small in booted eagles, rarely more than 3 eggs are laid, and most parents will manage to produce only one to two fledglings depending on species. In most booted eagles, beyond threats from the outside world, most eggs are laid and hatched at intervals, thus one sibling is usually considerably bigger and often kills its younger siblings. While brood size and fledgling rates are typically low, booted eagles may have even lower productivity due to the long dependence period of the young relying on their parents for food and protection, and some species may only nest every other year. General status Due to their large territories and low productivity, most booted eagle species are sparsely distributed and not infrequently uncommon-to-rare even in regional strongholds where ample habitat remains. Booted eagle species tend to be highly sensitive to human activities, mainly habitat alteration or destruction, human disturbance, collision with man made objects (especially non-insulated electrical pylons and wind turbines), accidental or intentional killing of staple prey species and various forms of persecution by humans. Due mainly to these factors, seven species of booted eagle are currently classified as Vulnerable to extinction by the IUCN. Four little-known forest dwelling species are classified in more severe status as Endangered: the Philippine hawk-eagle (Nisaetus philippensis), Pinsker's hawk-eagle (Nisaetus pinskeri), Javan hawk-eagle (Nisaetus bartelsi) and the black-and-chestnut eagle (Spizaetus isidori). A very different eagle, the steppe eagle, is also considered Endangered despite having been considered one of the most numerous of all eagles after a disastrous, ongoing decline mostly due to electrocutions from dangerous powerlines, poisonings and increasing steppe fires around nests, these killing them off en mass while breeding and migrating. An even more drastic classification of Critically Endangered was given to the Flores hawk-eagle (N. floris). In all five endangered hawk-eagles, near epidemic levels of forest habitat degradation, primarily direct deforestation, has been determined as the primary cause of their declines. Systematics SUBFAMILY AQUILINAE References Eagles Bird subfamilies