Editing Accipitridae (section)

== Reproductive biology and populations ==
In terms of their reproductive biology and socio-sexual behavior, accipitrids share many characteristics with other extant groups of birds that appear not be directly related, but all of which have evolved to become active predators of other warm-blooded creatures. Some of the characteristics shared with these other groups, including [[falcon]]s, [[owl]]s, [[skua]]s and [[shrike]]s, are sexual dimorphism in size, with the female typically larger than the male; extreme devotion of breeding pairs to each other or to a dedicated nesting site; strict and often ferocious territorial behavior; and, on hatching, occasional competition amongst nestlings, including regular [[siblicide]] in several species.

Before the onset of the nesting season, adult accipitrids often devote a majority of their time to excluding other members of their own species and even of other species from their nesting territories. In several species, this occurs by territorial display flights over the border of their breeding ranges. In several forest dwelling varieties, however, vocalizations are used to establish territories. Due to the density of the habitat, display flights are apparently impractical.

While a single devoted breeding pair is considered typical, research has revealed that in varied accipitrids, multiple birds engaging in nesting behavior is more commonly than previously thought. Some [[Harrier (bird)|harrier]]s have evolved to become polygynous, with a single smaller male breeding with and then helping multiple females raise young.{{sfn|Korpimäki|1988}} The most extreme known species of accipitrid in terms of sociality is the [[Harris's hawk]]s (''Parabuteo unicinctus''), which up to seven fully-grown birds may hunt, nest and brood cooperatively, with the extra birds typically being prior years' offspring of the breeding pair.<ref>Bednarz, J. C. (1987). "Pair and group reproductive success, polyandry, and cooperative breeding in Harris' Hawks." ''The Auk'' 393-404.</ref><ref>Bednarz, J. C., & Ligon, J. D. (1988). "A study of the ecological bases of cooperative breeding in the Harris' Hawk." ''Ecology'' 1176-1187.</ref>

Unlike the other two larger groups of raptorial birds, the owls and most falcons, accipitrids typically build their own nest. Nest sites are typically in relatively secure places, such as the crook of a large tree or an ample cliff ledge, and can vary in elevation from the flat ground of [[prairie]]s or [[steppe]] to near the peaks of the tallest mountains. Accipitrids will readily return to use a nest site repeatedly, which has resulted in several of the largest bird's nests known, as a single nest may see decades of use, with more material added each breeding season. The single largest known tree nest known for any animal, belonging to a [[bald eagle]] (''Haliaeetus leucocephalus''), was found to be {{convert|6.1|m|ft|sp=us|abbr = on}} deep and {{convert|2.9|m|ft|sp=us}} across, and to weigh {{convert|3|ST|t|1|sp=us|abbr = off}}.<ref>{{cite web |author=Erickson, L. |year=2007 |publisher=Journey North |url=http://www.learner.org/jnorth/tm/eagle/NestAbout1.html |title=Bald Eagle, About Bald Eagle Nests |access-date=2014-09-30 |archive-url=https://web.archive.org/web/20120830211627/http://www.learner.org/jnorth/tm/eagle/NestAbout1.html |archive-date=2012-08-30 |url-status=dead }}</ref> Some species, especially eagles, will build multiple nests for use in alternating years. Although they usually use nests they build themselves, accipitrids sometimes use abandoned nests build by other animals or pirate nests from other birds, typically other types of accipitrid.

Compared to most other types of birds, the stretch from egg-laying to independence in young birds is prolonged. In accipitrids, the breeding season ranges from about two to three months to roughly a year and a half, the latter in some of the larger tropical eagles. Species inhabiting temperate ranges as a rule have shorter breeding seasons due to the shorter stretches of warm weather that facilitates ready capture of prey.

Usually from 2 to 6 eggs are laid in accipitrids, a relatively small clutch, and some species may lay only one egg. In almost all accipitrids, eggs are laid at intervals rather than all at once and in some larger species the intervals can be several days. This results in one of the hatchlings being larger and more advanced in development than its siblings. The benefits of siblicide, which is at least occasionally recorded in many species and almost always occurs in some, such as tropical members of the booted eagle group, is that the smaller siblings are a kind of insurance policy that if the oldest, strongest nestling dies, one of the smaller siblings may take its place. In most species that have displayed siblicide, times of food plenty may result in two or more the nestlings being successfully raised to fledging.

In most accipitrids, the smaller males typically obtain food both for the incubating and brooding female and the nestlings. Males, however, occasionally take a shift incubating or even more sporadically brooding the nestlings, which allows the female to hunt. Most accipitrids feed their nestlings strips of meat or whole prey items, but most [[Old World vultures|vultures]] feed their nestlings via regurgitation.

Fledging often takes considerable effort for young birds and may take several weeks as opposed to days in many other types of birds. Once independent of their parents, young accipitrids often most wander for considerable stretches of time, ranging from 1 to 5 years, before they attain maturity. Most accipitrids have distinct plumages in their immature stage, which presumably serves as a visual cue to others of their species and may allow them to avoid territorial fights. Shortly after attaining mature plumages, pairs form, with a male typically displaying, often in flight but sometimes vocally, to win over a female. Many accipitrids breed with the same mate for several years or for life, although this is not the case for all species and, if a mate dies, the widowed bird will typically try to find another mate the next breeding season.{{sfn|Ferguson-Lees|Christie|2001|p=}}<ref>{{cite book |title=Eagles, Hawks and Falcons of the World |first1=Leslie |last1=Brown |first2=Dean |last2=Amadon |publisher=The Wellfleet Press |date=1986 |isbn=978-1-555-21472-2}}</ref>