Dietary biology of the Eurasian eagle-owl
Throughout the western Mediterranean region, the Eurasian Eagle-Owl is something of a specialist on a single prey species: the European rabbit. The rabbit historically reached extremely high densities in Iberian scrub, i.e. more than 40 per every 1 square hectare (2471 square acres). In central Spain, up to 73.1% of the prey that were recorded for Eurasian eagle-owls, by number, can be rabbits. Where still available, they are also the main prey in Portugal and central France. However, following the devastation of the wild rabbit due to rabbit haemorrhagic disease, the local eagle-owls have frequently had to adapt to other, often smaller, prey. On the other hand, given the now much reduced numbers of rabbits, the eagle-owls still regularly select rabbits, seemingly out of proportion to their commonality. Although large mature wild rabbits commonly weigh , the eagle-owls usually hunt smaller specimens, often with an average weight around , with young rabbits usually selected in spring and summer and subadults selected in the autumn and winter. This is largely due to the behaviour of rabbits, with younger rabbits being forced to distribute following weaning, being less cautious in behaviour and occupying less primary habitat, thus being forced out of the confines of their burrows more regularly than mature adults. However, the estimated average weight of rabbits taken can be variable, reported from as little as in a study from Spain to as much as in the Netherlands.
Eurasian wren
The Eurasian wren ("Troglodytes troglodytes") is a very small bird, and the only member of the wren family Troglodytidae found in Eurasia and Africa (Maghreb). In Anglophone Europe, it is commonly known simply as the wren. It was once lumped with "Troglodytes hiemalis" of eastern North America and "Troglodytes pacificus" of western North America as the winter wren. The Eurasian wren occurs in Europe, a belt of Asia from northern Iran and Afghanistan across to Japan. It is migratory in only the northern parts of its range. It is also highly polygynous, an unusual mating system for passerines.