Breaking the vulture monopoly on scavenger restaurants

Griffon Vulture (Gyps vulvus).A recent observational study in northern Spain reveals that making a dinner reservation is important even for diners at a vulture restaurant.

As a sanitary disposal area of animal carcases, vulture restaurants provide a dual purpose of preventing contagious diseases such as bovine spongiform encephalopathy while serving as feeding stations for scavenging bird species that might otherwise be declining due to habitat loss.

However, these feeding stations do not mirror traditional patterns of carcasses found in the scavengers’  traditional habitats and may be favoring some species over others, at least in Europe.

A research team led by Ainara Cortés-Avizanda monitored feeding patterns and relative abundance of six bird species at 17 “vulture restaurants” during both summer and winter seasons. 

At these stations, the griffon vulture, the most common species in the region, dominates the feeding activity with negative consequences for other scavengers.

Scavenging birds do not simply take turns at carcasses - they are involved in both facilitatory and competitive relationships with one another.

For example, vultures are able to tear open carcasses that smaller species are incapable of accessing.  Once the vultures have eaten their fill, the opened carcass is then available for the smaller species.

When one species dominates in sheer numbers, such as the case with the griffon vulture, it throws these relationships off-kilter, to the detriment of the diversity and size of the overall suite of scavenging birds. 

The study identified two patterns resulting from both concentrated feeding locations and imbalances in species diversity.

First, the presence of smaller species and the overall diversity of scavengers were negatively correlated with the presene of large numbers of griffon vultures.  Red kites, in particular, seemed to selectively visit feeding stations at times of the day when griffon vultures were not likely to be present. 

Second, smaller scavenger species were found in larger numbers at feeding stations supplied with small carcasses.  At stations supplied with larger carcasses, vulture species predominated. Across all 17 feeding stations sampled, large carcasses were present much more frequently.

These patterns offer suggestions for creating “vulture restaurants” that do not cater only to vultures, and which might serve to enhance biological diversity of scavenger species.  They also illustrate unintended consequences possible in conservation efforts.

Providing additional feeding sites to support healthy populations of scavenging birds is a good idea in theory, but the reality is more complex.   A cow carcass does not look the same to a kite as to a vulture.  And the vulture itself looks intimidating to the kite. 

With feeding stations predominantly offering large carcasses on their menus, the scale is tipped toward the vulture.  The appeal to vultures means that larger flocks will congregate, putting up a barrier to smaller species’ use of the feeding stations.

According to the study authors, legislation governing the disposal of animal carcasses has a big potential impact on scavenging bird populations. 

In the absence of legislative corrections, however, they argue for a greater number of feeding stations to decrease the concentration of large-bodied species.  They also recommend the inclusion of a diversity of carcass sizes placed throughout the day, to accommodate differing feeding strategies of the various user species.

Vulture restaurants are being created in many different countries, most recently in Nepal and Pakistan.  These, and future supplemental feeding efforts, will hopefully take into consideration the needs of a diverse array of scavengers.  

Not all visitors to these restaurants are interested in filet mignon - some prefer chicken Kiev.

--Karren Bassler is  a consultant with Superior Nonprofits, LLC and a contributing writer based in Madison, WI.

Cortés-Avizanda, A., Carrete, M., & Donázar, J. (2010). Managing supplementary feeding for avian scavengers: Guidelines for optimal design using ecological criteria Biological Conservation DOI: 10.1016/j.biocon.2010.04.016