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.”

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.

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.


By Keith L. Bildstein, Ph.D.
Hawk Mountain Sanctuary
20 May 2015

Studying the movement ecology of a vanishing species is quite new to me.

Throughout my professional career, which stretches back more than 40 years, almost all of the raptors I have worked with have been relatively widespread and common. And indeed, most have been abundant. Even the endemic striated caracaras, or Johnny Rook, a species that I now study on in the Falkland Islands, are reasonably abundant there. Simply put, none of the species I have spent time studying has been ranked as Globally Endangered by the International Union for the Conservation of Nature (IUCN).

None of them, I should say, until I started working with Africa’s hooded vulture in 2013.

With a world population estimated at fewer than 200,000 birds and with numbers in many part of its range shrinking as I write this vanishing species clearly is in trouble. Although populations of hooded vultures remain healthy in parts of West Africa, in parts of Central, East, and southern Africa they in rapid decline. As a result, my work with hooded vultures not only focuses on gaining insights into the species’ basic biology and movement ecology, but also on understanding the many factors that threaten its existence in Africa.

The causes for hooded vulture declines are many. Both targeted and unintentional poisoning rank high, as does the use of body parts in “muti” and other types traditional medicine. On top of that, in many places hooded vultures are shot and trapped for “bush meat.”

Like other vultures, “hoodies” feed on dead animals including elephants and rhinos, two species that are themselves declining catastrophically due to poaching. Evidence suggests that 30 to 40,000 elephants are being poached annually. If this keep up, they will be functionally extinct in 20 years. The numbers differ somewhat for rhinos, but the story is the same. Unless things change, they too, will be functionally extinct in two decades.

The author near an elephant carcass in South Africa.

The author near an elephant carcass in South Africa.

But what about the vultures?

In the short run it would seem that hoodies and other vultures are living in a land of plenty. Lots of dead elephants and rhinos, however unfortunate ecologically, can’t be a bad thing for the scavenging birds of prey, right? But wait a minute…humans are involved in the wildlife slaughter for horns and tusks, and things are not as simple as they appear.

Poachers break the law when they shoot wildlife and in many places in Africa, poachers themselves are shot when game protectors attempt to apprehend them. Flocks of vultures circling over freshly poached carcasses often lead game wardens to these criminals while they they can be caught in the act. For this reason, the poachers have taken to lacing the elephant and rhino carcasses they poach with poisons to kill carcass-feeding vultures in an attempt to remove them as useful sentinels of poaching activity. Because hundreds of vultures can feed at a single elephant or rhino carcass, lacing several dozen carcasses with poison can remove thousands of vultures from entire landscapes.

This is exactly what is happening in parts of Africa.

Our work with hooded vultures began in September 2013 when Hawk Mountain Research Associates Drs. Corinne Kendall, Marc Bechard and I, working together with local Gambian conservationists, placed satellite tracking devices on four hoodies in The Gambia, a stronghold for the species in equatorial West Africa. Since then, colleagues have placed additional units on four individuals in Ethiopia, an East African stronghold, and on eight individuals in and near Kruger National Park in northeastern South Africa, a region with far fewer hoodies than The Gambia and Ethiopia.

One of our South African hoodies, a juvenile named Ngotso that was tagged in August 2014, has a club-shaped home range that stretches for just over 400 kms (250 miles) from northeastern South Africa into southern Zimbabwe. It turns out that Ngotso is, quite literally, living on the “front line” of vulture conservation in the region. Its movements, which we have now tracked for 10 months, clearly illustrate its use of areas within Kruger National Park and several protected areas in southern Zimbabwe (see movement map below), as well as its avoidance of areas in bordering Mozambique, where poaching has eliminated most of the large game regionally. He has even been re-spotted in the field a few times (see photo below courtesy of Andre Botha).

Movements of Ngotso from August 2014 to March 2015

Movements of Ngotso from August 2014 to March 2015

NGOTSO 2 Resighting

Ngotso resighted by Andre Botha

Unfortunately, poachers from Mozambique recently have moved into Kruger and are now poaching there as well. In fact, one of the trap sites we used in December 2014 was the carcass of a poached elephant well inside the National Park. Preliminary results from our Pan-African studies suggest that densities of hooded vultures are more than 500 times greater in The Gambia than in Kruger National Park and that their home ranges are more than four times larger in Kruger than in The Gambia. Part of this geographic difference in abundance clearly results from the fact that Kruger supports higher densities of larger and competitively superior species of vultures that out compete the smaller hoodies at carcasses.

A significant part of the difference, however, is due to human activities. In The Gambia, the hoodies live in harmony with people, both in natural and in human-dominated landscapes. Whereas in South Africa, the species usually is not tolerated by people and is now restricted to ranging in large protected areas.

The larger home ranges in South Africa are particularly unfortunate as expansive foraging areas substantially increases the risk. A single poaching event coupled with poisoning of the resulting carcass can kill a large proportion of a regional population of hooded vultures.

Our preliminary results, which we recently shared with African conservationists in the field, should help colleagues there better protect this this critically important avian scavenger. The plan is to expand our studies of hoodie movement and home-range ecology in other parts of Africa including Zimbabwe, Tanzania, and Uganda, and to extend our use of camera traps at nest sites to better assess their breeding success both within and outside of protected areas. We believe that the information we are now gathering and sharing with colleagues will help us and them to better protect this species. That said, expanding our efforts is essential.

All of this costs money…actually, a lot of money. Camera traps cost several hundred dollar each and satellite tracking devices cost $4,000 each to buy and an additional $600 per device per year to download the data they collect. And then there are travel costs associated with fieldwork. So far the project has cost close to $100,000. We estimate that expanding and completing our work will cost an additional $150,000.

If you or someone you know has the capacity to help us in this effort, please contact me via email bildstein@hawkmountain.org, by phone at 1-570-943-3411 ext. 108, or via regular mail at Keith L. Bildstein, Hawk Mountain Sanctuary, Acopian Center, 410 Summer Valley Road, Orwigsburg, PA 17961.

Expect additional updates soon.


28 April 2015
By Keith Bildstein, Ph.D.

From its humble beginning in the early 1980s, Hawk Mountain’s internship program has grown into a fully-fledged graduate-student level Traineeship, which, over the years, has offered academically rigorous training to more than 380 students in 75 countries on six continents.

The proof of success they say is “in the pudding,” and as I sit in the Johannesburg Airport in South Africa this evening pouring over VULTURE NEWS–the official publication of the International Conservation Union for Nature’s Vulture Study Group–I am reminded of just how far and wide our training efforts have taken root.

Volume 67, the current issue of VULTURE NEWS, has two main articles, four short communications, and several reports that run for a total of 80 pages. Both main articles in Volume 67 were co-authored by former Sanctuary trainees, two from Kenya, and one each from Nepal and New York. And as if that were not enough, one of the four Short Communications in Volume 67 was coauthored by three Sanctuary Research Associates and me.

The first major article, Assessment of the occurrence and threats to Hooded Vultures in western Kenyan towns, was coauthored by former Sanctuary trainees Martin Odino– now of the Raptor Working Group of Nature Kenya–and Titus Imbomba–now of the National Museums of Kenya– and conservation colleague Darcy Ogada. The paper confirms significant recent declines in the currently globally endangered Hooded Vulture in western Kenya, where large numbers of “hoodies” once foraged in local slaughterhouses and city dumps. This species is the object of my current efforts here in South Africa,  and although there was little evidence of exploitation of the birds for witchcraft in Kenya–something that is common in other parts of Africa–the introduction of modern closed-system (i.e., sanitary) slaughterhouses and the widespread and increasingly popular poisoning of stray dogs is thought to have contributed to the declines, which appear to have been underway for about 15 years.

Martin Odino stands second from left in a “trainee class” photo taken in Kenya in 2009.

Martin Odino stands second from left in a “trainee class” photo taken in Kenya in 2009.

The authors surveyed elders in eight towns, and although attitudes there are largely neutral, little in the way of local protection is underway. The authors call for a vulture awareness campaign to help and possibly reverse the declines. This this is exactly what needs to be done and the Sanctuary hopes to help.

The second main article in the NEWS, Population and breeding success of Red-headed Vultures and Egyptian Vulutres in central west Nepal was coauthor by former Sanctuary trainees Tulsi Subedi (see photo below), now of Himalayan Nature, and Robert DeCandido of New York City. Although both species of vultures currently are doing fine in Nepal, both are in catastrophic decline in other parts of their ranges. In India, for example, declines in Red-headed Vultures are estimated to be at 44% annually and those of Egyptian Vultures at 35% annually. The veterinary drug diclofenac has been implicated in the precipitous population falloffs. Subedi and DeCandido’s monitoring efforts offer baseline data for a continuing monitoring effort.

Tulsi Subedi in his native Nepal

Tulsi Subedi in his native Nepal

The short communication, Avian Scavengers, but not conspecifics, feeding on the carcasses of storm-killed Turkey Vultures on the Falkland Islands was coauthored by me and Sanctuary research associates Micky Reeves of Falklands Conservation, Melissa Bobowski of Michigan, and Anna Autilio of Boise State University. The piece reports on winter-time observations of opportunistic scavengers including Variable Hawks and Striated Caracaras feeding on the carcasses of two storm-killed Turkey Vultures.

The author (upper right) with Sanctuary research associates Micky Reeves (upper left),  Marc Bechard (lower left), and Melissa Bobowski.

The author (upper right) with Sanctuary research associates Micky Reeves (upper left), Marc Bechard (lower left), and Melissa Bobowski.

Although flown over regularly by at least six other Turkey Vultures from a nearby roost, the carcasses were not fed upon by these conspecifics. This intriguing natural-history note describes an honor of sorts among this, the world’s most common and widespread obligate avian scavenger. The article, which represents the 250th Sanctuary contribution to conservation science since 1992, is, in fact, the tiny tip of a very large “iceberg of information” contributed by the Sanctuary and its colleagues across the years. It also suggests that the training of young conservationists at Hawk Mountain is having its intended effect.

Next month I will accompany former trainee Anna Autilio to The Falkland Islands as she continues her studies of the feeding and social behavior of the globally near-threatened Striated Caracara. Stay tuned for update on this exciting project.

Keith L. Bildstein

One of several dead mice offered to a group of more than a dozen Johnny Rooks on Steeple Jason Island, the Falkland Islands, in August 2012.

By Keith Bildstein, Ph.D.

Sarkis Acopian Director of Conservation Science

13 August 2014

Striated caracaras, or Johnny Rooks as the Falkland Islanders call them, by far are the most curious birds I know. Inquisitive beyond initial belief Johnny Rooks will walk more than a kilometer to learn what you are up to, and many appear to thrive on dismantling and flying off with anything new–and small enough to carry–that they encounter. Famed 20th Century evolutionary biologist Ernst Mayr, once classified such birds as being an “open programmed” species, or in layman’s terms, a species constantly curious about their environments. Island-dwelling birds in particular appear this way. By all accounts the small dark parrots called Keas that inhabit many of New Zealand’s more remote areas are every bit as inquisitive as Johnny Rooks, and in many ways, so too are Galapagos hawks.

The Johnny Rook’s extraordinary curiosity is thought to increase feeding opportunities on the Falklands and, indeed, curiosity appears to work quite well in this regard, as Johnny Rooks appear willing to feed upon all varieties of meat they encounter, both fresh and rotting, and even processed and extruded, as when they consume Sea Lion feces.

That said there does remain one mysterious exception in what they are willing to eat: small rodents. Rats and mice, both of which were introduced to the islands by humans, do not appear as items on the caracaras’ dinner plate, even though they occur on many of the islands in the archipelago. Why this is so continues to baffle those who study the birds, including me and my coworkers.

First hearing about this dietary prohibition tends to engender disbelief. Surely the birds can be coaxed into eating rats and mice. At least that is what I thought. I had the chance to test this hypothesis when I visited tiny Steeple Jason Island at the northwestern tip of the archipelago in August 2012, in the middle of the region’s austral winter. The site is home to an estimated 85 nesting pairs of rooks and surely some of them would be willing to consume a few mice. I was traveling with a team of biologists that were trying to assess the possibility of “de-mousing” the island with a rodenticide to reduce mouse predation on nestling seabirds there, and had access to plenty of freshly killed, snap-trapped house mice that were part of an ongoing distribution and abundance study of the pests.

Offering the mice to the rooks was easy enough. Within hours of my arrival the birds had learned that I was trying to trap and band them using mutton as bait, and I quickly became a rook magnet. Tossing small “mouse-size” bits of mutton to peak their interest, a crowd of several dozen birds all-but-immediately appeared at my feet. But a funny thing happened when I tossed the birds the real thing. At first they backed off a bit before returning to look them over and, in a few instances, picked them up and nibbled them. At least one rook cached, or stored, a mouse in some tussac grass, and eventually one pulled on a mouse it was holding in a seemingly, but somewhat tentative, attempt to prepare it for consumption. None, however, actually ate a mouse and most definitely, none of the birds gobbled them up as they did with the mouse-size bits of mutton I was tossing at the same time. Similar experiments by others have yielded similar results… occasional caching, investigation, and nibbling, but nothing that could be called even regular feeding.

Why would a bird so darned curious as about it environment be so cautious, albeit almost fearful of this perfectly harmless potential prey item, an item the islands variable hawks routinely kill and consume. Is it because these prey are “hairy?” This doesn’t seem likely, as rooks frequently scavenge the remains of rabbits that variable hawks have killed and partially eaten. And Johnny Rooks are not put off by the wool of dead sheep.

That said, the answer to this question–and I don’t believe I know it quite yet–may lie in the similarly cautious behavior that many avian scavengers exhibit when approaching seemingly fine carcasses. The large Gyps vultures of Africa are said to ignore the carcasses of carnivores including lions, as well as those of primates, including baboons, while ravenously consuming those of zebras, wildebeests, and dozens of other species of ungulates. Northern ravens, which routinely feed alongside wolves that have killed deer and elk, as well as upon gut piles left behind by hunters, often appear fearful of intact deer carcasses that have been slit from abdomen to throat by researchers wishing to study the species scavenging behavior. And, I have seen similar behavior at road-killed carcasses of squirrels and ground hogs that I have used as bait while trapping black and turkey vultures who have spotted and directly passed over and looked at these offerings before turning way and flying off beyond the horizon.

Some researchers have concluded that when it comes to carcasses, novel food items, particularly when offered in novel setting, no matter how appealing they may be to humans, are just too suspicious to the scavengers involved to merit more than a passing glance.

For well over two years human settlers on the Falklands have been butchering marine mammals, seabirds and their young, and, more recently, livestock, for their own consumption, and in so doing have attracted Johnny Rooks to their actions. How long it took for the first starving rook to feed upon this new human largess is unknown, but certainly it happened a long, long time ago.

Apparently other rooks eventually caught on, and what had once been a suspicious carcass situation became common place and attractive. How many times, by comparison, have humans offered rats and mice to rooks? Aside of the inquisitive researcher, probably not very often… at least not often enough. This is my working hypothesis.

I am not alone in this regard. More than a few researchers working with northern ravens have reached a similar conclusion. The relationship between wolf killed carcasses and a safe food base goes way back, presumably hundreds of thousands of years. And the relationship between hunters and their gut piles of deer and elk, at least several hundred years. The relationship between human researchers and the carcasses they put out–slit open or not–remains too novel to be accepted as safe.

One of my students is deeply immersed in trying to solve this puzzle, and I am convinced, that given sufficient time, eventually she will solve this mystery. In the mean time I wonder what the rooks would do if we offered them an ice cream sundae or a banana split?

To help support our efforts to better understand and protect the near threatened striated caracara email me at Bildstein@hawkmtn.org




The team pauses to take a self: From left, Jean-Fancois Therrien, Marc Bechard, Jennie Duberstein and Keith Bildstein.

The team, from left, Jean-Fancois Therrien, Marc Bechard, Jennie Duberstein & Keith Bildstein.

By Keith Bildstein, Ph.D.
Sarkis Acopian Director of Conservation Science, Hawk Mountain Sanctuary
May 26, 2014

I have just returned from field work on the northernmost population of North America’s southernmost race of turkey vultures, Cathartes aura aura, a diminutive and largely tropical sub-species that weighs only two-thirds as much as other North American turkey vultures.  Our field team was made up of Hawk Mountain Research Associate Dr. Marc Bechard of Boise State University, former Sanctuary trainee Dr. Jennie Duberstein of the U.S. Fish and wildlife Service, me, and Hawk Mountain’s Senior Research Biologist Dr. Jean-Francois Therrien.

Our work in the approximately 100,00-square-mile Sonoran Desert in southern Arizona which included placing satellite tags on both turkey vultures and black vultures, turned out to be—as  often is true of field work–full of surprises.  Our new trapping site at a pair of dairy farms on the outskirts of Buckeye, Arizona, southwest of Phoenix, was far better managed than many of the farms we had visited before, and its owners were gracious beyond belief. One of the potential trap sites offered little in the way of clear views of any traps we might put out, but a second site near a massive ossuary, or boneyard, proved to be perfect.

A bone pile provided an ideal trapping site in the Sonoran Desert west of Buckeye, Arizona.

A bone pile provided an ideal trapping site in the Sonoran Desert west of Buckeye, Arizona.

Our plan was simply enough to trap and tag six turkey vultures and four black vultures, conduct a few day-long roadside counts, and spend a day looking for several of the individual vultures we had tagged in May 2013. We had nine days to accomplish all of this and, as there was no rain in the forecast, the plan seemed quite reasonable.  In the past, our experience with trapping turkey and black vultures has been that the latter species is easier to trap than the former, in part because black vultures dominate turkey vultures at carcasses, and in part because of the black vulture’s more social nature (i.e., if you catch one you are likely to catch many).

But not this time around.

The first six birds we caught were turkey vultures!  Blacks, although relatively common in the area, rarely showed up at our trap site, and were more skittish than the turkeys. We did catch one on the sixth day of trapping, but decided to turn to road surveys on the seventh day, as the likelihood of trapping more black vultures seemed rather low.  Presumably most black’s in the area were feeding somewhere else, and unfortunately, we never found that location.

A perched turkey vulture along one of our survey routes near the ghost town of Ruby, Arizona.

A perched turkey vulture along one of our survey routes near the ghost town of Ruby, Arizona.

We spent the next two days counting vultures along two road-survey routes that covered more than 300 miles of Arizona secondary roads south of Gila Bend and Tucson Arizona, mainly in the Tohono O’odham Indian Reservation and the Coronado National Forest.  Unlike the counts we conducted in January, the routes were filled with single and small groups of turkey vultures, many of which appeared to be searching the roadways for road-killed carrion, including snakes. Overall, we saw more than 10 times as many birds as we had seen along the same routes in winter, suggesting that the bulk of the population migrates south from the region in winter.

We spent the final day in the field searching for the five vultures we had tagged last May. The first one we searched for was “Jennie,” a vulture that, having migrated about 250 miles into Mexico last October, returned to Arizona less than a week later and overwintered in the area south and west of Gila Bend.   Unfortunately, Jennie was roosting in the Barry M. Goldwater Air Force Range, a bombing range south of Gila Bend that was off bounds for us, and was feeding at a dairy farm west of Gila Bend that the owners would not allow us to enter.  The next three birds were roosting and hunting closer to Maricopa Arizona and we set out in search of them just before noon.

The last known location of the next bird, “Desert Rat,” took us to a roosting site in a nut grove across the street from a large dairy farm.  Although we did not actually see the bird, we did find a number of molted feathers under a nut tree, confirming the presence of vultures at the site.

Keith and Linda Wallace-Gray with her vulture namesake in May 2013.

Keith and Linda Wallace-Gray with her vulture namesake in May 2013.

The next bird we looked for was “Julie,” who had last been sighted over a recently cut  north of Stanfield, Arizona.  Although we failed to see Julie, we did see another tagged vulture, “Linda” feeding together with six other birds on a road-killed jackrabbit at the edge of the hay field. Linda’s transmitter had been “misbehaving” and was sending signals episodically, with the last fix being recorded more than a month earlier in early April.  She was close to where she was then, and our sighting of her helped explain the episodic nature of her signals.  Although her tracking device was still in place on her back, the antenna for it was missing, a fact that almost certainly explained the spotty nature of her signals.  Given that we had seen close to 100 birds the day we were searching for the tagged individuals, and that as many as 500 birds almost certainly were using the area, our visual sighting of Linda, albeit without her antenna, was like winning the lottery … a “grand finale” of sorts for our field work.

Our plans are to revisit Arizona next January, not only to finish our tagging efforts there, but also to conduct additional road surveys. Although we are but one year into our studies of Arizona’s Sonoran Desert vultures, we already have learned much about their ecology.  Equally importantly, we also have learned to expect the unexpected in this population, which gives me reason to believe we need considerable additional monitoring to understand this most-southern race of North America’s most common and widespread avian scavenger. So please stay tuned.


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