Bonelli's eagles are medium-sized as eagles go: about 65 to 75 centimetres long with a wingspan of around 1.5 to 1.8 metres - long enough to nearly fill a single-person bed. Adults have a brown back and pale chest streaked with dark lines. Young Bonelli's eagles look quite different, with much warmer rusty-brown chests, and they don't get their grown-up feathers until they are about four years old.
Most eagles use slow flight and patience. Bonelli's eagles use speed and surprise. They often hunt in pairs - one eagle flushes the rabbit or bird out into the open, the other dives in to catch it. It is teamwork in the sky. The Spanish call them '谩guila perdicera' - the 'partridge eagle' - because partridges are one of their favourite meals.
A pair of Bonelli's eagles stays together for life, building a giant nest on a cliff and using the same one year after year, adding to it each season. After a while the nest can be huge - over a metre across. The pair raises one or two chicks each spring.
Bonelli's eagles are rare in Europe today. Spain is one of the most important homes for them - about half of all European Bonelli's eagles live there. Scientists in Spain put little trackers on some of the eagles' backs to learn where they fly, what they eat, and what dangers they face.