Despite being one of the most threatened species on the International Union for Nature Conservation (IUCN)'s red list, the Spanish imperial eagle (Aquila adalberti) is recovering in Spain. The species has undergone an increase from 38 pairs in 1974 to 253 in 2008, data viewed as hopeful by the scientists who carried out the demographic study on the Iberian Peninsula.
"This study shows that the species has recovered and has responded well to conservation initiatives. Although it has been known for a long time, the study shows once again that this species is highly affected by changes in adult survival rates", Santi Mañosa, one of the authors of the study and a researcher at the University of Barcelona, tells SINC.
Some of the most important reasons behind the failure of the Spanish imperial eagle (Aquila adalberti) to increase its numbers have been premature adult deaths resulting from electrocution on electricity lines and the consumption of poisons used to control predators.
Although the major threat to the birds differs from region to region in Spain, Mañosa says that habitat conservation is essential in order for the bird to be able to nest and hunt. For this reason "it is essential to manage the rabbit population well, because this is what makes up its diet during the breeding season in all areas", adds the researcher.
A textbook recovery over 30 years
The study, which has been published recently in the journal Oryx, shows that the species has recovered "spectacularly" over the past 30 years. "Things have gone well over these past decades, but this could all be lost within five or ten years if things start to go wrong. It is a question of making improvements - electricity lines continue to pose a serious threat to this species, and efforts to resolve this problem are going very slowly," the biologist tells SINC.
The research team points out that the eagle population went from 38 pairs in 1974 to 198 in 2004, with a productivity rate of between 1.19 and 1.29 chicks per female per year and an adult survival rate of between 0.92 and 0.99, according to the period. "The ongoing increase in the species' numbers over the study period was only interrupted during the 1990s, with a spike in adult mortality during this period," says Mañosa. However, the rate of increase accelerated again between 2000 and 2004, both in terms of the decline in adult deaths and juvenile mortality, and a decrease in the age at which the birds first reproduce.
Data from the Ministry of the Environment and Rural and Marine Affairs (MARM) show that there were 253 pairs of imperial eagles in 2008. The species has experienced an increase throughout its entire area of reproduction, except in the Doñana National Park in Huelva, where the population has been seriously affected by the illegal use of poisoned bait, especially during the 1990s. "Here, the population fell from 16 reproductive pairs to just seven," Luis Mariano González, another of the study's authors and an expert in the MARM's General Directorate of Biodiversity, tells SINC.
"More important than the number of pairs reached is the trend towards recovery, which has resulted from controlling the causes of death caused by humans," says Mañosa. The scientists believe "the situation is not desperate, it is in fact encouraging, but we must not lower our guard".
Collaboration between various social agents (researchers, hunters, farmers, forest managers, the energy industry, etc.) is important to ensure the existence of "nationwide consensus between all the autonomous regions, and to regulate all those activities that could affect the species". The researchers conclude that "no group should bear the full burden of conservation - the responsibility should rather be shared by all".
- Ortega, Enric; Mañosa, Santi; Margalida, Antoni; Sánchez, Roberto; Oria, Javier; González, Luis Mariano. A demographic description of the recovery of the Vulnerable Spanish imperial eagle Aquila adalberti. Oryx, 2009; 43 (1): 113 DOI: 10.1017/S0030605307991048
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