Wednesday, 21 December 2016

Spain 5: Eagles

Golden Eagle
In the UK we only have two breeding species of eagle, Golden Eagle Aquila chrysaetos and White Tailed Sea Eagle Haliaeetus albicilla. The rest of Europe has many more species, and this trip we managed to get good views of three, Golden eagle, Bonelli’s Eagle Aquila (formerly Hiraeetus) fasciatus and Booted Eagle Aquila pennatus.

The Spanish population of Golden Eagle is one of the largest concentrations in Europe, with around 1400 pairs of the subspecies A.c homeyeri. The species itself has a vast range, including western  North America south to Mexico. It is one of the largest eagles in Europe, with wingspans in some individuals over 2m. It is a fairly generalist predator, mostly preying on medium sized mammals and birds, but it will also take adult chamois and mountain goats by driving them over cliffs. They are almost entirely a mountain species, needing large open areas to hunt over and cliff ledges or large trees for nesting.

Golden Eagles are long lived as with many large raptors. They do not usually breed before 5 years old, and have a lifespan in captivity recorded at 57 years, although this will be rather less in the wild. Combined with a low reproductive rate this makes them very vulnerable to human persecution and habitat alteration. Despite these threats, in Europe the population is actually increasing in many areas, and as a result of its large range the species is listed as Least Concern.
Bonellis Eagle
Still listed as Least Concern, but currently declining, is the second species we found, Bonellis Eagle. A smaller species, most of the total European population is in Spain with around 750 pairs. Further east it ranges as far as Thailand. Bonellis are smaller than Golden, with a wingspan of around 1.6m, and prefer rocky areas with more trees than Golden. They are more specialised in their choice of prey than Golden, taking a high proportion of Red Legged Partridge and especially European Rabbit. It may be their habit of quartering the ground in search of prey that seems to make them vulnerable to being killed on power lines. Many raptors and other large birds are killed by flying in to power lines, and given their keen eyesight one may wonder why they do not avoid them. In many cases, it may simply be that birds typically look down rather than ahead when hunting, but increasing the separation distance between power lines prevents a large bird perching on a wire accidentally electrocuting itself when stretching its wings.
European Rabbit
In Spain these sort of fatalities are heavily implicated, but a decline in the rabbit population is also a large factor. Persecution and changes in land use have caused a major decline, but Myxomatosis and Rabbitr Haemorrhagic Disease have been even worse. In its former native range of Iberia and western France the population has declined by 95% since 1950. Australian readers may not believe this, but it actually classed as Near Threatened by the IUCN in its native range, although the species itself is not.  This loss of a keystone species has seriously undermined the potential productivity of Bonellis Eagle nests, and also other Iberian predators, most notably the Iberian Lynx.
Iberian Lynx
The smallest of the eagles we found was a wintering Booted Eagle. Unlike the previous two species, Booted is mostly migratory, travelling to Africa for the winter and with only a few individuals remaining. Booted is the smallest eagle in Europe, with a wingspan of around 1.3m. They take much smaller prey, down to the size of insects, although the bulk of the prey are birds. With their smaller size they need less room to breed and their populations are much higher, with around 3,000 pairs in Spain alone. Their range extends eastwards to the Himalaya and north to Mongolia and Russia. Eastern populations winter in India. They prefer open woodland for hunting, and will even hunt in cities sometimes. As a result agricultural landscapes are quite acceptable for them as long as there is some woodland for them to use. Deforestation or pesticides may be a cause of local declines, but as a whole the species is listed as Least Concern.
Booted Eagle
(Images from Wikipedia)

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