Science

Striated Caracaras

Study of scavenging turkey vultures and striated caracaras

Read Nov 2012 paper in Polar Biology 

View Raptor Tracking Maps (use Movebank.org)

Goals of the Study

  • Identify factors limiting populations of scavenging-raptors on the Falkland Islands
  • Work with government officials, local residents, and local conservationists, to improve the conservation status of scavenging raptors on the islands
  • Understand how widespread and common scavengers such as Turkey Vultures coexist with limited-range and rare scavengers such as Striated caracaras

Background: history of persecution

An "Ordinance for the Destruction of Birds of Prey" issued by the Falkland Islands Government in 1908 resulted in rapid declines in most species of raptors, including both Turkey Vultures and Striated Caracaras.

The latter was reported by Government Naturalist J. E. Hamilton to have been subjected to “a remorseless process of extermination” in the process. Consequently, the Striated Caracara was removed from the list in the 1920s, but the Turkey Vulture bounty remained until 1972. Today, vultures are still thought to be a problem to farms, and permits to kill Turkey Vultures are issued by the government of the Falklands Islands to sheep farmers.

Our work with Turkey Vultures in the Falklands supports Hawk Mountain’s long-term study of New World vultures, and offers a place to monitor their success where numbers are affected by legal shooting. However the Turkey Vultures here also co-occur and compete with the globally near-threatened Striated Caracara, another scavenging but island-dwelling raptor.

Conservationists believe that the bulk of the world population of Striated Caracaras, or “Johnny Rooks” inhabits the Falklands where gangs feed on farm leftovers and scraps. Because the species is passionately curious, these birds are easily trapped and re-trapped. That means they are ideal for saturation banding and detailed studies of its behavior and ecology, as well as its nutritional physiology. 

Findings to date

Volunteer Kalinka Rexer-Huber with a Striated Caracara

  • Turkey Vultures do not take healthy lambs, but do gather near lambing operations to feed on afterbirth and still-born lambs.
  • Turkey Vultures do feed on old and fallen “cast” sheep before they die, but they are of no economic value to farmers.
  • There is no evidence that Turkey Vultures economically impact sheep farmers.
  • Striated Caracaras compete with Turkey Vultures for carrion and other food year-round. The extent to which such competition affects populations of the two species remains unstudied.
  • So called “marine subsides,” including the eggs and carcasses of seabirds (e.g., albatrosses, cormorants, penguins, prions, and shearwaters, etc.) provide important nutritional resources to breeding and non-breeding Turkey Vultures and Striated Caracaras during the summer breeding season.
  • “Human subsides,” including leftovers and scraps from farming operations, as well as edible garbage in municipal and private dumps, provides important nutritional resources to Turkey Vultures and Striated Caracaras in winter.
  • In the short-term, the conservation of both Turkey Vultures and Striated Caracaras appears to be well within the management capacity of the people of the Falkland Islands.
  • Striated Caracaras are nutritionally stressed in winter. The degree to which this limits their populations is likely to be significant and requires additional study.  
  • The movement ecology of both vultures and caracaras, as well as the elaborate social behavior of Striated Caracaras, needs additional study.
  • The effect of climate change in the region, particularly on the so-called “marine subsidy” that both vultures and caracaras depend upon, needs to be investigated.
  • There is tremendous opportunity to study the social ecology, movement ecology, and physiological ecology of Striated Caracaras, and the fitness consequences of each, on the species.

The future

Attaching colored leg bands to study movement ecology

The next steps in this important work are to:

  • Saturation band Striated Caracaras at an important nursery island in the Falklands to better understand how individual caracaras manage to survive to adulthood (completed 2011-2012)
  • Begin to track the movements of Turkey Vultures and Striated Caracaras both within and among islands on the archipelago (ongoing)
  • Initiate studies of breeding adult caracaras to better understand reproductive success and failure in the species. 

Overall this work will allow us to alert colleagues of the factors that enable common and widespread scavengers as well as rare and endemic scavengers to survive on islands and other ecosystems.

The Hawk Mountain philosophy

This study typifies the Hawk Mountain approach to raptor conservation. Working together with the local government officials, land owners, and local conservationists, the Sanctuary is helping to keep common raptors common, while we also develop an understanding of the ecology and human factors that limit their populations now and in the future. 

In the case of Turkey Vultures, Sanctuary conservationists are working to change human attitudes about the bird’s role as aggressive scavengers.  In the case of Striated Caracaras, the Sanctuary is working to better understand how nutritional stress in winter limits the current population, and how local peoples may help lessen this effect. 

Practical and effective conservation of raptors on the Falklands Islands depends upon two things: understanding the current ecology of the species, and working with local stakeholders to ensure the protection of these birds. 

We thank our research supporters

Generous support for this study has been provided by:

The Acopian family
Wallace Research Foundation
Ben Olewine, IV
Dr. Joseph Jehl, Jr

Berks County