Archive for the ‘Uncategorized’ Category

5 March 2018

Keith L. Bildstein, Ph.D.
Hawk Mountain Sarkis Acopian Director of Conservation Science
Jean-François Therrien, Ph.D.
Hawk Mountain Senior Research Biologist

We’ve all seen the classic cartoons of iconic “desert” vultures; the ones featuring cacti, watering-holes and, of course, thirsty cowboys. But just how true-to-ecological-life are these cartoons? Not much it seems.

The two of us have been surveying and trapping black and turkey vultures in the Sonoran Desert of southwestern Arizona for five years now, and the picture that emerges from our studies is quite different than that portrayed in the cartoons.

Vulture Chron1

Keith Bildstein and Jean-Francois Therrien at work in the Sonoran Desert


In reality both black and turkey vultures are far less likely to be found in the interiors of expansive desert than along their edges, as well as in pockets of human-dominated landscapes within the desert where water is pumped to the surface for irrigation.

A bit of background helps. The Sonoran Desert, our principal Arizona study site since 2014, differs from America’s three other deserts, the Mohave, the Chihuahuan, and the Great Basin, in having relatively mild winters. Because of this, small numbers of black and turkey vultures occur in the Sonoran year-round, and we have been able to study their movements seasonally. It turns out that most of the birds do not occur in the so-called “desert proper.” In fact, most of the birds occur in relatively small parcels of irrigated agricultural lands that consist of enormous dairy farms crowded with 10,000 to 100,000 or more cows, and others that are covered with 1,000s of acres of leafy vegetables. In the first, natural livestock mortality provides black and turkey vultures the chance to feed on relatively fresh cattle carcasses daily. And not surprisingly, that is what most of vultures do. So much so, that we routinely set our traps to catch and tag vultures at or on such farms.

But dead cows are not the only carcasses that attract the vultures to these sites.

The Central Arizona Project, a massive construction including a more than 330-mile-long diversion canal, channels millions of gallons of water from the Colorado River into central and southern Arizona, providing surface water sufficient for the dairy farmers to grow the hay needed to feed the millions of dairy cows in the region. It also creates enough wetlands to attract fish-eating ospreys and other waterbirds, together with enough dead and dying fish to attract numerous scavenging vultures. In addition, the Colorado River, which itself runs close to the western border of Arizona, provides vegetable farmers along its course with enough water to grow kale, cabbage, and other thirsty vegetables, and in so doing attracts rodents and rabbits, which also, eventually, supply carcasses for the vultures.

All of this means that “desert vultures” are far more abundant in human-dominated landscapes away from the natural desert proper than the vulture cartoons indicate. Indeed, pumped surface water rules both the distribution and abundance of vultures in the Sonoran desert.

The water, itself, is important is it to desert-dwelling turkey and black vultures. In addition to quenching their thirst, water helps cool vultures in the hot desert. Both black and turkey vultures routinely pee on their toes and feet (the biological term is urohydrosis) to aid in evaporative cooling in the hot desert, but although turkey vultures manage to do so successfully with “metabolic water” supplied from the metabolism of their food alone, black vultures need to drink additional water to accomplish such body-surface cooling, making the latter even more beholden to available surface water. And both species certainly drink and bath in surface water, at least episodically using both pumped-irrigation and natural rain water.

So there you have it: cartoons simply don’t depict the true nature of the desert’s vultures. At least not in the American Southwest.

We plan to conduct additional roadside counts and to trap vultures in southwestern Arizona next year. We will keep you posted on what our efforts reveal about vultures and their needs as soon as we decipher them. Thank you in advance for your interest in and support of our work.

Read Full Post »

By JF Therrien, Hawk Mountain Senior Research Biologist

07 Aug 2017


JF reviews American kestrel nest box data with summer intern Jenna Schlener.

Hawk Mountain has a rich research and monitoring history. For several decades now, on-staff researchers have been carrying the torch, keeping numerous inestimable monitoring projects going. The migration counts conducted at Hawk Mountain indeed represents the longest running raptor monitoring project in the world.

Starting some 80+ years ago, the counts were first designed to assess the usefulness of the protection offered by the newly created Sanctuary. Not long after, Hawk Mountain’s curator Maurice Broun and others realized the invaluable long-term dataset that those counts represent and they could be used to study population trends of 16 North American raptor species. Then in the mid 1950s, Alex Nagy, then Hawk Mountain’s assistant curator, installed a few bird boxes on his farm to see if he could get American kestrels to use them. What most likely started as a humble backyard experiment resulted in what is now the American Kestrel Nest Box Program, which will proudly celebrate its 65th anniversary next spring.

Research and monitoring projects sometimes begin after a carefully designed approach. However, in reality, many such projects simply start serendipitously, as in the previous examples. Traveling around Hawk Mountain to visit the 125 man-made nest boxes of the American Kestrel Nest Box Program during summer 2017, we noticed odd and conspicuous behaviors of bigger, darker birds. Indeed on distinct occasions, black vultures would suddenly appear flying low overhead or even flying out a window from the very barns our kestrel nest boxes are attached to. At that point, we had little doubt; those vultures are likely using the building to nest.

Black vulture chick named Versace wearing wing tag and transmitter photo credits R.Smith

JF holds a newly tagged black vulture named Versace.

From a research point of view, having access to nest sites is highly valuable. In addition to being able to handle adults and chicks to assess their life history traits (body condition, growth rate, disease prevalence, etc.), monitoring nesting activities allows us to assess breeding success and breeding rate, age at first breeding, and nest site fidelity on the population level over time. Those aspects are all immensely important to understand the complete cycle of individuals that compose populations.

Finding this access to several nests for any raptor species is challenging, because individuals are often territorial. Their nests occur at low density and are usually concealed. Therefore, monitoring nesting raptors often becomes an unrealistic task, given the time required and the area that would need to be covered to locate a fair number of them. A good breeding monitoring project requires a relatively easy way to access several nests across a relatively small area to allow researchers to visit them periodically.

Black vulture chick photo credits J.Dallas

Black vulture chick found in a local barn. Photo by J. Dallas. 

During summer 2017, our team found just this. We were able to successfully monitor 3 black vulture nests that we found without even searching while checking our kestrel nest boxes. Those birds were using Pennsylvanian barns just like giant man-made nest boxes, and thankfully they were all in a relatively small radius around Hawk Mountain.

This project has just begun, and we are now looking to double or triple the number of monitored nests in the coming years. So if you notice black or Turkey vultures flying out of abandoned buildings or barns, please let us know. We would be thrilled to add new nest locations to our newly-born monitoring program.

tagged at nlo by holly mercker

Tagged black vulture. Photo by Holly Merker.

By using individual markers (such as wing-tags and telemetry transmitters), we will be following the where and wherefore of those individual birds through their lifetime. Anytime you see a vulture, keep an eye out for wing-tags (a brightly colored tag showing a distinct number). Any sighting of a tagged individual represents important information for locating roost sites, feeding hot spots, survival rates, and dispersal behavior. Help and support these studies by reporting any sightings at this link.

Monitoring programs such as these are an essential part of conservation science: they form the backbone of long-term population assessments. They allow researchers to keep track of historical population size and productivity in order to identify declines in a timely fashion and become aware of problems that otherwise could have gone undetected.

To learn more about our work with North American vultures or any other species of raptors, or if you wish to support our monitoring efforts financially, contact me at therrien@hawkmountain.org.

Read Full Post »

Flexible flyers

wingtagged vulture 70 by jeff dietschBy Keith L. Bildstein, Ph.D.
Sarkis Acopian Director of Conservation Science
Hawk Mountain Sanctuary

8 January 2016

Why are some species of birds of prey widespread and abundant whereas others are not?

It turns out that this critical ecological question, one that is fundamental to understanding biological diversity, along with many other aspects of ecology, is easy to ask, but not easy to answer.


Article in The Auk

Earlier this month two former Hawk Mountain trainees, Dr. Todd Katzner (now the head of the U.S. Bureau of Land Management’s Boise State University Raptor Research Center) and Julie Mallon (now a Ph.D. student at the University of Maryland) and I published an article in the ornithological journal The Auk that helps to explain why turkey vultures are one of the world’s most abundant and widespread avian scavengers. The field work was conducted while Julie was a Master’s degree student at West Virginia University.

The short answer to the question is that turkey vultures have evolved two so-called “key innovations” that, together, make them decidedly “above average” as avian scavengers. The long answer, which follows, is a bit more intriguing.

The turkey vulture’s first key innovation is their acute sense of olfaction. This is something that is quite handy when the food you are searching for is decaying carcasses and smells.  Turkey vultures have the largest nostrils of all New World vultures, including the far more massive California condor and Andean condor, as well as the largest olfactory bulbs in their brain–the next largest being those of the king vulture, a species that does not appear to use olfaction in its search for carcasses. Two other Central and South American species of vultures, the lesser yellow-headed vulture and greater yellow-headed vulture, are both close relatives of the turkey vulture and also locate carcasses by both smell and sight.

turkey vulture 03 03 15 bill moses, at french creek .jpg

Turkey vulture at carcass by Bill Moses

Intriguingly, although there is no evidence that black vultures are able to locate carcasses by smell directly, the species indirectly locates carcasses by smell. Indeed, black vultures routinely seek out turkey vultures and then follow them to carcasses, capitalizing on the latter’s olfactory capacity. Old World vultures, on the other hand, show no evidence of locating carcasses via their sense of smell.

The turkey vulture’s ability to locate carcasses by smell is a key innovation because it allows individuals to search over forested as well as more open habitats for dead animals, thereby considerably expanding their feeding habitat. This key innovation explains–at least in part–why turkey vultures are the most wide-ranging of all vultures.

The turkey vulture’s second key innovation and the focus of our recent publication in The Auk provides the rest of the story. This innovation is the species dihedral wing posture, which allows it to engage in what my coauthors and I call “contorted soaring” while flying close to the ground in search of carcasses. What atmospheric scientists call “small-scale, shear-induced atmospheric turbulence” routinely occurs close to the ground. It happens anywhere the topographic features such as mountains and valleys, forest edges, and small-scale thermal mosaics, disrupt the flow of wind near the earth’s surface. This creates small pockets or eddies of swirling air that alternately push and pull on objects flying through them. Many of us have experienced this kind of turbulence during bumpy take-offs and landings at airports.

Turkey vultures are lightly-wing loaded (i.e., they have big wings for their body mass), making it easy for them to soar in large packets of warm, rising air called thermals. Other vultures, too, are able to do this. Close-to-the-ground, contorted soaring, however, is another matter entirely. It is close to the ground where the dihedral (“V” shaped) configuration of the species’ wing profile comes into play.

DSC_9244 turkey vulture 10 14 18 bill moses

In addition to a relatively long, rudder-like tail that allows them to turn in tight circles while soaring in small-scale turbulence, turkey vultures have long, narrow wings that they hold above their backs in a dihedral. The latter is a key innovation that serves as an “aerodynamic self-righting (or stabilizing) mechanism.” This allows the bird to continue to soar in turbulent air even when its two wings are exposed simultaneously to different up- and down-drafts.

The unusual wing profile functions whenever one wing (either the left or the right) experiences more lift than the other. When this happens the wing experiencing greater lift tilts upward making it less parallel to the ground and reducing its aerodynamic surface and, hence, lift while the opposite occurs to the other wing. The side-to-side rocking, which at first suggests instability, actually is an energy-efficient, soaring flight that allows the birds to stay aloft. It also allows them to continue soaring without having to flap its wings to right itself, which is usually what happens when “flat-profile-wing” soaring birds encounter small-scale turbulence.


Other lightly wing-loaded soaring birds that regularly scavenge for food close to the ground, including greater and lesser yellow-head vultures, Egyptian vultures, black kites, bateleurs, and zone-tailed hawks, all have slight to strong dihedral wing configurations, as do more predatory harriers, which also forage close to the ground. Intriguingly, turkey vultures soaring at greater heights tend to do so in a less pronounced dihedral, whereas black vultures flying close to the ground frequently adopt a slight dihedral rather than their more typical flat-wing profile.

That they are able to extract useful updraft energy while soaring in small-scale turbulence near the ground means that turkey vultures can soar closer to the carcasses they are both looking and smelling for, which makes them easier to locate before turbulent winds jumble and disperse odors associated with them.

Low soaring flight has a second benefit as well. Contorted soaring allows low-flying turkey vultures to stay below the radar screen of potential competitors. This is important when a located carcass is squirrel-sized rather than deer-sized and there might not being enough food to share with others.


Ornithologists speak in awe of just how high vultures can fly while searching for prey. The world record, for example, is held by a Rüppell’s vulture that was sucked into a jet engine while soaring 37,000 feet, an altitude high enough to require special hemoglobin to capture oxygen sufficient for metabolism. But the ability to soar close to the ground also has benefits, particularly if you are searching by smell and want to keep a carcass to yourself. A keen sense of smell, coupled with a wing dihedral help makes turkey vultures what they are today, one of the most abundant and widespread of all raptors.

But of course the question then becomes “why don’t other vultures do the same?” The short answer is because they have not evolved these two key innovations. The long answer requires another blog.

You can find our paper on turkey vultures, “In-flight turbulence benefits soaring birds” on the Sanctuary’s website under “Numbered Publications” on our Science tab. Look for contribution to conservation science number 258.

Finally, if this work interests you, or any of our other research projects that better conserve raptors, please consider making a gift now. Just click here to donate now, writing “research” in the comments.

Read Full Post »

Vulture Restaurants

By Keith L. Bildstein, Ph.D.
Sarkis Acopian Director of Conservation Science
Hawk Mountain Sanctuary
9 December 2015

Together with African colleagues and Hawk Mountain research associates, I have been studying the “Critically Endangered” hooded vulture for going on three years. The work is beginning to pay off. I have just returned from 10 days in the field in and around Kruger National Park in northeastern South Africa where temperatures soared to 108 °F, and I have much to report.

As of early December 2015 we have placed satellite tracking devices on four “hoodies” in The Gambia, four units on birds in Ethiopia, and nine units on birds in South Africa. We also have placed “camera traps” at a number of hoodie nests in South Africa, as well as at several “vulture restaurants” there. Initial results at the latter are fascinating. But first some background…

hooded vulture nestling with tag

Fitting a tracking unit on a young hoodie

This summer, a second round of roadside counts in The Gambia indicated that hoodie populations there continue to do well, with numbers in the western part of the tiny African nation hovering at an astounding 15 birds per square kilometer, a density that makes the region home to the highest population of hooded vultures anywhere. Unfortunately, things are not nearly so good in South Africa where roadside counts in Kruger National Park, a supposed stronghold, indicate a population of far less than a single bird per square kilometer. My field work in South Africa earlier this mont

olifants river, kruger national park

Olifants River in Kruger National Park, South Africa

h also produced close-up looks at more than 10 active nests in private game reserves immediately west of “The Kruger,” where nests along some sections of the Olifants River are sometimes as close as 100 meters or less.


As in any collaborative endeavor, working with the right people makes all the difference and the Sanctuary’s hooded vulture studies in South Africa are not exception. Kerri Wolter at VulPro (a vulture NGO outside of Pretoria), consistently offers up exciting results and insights regarding hoodies breeding in the Olifants River Private Game Reserve. And Andre Botha at the Endangered Wildlife Trust (an NGO in Johannesburg) is doing likewise for birds breeding and feeding in The Kruger, as well as several adjacent private reserves. Dr. Marc Bechard at Boise State University continues to help with trapping and harnessing hoodies with satellite tracking devices, as well as helping on road counts within The Kruger.

Lindy, Marc, and Andre at the Selati Vulture Restaurant

Lindy, Marc and Andre at the Selati “vulture restaurant”

The newest addition to the South African team, Dr. Lindy Thompson, a Post-Doc in the Department of Biology in at the University of Kwa-Zulu Natal, adds an additional level of excitement and expertise to the team. On the job for less than a year, Lindy is following the nesting successes and failures (baboons and a hail storm appear to be responsible for at least some of the latter) of a number of hoodie nesting pairs in private reserves west of The Kruger.


Lindy also has initiated studies at several “vulture restaurants” in the region, where human provisioning of hoodies and other vultures with offal and assorted body parts of domestic animals slaughtered at local abattoirs, is helping the birds meet their daily caloric needs. Although such provisioning can disrupt the normal behavior of avian scavengers, human “nutritional assistance” at vulture restaurants provides “clean” food to birds in areas where poachers have been known to purposely lace with poison the carcasses of rhinos and elephants they kill for their horns and tusks. Their intent is to kill the vultures, whose flocking behavior often alerts game rangers of poachers’ activities.


Having spent considerable time in the field at a vulture restaurant last week, I now have a much better understanding of how hoodies and other vultures use the restaurants, as well as of the benefits of such sites in providing close-up looks at several of our satellite- and wing-tagged individuals. The vulture restaurant at the Selati Game Reserve, for example, routinely attracts dozens of hoodies, with attendance on some feeding days reaching 25% or more the regional breeding population. And indeed, I managed to visually locate two of our satellite-tracked birds at the site–both of which appeared healthy. (Actually, our tracking records indicate that four of the nine birds we are tracking visited the site while I was there.) Later this month Lindy and Andre plan to trap and measure up to three additional hoodies at this important site and place satellite tracking units on them.

Lindy and Marc at the Selati trap sitre

Marc and Lindy at the Selati trapping site

Trapping birds at the Selati site and, possibly, at other restaurants will help speed our wing-tagging and satellite-tagging efforts and also will provide us with much needed information on the health of individuals captured and examined there. Given the precarious nature of the species in South Africa, the restaurant work may make all the difference in helping us offer solutions for better managing this declining population.


Lindy will visit the Acopian Center this spring

Finally, Lindy plans to visit Hawk Mountain’s Acopian Center for Conservation Learning for several months this spring, at which time the two of us will begin to analyze tracking and nesting data already collected. Plans for 2016 also call for me to make two additional trips to Africa or field work in South Africa and The Gambia.

No one has assembled a better team of vulture specialists and is working as hard as we are to protect this globally endangered species and I very much look forward to keeping you up-to-date with our field efforts in the coming months.

Do not hesitate to contact me by phone (610-781-7358) or email (Bildstein@hawkmountain.org) if you are interested in supporting our work.

Until then, all the very, very best,  Keith

Read Full Post »

By Keith L. Bildstein, Ph.D.
6 August 2015

Vulture survey route along the California coast.

Vulture survey route along the California coast.

I have dreamed about surveying turkey vultures in California for a long, long time. The opportunity finally arrived this July when spring 2015 Hawk Mountain trainee Katie Harrington returned to her home base in San Francisco late last month. Katie and her fiancée James Fahlbusch volunteered to help and the three of us mapped out seven, day-long road surveys that would follow the coast north and south of San Francisco as well as inland from just north of Redding to south of Bakersfield. The plan was to travel the roads at 35 mph and record all of the turkey vultures we saw. Then, repeat the same route in mid-winter 2015-2016 to investigate seasonal changes in vulture distribution and abundance. We also planned to record the flight heights and group sizes of all of the birds we saw, as well as to look for and record the locations of California condors along the way.

Having conducted road surveys in 22 other regions stretching from Canada at the species’ northern limits to Tierra del Fuego, at its southern limits, I was excited to say the least. The fact that California was exceptionally hot and tinder-box dry this summer only added to my excitement.

A California condor with wingtag soars overhead.

A California condor with wingtag soars overhead.

Our surveys, which covered 1,280 miles, produced 1,306 sightings of turkey vultures, or more than one vulture per mile, a relatively surprising find given that several of the routes passed through “agro-industrial” and suburban areas. We also saw seven California condors, most of which flew close enough for us to read their wingtags. Intriguingly, all but one of the condors sighted were flying in close proximity to turkey vultures.

Remarkably enough, the ecological relationship between these two species has been little studied. Except for the not-surprising fact that turkey vultures are known to be behaviorally subordinate at carcasses to the more massive condors we know little of the ecological relationships between these two avian scavengers. What we do know is that while larger and more-agile avian scavengers typically dominate smaller and less-agile ones at food sources, numerical abundance at a carcass sometimes allows smaller scavengers to dominate larger scavengers. And this is exactly what happens when large gangs of black vultures overwhelm and dominate far larger, but less numerous, Andean condors at carcasses in South America.

A turkey vulture feeding on a racoon.

A turkey vulture feeding on a raccoon.

Although turkey vultures are far less social than black vultures and rarely group in large numbers at carcasses, they may out-compete the large California condor in other ways. First, their keen sense of olfaction should allow them to locate rotting carcasses faster than condors, and thereafter consume at least smaller ones before the condors find them. Second, their larger numbers might allow them to finish off larger carcasses partially fed upon by condors–and then left for later–more rapidly, thereby reducing the amount of food available to the larger birds.

Intriguingly, our miniscule one-week field effort suggests that the two species sometimes share the same airspace and, presumably, the same carcasses. Given the current status of condors as a globally-endangered species and the amount of field work and funding now focused on speeding their recovery, careful studies of interactions–both behavioral and ecological–between condors and turkey vultures would seem to be in order.

Keith and Katie examine the racoon.

Keith and Katie examine the raccoon.

Our next road surveys in California are scheduled for winter 2015-2016. Katie, James, and I look forward to exploring the distribution and abundance of vultures then, as well as to observing the behavior of vultures and condors as they search for food across the California landscape.

At long last, my “California dreamin’ is becoming a reality.”

Read Full Post »

By Keith L. Bildstein, Ph.D.
21 June 2015

Yesterday, Hawk Mountain Sanctuary Summer Field Experience Interns Kaitlin Schafer and Emile Luttman, and I drove more than an hour through pouring rain to try to find a special Turkey Vulture.

Named in honor of Irma Broun, the wife of the Sanctuary’s first ornithologist Maurice Broun, Irma the Turkey Vulture had been caught by then Hawk Mountain Graduate Student Jamie Mandel at a garbage dump in Penn Argyl, Pennsylvania, in August 2004. Shortly thereafter she was tagged with a solar-powered satellite tracking device. We also placed a data logger in her body cavity to record her core body temperate and heart rate. Placing the latter in Irma meant that we would need to recapture her the following year to extract the logger and download the data.

Former Hawk Mountain Graduate Student Jamie Mandell

Former Hawk Mountain Graduate Student Jamie Mandel at work in the field.

The bad news is we were never able to re-catch Irma in 2005 despite numerous attempts to do so. The good news is that both she and her tracking device are both still ticking more than a decade later. The tracking devices have a life expediency of three to five years, so Irma’s unit by far is our best overachiever.

This summer Kaitlin and Emilie have been spending time mapping Irma’s movements. Although she migrated to South Jersey during the winters of 2004-2005 and 2005-2006, since then she has been a year-round resident of an area near Easton, Pennsylvania, and Phillipsburg, New Jersey, shuttling between feeding and roosting sites on both sides of the Delaware River. Last week we decided to try and reconnect with her.

Using the movebank.org website that we use to store our tracking data, we located Irma’s roost site on the evening of Friday 19 June. She appeared to be resting for the night in the middle of a hilly old-growth forest outside of Riegelsville, New Jersey. Our plan, outrageous as it seemed, was to go to the forest, spot Irma, and photograph her.

We arrived at the forest a little after 8 a.m. on June 20. The rain had kept the vultures in their roosts later than normal so we thought that we might get lucky. As we approached Irma’s last location GPS location, we slowed the car to a crawl and began to search for basketball-sized black objects perched in trees.

Almost immediately Emile screamed from the back of our Subaru Forester, “Stop, stop!! Backup … I saw her.” Backup we did, and there she was, soaking wet, 30 feet up in a large sycamore, 30 yards from the side of the road. As soon as we put  binoculars on her we could see the antenna of the tracking device.

Irma then accommodated us by turning completely around to show us both the antenna and the device. Although feathers normally cover the device on perched birds, the rain had soaked her feathers permitting us to see the unit itself. After 15 minutes of snapping photos (and yes, we took dozens) and looking for other vultures in the forest (we saw none), we got back in the car just as the rain picked up and drove off… all three of our heads spinning. Fifteen minutes later we were having a hot breakfast in Riegelsville.

Irma and her tracking device, spotted more than a decade after this vulture was first tracked and tagged.

Irma and her tracking device, spotted more than a decade after this vulture was first tracked and tagged.

To successfully catch and satellite tag a wild bird is one thing. I still get chills when I do so. But to be able to track a wild bird and its movements for more than a decade is something else again.To be able to spot the same bird perched in a thick forest on a rainy morning more than 10 years after first releasing it is truly is an ornithological epiphany.

Emilie, Kaitlin, and I plan to finish our analysis of Irma’s movements this summer, and I plan to spend September writing up the results. All of the publications I have been involved with over the years have been unique, but this one not only will be unique, but remarkably unexpected as well.

And yes, pending funding, I plan to mount an effort to re-catch Irma later this summer, so that we can replace her current tracking device with a new one and keep the information rolling in.

More later.

Another view of Irma on the morning of June 20 in a wet forest outside Riegelsville, New Jersey.

Another view of Irma on the morning of June 20 in a wet forest outside Riegelsville, New Jersey.

Read Full Post »

By Keith L. Bildstein, Ph.D.
Santiago, Chile
31 May 2015

I have been studying Striated Caracaras, a.k.a. Johnny Rooks, on the Falkland Islands since December 2010. Until my most recent trip I have timed my visits to study the birds either in mid-summer or mid-winter. The plan had been to contrast rook ecology in those two seasons and to draw conclusions regarding seasonal differences in their behavior.

The trip I am now returning from has been a “temporal anomaly.” I spent two weeks on the islands in late May, which is “austral autumn’’ (think late November north of the Equator), to learn how the birds make the transition from the summer food largess to the cold and snowy winter lean times.

I have known for some time that the bulk of the 150 or so rooks that inhabit Saunders Island in the northwestern part of the archipelago spend most of their summers at and around Gentoo and Rockhopper penguin colonies at the wind-swept “Neck” in the northwestern part of the island (see first photo below) and then move from there to a farm settlement (second photo) at the eastern edge of the island in winter. Penguins and their young provide the rooks with food in summer and the island’s farmer-owner and his family provide most of the food in winter. Ten miles separate the Neck from the Settlement sites and I have seen individually-marked rooks at both locations on the same day, meaning they are able to make the journey between the two sites in a single flight or rapid series of flights.

A penguin colony at "The Neck," a summer hotspot for Johnny Rooks.

A penguin colony at “The Neck,” a summer hotspot for Johnny Rooks.

Rooks waiting to feed at the Settlement. The rook on the rail at the far right is a juvenile.

Rooks waiting to feed at the Settlement. The rook on the rail at the far right is a juvenile.

When I arrived on Saunders on the 18th of May the overwhelming majority of birds, and almost all of the young birds-of-the-year, still were at the Neck and consuming an unusually large number of dead Gentoo Penguins that had washed up along drift lines surrounding the Gentoo breeding colony. It wasn’t clear what had killed the penguins, but more than 100 rooks were taking advantage of the carcasses nevertheless. And so were several dozen Turkey Vultures. Indeed, there was so much food laying around that the rooks and vultures were feeding relatively amicably without the normal food-fighting that characterizes most of their feeding events. And most of the rooks had clearly bulging crops suggesting that they were “filled to the rim” with penguins.

Within a week, however, things began to change. Cold, southerly winds blowing in from Antarctica chilled the island with the first dose of winter weather, the penguin food largess shrank, and the birds began their mini-migration toward the Settlement.

They did so in a way that surprised me. Groups of four to 10 rooks–overwhelming young-of the year—took several days to make the 10-mile journey, moving about two to six miles each day and sampling habitats along the way. Relatively little in the way of food exists in the treeless Patagonian steppe between the Neck and the Settlement, and after several days of meandering, the birds arrived. In a manner of speaking, the birds seemingly “settled in” for the winter. By the time I left Saunders Island on May 28, more than 60 of the rooks had made the autumn transition during a period in which temperatures dropped below freezing for the first time since the last austral winter.

I had not given it much thought but the onset of cold weather and the lack of available food immediately shifted the birds’ behavior. Until the first freeze, rooks and vultures were feeding together at carcasses. The day after the freeze, gangs of rooks dominated Turkey Vultures at food resources as they normally do in mid-winter. The change literally happened overnight. Unfortunately I was not there to see if the situation reversed itself when warmer temperatures returned the day I left, but the switch was obvious.

Boise State University graduate student Anna Autilio and I were conducting observations of feeding behavior at experimental goose carcasses we had arranged for the birds. The observations will form a main part of Anna’s master’s thesis.The afternoon after autumn’s first frost, rooks feeding on the goose were noticeably ravenous, much more so than they had been in the days leading up to the arrival of cold front. It was as if a physiological trigger had gone off and the birds clearly were in “feeding frenzy” mode. For many of the individuals involved it would have been the first frost of their life… and something of a “difficult learn.”

Anna and I had conducted a survey of rook distribution and abundance in the area immediately surrounding the settlement earlier in the day. As we began the survey on our all-terrain vehicles at the edge of the settlement, a first-year rook flew up and perched several meter away. The bird then proceeded to walk up to a puddle of ice-covered water along the track in front of us and tried to skim a drink from it. As its beak skidded across the ice that glazed the puddle I couldn’t but help imagine what was going through its head.

Without parental guidance, the first-year hadn’t a clue how to drink from the ice-covered puddle. The bird flew off several seconds later and I spent the next hour and half on the survey aiming my ATV at the frozen-over puddles that dotted our route. I couldn’t help but break the ice, making the water below potentially available to the young rooks, thinking all the while about what was in store for these youngsters as their first winter approached… a time of the year when as many as a third or more of them would perish.

Everyone faces a number of challenges in life, but the longer I study Johnny Rooks the more I appreciate just how lucky we humans are compared with our raucous avian friends.


Read Full Post »

Older Posts »