Top row, left to right: Barn Swallow, Tree Swallow, Purple Martin (adult male).
Bottom row, left to right: Bank Swallow, Cliff Swallow, Northern Rough-winged Swallow, Purple Martin (female/young male).
Images are edited so species size is to-scale.
Swallows spend much of their time in the air, catching insects. This makes for an impressive spectacle but also creates an identification challenge that puts off many birders.
People may be quick to give up on identifying swallows in flight, or any birds in flight for that matter, because they are missing a key piece to the puzzle: it is more important to look for the small number of field marks that are most obvious than it is to look for a lot of details that you won’t be able to see–knowing the difference between the two is the trick. For example, with flying swallows, it is usually more important to look for areas of strong contrast than it is to look for detailed color patterns, as you might on say, a ground-feeding sparrow. That is why you will see the words “dark” and “pale” more often here than mention of specific colors; you simply don’t have time to discern such details when a bird is zipping by in a fraction of a second!
Below are the few field marks which were most obvious for me as I started to unravel swallows in flight, with the most useful features in bold. This guide deals with adult birds only. Juveniles add another level of variation to certain species, so it is best to start learning what to look for with adults. Species are listed in vague order of difficulty to ID, with the first three species more obvious and unique, and the next four (including the “female-type” of Purple Martin) more subtle. At the end there is a list of spots that are good for watching swallows during the summer in Chicago.
Tip: for a couple species it is helpful to look at flight style. Remember that flight is variable among individuals. Watch an individual for a while, compare it to another swallow of known species, and try to look for average differences.
Barn Swallow
Tail shape is the most obvious feature, with uniquely long outer tail feathers. Most of the time the tail is held closed and appears long and skinny, especially at a distance. Many individuals have obvious orange underparts, which are unique to Barn Swallow, while in other individuals the color is subtle and sometimes indiscernible.
The long outer tail feathers on adult Barn Swallows, called “streamers,” are unique–and very cool!
Purple Martin - adult male
Uniform dark color is unique and is enough to ID. Flight and build are also distinct (see Purple Martin - female and young male).
Tree Swallow
Uniform white throat and underparts are unique and show a hard-defined contrast with dark upperparts. Especially in males, the upperparts are much darker than the non-iridescent species Bank and Rough-winged Swallow. Small white notches on the upper side just behind the wings are usually noticeable against otherwise uniform upperparts. Tree Swallow is a larger species than all but Purple Martin; its flight averages more steady, with slower wingbeats, less changing directions, and less bouncing with each wingbeat when flying from point to point. Tail is moderately forked, more so than in Rough-winged and Cliff Swallow.
Note the pale notches behind the wings. These are often hit by the overhead sun, making them contrasting and noticeable at a distance. This is especially useful when the bird is flying away from you.
Bank Swallow
Clean white throat contrasts with a dark chest band. Even at a distance when underparts are obscured, white throat pops when hit by the sun. Smallest species, flight and build more distinct than in other species. Flight has quicker wingbeats, more wingbeats with less distance traveled, more changing directions, more bouncing with each wingbeat when flying from point to point. Entire body is thinner than other species, with a longer, thinner rear end and tail.
Note how the white throat can show in the light even while the underside is indistinct in shadow. That white throat combined with features of flight and build are enough to ID a Bank Swallow.
Cliff Swallow
Strong, sharp contrast between dark throat and pale chest and underside. In many cases (viewed from below, at a distance) the appearance of the underside is effectively black and white. Look for the distinct pale rump on the upper side when the bird banks, although this can be lost at longer distances. No pronounced longer outer tail feathers.
If you are unsure if you have a Cliff Swallow, wait for the bird to bank and check for a pale rump–this mark is noticeable except at longer distances.
Northern Rough-winged Swallow
Notable for lacking marks of other species. Appears to have dark throat and pale underside, but with no strong contrast between throat and chest. Plain brown above, not as dark as Bank Swallow. Body is subtly thicker than Bank Swallow, without the long, thin rear end. No pronounced longer outer tail feathers.
Purple Martin - female and young male
Dark throat and variably pale underside are similar to other species. Flight style and shape are the most important field marks. Glides more often than other species, with noticeably slower wing beats. Noticeably longer outer tail feathers, though not as exaggerated as Barn Swallow. Wingtips are more tapered than other species.
Note how the tail can lose its “fork” when fanned, but the longer, pointed outer tail feathers still create a different tail shape compared to similarly patterned species.
Where to see summertime swallows in Chicago
The best places for swallow-watching in the summer depend on where each species breeds. Barn, Tree, and Rough-winged Swallows are usually easy to see along the lakefront or in city parks, while Purple Martins are a little more concentrated around Martin houses (the human-made structures that are now their preferred nesting spots). There are many Purple Martin houses throughout the city, but some locations are: Gillson Park, Montrose Harbor, Jarvis Bird Sanctuary, Jackson Park, and South Shore Cultural Center. Bank and Cliff Swallows are even more tightly associated to their breeding sites during the summer, only being seen in small numbers elsewhere. Bank Swallows can be seen in good numbers at Big Marsh and Montrose Point Dunes, while Cliff Swallows nest on the Northwestern University campus, under the bridges at Jackson Park, and at the beach house near 31st St. Beach. Northern Rough-winged Swallows breed in larger numbers at Steelworkers Park.
Photos by Woody Goss