Archive for March, 2018

20 March 2018

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

Brandon trap shot

The walk-in trap used to capture vultures at the Eliza Cove dump (Photo by Brandon Breen)

An e-mail from birding phenom Noah Strycker earlier this week reminded me just how interconnected our natural world of vultures really is.  Noah’s recent “big-year” book Birding Without Borders has made him an international birding super-star, and that is what brought him to Hawk Mountain for a fall lecture last autumn.  While at Hawk Mountain, Noah mentioned that he would leading a birding cruise in and around the Falkland Islands in March 2018, and I suggested that he be on the lookout for our color-banded striated caracaras there.  (You may recall that we have banded more than 1200 of these enigmatic raptors over the past eight years on the Falklands, and I was certain Noah would spot one or more of them on his visit.)  And indeed he did–R36 yellow, a juvenile we had banded on one island last summer, was seen by Noah almost 20 miles away on another island, a sighting that adds significantly to our knowledge of movement ecology in the species.


Noah, who was traveling on the M/V Ocean Adventurer, chartered by Quark Expeditions on a 33-day Atlantic Islands voyage from Ushuaia to Cape Verde, stopped for the day on March 13, and he and some others on the tour went to Gypsy Cove near Stanley to look for birds. They spotted two wing-tagged turkey vultures, a species we have studying and tagging in the Falklands since 2006.  One was tagged with number 10 yellow, the other with 37 yellow, two individuals that had been tagged as adults on two successive days in early July 2010 at a municipal garbage tip near Stanley.  That the two were still hanging around together more than seven years later is testimony to the longevity of the tags (take a look at them on the accompanying photos), as well as to the relationship of the two birds involved, both of which most likely roost with dozens of other turkey vultures on one of two small tussac islands near by.

Although we’ve had hundreds of reports of many of the 52 vultures we have tagged in the Falklands, Noah’s observations are the first in several years to report two birds simultaneously.

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A wing-tagged vulture at a municipal garbage tip near Stanley in 2008 (Photo by Alan Henry)

Somewhat surprisingly, most of the tagged birds have remained near Stanley (and the dump) confirming that human rubbish plays an important role in the diets of these birds.  I say “confirming” because a study of regurgitation pellets from turkey vultures collected by Amélie Augé of the South Atlantic Environmental Research Institute suggests a strong rubbish relationship.  Amélie collected her pellets in and around Stanley in 2015 and published her work in the journal Polar Biology in 2016.  Most of the regurgitation pellets she collected contained “anthropogenic debris,” including plastic, glass, paper, fabric, and/or aluminum in addition to more natural remains.  The relatively low human density of the Falklands (fewer than 3,000 on an archipelago the size of Connecticut) emphasizes the extent to which even small numbers of people can influence and contaminate the diets of raptors even on relatively remote areas.


I look forward to re-connecting with yellow 10 and yellow 37, as well as other wing-tagged turkey vultures on my next visit to the Falklands in August.  Assuming I do re-connect, I will let you know.

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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.

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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.

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