some ground-dwellers have long tails, such as California Thrashers, but they have developed the behavior of cocking their tail upward when running to avoid abrasion.
California Quail have sturdy legs and large feet, good for supporting its rotund body, and to scratch away dirt to reveal seeds and other prey items.
The general structure of a bird’s legs can often tell us something about their life history. Thick, strong legs support birds that spend a lot of time on the ground or use their legs and feet to seize and carry prey. California Quail have sturdy legs and large feet, good for supporting its rotund body, and to scratch away dirt to reveal seeds and other prey items. Raptors such as Peregrine Falcons have strong, short legs and powerful talons with long toes, used to rake prey in flight and then capture and carry it on the wing.
Many songbirds have relatively weak legs and feet. These light and small species generally eat insects and fruits, not requiring sturdy legs or talons. While many of these species share similar legs and feet, they have adapted unique bill structures to take advantage of their primary food sources. Sparrows and finches have short conical bills for breaking seeds open, while warblers have finer bills for gleaning insects.
When observing birds, try to take your understanding of a species to another level by looking at its structure, observing its behavior and making connections between them. Next time you’re out birding, take a look at a bird, and ask yourself a question about it. Why does that phalarope have webbed feet? Through observation, you’ll soon discover the answer.
Want to learn more about a bird's body?
A Wild Bird's First Plumage