Conservation Biology Group

Threats and solutions

Low reproductive rates during 2012 in the Catalan population of the Bonelli’s Eagle

As in previous years, the Biology Conservation Group of the University of Barcelona has monitored the Catalan population of the Bonelli’s Eagle during the breeding period (from January to July), which allowed us to estimated the reproductive rates and the ringing of chicks.

Results showed that the territorial Bonelli’s Eagle in Catalonia had a productivity (chicks flying per pair) of 0.9 chicks on average during 2012 (n=49). It is an anomalously low value of productivity compared to other periods and other neighbouring populations. Productivity in 2012 is one of the lowest values of the latest 30 years. Worth noting that from 2006, there have been up to 5 years with the lowest values of the latest three decades. This is particularly serious in the Barcelona area, where productivity was 0.7 chicks per pair during 2012, the lowest since 1982. We only find lower productivity values in the populations of the North and the North-West of the Iberian Peninsula, which actually are on the threshold of extinction.

These low productivity rates in Catalonia are caused by several circumstances which could act together. First of all, in recent years it seems that there is been a decreasing of the Bonelli’s Eagle preys related to changes in its territories. On the other side, disturbances caused by human activities such as hiking, climbing or cycling, amongst others, especially during the breeding period, cause that eagles abandoned the incubation in 40% of the cases during 2008-2012. However, the main factor negatively affecting the reproduction is the high mortality of territorial individuals. Very often adult eagles deaths which are replaced by sub-adult individuals which are inexpert and are still not able to breed successfully, or they dye even before breeding. As a result, the population enters a very negative dynamic for territory occupation and reproduction.

Until now there has not been much information about population dynamics of the Bonelli’s Eagle in the Iberian Peninsula, and how these are demographically related to each other. In addition, very few is known about surviving and movements of young eagles of the Catalan population that are able to replace and adult in a territory after its death.

For this reason, during the breeding period of 2008-2012, the Biology Conservation Group of the University of Barcelona marked 198 Bonelli’s Eagle chicks with a conventional metallic ring and an alphanumeric coded band (readable from long distances) in Catalonia, Andalusia and Castilla y León. This year, 39 chicks from 25 territories in Catalonia (5 in Barcelona, 4 in Girona and 16 in Tarragona) and 3 in Castilla y León were ringed. We hope this ringed individuals will survive and provide us some valuable information in order to optimize actions to benefit the conservation of this wonderful raptor.