Posts Tagged ‘south america’

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.

DSCN7382 - Copy (2)

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.

DSCN7384 - Copy (2)

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.


Read Full Post »


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.)


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.

Read Full Post »