BIRDING BY HINDSIGHT: A Second Look at Swallows
It was over 20 years ago, but I still fondly remember when my old bird identification classes in Duluth were at their peak in popularity. There was even one fall with so many birders registered that I experimented with offering a so-called advanced class for those with more experience. The experiment didn't last long. The first field trip of the season was in mid-August, the swallows were on the move, and not one of my prized pupils was able to successfully sort through them. Indeed, their teacher found himself hesitating a time or two over the identity of some of the swallows flying around us at Park Point.
So, what was the problem? There are only six swallows Minnesota birders have to deal with, and even novice birders can tell a swallow when they see one. And a basic lesson in Bird Identification 101 is to first fit the bird in question into its family group, and then work from there down to the species level. Accordingly, as I often point out to beginners, if you just know it's a swallow, you've already accomplished a lot, narrowing down the ID possibilities from 300+ regular Minnesota species to just six.
But successfully getting from six species to just one is often tough, partly because those things swooping around in front of you are hard to follow through your binoculars. One strategy is to put the binoculars down and watch with your naked eye: often swallows will eventually fly by close enough to identify without optics. Another method for learning swallows is to wait until you find some perched on wires, so they can then be scoped and studied at leisure.
Despite the difficulties many have with swallow ID, there have been surprisingly few articles on the subject. I could find nothing in American Birds/North American Birds, while Birding has had only two articles over the years, and these were limited to separating Bank, Rough-winged, and juvenile Tree swallows (Birding 17:209-211 and 28:111-116). Thus, it's about time that Hindsight took a look at this deceptively difficult group of birds.
One thing I like about the six species of swallows regularly occurring here is how nicely they can be organized into three groups of two. The blue ones (Purple Martin and Tree Swallow) nest in bird houses (and in natural cavities); the two brown ones (Bank and Northern Rough-winged) nest in holes in the ground (e.g., in sand piles and river banks: the Bank colonial and more in flocks than the more solitary N. Rough-winged); and the two with dark red throats (Barn and Cliff) construct mud nests under eaves, bridges, and other structures.
Another nice thing is how easy it is to find swallows for study, since all six species occur statewide, at least in migration. Note, however, that Purple Martins are essentially non-existent as breeders north and northeast of Duluth. (Even in Duluth, there are only two neighborhoods I know of with occupied martin houses.) Also, birders often find the uncommon Northern Rough-winged Swallow missing from their lists at days end, especially in northern and western Minnesota. And if there are no big sand piles around, one may not see any Bank Swallows. On the other hand, note how abundant Cliff Swallows are in northwestern Minnesota counties, where they swarm out from under many of the bridges you drive over.
At the same time, you can't use range/relative abundance much as an ID tool if all six swallows are mostly distributed statewide. Habitat clues usually don't help either, since swallows are seen well away from their nests perching on wires or feeding over bodies of water (especially sewage ponds; especially on stormy days). Learning calls might help occasionally, but I've only found it useful when telling the brown ones apart: listen for the Northern Rough-winged's one- or two-syllabled "raspberry" call, different from the Bank's multi-syllabled buzzy chattering.
Except for the relatively slower, deeper wing beats and longer glides of Purple Martins (and Northern Rough-wingeds, to some degree), differences in swallow behavior will figure little in most IDs. Nor will time of year tell you that much, with all six species mostly arriving in April and departing before the end of September. An early swallow before the first of April, though, will almost always be a Tree, while one lingering into October will probably not be a Bank or Purple Martin.
So, we're basically left with considering visual features alone to make identifications. When seen well enough, of course, the field marks involved with swallow identification are pretty straightforward, and there is no need here to repeat the basics. But following are some comments on what to watch (and watch out) for with each species – i.e., notes on what the field guides may have overlooked. Included below are Violet-green Swallow, a species with two sight-only state records, and Cave Swallow, a rapidly expanding species which will eventually occur in Minnesota, given the multitude of records from the northeastern U.S. and eastern Great Lakes.
As noted earlier, a Purple Martin's flight looks different from other swallows, enough so that this alone can serve to identify one, especially when its superior size is also noted. But because of its un-swallow-like flight and size, I have occasionally seen birders mistake the silhouette of a distant martin for a Merlin. The plumage of adult male martins may be distinctive enough, but be sure to take a second look at females and young. With their browner overall plumage and dusky throats, these can certainly look enough like Northern Rough-winged Swallows to cause potential confusion.
More than once when looking for bluebirds along the road, I've backed up or turned around when a blue-backed Tree Swallow at a bird house caught the corner of my eye. But not all Tree Swallows are blue; females and young can look as brown as any Bank Swallow. While that may not be news to most birders, many are quite unaware that fall Tree Swallows, especially juveniles, show a Bank Swallow-like breast band. This is the source of what is probably the most frequent swallow misidentification of them all. So, before calling that breast-banded swallow a Bank, make sure it's not a Tree. Note that the Tree Swallow's band is more gray than brown, that it's more diffuse and less solid, especially in the center of the breast, and that it lacks the downward "spike" that characterizes the center of a Bank Swallow's band.
But not all Tree Swallows are blue or brown; some adults can look quite green above, especially in fall, or at any time when the angle of the sun is just right (or wrong). Now, be sure to note as well the Tree Swallow's white underparts which curves up at the flanks towards the sides of the rump. While this feature is a good way to distinguish Tree from Bank swallow, it is curious that neither the Geographic nor Sibley field guide adequately illustrates or mentions this important field mark. But at the same time, this little-known Tree Swallow feature also provides a way for someone to mistake one for a Violet-green. Yes, there may be more white on the sides of a Violet-green's rump, but the Tree Swallow shows almost as much white in this same area to possibly lead birders astray.
As mentioned in the introductory comments, there are only two accepted sight records for this swallow, which occurs regularly in South Dakota just 300 miles or so west of Minnesota. But before you claim the third record, be sure to read the caveats in the paragraph above to make sure you're not just seeing a Tree Swallow. If it really is a Violet-green, you'll need to see more than its rump: at all ages its most important field mark is the white area above the eye. And, if the swallow is perched, try to see its wing tip extension beyond the tail (tail and wing tips closer to even on Tree Swallow).
Northern Rough-winged Swallow
Now that you've read this far and are aware of the similarity between this species and female/young Purple Martins, and know about the difference between the rough-winged's and Bank Swallows calls, and can begin to look for its somewhat slower and deeper wing stroke, there is no need to confuse this swallow with any other. But if you're still looking for more on Northern Rough-winged Swallows, note that juveniles have broad cinnamon-colored wing bars, unlike any other species. In addition, when studying perched brown swallows, it may be helpful to know that rough-wingeds of all ages lack the white "comma" which both Bank and juvenile Tree swallows show curving up behind their ear coverts. And note that you won't see any white tertial tips on a perched rough-winged, while such tips are often visible on both juvenile Bank and fall Tree swallows.
And now that you've read this far, especially the part above about the breast band on some Tree Swallows, there's also no need to confuse this swallow with any other. But take note of two other Bank Swallow features, which will often help you sort through the swallow flocks. First, the Bank Swallow is smaller than all the others, and this feature is especially noticeable and useful when examining swallows perched on wires. Second, a Bank Swallow in flight often stands out from the others due to its paler lower back and rump, which contrast especially with its darker tail.
As any field guide reader knows, the tail tip on this swallow is less notched and more squared-off than any other swallow. In addition, Cliffs in flight can fan out their tails to make them frequently look quite rounded; perhaps only the rough-winged's tail could approach or match this shape. Of course, the field guides also show the Cliff Swallow's dark throat and distinctive buff rump patch: what ID could be more straightforward? Up until the last 20 years or so, that would indeed have been enough for any birder in this part of the continent, but now you need to be aware that a Minnesota record of the rapidly expanding Cave Swallow seems inevitable.
Back to the field guides for a second look. While the Cave Swallow also has a buff-colored rump, note its buffy throat and dark red forehead, just the opposite of the Cliff Swallow's pattern. Sounds simple enough: while that inevitable first Minnesota Cave Swallow may not be easy to find, it should at least be easy to identify, right? Sorry. The serious catch here is that juvenile Cliff Swallows can have pale throats and/or dark foreheads, just like adult Cave Swallows.
So, it will take a careful look and thorough documentation to make sure any possible Cave Swallow sighting does not actually refer to a juvenile Cliff Swallow. Juveniles, of course, would only be seen in summer and fall, and it is likely that any stray Cave Swallow would probably show up here in fall, most likely in late October or November, when most of the other eastern Great Lakes and northeastern U.S. records have occurred. (And a footnote, which is probably purely academic: As both Geographic and Sibley show, the southwestern race of the Cliff Swallow (melanogaster) has a dark red forehead. But let's assume an individual of this race would "never" stray this far and get mistaken for a Cave Swallow.)
With its deeply forked and, well, swallow-like tail, at least the Barn Swallow shouldn't present any ID difficulties. And, indeed, the adults don't. But juvenile Barn Swallows do present some potential for confusion before their tails are fully grown. It seems these shorter-tailed young have buff forehead patches along with a dark throats, just like Cliff Swallows. Unless the birder is aware of this and takes a second look for other field marks, it's certainly possible that a Barn might be miscalled a Cliff.
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As the swallows gather in flocks on wires this month, now is the perfect time to assimilate the tips in this article and work on your swallow identification skills. You may still face some difficult IDs, though, so be prepared to swallow your pride and admit you might make a few mistakes. (But at least identifying swallows is easier than some things – like the ten-hour drive I just made for a Brown Pelican that wasn't where it was supposed to be....)