a blog by Bruce Lieberman and Niles Eldredge that focuses on Current topics in evolution, paleontology, science & society

When is a raptor a parrot? The curious case of the American Kestrel

When is a raptor a parrot? The curious case of the American Kestrel

Happy New Year! We hope it’s been a great 2018 and we wish you all the best for an awesome 2019. Further, we most sincerely thank you for joining us on this adventure in macroevolution and natural history. The number of visitors to our site has been growing and we very much appreciate each and every one of our readers. As many of you know, we’re paleontologists that study long extinct marine invertebrates. Thus, if we had to turn our attention to modern life forms in nature, you might perhaps expect that the things we’d be most excited to observe would be found by poking around tide pools, and involve searching for starfish, or mulling over, and under, stones in pursuit of mollusks. And undoubtedly such activities can be pretty cool. But if you asked us what animal we most enjoy observing in the wild, even in the “wilds” of New York City’s Central Park, hands down we’d say “birds”. (Once one of us [BSL] saw a pack of rats milling around mid-morning in the Strawberry Fields section of New York City’s Central Park, but that was definitely not enjoyable, although it was a bit ‘startling’.) Thus, in their honor, today we tip our cap to some of the representatives of the “charismatic vertebrate macrofauna”, those fascinating, multi-colored, beautifully diverse, sometimes denizens of the air: the Class Aves.

Bird watching is a past time that many find relaxing and inspiring (even if it sometimes leaves you with a stiff neck); still, identifying the precise species you’ve seen or heard is not always easy, especially if you’re inexperienced or encounter something novel. In the “old days”, and by that we mean the late 20th or early 21st century, if you saw something new and unfamiliar, absent an experienced bird watcher in your midst, in order to obtain an identification you’d have one of two choices. You could try to remember what you saw until you got home, when you could thereby peruse the titles in your library, or you’d lug around your one ‘go to’ guidebook that you could refer to out in the field. Today’s identification process, however, has been dramatically enabled by electronic resources that simply did not exist just a few years ago. For instance, now you can get an app on your phone, and one we find particularly awesome and efficacious is the Cornell University Merlin ID . Fire up the app, it will ask you questions about where you saw the bird, what day it was, was it in a bush, on a power line, etc.; then you get offered a range of sizes, colors, habits, etc., you choose the correct option for each of those, and then the app provides you with pictures and descriptions of the one to many species it might be. (You can even take a photo and the app can use that for identification purposes.)

Circling back to our discussions of stasis last time, we find it amazing that anyone would challenge the notions that stasis prevails and, further, that species are real when some bird, let’s say the Eastern Phoebe, always shows the same diagnostic characteristics of color, shape, and size, and warbles the same distinctive call:

Indeed, this is one of the things that we believe makes bird watching so exciting and entrancing. There is a profuse diversity of traits and appearances that exist among the various species that can be encountered, yet these traits show consistency within certain narrowly circumscribed groups - species.

Also awesome, these birds display consistent behaviors (beyond just the behaviors involving their songs and calls). For instance, the Eastern Phoebe is known for its “tail wagging”. In fact this is one of the omnipresent behaviors that eases identification of the species.

Be you in Florida or the Northwest Territories of Canada, when you see an Eastern Phoebe there’s going to be a darn good chance it’s bobbing its tail up and down in the distinctive way shown in the previous video. Score one more for stasis, the reality and individuality of species, and hence macroevolution!

Electronic resources have not only stepped up our ability to identify birds, but they’ve also made it easier to see where species occur throughout the year. Again, the folks at the Cornell Bird lab are doing amazing things with range maps of species showing how they change week by week across the different seasons. Check out this example, again involving one of this week’s “It birds”, by clicking on the blue text

the eastern Phoebe.

(Note, in the 1960’s, people used to talk in a rather sexist way about “It girls”, for instance, Edie Sedgwick,

Edie Sedgwick, from .

Edie Sedgwick, from .

who was considered a famous “It girl” of the 1960’s and was perhaps the subject of several Bob Dylan songs including “Like a Rolling Stone”:

Now in the more enlightened 2010’s why can’t there be “It birds”?!?!; to learn more about the “It girl” concept check out: .)

Back to the spectacular dynamic range map, which is built up from observations by amateur and professional bird watchers. It shows us that you’re unlikely to spy an Eastern Phoebe in the northern or central part of the United States in the month of November.

Perspicacious bird watchers want to know the veracity of their identifications; they also want to know more about how the myriad bird species are classified, which is a question of bird phylogeny or evolutionary relationships. Coincident with the recent advances in technology assisting bird watching, there have been new developments in bird phylogeny and it is to these that we will turn as they provide a fascinating perspective on the affinities of another bird.

The American Kestrel

Last November one of us (BSL) pulled up to a traffic light near the banks of the Kansas River. The Kansas River, or Kaw to the locals, is a relatively large river, by midwestern standards, that serves as a corridor for migrating birds. In his peripheral vision a robin-sized bird alighted on a street lamp. It was evening, and he turned, but in the gloaming all he could discern was that it wasn’t a robin, its breast had a slightly reddish tinge above white, its head and back were dark, maybe bluish-grey, and it had a beak distinctly larger than the type common to fly catchers or warblers. The light changed, and although in Kansas contra New York City or Boston a brief pause after a manifest green signal is considered permissible and does not precipitate attendant honking, there clearly was no time to fire up the Cornell Merlin App. (This is not to speak of the concomitant distracted driving such would have entailed.)

There was a vague sense that the size, robust beak, reddish breast, and blue grey back and tail possibly connoted a male Rose-Breasted Grosbeak, but the hypothesis was considered ill formed, tentative, and probably loopy. Especially because, although not color blind, poor judgement and bad taste, not to speak of the muted shades brought on by twilight, meant that BSL recognized his initial assertion of “reddish” when it came to the bird’s upper breast might actually constitute a much broader part of the visible spectrum of light than typically consigned to the color red. BSL also happened to be thinking about the awesomeness of U.S. Supreme Court Justice Ruth Bader Ginsberg, sometimes referred to respectfully as the Notorious RBG,

Image of U.S. Supreme Court Justice Ruth Bader Ginsburg, a truly great American, from  .

Image of U.S. Supreme Court Justice Ruth Bader Ginsburg, a truly great American, from .

and thus mayhaps a connection via acronym to this charming bird was forged - wouldn’t it be great to have a songbird with the nom de plume “Notorious RBG”, where RBG stands for “Rose-Breasted Grosbeak”?

However, after arrival at his domicile a short time later, subsequent research made it clear to BSL that he had not seen this bird:

The avian Notorious RBG (Rose-Breasted Grosbeak). Image by John Harrison, CC BY-SA 3.0,  .

The avian Notorious RBG (Rose-Breasted Grosbeak). Image by John Harrison, CC BY-SA 3.0, .

The breast of the RGB was way too red and also its tail was shorter and stubbier than the bird BSL had seen. Moreover, Cornell’s ebird revealed that avian RGB’s are not likely to be found in Kansas in November: only a single November sighting was made in Lawrence, Kansas in the last 10 years. The initial hypothesis was not looking good, and there was more exploring to be done.

We both have been blessed with careers at natural history museums. Such employment has many perquisites, not the least of which are the opportunities to interact with expert naturalists. One of these pivotal to this story is Mark Robbins, the ornithology collections manager at the University of Kansas (KU) Biodiversity Institute. Thanks to him the hypothesis was revised: this was afforded by his knowledge and also the opportunity he provided to examine actual specimens. In previous blog posts we have sung the praises of natural history museum’s and the treasure trove of biodiversity specimens they contain, for in this case they provide fundamental data about bird morphology (and also distribution and habitat). BSL’s bird was actually a male American Kestrel:

Specimens of the American Kestrel in the KU Biodiversity Institute, photograph by Mark Robbins.

Specimens of the American Kestrel in the KU Biodiversity Institute, photograph by Mark Robbins.

BSL realized that orange can look red at night, especially if you’re myopic. And these tiny birds of prey love to perch on lamp posts at dusk to be on the look out for food. As Ray Charles said in a different context, “Night Time is the Right Time” …

to catch something to eat if you’re an American Kestrel. Note further that November is also a good time to be an American Kestrel in Lawrence, Kansas: click here.

However, not only was BSL to be disabused of his initially faulty identification, but he was also to be flummoxed by his entire weltanschauung on birds of prey and their origins and affinities. Some might associate this bird, in an evolutionary sense, with hawks; BSL had, and many other hawks are common in this part of the world, including the Red-Tailed Hawk.

Red-Tailed Hawk, photo by Don DeBold. CC BY-SA 2.0,

Red-Tailed Hawk, photo by Don DeBold. CC BY-SA 2.0,

But Kestrels aren’t hawks, they’re falcons. Same difference, or close enough, right? Wrong. Big time. Again, thanks to Mark Robbins, it became clear to us that kestrels and falcons are not even closely related to hawks. Click here to see the article by Suh et al. in Nature Communications in 2011, based on the latest phylogenomic techniques, that shows why, and click here to see an excellent account of this research in the Guardian, written for a non-technical audience. (Note, the result from Suh et al does not appear to be weakly supported and it probably won’t be a “flash in the pan” or evanescent on the scientific stage. Instead, it bolsters previous research, including work by Hackett et al. published in Science in 2008, click here [to see more than the abstract you may be stopped by a pay wall, sorry about that … but don’t blame us], again based on what were at the time the most modern approaches to reconstructing evolutionary relationships.)

Kestrels and falcons are in fact closely related to parrots.

Figure of the bird tree of life from Suh et al. (2011)  Nature Communications  DOI: 10.1038/ncomms1448 | , Macmillan Publishers Limited all rights reserved.

Figure of the bird tree of life from Suh et al. (2011) Nature Communications DOI: 10.1038/ncomms1448 | , Macmillan Publishers Limited all rights reserved.

Hawks (and eagles) sit well outside of these and nest, evolutionarily that is, with vultures. Macroevolution is like family relations, you don’t always get to pick who you are related to. You may love all of your relatives, and if so great, but if not, tough luck. At the scale of the history of life, sometimes you get cousins that are brightly colored, long lived, and can say vivacious things like “Pieces of Eight”. Other times, your cousin is a carrion eater with a proclivity for munching on roadkill.

We can be awed by the similarities between kestrels and hawks, and the thought that these seem to have evolved independently. But we shouldn’t be overawed. At the scale of the history of life, sometimes convergence happens. Moreover, kestrels were at least partly grouped with hawks based on evidence that was pretty weak: traits such as “likes to eat meat”, or “flies fast”, “reddish”, etc. Detailed comparisons not only of molecules, but perhaps of morphology, including that somewhat stubby beak we mentioned previously, might bolster the kestrel/parrot affinity.

In any event, to get here we’ve utilized information based on the latest technology, like dynamic range maps and studies that incorporate large portions of the genome to reconstruct evolution. But just as importantly this tale was driven by expert knowledge and the ability to access specimens collected decades ago. That is to say, advances happen, but the fundamental things apply as time goes by:

Where will we go next? Who knows, but we hope you’ll stick around for next month’s post, and we thank you for reading.

This blog was written by Bruce S. Lieberman and Niles Eldredge. The current manager of the website is named below.

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