Brian L. Sullivan
The Northern Wheatear in the Arctic fills the same ecological niche as the Dark-faced Ground-Tyrant in South America.
With just a little traveling, birders can recognize the similarities between many North American birds and other species found elsewhere around the globe. If you see Carolina Wrens in your yard in the southeastern states, you’ll note similar-looking and -sounding species throughout the tropics. If you’re familiar with Peregrine Falcons, you’ll note that species on other continents plus the traits that all falcons share around the world.
In my travels, often I’ve been struck by the resemblances between North American birds and some altogether different ones found elsewhere. Two completely unrelated groups can occupy the same habitat and appear overall similar but occur at opposite ends of the world.
These similarities result from a process called convergent evolution, where otherwise unrelated animals evolved to occupy the same ecological niches — and, in many cases, developed similar morphological traits to better exploit those habitats. Many examples of this occur in birds, and these are some of the more obvious cases I’ve noticed over the years.
In the Northern Hemisphere, our arctic waters are occupied by a variety of alcids. Usually nesting far from human disturbance, the vast majority of Alcidae species occupy remote oceanic islands when breeding and then spend the winter at sea, far from land and the ever-watchful eyes of birders. Some alcids are familiar, especially the more southerly breeding puffins and murres, and the diverse family includes auklets, murrelets, Black and Pigeon Guillemots, Razorbill and Dovekie.
Alcids and penguins have evolved to exploit a rather unique ecological niche. They dive below the surface to catch fish in their bills, sometimes searching for food hundreds of feet below the sea surface. They ride low in the water when on the surface and have thicker, denser bone structure than other birds to help them stay submerged.
Birds like the Crested Auklet fill the same ecological role in the north, as penguins do in the south.
Perhaps their most striking adaptation is their use of the wings as flippers, helpful for swimming but compromising the ability to fly. Indeed, the penguins have given up the ability to fly, instead allowing their need to swim and dive efficiently to outweigh the ability to fly.
Alcids can still fly — but just barely. Indeed, flying alcids resemble missiles on a collision course with their targets. Alcids’ short, narrow wings are modified for underwater propulsion and make flying through the air an ungainly process. Unlike the penguins, however, alcids need to retain the ability to fly so they can continue to nest on steep vertical sea cliffs that would be otherwise inaccessible.
Just about everyone in North America knows crows. The big, black birds occupy a diverse array of habitat across the continent, often in large flocks, and have adapted well to the presence of humans. Certain species can be seen at landfills, picking through garbage dumpsters, poking around lawns, essentially making a living on the excesses of man.
The Crested Caracaras share many crowlike habits, even though they are completely different species.
In South America, though, a completely different group of birds has taken on this role. At the dumps in southern Argentina, you don’t see crows but caracaras. One species in particular, the highly social Chimango Caracara, loves to exploit the excesses of man and is particularly crowlike in its habits.
This is a good case where two completely unrelated groups have produced species that occupy a similar ecological niche but didn’t evolve to look alike. Caracaras are most closely related to falcons, whereas crows are actually among the largest species in the broad family of passerines, or perching birds.
Nonetheless, a similar open niche was available on two continents, and these otherwise dissimilar species decided to fill it. It is shocking to see so many caracaras in one place, and at the Ushuaia landfill in Argentina, you can see three species of caracaras on any given day.
In the United States, flycatchers and thrushes do not look very similar… but it depends on which flycatchers you’re comparing with which thrushes. I can see how a birder might mistake a female Western Bluebird for an open-country flycatcher. While bluebirds do not often "fly-catch” in the true sense of the word, they do eat insects and perch conspicuously on fences, roadside posts and power lines.
Nonetheless, these two families are usually quite distinct in North America.
In the high Arctic, we see Northern Wheatear, an open-country relative of the more familiar thrushes. It forages for insects in bluebird-like fashion, searching for prey visually and then pouncing on it from above. In the barren, open habitats of the southern tip of South America and its offshore islands, a different group has evolved to exploit this niche: the various ground-tyrants, such as Dark-faced Ground-Tyrant.
Students of systematics will recognize "tyrant” in their common name, which helps observers realize that these are indeed flycatchers. "Our” kingbirds are in the genus Tyrannus.
Although ground-tyrants are quite different from Northern Wheatear in taxonomy, they have evolved similar habits and appearance. Both perch on the ground or on rocks in open country, share a rather upright stance and have short tails and an overall stocky build. Observers familiar with Northern Wheatear will recall that species upon seeing their first Dark-faced Ground-Tyrant.
These are but a few examples of convergent evolution throughout the world of birds. When we make the connections between birds, the habitats they occupy and the food they eat, we become better birders. These things shape the development of birds and produce the traits that we use to identify them.
Next time you’re birding in a particular habitat, take note of the species, and ask whether similar habitat or species could exist elsewhere in the world. Most of the time, the answer will be yes!
Want a chance to see these awesome birds? Go birding with these tips:
25 Tips to Better Birding
25 Tips for Bird Photographers