There is little doubt that Vultures are amazing, despite the completely unfounded bad press they sometimes receive Here in the Straits we are blessed with them being a garden bird for us! Not only we do we get to witness their amazing antics and all important ecological functions, but twice yearly we watch as masses of them stream through the Straits in biblical proportions. This is the only place in the world where such an event occurs! It is amazing!
Much of the conservation work of Vultures is to be lauded, as there has been a lot of work to recover numbers of these enigmatic birds and important eco-system service providers throughout Europe, but there is clearly much more needed to be done (such as the removal of the licencing of veterinary diclofenac within the EU).
Most of us will remember the outbreak of BSE (Bovine Spongiform Encephalopathy), an animal disease at its peak between 1986 and 1990. As well as being transmitted through the food chain, the disease could also be spread through the presence of dead infected cattle. Following the outbreak, in 2001 the EU prohibited the abandoment of livestock carcasses in the field. This action clearly would have an impact on scavenging Vultures, therefore was not applied mandatorially across EU member states. This allowed for each member state to adopt their own regulations concerning livestock carcass disposal, allowing the issue to be dealt with at a local level, but consistent with the overriding principles to tackle the disease issues.
Spain is home to c. 95% of European Vultures and here farmers can leave some carcasses where Vultures occur. This obviously benefits the birds but also farmers and tax-payers too, saving time, money and environmental costs from incineration. In contrast to this approach, the Portugese government decided that removal of livestock carcasses is still required, save for a few specific licenced Vulture feeding stations.
The authors of a recently published paper in Biological Conservation (Volume 219, March 2018, Pages 46–52) observed that there was an abrupt decline in the number of Vulture locations across the Spanish-Portuguese border. Modelling showed that this was unlikely to be related to differences in land cover or topography, but simply on differences in carrion resource availability, namely carcasses from extensive livestock husbandry.
Vultures are capable of exploiting huge areas in search of food, and often will perform transnational flights. Yet, despite broadly similar habitats and their abilty to transverse countries, both Griffon and Cinerous Vultures of Spanish origin were rarely located in Portugal as these maps of GPS tracked birds below show from the study.
Griffon Vultures were marked in two populations: 30 adult birds in the Ebro Valley, northern Spain, and 30 adult birds in Guadalquivir Valley, southern Spain. Cinereous Vultures (11 fledglings) were marked in Cabañeros National Park, central Spain.
One potential problem with this study was that the authors did not track Vultures from Portuguese breeding colonies, which are mainly located close to the border and thus might use the Portuguese areas more than individuals breeding in Spain. However, some previous although limited GPS tracking of both Cinereous and Griffon Vultures tagged in Portugal has shown that the individuals tend to cross the border to feed in Spain, which is line with the results of this study.
Griffon and Cinereous Vultures are known to differ in food resources used. Griffon Vultures are very much dependent upon carcasses of domestic livestock, where the diet of Cinerous Vulture is broader, including the remains of smaller mammals and sometimes even live prey. This difference in feeding behaviour for us is demonstrated in the GPS maps, showing a much closer need for Griffon Vultures to stick to Spain whereas there are some broader transnational flights (although limited) by Cinerous Vultures.
The findings of this study are also unlikely to be influenced by habitat differences across borders as anyone who has visited both the areas Alentejo (Portugal) and Extremadura (Spain) will testify. Dehesa habitat – known to be good for both species – is relatively widespread across both the areas.
One thing is for certain – this study shows the need for continued research on vulnerable Vulture species and this should be extended to other species such as Egptian Vultures. Telemetry data is providing new insights into the movements of species and how they utilise the landscape and for highly mobile Vultures, this is invaluable information to form cross border conservation prorities and techniques.
There is a need to evaluate the potential ecological consequences of the implementation of restrictive husbandry and sanitary policies, especially when they affect highly mobile, endangered species such as Vultures. It also serves the point that conservation should not observe borders and that joined-up conservation implementation – especially for endangered Vulture species – is required and that is something that the EU has within its gift to pursue.
Invisible barriers: Differential sanitary regulations constrain vulture movements across country borders