As predators, owls are on the top of the food chain and are susceptible to changes in the habitat so they have a special significance as indicators of the stability of land (island) eco-systems.
That's particularly true for Eagle Owl, a big bird and an appropriate "night watch" for eagles' "day watch".
Eagle Owl (Bubo bubo) is a rare and endangered species in most of Europe nowadays. In Croatia, both the biology and the ecology of Eagle Owl are poorly researched. However, even the scant information available shows that their numbers dropped significantly and that their habitat was sharply reduced. A hundred years ago, this bird nested all over Croatia, both on the islands and on the coast as well as in the interior. Today, Eagle Owl is most probably extinct in Central and Eastern Croatia, while it holds on in a relative abundance only in the coastal areas.
Eagle Owl is a very attractive bird. It's the largest European owl, about 70 cm in length, with the wingspan of 160-190 cm. It has distinctive orange eyes and feather tufts on its head that gave the owl its Croatian name – ušara, the big-eared one. Eagle Owl (as all the other owls) has an interesting adaptation: its flight is silent. The flight and tail feathers don't have sharp edges as in other birds but are fringed. In that way its flight is made inaudible so the bird approaches its prey undetected and kills it with its huge and powerful talons. As to their sight and hearing, eagle owls are without peer. Both senses are extremely well developed and it uses both for survival, depending on the situation.
Eagle Owl lives in open areas and karst pastures (the most common habitat on the islands) are ideal hunting grounds for this species. It usually nests on rock ledges, caves, holes, bigger cracks or even on the ground itself (for instance, under a holm oak). It lays eggs (2-4) on the bare ground, that is, it doesn't build the classic nest. Chicks hatch after a bit more than 30 days, covered in thick downy feathers. While they are growing up, there are many bones, wings and feathers (mostly young seagulls) around the nest but the most numerous are pellets.
What are the pellets?
The pellets, or castings, are indigestible parts of prey that owl regurgitates. In other words, it's a mixture of bones, feathers or hair nicely rolled up in clumps.
At the age of six months, the chicks become independent and start looking for their place under the sun.
The species is on the list of endangered breeding birds of Europe because it became rare, while in Croatia it's comparatively numerous on the coast and islands so it was put in the "vulnerable" category – it's not about to go extinct, but may be soon.
It is estimated that there are 5-7 breeding pairs in Kornati National Park.