Dietary biology of the Eurasian eagle-owl
Equally or even more so than the great horned owl, the Eurasian eagle-owl is a threat to any smaller type of raptor it encounters, whether other owls or diurnal birds of prey. All told, more than 20 species of accipitrid, 15 species of owl and 9 species of falcon have been found amongst their prey. The Eurasian eagle-owl is the primary predator of other birds of prey throughout Eurasia, not even the prolific raptor-killing northern goshawk ("Accipiter gentilis") equals the sheer number of raptors taken. Up to 6% of the overall food by number and 36% by prey biomass for Eurasian eagle-owls can be comprised by other raptorial birds. The primary raptorial prey taken by Eurasian eagle-owls in Europe are two species: the long-eared owl and the common buzzard. Both are taken in such large numbers that they rank in the top five most regularly hunted bird species in Europe. In Luxembourg, the long-eared owl and common buzzard were the fourth and fifth most regularly hunted prey species. Other high rankings have included the long-eared owl being the fourth most regular prey species in Bavaria and the buzzard being the third most regular prey species in a study from the Czech Republic. While migrating, long-eared owls appear to select areas to move through partially based on whether or not eagle-owls are detected, thus eagle-owls have a very serious influence on the behaviour of this prey. Despite the large numbers taken of both of these, the more scarce eagle-owl does not seem to have a serious deleterious effect on their overall population, especially compared to anthropogenic factors.
Other than these two species, a large share of the raptorial prey for eagle-owls is made up of other owls. Given that all European owls are to some extent nocturnal, they may be encountered and killed upon detection by the Eurasian eagle-owl. In Europe, it has killed every other species of owl, from the tiny pygmy owl and scops owl to the large great grey owl and the snowy owl. The Eurasian eagle-owl is the only raptor that has been known to prey on snowy owl on multiple occasions. However, the threat Eurasian eagle-owls poses to other raptors can be exaggerated. Occasionally, with adequate mammal prey populations, they can nest as close as a few dozen meters of other raptors and never harass them. When nesting in the same groves as the long-legged buzzards ("Buteo rufinus") in southeastern Bulgaria, Eurasian eagle-owls did not predate the buzzards at any point. Long-legged buzzards have been killed however in Kazakhstan. Even in those occasional cases where they pick off one or several raptors, they do not effect the overall population, unless the raptorial prey is already heavily diminished due to some other (often human-based) cause. For example, despite both being a known predator of both, they did not significantly depress numbers of either northern goshawks or tawny owls in southern Finland. One study showed that many raptors engage in spatial avoidance during potential encounters with Eurasian eagle-owls and while the predation by eagle-owls did decrease raptor population densities, they seldom caused declines in breeding success or altered habitat occupancy.
Eurasian jay
Eight racial groups (33 subspecies in total) are recognised by Madge & Burn (1994): Jena Phyletic Museum, in Germany, features an excellent display of plumage variations across these races, which is used as a particularly striking example of the variation that can be found within species.A member of the widespread jay group, and about the size of the jackdaw, it inhabits mixed woodland, particularly with oaks, and is a habitual acorn hoarder. In recent years, the bird has begun to migrate into urban areas, possibly as a result of continued erosion of its woodland habitat. Before humans began planting the trees commercially on a wide scale, Eurasian jays were the main source of movement and propagation for the English oak ("Q. robur"), each bird having the ability to spread more than a thousand acorns each year. Eurasian jays will also bury the acorns of other oak species, and have been cited by the National Trust as a major propagator of the largest population of Holm oak ("Q. ilex") in Northern Europe, situated in Ventnor on the Isle of Wight. Jays have been recorded carrying single acorns as far as 20 km, and are credited with the rapid northward spread of oaks following the last ice age.