Bird Bullies

Regular supplies of food for scavenger birds in Spain may not be the most effective conservation strategy, as smaller birds are bullied away.

Jun 1, 2013
Jef Akst


DIVERSITY BUSTERS: Griffon vultures (Gyps fulvus) dominate established feeding stations, keeping out less aggressive scavenger birds.© STEVEN RUITER/FOTO NATURA/MINDEN PICTURES/CORBIS

The paper
A. Cortés-Avizanda et al., “Resource unpredictability promotes species diversity and coexistence in an avian scavenger guild: a field experiment,” Ecology, 93:2570-79, 2012.

The natural experiment
Since the early 1970s, conservationists in northern Spain have encouraged farmers and hunters to dispose of animal carcasses at what have come to be known as “vulture restaurants” to buffer against the decline of scavenging birds in the area. But while some species have begun to rebound, many are still endangered, prompting Ainara Cortés-Avizanda of the Estación Biológica de Doñana (EBD-CSIC) in Seville and her colleagues to investigate the effectiveness of this conservation effort.

The bullies
The researchers placed 58 carcasses around the study site—either at established vulture restaurants, where birds routinely waited for food, or at random in the field—and monitored the scavengers that devoured the remains. While both types of locations attracted a variety of scavenger species, the vulture restaurants were dominated by aggressive griffon vultures (Gyps fulvus), which camped out at the sites “waiting for food,” Cortés-Avizanda says. Smaller, less aggressive species, such as the common raven—which often arrived at randomly placed carcasses first and even benefited from the arrival of bigger birds that could tear the carcasses apart—were unable to elbow their way to the food.

Natural disruption
A “stable” resource, like vulture restaurants, may not be the best conservation tactic, as it can upset the natural social interactions of the scavenging birds, says Daniel Sol, an ecologist at the Center for Ecological Research and Applied Forestries in Barcelona.

Implications for conservation
The study highlights the importance of using research results to design more-effective conservation programs, says Sol. It also contributes to “the current debate on the utility of permanent supplementary feeding stations to preserve the rarest scavenger species.”