Feeds:
Posts
Comments

Posts Tagged ‘Hawk Mountain’

L1290372

Dr. Keith Bildstein about to release one of the northern breeders this January.

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

17 March 2017

Most studies of bird migration focus on the movements of birds that ornithologists refer to as “complete migrants,” species whose global populations evacuate their breeding grounds each year while traveling to geographically distant wintering areas.  Although Arctic Terns, Black-and-white Warblers, and Broad-winged Hawks, along with a small percentage of other species of migratory birds, do follow this pattern, most migratory species of birds are “partial migrants,” species whose populations include both sometimes-migratory and non-migratory individuals, and whose migratory populations sometime overwinter in areas already occupied by non-migratory members of the same species.  It turns out that partial migration is a lot more complicated than complete migration, and although the former is little studied compared with the latter, its complexity makes it a lot more intriguing, as well as a lot more challenging, both to investigate and to understand.

New World Turkey Vultures are a good example of partial migrants, with some populations consisting entirely of migratory individuals, whereas other populations consist of both migratory and non-migratory individuals, and still other populations consisting entirely of non-migratory individuals.  The degree to which different populations of Turkey Vultures interact, and the effects they have on each other is not well known.  One place where such interactions have been explored is in the Llanos, the enormous freshwater wetland of central Venezuela, where Turkey Vulture migrants from western North America, which are larger and more massive than the region’s non-migratory, year-round residents, displace the latter from the best available habitats and gain weight after their arrival while the supplanted residents simultaneously lose weight.  Indeed, the so-called Llanos “residents” appeared to “migrate reciprocally” to avoid competing with of the larger North American birds.

But what happens in areas in which some breeders migrate south in autumn, whereas other stay put, while still others from more northern breeding sites migrate into the region and over-winter there?  Such is the case in the Sonoran Desert of southwestern Arizona, where members of the breeding population include both migrants and non-migrants of the aura race of Turkey Vultures, whereas as the winter-only individuals are migrants from the larger and more massive meridionalis race from farther north.  (Note: There are six subspecies of Turkey Vultures, three that breed in North America, along with two that breed in Central America, and three that breed in South America.)

L1290369

Keith and Hawk Mountain Sanctuary Senior Researcher Dr. Jean-Francois Therrien fitting a satellite to one of the norther breeders this January.

We began satellite tracking members of the Sonoran Desert breeding race in 2014 and have followed the movements of nine birds since then.  All but one have proved to be migratory, with some individuals overwintering consistently in Mexico, whereas other have overwintered consistently either in Guatemala, El Salvador, Panama, or Colombia.  In late January of this year my Hawk Mountain colleague, Dr. Jean-Francois Therrien, and I traveled to our tapping site outside of Phoenix and successfully trapped two winter-only individuals of the meridionalis race of Turkey Vultures.  Although we don’t know exactly where these two breed, as of early-March one was on Vancouver Island in south western most Canada, and the other was in Death Valley California in late March, with both north of their Arizona trapping site.

Tracking the movement of all of these Sonoran birds for several years will allow us to determine if the northern breeders crowd out the smaller year-round residents from Arizona, and if so, whether or not the smaller southern migrants leave in autumn in advance of the arrival of the larger northern migrants and time their returns to avoid the departing northern migrants in spring.

Although this may seem a bit esoteric to some, understanding the extent to which the two subspecies interact in the Sonoran Desert has important implication for conservation.  Suppose, for example, that in Arizona the larger northern breeders consistently dominate the smaller southern breeders.  If so, the size of the former’s populations could limit the size of the latter’s, particularly in winter when food may be limiting.  If so, the fate of the latter would be affected by the fate of the former.  Thus, if global change were to affect the former–either positively or negatively–the latter might “respond” as well, albeit indirectly, in-kind.  Although, all of this remains highly speculative, the extent, if any, to which populations of the two races merits examination, and I very much look forward to doing so over the course of the next few years.

I will keep you posted of the arrivals and departures of both our “northern” and “southern” Arizona migrants this summer.

Advertisements

Read Full Post »

Johnny Rooks digging for kelp maggots on the Falkland Islands.

By Keith L. Bildstein, Ph.D., Sarkis Acopian Director of Conservation Science
and  Katie Harrington, Hawk Mountain Research Associate
Hawk Mountain Sanctuary

29 August 2016

Bear with me on this; it is really quite exciting…

Kelp maggots are the larvae of coastal dipterid flies that feed on rotting seaweeds, including kelp that drifts up along sandy shorelines.  In the northern hemisphere, these larvae (aka maggots) are themselves fed upon by shorebirds and passerines, including crows, which excavate them from kelp wracks that accumulate along the shorelines of sandy beaches.  Although studied little south of the equator, kelp maggots also inhabit the rotting kelp that drifts up along the shorelines of the Falkland Islands, including those on Saunders Island, a 49-square mile landmass in the northwestern part of the archipelago.

Neck Maggot Feeding Summer

Johnny Rooks digging for kelp maggots

For more than four years, we and our colleagues have watched the Striated Caracaras (aka Johnny Rooks) that we have been studying on Saunders Island, digging and probing beached kelp adjacent to penguin colonies there, and have wondered if these largely scavenging birds were receiving ecologically significant amounts of nutrition from the buried invertebrates.  In February of this year, we began to study this feeding behavior in detail using a protocol that allows us to quantify the rate at which individual caracaras secure maggots.  Our observations involve counting the numbers of maggots individual birds catch and consume during 30-sec feeding bouts.  We continued to collect data using this protocol on our most recent trip this August to assess the extent of seasonal differences in feeding rates.  We also collected maggots and weighed them to determine their individual mass, allowing us to determine their nutritional value. Our results, albeit preliminary, suggest that although birds capture maggots at higher rates in austral summer than in austral winter, in both seasons they manage to do so at rates of capture that are high enough to provide substantial nutrition for the birds engaging in this behavior for several hours or more daily.

The dogged determination and methodic nature with which the rooks dig is impressive, with many birds digging alternately with their left and right feet five inches or more into the rotting kelp while securing dozens of maggots over brief periods.  Clearly, more study is needed, but our initial observations suggest that this nutritional resource plays a significant role in the life of Striated Caracaras year round.

Summer maggots

Exposed kelp maggots

Intriguingly, on the most recent trip we also saw groups of rooks digging in upland pastures where they were feeding on what appeared to be small earthworms and grass grubs, with about the same rate of capture as when they were catching kelp maggots.  On our next trip in February 2017, we plan to expand our observations considerably.  In the interim, we will be presenting preliminary results of our work at the annual meeting of the Raptor Research Foundation in Cape May, New Jersey, in October.

Of course, insect eating is not unknown in raptors.  Kites, American Kestrels, and many other falcons routinely do so, as do larger birds including Steppe Eagles overwintering in Africa.  However, digging in the ground for insects is relatively uncommon among birds of prey.  Honey buzzards reportedly do so, and kites and Common Buzzards dig for earthworms in recently plowed fields in Europe.  That said, at least some rooks appear to do it routinely as well, and not only on Saunders Island.  In August 2013, during a short trip to Steeple Jason, a tiny island in the Falklands more than 50 kms from Saunders Island, one of us saw large numbers of caracaras digging for earthworms in peaty soil at the base of the island’s steep escarpment.

Our work with caracaras indicates that they are severely food stressed in winter on the Falklands.  Digging in the ground for invertebrates at first may not seem “raptorly,” but beggars cannot be choosers, and the taste of a live invertebrate may beat that of a rotting vertebrate anyway.

Read Full Post »

Red-backed rescue - cropped

Keith rescuing the female Red-backed Hawk from a pack of Striated Caracaras.

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

24 August 2016

With an extensive open-country distribution throughout much of southern South America, Red-backed Hawks are the functional equivalent of North America’s widespread Red-tailed Hawk. The mid-sized Buteo—red-backs weigh in at just over one kilogram, or roughly the same body mass of a Red-tailed Hawk—feeds mainly on small birds and small mammals across much of its continental range.  But on the Falkland Islands, where the species also is common, red-backs focus on Upland Geese, a large terrestrial goose that weighs 3.5 to 4.0 kilograms, or more twice the body mass of a Red-backed Hawk.  Given this rather unusual predator-prey size relationship, red-backs, which are non-migratory on the Falklands and remain paired-bonded throughout the year, hunt geese together in male-female duos with one hawk distracting the goose while other surprises and “takes down” the un-suspecting waterfowl.  In many instances, both members of the pair kill the goose before feeding on it simultaneously, with both gorging themselves and often returning to the carcass for a day or more as they strip every last piece of edible tissue from it.

This cooperative feeding routine works well for the red-backs on the main islands of East and West Falkland, where there are few if any Striated Caracaras to worry about, but such is not the case where the two species co-occur on the smaller, peripheral islands.  Our principal Striated Caracara (aka Johnny Rook) study site, Saunders Island, which is inhabited by several dozen Red-backed Hawks, as well as over 80 Striated Caracaras, is a case in point.  On Saunders Island as elsewhere, caracaras may be incapable of subduing and killing Upland Geese on their own, but they are not above competing for a dead goose once a pair of red-backs have killed it.

Such was the case on Saunders last week when my colleague Katie Harrington and I came upon a pair of Red-backed Hawks feeding upon a recently killed Upland Goose in a sheep meadow at the eastern end of the island one morning earlier this month.  Both hawks, but especially the female, had already gorged themselves on the carcass while cooperatively fending off several dozen, mostly juvenile caracaras that were attempting to partake in the feast. As we approached the group to read the bands on the caracaras—we have fitted more than 1,100 of Johnny Rooks with individually numbered rings as part of our long-term studies of the species—the male red-back took off. The female tried to do the same but was unable to do so given an enormously over-filled crop, which made it impossible while she was being attacked by more than a dozen caracaras that had pinned her down on her back and were feverishly “footing” and pecking at her.  Sensing that she was not long for this world, I jumped off my ATV and ran her down after she broke free from the swarming caracaras.

Keith with red-backed

A close-up of Keith holding the female hawk, with it’s bulging crop.

My decision was instantaneous, our initial approach, which had spawned the male’s successful departure, had left the female vulnerable, and although interfering in nature is not something I typically do, in this case our approach had tipped the competitive balance in this ongoing interaction, and my rescue attempt was aimed at minimizing the consequences.  The carcass was a little more than a kilometer from our cottage at our farm-settlement headquarters, and I remounted my ATV, cradling the hawk in my left hand while steering and thumb-throttling the ATV with my right.  We reached the settlement several minutes later where I placed the female in a dog kennel to give here time to digest her crop peacefully.

Four hours later I released the hawk, who by then had digested about half of food in her crop, but to no avail, as a group for more than a dozen caracaras appeared as out of nowhere and proceeded once again to pin her down in what appeared to be a death grip.  Once more I sped toward the hawk, ran her down, and re-rescued her, placing her back in the kennel with a plan to release her the following morning.

By the time I had grabbed her from the kennel the next day morning, the distended crop was no longer visible, and although half-a-dozen caracaras again initially pursued her, this time they kept their distance, as the lack of a crop most likely signaled them as to the danger in approaching too closely.  After flying off and perching on a fence post for about 5 minutes, the hawk flew off un-pursued in the direction of the goose carcass and her mate.  She was re-sighted at the settlement several days later holding her own against a group of caracaras fighting over a goose carcass that had been fed to the farmer’s pigs.

The sharper talons of the predatory Red-back Hawk make them formidable opponents to the less predatory and less well-armed caracaras—at least when not encumbered by an over-filled crop.  However, when they do have a large crop, the interspecies-competitive relationship changes, and in mid-winter (austral-winter August is the equivalent of boreal-winter February) when both species are hard-pressed for food, it becomes something of a raptor-eat-raptor world on the Falklands Islands where things can change rapidly for individual birds.

Stay tuned… next week I will blog about yet another potential dietary item for food-stressed Johnny Rooks: kelp maggots.

Read Full Post »

Skyline drive survey

Our survey vehicle on Skyline Drive in the Shenandoah National Park during our initial survey in the summer of 2005

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

20 July 2016

I realize that I am running a risk with this column in talking about raptor monitoring. Indeed, when I begin to talk about monitoring, my audience often begins to doze off.  If I continue to talk long enough, some may even fall asleep.  Nevertheless, monitoring not only is a useful tool in raptor conservation; it is an essential tool.  When we in raptor conservation fail to monitor populations of birds of prey we often pay a steep and, in some instances, an irreversible cost.

Consider the current plight of the Indian Long-billed and Asian White-rumped Vultures, two species that 40 years ago ranked as the world’s most abundant large raptors.  Both species were then common and widespread throughout southeastern Asia.  When populations of both species crashed by more than 95% in Bharatpur, India in less than two decades in the late 1900s, the problem was thought to be pesticides.  But when similar reports were received for other populations elsewhere in these species wide ranges, a lack of earlier population monitoring made it difficult initially to ascertain the actual magnitude of the declines.

Two vultures that had once been so common that no one thought to monitor the sizes of their populations were now so uncommon that some conservationists were suggesting that they were in the “fast-lane” to extinction.  Half of a very large number is still a very large number, and by the time people were paying attention to these formerly species few knew what their once very large numbers had been.

Eventually conservationists learned the problem was an FDA approved drug, diclofenac, then in use on livestock.  Diclofenac, a non-steroidal anti-inflammatory substitute for aspirin that, while non-toxic to humans, turned out to be highly toxic to vultures in the genus Gyps.  But without proper population monitoring, we had reached a point where expensive captive breeding was necessary to reverse the trends.  Had we been monitoring these populations earlier, such extreme measures would not have been necessary.

Which brings me to my point.  Monitoring populations of raptors—even common and abundant species—is a critical component of practical and effective raptor conservation.  This is why Hawk Mountain decided to begin doing so with two species of common and widespread New World vultures in 2005.  As of late 2015, the Sanctuary has surveyed Black, Turkey, and other vultures in 23 locations throughout the Americas: from central western Canada in northcentral North America all the way south to Tierra del Fuego in southern South America and the Falkland islands in the South Atlantic.

Our surveys include both winter and summer counts totaling more than 24,000 miles of road counts across 14 United States, 4 Canadian provinces, and 6 central and South American countries.  Surveys are conducted by a driver and one official observer along secondary routes at 30 to 40 miles an hour on rain-less and fog-less days.  Counts begin at nine in the morning and end at four in the afternoon after and before most of the birds have roosted for the evening. In addition to Black and Turkey vultures, all other scavenging birds of prey are counted as well, including all other vultures, condors, and caracaras.

When we began the counts in 2005, the plan was to survey both Turkey Vultures and Black Vultures in representative areas across much of their geographic ranges and to redo the surveys once a decade in both winter and summer, so that populations of both migratory and resident populations of these common scavengers could be monitored routinely. Declines in numbers could be assessed in a timely fashion, and conservation action taken as necessary, before populations had declined catastrophically.

Black bear scvenging a road-killed deer

An unexpected “non-vulture” scavenger feasting on a road-killed deer along Skyline Drive during our second round survey in the summer of 2016.

Round two of our surveys began in early July 2016 when three Summer Field Experience Interns and I redid two day-long road counts in northern Virginia that were originally undertaken in the summer of 2005.  One of the routes was a mountainous 195-kilometer meander along Skyline Drive in the Park Service’s Shenandoah National Park and the northern-most section of the Blue Ridge Parkway.  The other was a 211-km route that followed the eastern shoulder of the upper Shenandoah Valley.  The numbers of vultures sighted were encouraging.  During two days of field work this summer, we counted a total of 253 Tukey Vultures and 14 Black Vultures, versus 124 TVs and 9 BVs seen on the summer 2005 counts.

Although this initial field effort was a modest one, we will ramp-up counts this winter to include 6 routes totaling 963 kilometers in western and central Panama, along with the two winter counts in northern Virgina.  Over the next five years, we plan to re-conduct all of our surveys from west-central Canada south to Tierra del Fuego.  We hope to find that all populations previously surveyed are stable of increasing.  However, if they are not, we plan to put conservation actions into play that will determine the cause or courses for the declines and begin work to reverse them.

Vulture perform important ecological services in the ecosystems they inhabit, not the least of which include nutrient recycling and reducing the likely spread of diseases including botulism, anthrax, and rabies.  Protecting their populations is a critical aspect of Hawk Mountain’s mission, and we plan to stay on top of this.  Our next surveys in Virginia are scheduled for December 2016.  We plan to redo our winter surveys in Panama in January 2017.  Once we have conducted them I will be in touch.

Between then and now let me know if you have any questions on this monitoring effort and how you can support the Sanctuary financially in carrying out this crucial part of our mission. Feel free to email me at Bildstein@hawkmtn.org or call me at 570 943 3411 ext. 108.

Read Full Post »

keith releasing vulture may 2016

Keith releasing “Calm Lady” at the Buckeye dairy-farm trap site.

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

27 June 2016

We’ve all seen the Gary Larson cartoons of vultures perched or soaring above one or two desiccated cowboys insightfully expounding on something comical.  Truth be told however, vultures are rare inhabitants of most of the world’s deserts.  Fortunately, this is not so in the Sonoran Desert of the southwestern United States and northwestern Mexico.

The Sonoran, a fascinating and ecologically rich region, is an important go-to place for vacationing Canadian and US snow birds, as well as home to 10 species of amphibians, 100 or so reptiles, 60 mammals, and more than 350 species of birds, including the world’s most northern breeding populations of Cathartes aura aura, a largely Neotropical subspecies of Turkey Vultures.  Investigating raptors at the limits of their geographic ranges has been a fascination of mine for more than 40 years, and this explains why I traveled to Buckeye, Arizona, 30 minutes west of Phoenix on Interstate 10 just before midnight on the night of Tuesday 17 May 2016.

Hawk Mountain’s Senior Research Biologist Jean-Francois Therrien and I landed at Sky Harbor Airport in Phoenix with an ambitious agenda.  The following day I would travel two hours south to Tucson to give a talk on our vulture work at the world famous Arizona Sonora Desert Museum, while at the same time Jean-Francois would hook up with Rich Glinski, the editor of The Raptors of Arizona, and try to catch vultures at a dairy facility outside of Buckeye.  Dairy farms are large in Arizona, and still-born calves would be the bait at our desert trap site.

Both Black and Turkey Vultures occur in Buckeye, and although we had begun our studies in the state in 2014 focusing solely on the latter, we have recently expanded the work to both species, as both were feeding, interacting at, and fighting over at the same nutritional resources, and fully understanding the feeding ecology of two species was only possible if we studied both of these competitors.

My talk at the museum was set for noon and a group of 40-plus museum workers and volunteers were eager to what I had to say as the museum had open an exhibit featuring both Black and Turkey Vultures a few months earlier.  Half way through the talk my mobile phone vibrated in my pocket.  Unfortunately, I ignored it as I didn’t want to interrupt the presentation.  That was a mistake, as Jean-Francois was calling from Buckeye to let me know that he and Ron had just caught and placed a satellite tracking device on an adult Turkey Vulture they had decided to call “Moo Moo,” the name the young daughter of our host blurted out when she first laid eyes upon it.  (Most of our trapping sites are on private land, and we always make certain to engage the land owners in all aspects of our field work, including watching us place tracking devices on the birds we catch and tag and helping us name them.)  The next phone call came two hours thereafter when JF called to let me know that he and Rich caught and tagged a second Turkey Vulture named “Gash.”  Both individuals, while quite healthy, weighed less than 70% of the Turkey Vultures we catch in Pennsylvania, which were members of the considerably more massive septentrionalis subspecies.  Needless to say we celebrated the day over dinner at a “wings” restaurant close to our motel.  We had brought four tracking devices with us, and after just one day of the four that we had allotted to trapping and tagging birds, we were half way to our goal.  The pressure was still on, but reaching our goal certainly appeared doable, and we were pleased.

Keith and AZ bird May 2016

Keith with “Calm Lady” at the trapping site.

We caught Turkey Vulture number three, “Calm Lady,” early afternoon the next day, and caught our fourth Turkey Vulture, “Early Bird,” before eight the following morning.  Four birds after a little more than two days in the field.  Not bad… not bad at all.  We took time off from the field the rest of day three while planning our work for the remaining two days we had scheduled to be in Arizona.  When we first started working in Arizona in May of 2014, our plan was trap and tag at least a dozen Turkey Vultures, and the four we caught in May of 2016 brought our total 15.  We also planned to conduct a series of six seasonal road surveys totaling 1,061 miles in southern and western Arizona.  The surveys would allow us to estimate the sizes of the wintering and summering populations there, providing us with critical information on regional numbers.

The next morning we set off a 166-mile road survey that began at Gila Bend and meandered through the towns of Ajo, Why, and Sells Arizona, while circling back toward Tucson.  We counted 63 Turkey Vultures and 3 Black Vultures along the way.  After overnighting in Tucson, we conducted a second, 152-mile survey that began at Three Points and continued south to Nogales on the border with Mexico, before turning north to Continental.  On that survey we counted 30 TVs and 1 BV along this route.  After finishing the survey we scurried back to Sky Harbor Airport in Phoenix to catch a red-eye flight back to Newark, New Jersey.  It was then onto Hawk Mountain by car, where we arrived mid-morning on Monday the 23rd.

Although we had spent but five days in the field, we had managed to catch and tag four new Turkey Vultures and had conducted two full-day roadside counts.  Our next trip to Arizona will be in January 2017, when we hope to catch and tag at least three Black Vultures and conduct as many as six road surveys.  Although the work—if you want to call it that—might seem tedious to some, for me and my colleagues it was as close to heaven as one comes in raptor biology…  a chance to catch up on all things “vulture” while trapping and tagging a few birds, surveying an important regional populations of two species, and getting the word out to the public about why we are studying Turkey and Black Vultures and what we are finding out about them.

In my next blog, which I hope to have out in several weeks, I will update you on our Arizona findings to date.

To learn how you can help support our studies, email me at Bildstein@hawkmtn.org or call me at 570 943 3411 ext. 108.

Read Full Post »

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.

Read Full Post »

Drs. Jean-Francois Therrien and Marc Bechard harnessing a turkey vulture,

Drs. Jean-Francois Therrien and Marc Bechard harnessing a turkey vulture,

By Keith L. Bildstein, Ph.D.
Sarkis Acopian Director of Conservation Science
28 May 2013

Thursday, May 24, turns out to be a special day. We catch two adult black vultures simultaneously (yellow wing-tag numbers 18 and 20) at 9:40, but more importantly, we catch and satellite tag three adult turkey vultures, which we name “Desert Rat” after Doug, “Jennie” after Jennie Duberstein, and “T. K. Red River,” after one the three dairy farms that have been providing bait. The three turkey vultures, which are all adults, bring our total of satellite tagged individuals to four. With four days of trapping left we are two-thirds of the way to our goal.

Friday, 25 May, turns out to be far less special. We have birds on the ground at 5:10, and high numbers throughout the day, but no one feeds and at 11 AM we pull the traps with no birds on the ground or in the air. Reality sets in. We have three more trapping days and two more turkey vultures to trap.

Saturday, 26 May, proves to be much more fruitful. At 5:30 AM two turkey vultures fly over, but do not land. Our donor arrives from Tucson for her third visit at 7:30. She has yet to see us trap a turkey vulture, and today, she promises, will be her last visit. The pressure is on.

Linda joins me in the blind at 7:30, and I tell her once again how difficult it can be to trap turkey vultures. At 8, two turkeys arrive at the site, land, and, almost immediately, begin feeding on one of our snared carcasses. Five minutes later the first of two trapped vultures for the day is caught. I run to the carcass as our donor snaps a series of photos. My ancient body speeding across the desert makes for quite a scene. “Linda,” named after our donor, is released 40 minutes later, but not before we catch our second vulture of the day.

“Edward Abbey,” so named for the western conservation writer, is caught at 8:05. Abbey quipped in his masterpiece Desert Solitaire that he wanted his remains placed in the desert so that turkey vultures could feed on it. Whether or not that happened after he died, his namesake now soars above the lands he so wanted to protect for all of us, and our trapping crew…Linda, Julie, Doug, Jennie, Jean Francois, Marc and I, are happy.

Dr. Jennie Duberstein describing our trapping effort to visitors at the trap site.

Dr. Jennie Duberstein describing our trapping effort to visitors at the trap site.

After releasing “Edward” we clean up our mess, offer our farewells to our hosts Doug and Julie, and head back to Tucson. We celebrate our victory at an Italian restaurant that evening and plan our routes for a 200-mile road-side count of vultures across the backlands of southeastern Arizona and eastern-most New Mexico that we plan to conduct the next day. The road survey takes us past numerous historic sites, including the place where Geronimo finally surrendered to the U.S. Calvary in the Skeleton Valley near the border with New Mexico in 1886. We also see 24 turkey vultures and return to Tucson that night for a second celebratory dinner. Jean Francois and I return to Hawk Mountain the following day.

Maps of the whereabouts of our tagged birds should appear on Hawk Mountain’s website next week. I have already started planning a trip to the southern cone of South America to capture and tag representatives of the one remaining race of turkey vultures that we have yet to study. Finding the right colleagues to work with will be key to our success in South America, but I am now more convinced than ever that I will find them, and that Cathartes aura jota too will join the other 5 subspecies in our grand studies of turkey vulture migration.

Read Full Post »

Older Posts »