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The Swifts of Mexiquillo

The Swifts of Mexiquillo

The waterfall (cascada) in Parque Natural Mexiquillo, Durango, Mexico. Photo by Roberto González (CC-BY-2.0).
The waterfall (cascada) in Parque Natural Mexiquillo, Durango, Mexico. Photo by Roberto González (CC-BY-2.0).

We were excited to arrive at Parque Natural Mexiquillo before the break of dawn in June.  This underappreciated park is right on one of Mexico’s most celebrated birding routes, the Durango Highway — but it is an hour or two farther east than the Tufted Jay Preserve, and much less frequently visited.  The drier forests of Mexiquillo host a noticeably different avifauna than the wetter areas closer to the coast. Mexiquillo is more likely to produce birds typical of the dry “sky islands” of southern Arizona: Buff-breasted Flycatcher, Western Bluebird, Plumbeous Vireo, and even American Robin.  It’s much better habitat for the likes of “Type 6” Red Crossbills (which we recorded) and Eared Quetzals (which we did not find). Of course, it also has Red Warblers, Elegant Euphonias, and Rufous-capped Brush-Finches.

And it has a waterfall.

This is particularly noteworthy because the mountains of west Mexico are high and dry — and not much water means not many waterfalls.  Which means not many places to look for waterfall-loving swifts.

We were very interested to see what kinds of swifts would be flying around the waterfall at daybreak. A report from 2013 had us wondering whether this would be a good place to record Black Swifts, and a tantalizing recording from Chihuahua had us wondering whether something super-rare might be lurking under the cascada (and under the radar), like the “avian unicorn” White-fronted Swift (Cypseloides storeri).

When we first arrived, before first light, all was quiet, except for the roaring water and the aerial singing of Violet-green Swallows. Off in the distance, a Spotted Owl hooted. No swifts. Soon a dawn-singing Pine Flycatcher became a serious distraction. By the time the sun was fully up, we were totally engaged in all the other wonderful birds in the park, and we had completely given up on the swifts.  Until suddenly, something dark swooped by overhead with a sound like the crackling of electrical wires.  Chestnut-collared Swift!

Then another group of swifts flew by, and I heard a sound familiar from the mountains of Colorado: Black Swift.

For the next hour, these two species swirled over our heads, sometimes swinging pretty low. The encounter was simultaneously a letdown and a thrill.  On the one hand, it woke us up from the pipe dream of documenting some ultra-rare Cypseloides vocalizations. On the other hand, it was a terrific opportunity to spend time with two species that it can be awfully hard to see and hear well. It cleared up a long-standing mystery about whether the Black Swifts of Mexico might sound different from the ones farther north (answer: they don’t). And it gave us the field experience necessary to help identify the Chihuahua mystery swift as the first Chestnut-collared documented in that state.  One key takeaway: Black and Chestnut-collared Swifts can look astonishingly similar, even when you get good, prolonged looks.  But by sound, they can be separated right away.

While I concentrated more on the audio recording, Andrew was able to get some decent flight shots of the Black Swifts:

We were hoping to figure out whether the Black Swifts of Mexiquillo belonged to the northern subspecies niger, which breeds in the United States and Canada, or the southern subspecies costaricensis, which breeds in — you guessed it — Costa Rica.  The birds in Mexico have been attributed to each of these subspecies by different authors. The Mexiquillo Black Swifts were surprisingly well marked, some with bright white foreheads, some with extensive white scalloping below. So we thought this might be a mark for costaricensis. But when Andrew reviewed and photographed Black Swift specimens in the Harvard collection earlier this week, he found it nearly impossible to separate the subspecies by coloration. The size difference is noticeable on the specimen table, but is subtle enough that it would be virtually useless in the field.

So, the subspecies of the Durango birds remains a bit of a mystery. Any comments or discussion would be appreciated!

My Sounds on the Radio

My Sounds on the Radio

My friend Jason Beason, the eminent Black Swift researcher, appeared today on Colorado Public Radio’s daily news show Colorado Matters, reporting on the recent breakthrough in Black Swift research.  The producer used my recording of Black Swifts at the beginning of the segment.  You can listen to the entire interview on the CPR website.

My recording of a Least Sandpiper also opened a BBC radio segment back in December, in an article on the crazy wave of vagrant birds that Britain had last year (including Least Sandpiper).  Unfortunately, you can’t listen to that show online — the BBC doesn’t roll that way — but you can read an online version of the article you’re interested in the boring old human-speech part of the broadcast.  (They didn’t bother transcribing what the Least Sandpiper had to say.)

For the record, I gave permission for the use of my sounds in these broadcasts at no cost, and without attribution.  I’m just happy to get bird sounds into radio listeners’ ears!


Black Swift Wintering Grounds Discovered

Black Swift Wintering Grounds Discovered

This bird is always late to the party.

It was one of the last North American bird species to be described to science, in 1857.  Its nest was not found until 1901.  The first audio recording of its voice was not made until 1993.  And every summer, across most of its breeding range, it is the last species to arrive from the south, often not appearing until the end of June.

But most remarkably of all, it was the only North American migratory bird to enter the 21st century with the location of its wintering grounds still a complete mystery.

The migration routes and wintering grounds of Black Swifts have remained unknown to science until now. Photo composite by Bill Schmoker, Zapata Falls, Colorado, June 2008 (click for link).

By any measure, Black Swifts are bizarre.  They nest in the spray zone of waterfalls, sometimes behind the water, so that  juveniles may never have dry feathers between hatching and fledging.  They take to the air before dawn, spend the entire day foraging for flying insects at altitudes so high that they often cannot be seen with the naked eye, and frequently do not return to the nest until after dark.  Then they get up several times during the course of the night to regurgitate insects for their only child, who sat hungry and wet at home all day.

The high-flying habits of Black Swifts make them almost impossible to track during migration.  The parents stay at the nest until the chick is old enough to fly in August or September, and then they vanish, not to be seen again until the following May or June.  A few anecdotal observations and a couple of specimens have suggested that Black Swifts may migrate south along the California coast, and that at least some reach Costa Rica or Colombia in migration.  But no observations, specimens, or band recoveries have ever revealed where the bulk of the population spends the winter.  The species is not large enough to carry satellite radio trackers or transmitters, so the mystery has seemed destined to persist, barring a major advance in technology.

The spring migration routes of the three Black Swifts whose geolocators were recovered in 2010. Fig. 1 of Beason et al. (2012).

But in 2009, a group of researchers from Rocky Mountain Bird Observatory caught four Black Swifts in Colorado and fitted them with geolocators. Geolocators are not radio transmitters or satellite recievers, but rather primitive devices — just a light sensor, a digital clock, and a tiny memory chip. All they do is record the time of sunrise and sunset each day. But that’s all the information one needs to reveal where the bird has been. The time of local sunrise, measured against GMT, allows you to estimate your longitude — that is, what time zone you’re in. The length of the day, combined with the calendar date, tells you your latitude — that is, how far north or south of the equator you are.

There’s just one problem — since the geolocators can only record data, not transmit it, the only way to find out from the device where it’s been is to recapture the exact same bird a year after you saddle it with the tiny light-sensing backpack.

Knowing that Black Swifts have a very high fidelity to their nesting sites, the RMBO team hung mist nets at the two places where they had outfitted birds with geolocators the year before. It took three different trips over the course of the summer, but they managed to recover three out of the four geolocators — a remarkable 75% success rate. Today they announced the results: those three Black Swifts carried their little backpacks all the way to South America and back — specifically to the Amazon basin of western Brazil.

At right are the maps from the article published today in the Wilson Journal of Ornithology by Jason Beason, Carolyn Gunn, Kim Potter, Robert Sparks, and James Fox.  The white lines on the three maps are the northbound spring migration routes of the three swifts whose geolocators were recovered in 2010. Fall migration routes, unfortunately, could not be accurately mapped, because the period of fall migration too closely coincided with the autumnal equinox, when day length is equal at all latitudes, making it difficult to measure north-south  movement accurately.

The colored blotches in the western Amazon are the areas where the swifts likely spent most of the winter.  They’re blotchy because the geolocators aren’t terrifically accurate, and also because the swifts apparently  moved around a fair amount during the winter.  It’s possible that they roosted in caves or cliffs for the night and then roamed extensively during the day, but the researchers raise the tantalizing possibility that wintering Black Swifts may actually stay aloft 24 hours a day, based on the behavior of the related Common Swift of Eurasia, which may be on the wing for up to 9 months of the year — or even several consecutive years, in the case of non-breeding individuals!

The authors stress, however, that no conclusions about roosting behavior can be drawn from the current study.  If the wintering birds do roost in dark crevices like they do in summer, they could skew the geolocator data, which is based on light levels.  Extensive cloud cover could also be an issue.  There’s evidence of at least some errors in the migration tracks at right: the researchers stress that bird 554 did not, in fact, probably take a quick jaunt to the Pacific Ocean off of Baja California after arriving in Colorado — that data point is likely due to some type of irregular shading event that messed up the geolocator data.  Nevertheless, the generally strong agreement between the tracks of the three birds provide a reasonable level of confidence about the quality of the data.

The Black Swifts were estimated to cover between 210 and 240 miles per day, on average, during their southbound and northbound migrations.  More study needs to be done to determine whether their migration routes and wintering areas are typical of Black Swifts, or whether they are specific to the Colorado population.

For more information on the remarkable Black Swift, check out the book The Coolest Bird by late, great Colorado swift researcher Rich Levad, published online by the American Birding Association.

Literature Cited

Beason, J.P., C. Gunn, K.M. Potter, R.A. Sparks, and J.W. Fox. 2012. The Northern Black Swift: Migration Path and Wintering Area Revealed. Wilson Journal of Ornithology 124:1-8.

The Coolest Bird

The Coolest Bird

The Coolest Bird, by Rich Levad. Click for link

I’ve posted a couple of times before [1 2] about the Black Swift, one of the most unique and mysterious birds in North America, but this news was too good not to report: Rich Levad’s book “The Coolest Bird” has been published online by the American Birding Association.  Click the link for the 152-page PDF.

I had the privilege of knowing Rich before his untimely death in February 2008 from ALS (also known as Lou Gehrig’s disease).  He was such a force of nature that even though his career as an amateur ornithologist didn’t begin until after he retired from teaching, he still managed to move our knowledge of the Black Swift forward as much as any other individual in the past three decades.  “The Coolest Bird” is part memoir, part historical narrative, part monograph.  Rich meant it to be a book for the masses — the story not only of the bird but of all those who have pursued it, including their rivalries and prejudices, their flashes of insight, their daring climbs to nest locations, and above all their passion for the bird.  It’s a fast and absorbing read — if you have any time to spare, I highly recommend it.

Swift Travels

Swift Travels

Where they go, nobody knows: The migration routes and wintering grounds of Black Swifts remain a mystery. Photo composite by Bill Schmoker, Zapata Falls, Colorado, June 2008 (click for link).

Last fall I posted about the project to put geolocators on Black Swifts in an effort to determine, for the first time, where the species spends the months from October to May.  I just got exciting news from Rocky Mountain Bird Observatory’s Jason Beason: on Wednesday night, the team succeeded in recapturing one of the birds wearing a geolocator!

Of course, this success will take a while to bear fruit.  First Jason has to hang the geolocator outside his house for a week so that it can be calibrated according to the sunrise and sunset times at a known location.  (All the geolocators were also calibrated in this way prior to deployment.)  Then, assuming that all has gone well with the device over a year of riding swiftback, the team can download the data and begin the complex task of determining the latitude and longitude of the device every day for the past year based on sunrise and sunset times.  Then, and only then, will the team be able to generate a map of the bird’s travels.

Only four geolocators were placed on swifts last year: three at a cave in the Flat Tops Wilderness and one at a nest at Box Canyon Falls in Ouray.  The geolocator recovered on Wednesday came from the Flat Tops cave. To have recaptured one of only three marked birds there is a tremendous success, but a calculated one, since Black Swifts have tremendously high site fidelity from year to year.  Jason and his collaborators (Kim Potter, Carolyn Gunn, Chuck Reichert, and Todd Patrick) will revisit the cave next month to try to snag one or both of the remaining geolocators at that site, and they will be attempting to recapture the Box Canyon bird tomorrow–it is believed to be attending the same nest as last year.

Thanks and congratulations to the intrepid explorers who are on the verge of solving one of the biggest remaining mysteries of North American bird migration!

The Coolest Bird Sound

The Coolest Bird Sound

In the opinion of the late Rich Levad, the Black Swift was The Coolest Bird, and in his still-unpublished manuscript of that name, he advanced a pretty strong argument for its coolness.  This is a bird that spends much of its time foraging so high in the air that nobody ever sees it.  It nests in the spray zone of waterfalls, so that a juvenile may never have dry feathers between hatching and fledging.  And it is poorly understood: to this day we really have nothing but educated guesses as to where the species spends the winter.

It appears that will change soon. My friend Jason Beason of Rocky Mountain Bird Observatory sent me this announcement:

As of the evening of August 24th there are three Black Swifts in Colorado wearing light-level geolocators! On that evening, Kim Potter, Carolyn Gunn, Todd Patrick, Chuck Reichert, and myself caught ten adult Black Swifts using mist-nets in the Flat Top Mountains in western Colorado. The locators were placed on two females and one male, all of which weighed greater than 50 grams (the minimum cutoff to stay less than 2% of total body weight). In just a few weeks the swifts will begin their migration to locations unknown. With string and ribbon included the total weight we added to the birds was only 1.8 grams! With luck, this time next year we will be able to report where these birds spent the winter of 2009-2010. If not for the help of Carolyn Gunn, a trained veterinarian with very nimble hands, we could not have placed these devices on the swifts in a reasonable amount of time. We are very thankful that she agreed to help with this project!

Black Swift in hand with geolocator. Photo by Carolyn Gunn.
Black Swift in hand with geolocator. Photo by Carolyn Gunn.

The light-level geolocators that Jason referred to are the same technology used by Stutchbury et al. 2009 to estimate the migratory paths of Wood Thrushes and Purple Martins, birds too small to carry the satellite transmitters like those the Pacific Shorebird Migration Program has placed on Bristle-thighed Curlews and Bar-tailed Godwits in recent years.  Jason later reported to me in a follow-up email that a fourth Black Swift was outfitted with a geolocator at Box Canyon, near Ouray, on 29 August.  Unlike the satellite transmitters, the geolocators do not send data in realtime; it will be lost unless the birds are recaptured next year and the data downloaded.  Since Black Swifts are extremely faithful to their nesting sites, the team thinks there is a good chance they will be able to retrieve one or more of their geolocators a year from now.

One of the reasons Black Swifts are so little known is that they are rarely observed, even near their nest sites.  I believe that one of the reasons they are rarely observed is that most people don’t know what they sound like.  Unfortunately, one of the reasons why most people don’t know what they sound like is that they’re devilishly difficult to record.  Over the past couple of years I’ve found that Black Swifts are actually quite vocal, particularly near the nest — but the nests are usually so near waterfalls that recording is basically impossible.

Thanks to Rich Levad and his army of Black Swift volunteers, the number of known nesting sites in Colorado has more than tripled in the last decade, and at some of these sites, it’s possible to get a reasonable recording.  With better recordings comes a greater chance of detecting Black Swifts when they are overhead.  I have sometimes been able to find this species by ear when I wasn’t expecting it or looking for it, and I’m not the only one.  So let’s spend some time on identification by ear.

The individual “pip” notes of the Black Swift are extremely similar to the “pips” of Pygmy Nuthatches, and they can sound similar to some notes of Red Crossbill.  Rarely, the swifts will make a longer, higher-pitched “squeak” noise.

Black Swift vocalizations, Larimer County, CO, 23 August 2007.
Black Swift pip & squeak calls, Larimer County, CO, 23 August 2007.

Sometimes Black Swifts give a relatively stereotyped “extended call” that starts with a rapid twittering series of “pips” and culminates in a clear “squeak.”  This is often followed by a decelerating series of “pips.”

Black Swift extended call, Larimer County, CO, 23 August 2007.
Black Swift extended call, Larimer County, CO, 23 August 2007.

Black Swift vocalizations in general, and the extended call in particular, appear to be correlated with aerial chases, although all vocalizations are also given by some solo flying swifts and by perched individuals at or near the nest.  Nor are these vocalizations limited to the daytime: at least at their nesting sites, Black Swifts will vocalize throughout the night.

You can hear more examples of Black Swift recordings in Xeno-Canto’s collection.