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Posts Tagged ‘road surveys’

20 March 2018

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

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

18 Jan 2018

Monitoring the distributions and abundances of birds of prey is “key” to tracking changes in their conservation status.  And this, in turn, is key to protecting them.

Indeed, lack of monitoring once-abundant Old World vultures in southern Asia during the height of their diclofenac-induced population declines in the 1980s and 1990s allowed populations of three species of widespread and common vultures to plummet catastrophically by more than 95%, unnoticed by the conservation community. Conservationists were caught by surprise at this greatest global loss of raptor populations in recorded history, necessitating expensive captive-breeding programs, which, unfortunately, some believe may offer “too little, too late” to restore these once-common species to their former status.

It was with this self-inflicted catastrophe in mind that Hawk Mountain Sanctuary embarked an ambitious intercontinental population monitoring scheme stretching from southern Canada to southernmost South America, aimed at tracking both short and long-term shifts in the distributions and abundances of populations of the world’s two most common New World scavenging birds of prey, the black and turkey vulture, along with other less common avian scavengers including caracaras and condors.

The Sanctuary’s effort began in 2004 with eight winter roadside-survey routes in Costa Rica, totaling more than 1200 kilometers.  Since then, a series of more than 150 seasonal (both winter and summer) roadside counts have been undertaken across Canada, the United States, Costa Rica, Panama, Venezuela, Uruguay, Chile, Argentina, and the Falkland Islands.  In 2017 we began resurveying these routes to assess the extents, if any, to which populations of scavenging birds of have changed over the years.  Seven roadside-counts in central Argentina were the first to be redone this July.  In late December 2017 I re-ran two of the southernmost surveys in southern Patagonian Chile.  The latter two surveys are the focus of this entry.

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Road sign indicating the highway goes to the end of the world (Ruta del fin del Mundo).

Although the two survey routes are just beyond the traditional southern distributions of both black and turkey vultures, both are within the distributions of Andean condors, southern crested caracaras, and chimango caracaras.  (The routes, themselves, are part of the “Ruta del Fin del Mundo,” or the “Highway at the End of the World,” as the Chileans call it on their road signs.)  The goal was to learn if black and turkey vultures, both of which are extending the northern limits of their ranges in North America were doing the same southward in South America.  I was on my way to field work in The Falklands, and had scheduled four days to survey scavengers along the two routes I had earlier surveyed in the austral summer of 2010-2011.  One route followed the northern shoreline of the Strait of Magellan for 205-kilometers from 40 kilometers south of Punta Arenas, Chile, to Punta Delgada, Chile, close to the border with Argentina.  The other stretched 193-kilometers from 40 kilometers north of Punta Arenas to Puerto Natales, Chile, near the southern terminus of the Andes.  Although the forecast called for rain on three of the four days, I planned to complete my surveys. Thankfully the wet weather held off, and I was able to conduct all four surveys without interruption.

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An old store in a ghost town on the shoreline on the Strait of Magellan in Patagonian Chile.

Both routes took me through spectacular treeless Patagonian Steppe, desert-like regions with little vegetation that superficially resemble parts of the arid American West–open areas ideally suited for spotting both perched and flying birds of prey.  Although the surveys are just “indexes” of populations of scavenging birds of prey inhabiting approximately half-a-kilometer strips along either side of the roads, they do provide relatively consistent counts of scavenging birds of prey in an area.  Indeed the two counts along the first route yielded survey totals of 13 southern crested and 1 chimango caracara, and 13 crested caracaras and 3 chimango caracaras on the 19 and 21 of December 2017, respectively, supporting the validity of the survey technique’s ability to assess regional populations.  The second route was more variable with no Andean condors seen on the first count day and 10 seen on the second, but all-in-all, these results and our earlier surveys suggest that populations of the three species seen had changed little across the eight years of the austral-summertime surveys.  Whether this will hold for scavenger surveys in other regions remains to be seen.

However, that is only part of the story.  Although I did not have time to record other species seen along the routes, I did see a number of other fascinating birds and animals, including handfuls of cinereous harriers and variable hawks, together with rheas, flamingos, black-faced ibises, southern lapwings, and guanacos.  One of the most fascinating behavioral aspects of the surveys was that road–killed rabbits and other small mammals that had been hit by traffic the evening before each survey were quickly fed upon by southern crested caracaras early the following morning, with the caracaras unquestionably out-competing kelp and dolphin gulls that tried unsuccessfully to “horn-in” on the action.

The situation reminded me of what I saw several years ago while studying Old World vultures in the Masai Mara of south-western Kenya, where in early-morning, first-in-the-air, ruppells, white-backed, and lappet-faced vultures congregated at and fed upon lion- and hyena-killed prey from the previous evening’s predation events.  Although my Patagonian observations occurred only across several days, there was little doubt that a daily feeding pattern existed.  The fresh-killed rabbits I spotted from early to mid-morning each day—and that each attracted as many as a dozen or more caracaras—had all but disappeared by late morning, with nothing but bright-red splotches on the concrete roadway offering evidence of what had happened the previous evening, an obvious example the unintended effects of human commuters.  Another intriguing behavior was that of Andean condors, several of which were seen in low-flying (<5 meters) flight along the roadsides, something I often associate with carrion-seeking turkey vultures in both North and South America.

These recent surveys convince me that even without black and turkey vultures, road surveys can be both fun and scientifically profitable, and I look forward to conducting them again in another 5 or 10 years.

More roadside scavenger counts are planned for central Argentina in January and in Arizona in February.  I will keep you posted on the results.

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