GPS tracking to reveal feeding behaviour of griffon vultures in Western Iberia

A group of five griffon vultures has been tagged with GPS transmitters by local partners of the ELP-funded Greater Côa Valley project in Portugal, Western Iberia. By shedding new light on the birds’ foraging behaviour, the data collected from the transmitters will support the restoration of natural food chains in the area and underpin the continued comeback of this magnificent species.

Newly fitted GPS trackers will provide vital information about griffon vulture’s feeding behaviour, and how best to support population comeback. Photo credit: Markus Varesvuo / Wild Wonders of Europe.

The transmitters fitted to the birds – which are mostly breeding adults – are also equipped with an accelerometer, which shows when they are resting, flying or foraging. Data supplied by the devices will provide invaluable insight into where the vultures go to feed and what types of carrion they feed on. This is the first time that the area’s griffon vulture population has been monitored in such a way. 

The vulture tagging was carried out this summer as part of the five-year “Creating a wilder future for the Greater Côa Valley project, which kicked off earlier this year through funding from the Endangered Landscapes Programme. This will see Rewilding Europe (through Rewilding Portugal) and local partners further develop a 120,000-hectare wildlife corridor in northern Portugal.

An essential element of restoring the valley is the recovery of trophic chains. Local populations of both griffon and Egyptian vultures currently rely on a network of artificial feeding stations (so-called “vulture restaurants”) provided by organisations such as ATNatureza. One of the aims of the project is to increase the availability of natural carrion in the area – thereby restoring a ‘circle of life’ – by encouraging Portuguese authorities to allow local farmers to leave domesticated herbivore carcasses in the field, and by boosting the local population of wild herbivores, such as roe deer.

Griffon vultures are currently being supported by ‘feeding stations’ which are undoubtedly useful, but this project hopes to find ways to further reduce interference with nature. Photo credit: Staffan Widstrand/Wild Wonders of Europe.

“The tagging will allow us to see whether the vultures are feeding mostly on the carcasses of domestic livestock, or also on wild herbivores, and how often they visit vulture feeding stations,” says Carlos Pacheco, a raptor expert, highly experienced tagger and project manager working for ATNatureza, a Rewilding Europe partner in Western Iberia. “This will ultimately enable us to improve the management of food sources for the birds and support the restoration of trophic chains.”

The griffon vultures were tagged in the SPA Vale do Côa (Côa Valley Special Protection Area) and the nearby Douro International Nature Park. Dedicated members of the vulture tagging team had to wake up at 4am, in order to reach the capture site in time to set traps. Incredibly intelligent, griffon vultures are typically very wary and won’t land at a site where they think something is out of the ordinary. This not only meant the team had to prepare the site well, but often had to wait for hours as the birds circled overhead.

On several days the patience of the tagging team was rewarded and the vultures eventually landed. As soon as a vulture was caught in a trap the team sprang into action, safely immobilising the bird and placing a hood over its head to keep it calm. Once the vulture was fitted with a transmitter it was immediately released, none the worse for its experience and ready to begin contributing valuable data.

Careful and swift tagging by the local team meant minimal distress for the vultures. Photo credit: Rewilding Europe.

Monitoring of raptor species in and around the Greater Côa Valley shows griffon vultures have made a dramatic return to the Western Iberia project area since the 1990s. There are estimated to be around 200 breeding pairs in the project area, which includes the SPA Vale do Côa, Serra da Malcata Nature Reserve and Douro International Nature Park. This comeback would be further supported if especially authorised Portuguese farmers chose to leave the carcasses of their domesticated herbivores in the field.

In 2001, after the bovine spongiform encephalopathy (BSE or “mad cow disease”) crisis, the European Union prohibited the abandonment of livestock carcasses in such a way. This had a huge impact on vulture populations, which relied on these carcasses in the absence of wild herbivores.

Today the subsequent relaxation of EU legislation has allowed livestock carcasses to once again be left in nature (under special conditions), but not all European countries have chosen to implement this change. Until very recently, this meant that farmers were allowed to leave carcasses in large swathes of the Spanish countryside, yet their Portuguese counterparts were compelled to remove them. This disparity was graphically highlighted in recent research, which showed GPS-tracked griffon and black vultures on the Iberian peninsula almost exclusively shunning Portuguese territory.

EU veterinary regulations mean that fewer dead domestic animals are left out in the open, and this has spelled disaster for all four European vulture species. Photo credit: David Thomas / Endangered Landscapes Programme.

Recent changes to Portuguese regulations mean that the carcasses of pigs, sheep, goats and horses (exclusively from farming) can once again be left outside of artificial feeding stations, in areas which the Institute of Nature and Forest Conservation (ICNF) considers important for vulture conservation.

“Going forwards, the Rewilding Portugal team and partners will work with national authorities to further develop an extensive network of farmers in the Côa Valley and Douro International Nature Park who are authorised to leave carcasses in the field,” expains Sara Aliácar, a conservation officer with the Rewilding Portugal team who took part in the tagging.

Another group of griffon vultures will be tagged towards the end of this project, which should highlight what impact the changes in the availability of food have had on the birds’ behaviour and distribution.

This article originally appeared on 18/07/2019 on Rewilding Europe‘s website, and an edited version is reproduced here with kind permission.