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Posts Tagged ‘vulture research’

By Katie Harrington, Hawk Mountain Sanctuary Research Associate

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Dr. Keith L. Bildstein, Hawk Mountain Sanctuary Sarkis Acopian Director of Conservation Science

Many birds of prey time their feeding efforts to take advantage of the cyclic abundance of their prey.  In East Africa, for example, Old World Vultures rush to flight each morning to search for ungulate carcasses created by previous night’s lion and hyena kills.  And in Europe and elsewhere rodent-eating Eurasian Kestrels synchronize their feeding efforts to co-occur with the four-hour activity cycles of voles they feed upon.  Other raptors, including most notably coastal populations of sea eagles and ospreys, set their hunting efforts to coincide with falling tides, taking advantage of the increased vulnerability of fishes in shallow waters created by the receding waters.  And now, thanks to the insightful field observations of former Sanctuary trainee and now graduate student Katie Harrington of San Francisco, raptor biologists can add Striated Caracaras to the list of tidally influenced birds of prey.

Found only on remote islands in Tierra del Fuego and the Falkland Islands, Striated Caracaras, or Johnny Rooks, are aggressive scavenging birds of prey.  Once thought to rummage almost exclusively on dead and dying seabirds and livestock (including penguins and sheep), human leftovers, and occasionally, marine-mammal feces, we have discovered that these cunning birds of prey also take a many kinds of terrestrial invertebrates, including both earthworms and grass grubs, and as well many intertidal invertebrates, including dipteran kelp maggots, limpets, barnacles, and even—believe it or not—octopuses.

Octopus predation 14

The early bird gets… the octopus. The first two rooks on the scene dislodge the marine predator from where it was sheltering in a tide pool and begin consuming its tentacles.

One of the primary efforts of our most recent field efforts on Saunders Island, in the Falkland Islands where roughly 150 Johnny Rooks spend the summer months, was to learn more about the importance of invertebrates in the Rooks’ diet. What factors influence the amount of time Rooks spend foraging for invertebrates each day, and does this strategy provide an ecologically significant amount of nutrition? To find out, we spent hours observing the Rooks raking for maggots in accumulated, decomposing kelp wrack, some determinedly excavating pits six inches deep, and many digging shoulder to shoulder for over an hour. During one mid-afternoon observation session, we observed what appeared to be a shift in their preferred entrée. The Rooks exited the kelp wrack and flew toward an adjacent rocky intertidal zone that was being slowly exposed by the falling tide. First one, then four, then up to twenty birds entered the rocky area, both by flight and by their often-preferred method of walking and running.

Octopus predation 1

In less than a minute, the word is out, and more than 10 Johnny Rooks surround the octopus. Many of the juveniles in this group were banded earlier this year.

Previously submerged, the rocks began to provide a platter of meal options, from blanketing mussels to limpets to innumerable species of invertebrates sheltered under flat rocks. We watched as the rooks began silently and systematically walking along the waterline, peering under overhanging rocks in search of limpets that had not yet suctioned tightly to survive the low tide. Unlike their foraging strategy within the kelp wrack, which can reach as many as fifteen individuals raking within 2 meters of each other, the Rooks searched the intertidal as individuals or in small, mixed-age groups. As the tide fell further, some even alit on the partially exposed adjacent kelp forest, searching the algae’s stipes for potential prey. Their persistence paid off as we watched many quickly consuming their quarry, some within two minutes of their previous catch.

Less than fifteen minutes from the time the Rooks shifted into the area, a juvenile bird encountered a Southern Red Octopus caught in a tide pool. The Rook immediately pulled the octopus up onto a rock where it laid overturned, struggling to right itself as nine juveniles began pulling on and partitioning its tentacles. Within six minutes, more than thirty Rooks encircled the octopus, which had been reduced to portions of its head, with which individual Rooks were then able to abscond. With full crops, the group dispersed, some Rooks sheltered aside nearby ledges to digest while others retreated to a fresh-water seep on the adjacent cliff to wash down the meal.

Previously, the only known predators of the Southern Red Octopus were Southern Sea Lions and humans that opportunistically fish for them during spring tides; yet the speed at which the Rooks dispatched the octopus suggested this was not the first time they had encountered the eight legged invertebrate. Octopus may be clever, but they have met their match in the Johnny Rook.

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

12 December 2016

We typically characterize vultures as gluttonous creatures, obligate scavenging birds of prey that engage in rough-and tumble feeding frenzies at large ungulate and pachyderm carcasses in the company of dozens of other “all consuming” vultures, scarfing up enough meat to last for several days.  And indeed, vultures sometimes eat so much food that they remain grounded for an hour or more after feeding for partial digestion to take place, before they are light enough to take off.  Having watched these birds feed for many years, I can tell you that all of this is true.  But watching vultures at so-called “vulture restaurants,” where humans routinely provide food, sheds light on an aspect of vulture feeding that goes largely unrecognized by the general public.

vulture-restaurant

The vulture restaurant at the Hoedspruit Endangered Species Centre in northeastern South Africa after dinner is served. Note the Marabou Storks in the foreground and the ling-necked African White-backed Vultures in the background. Hoodies are nowhere to be seen in the initial scrum.

In fact, some vultures are “finicky” as well as “voracious,” feeders; especially at vulture restaurants where daily meals are typical.  The world’s first vulture restaurant, in the Drakensburg Mountains of South Africa opened in the 1960s to help supplement the diets of local Bearded Vultures.  Today, vultures restaurants (bird feeders for vultures, if you will) are used to provide “clean,” lead-free meat to recently released California Condors in the American West.  Many of the restaurants are associated with ecotourism, serving a useful purpose in bringing vultures and people together.  One such restaurant at the Hoedspruit Endangered Species Centre near Kruger National Park in northeastern South Africa has been feeding wild vultures and other scavenging birds for more than 30 years.  The restaurant works well at attracting handfuls of Pied Crows and Black Kites, dozens of Marabou Storks and Hooded Vultures, and hundreds of African White-backed Vultures, the latter two of which are now Critically Endangered.

Earlier this month, University of KwaZulu-Natal post-doctoral student and Hawk Mountain research associate, Dr. Lindy Thompson, and I spent four days at the Centre near Hoedspruit trying to catch Hooded Vultures.  During that time we learned a lot about the finicky feeding behavior of the birds.  Our goal was simple enough: catch as many as three of the Hooded Vultures visiting the restaurant, and fit them with satellite-tracking devices that would allow us to monitor the movement ecology of the species, including information on how dependent individuals were on vulture restaurants in the region versus how much time they spent in the nearby Kruger National Park feeding on native wildlife, and how they interacted with other species in the region.

hooded-vulture_imm_release-at-selati-game-reserve-limpopo_13-2-2016-1

Dr. Lindy Thompson, releasing “Don King” after his capture in February. Note his downy top-knot and relatively thin bill.

We already had caught and fitted 10 Hooded Vultures with tracking devices in South Africa, and two of our previously tagged birds actually showed up at the restaurant during our four days of observation, even though neither has been tagged there.  One of the two, Don King, had been caught at a private nature reserve 45 miles north of the Hoedspruit restaurant in February of 2016.  Don looked healthy enough, although he had lost his downy top-knot that led to its name.  The second tagged bird, Mopane, had been caught in Kruger National Park about 60 miles northeast of the restaurant in August of 2014.   It, too, looked quite healthy.

The two marked birds were joined by about 30 unmarked individuals that visited the restaurant daily.  Unfortunately we were unable to capture any of them.  We did snare several of the far larger African White-backed Vultures that clearly dominated the smaller “hoodies” at the restaurant’s offerings.   Hooded Vultures, it turns out, are finicky feeders when feeding in the company of White-backed Vultures, pecking at and gleaning only tiny scraps of meat with their small, thin bills, after the meat had been torn apart by the larger white backs during feeding frenzies.  By the time the hoodies got close enough to our traps, the snares we had set already had been pulled closed by the white-backs, making capturing the former all-but-impossible.

Lindy Thompson and Andre Botha of the South African Endangered Wildlife Trust will try to capture the hoodies at other feeding sites that attract fewer white backs.   Older elephant carcasses work well for this purpose, as they often continue to be visited by the more fastidious hoodies for several days after larger vultures, hyenas, and jackals have stripped most of the flesh from carcass.

The finicky feeding behavior of hoodies is well known among those of us that study the birds.  It appears that hoodies have instituted their own specialized feeding niche, one that involves “cleaning up” after the larger and less finicky species.  Although this makes hoodies a bit more difficult to capture, it is somewhat endearing as well.  As I see it, a vulture that cleans up after other vultures can’t help but be appreciated.

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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.

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