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FALCONIFORMES (Diurnal Birds of Prey) - Management Guidelines for the Welfare of Zoo Animals
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SECTION 1: Biology and Field Data

Suborder - Accipitres (Family - Accipitridae)

Suborder - Accipitres

Family Accipitridae (hawks Old World vultures and eagles).

[It should be noted that in this instance the term ‘hawks’ covers hawks, kites, buzzards and many others]

  • Tiny to huge birds of prey, diverse in shape, size, evolution and hunting methods.
  • Worldwide distribution.
  • Diverse habitats from dense forests to open plains, mountains to highly populated river valleys.
  • 64 Genera.
  • 237 Species. (Although in some reference books the numbers range from 212 - 240 species).
  • 535 Taxa.

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1.1 Morphology / Description

This is a huge family, indeed not only in relation to the raptors but also in comparison to all the avians. This family can be divided into ten groups:

  • Kites - this includes the baza’s, the honey buzzards, and 14 genera of kites, the last genus being the fishing kites.
  • Fish Eagles - 10 species, the largest being Steller’s Sea-Eagle Haliaeetus pelagicus. The best recognised vocally is probably the African Fish Eagle Haliaeetus vocifer and the most well known is the Bald Eagle Haliaeetus leucocephalus.
  • Old World vultures - ranging from the Egyptian Vulture Neophron percnopterus as the smallest to the Eurasian Black Vulture Aegypius monachas which is probably the largest.
  • Snake eagles - the common name of some of the species being serpent eagle, with their bare legs covered in very close scales they are well adapted to catching the quarry after which they are named.
  • Harriers, harrier hawks and the Crane Hawk Geranospiza caerulescens from South America. All this group have long legs, fairly weak feet and light wing loading.
  • Sparrowhawks and goshawks – the largest of all the groups with 58 species. This group ranges from the African Little Sparrowhawk Accipiter minullus which is the smallest, to the Northern Goshawk Accipiter gentilis as the largest representative. Included in this group are the chanting-goshawks that are really closer to the harriers and also the Lizard Buzzard Kaupifalco monogrammicus, which probably lies closer to the sub-buteonines.
  • Sub-buteonine Raptors - including such as the well known Harris Hawk Parabuteo unicinctus, a bird widely kept in captivity and used in demonstrations and in falconry.
  • Buzzards - mostly medium sized birds, often soaring, armed with heavier feet and shorter toes than the accipiters.
  • Large tropical rain forest eagles - two of which, the Philippine Eagle Pithecophaga jefferyi and the Harpy Eagle Harpia harpyja are amongst the largest of birds.
  • Booted or true eagles - those with feathered tarsi. The hawk eagles are the least known and probably one of the most threatened genera. The best known are the Aquila’s which include the most commonly recognised, the Golden Eagle Aquila chrysaetos, and one of the rarest, the Spanish Imperial Eagle Aquila adalberti declining to the point where captive breeding programmes are being initiated. The Verreaux Eagle (Black Eagle) Aquila verreauxii is probably one of the most studied eagles in the world. This group is the most highly evolved in the family Accipitridae.

As can be seen this huge family ranges in size dramatically. The smallest is the Pearl Kite Gampsonyx swainsonii at 25 cm in length and weighing only 80-100gms. Some of the male sparrowhawks are also very small. Because of the reversed sexual size dimorphism between the males and females, the smallest of the birds will tend to be male and the largest female. The female Harpy Eagle Harpia harpyja and Steller’s Sea Eagle Haliaeetus pelagicus are the heaviest flying birds together with some of the Old World Vultures. The size difference between males and females tends to be less marked in those birds that eat insects or rodents and most greatly marked in the more rapacious bird eating species. The female Eurasian Sparrowhawk Accipiter nisus is almost twice the size of the male.

All the Accipitridae have the familiar hooked beak of birds of prey, some are much more markedly hooked and stronger than others. The insect eating birds, such as the baza’s, have a fairly shallow hook and weak beak, whereas the large vultures, such as the Lappet Faced Vulture Torgos tracheliotus have a large, strongly curved and very powerful beak. Some of the species have developed specialisation’s, such as the Snail Kite Rostrhamus sociabilis with its very long and slender curved beak adapted for winkling snails out of their shell.

Similarly the feet are adapted to the quarry species taken. Those catching large powerful quarry have large powerful feet, whilst those hunting small or sedentary quarry have feet appropriate to requirements.

All of the Accipitridae fly well. The large soaring birds such as the plains and mountain eagles, the Golden Eagle Aquila chysaetos and the Martial Eagle Polemaetus bellicosus, as well as the huge vultures, the Bearded Vulture Gypaetus barbatus and the Eurasian Black Vulture Aegypius monachus, require mountainous areas or hot weather to create thermals so they can get airborne efficiently. Once aloft they can soar for hours watching for prey. The vultures tend to drop earthwards at a gentle pace, but the eagles can stoop at high speeds. The bird catchers such as Sparrowhawks with the short round wings and long tails can manoeuvre rapidly after their extremely evasive quarry. Many of the Accipitridae migrate, often covering thousands of miles each year.

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1.2 Distribution / habitat

The Accipitridae are distributed worldwide.

The baza’s tend to be forest birds, the honey buzzards and specialist kites inhabit open woodland.

The fishing kites and the fish eagles by definition live near water, be it coastline or inland waters or marshlands.

The Old World vultures need open spaces so inhabit either mountains or plains and savannahs in hotter climes. The exception is the Pondicherry Vulture Sarcogyps calvus that is a forest dweller, the Old World equivalent of the King Vulture Sarcoramphus papa.

The snake eagles all live in the Old World and inhabit the open woodlands in warm climates. The Madagascar Serpent Eagle Eutriorchis astur is the main exception here preferring primary rain forest.

The harriers and harrier hawks are slow flying birds that dwell in open woodlands, often fairly sparsely dotted with trees or open areas of marshland or long grass.

The sparrowhawks and goshawks are almost all woodland and forest birds, being well adapted to hunt in enclosed habitats.

The sub-buteonine birds, some of which resemble the ‘true’ hawks whilst some are more like the buzzards, cover a variety of species with a very varied range of habitats including open forests, forest edges and open areas.

The buzzards with their broad wings and short tails are less adapted for dense forest and so inhabit more open woodlands, forest edges, clearings, river banks and open farmlands, uplands and rough pastures.

The four large rain forest eagles inhabit the forests of South American and Southeast Asia.

Lastly the ‘true’ eagles, like the large vultures need open space and so live in the plains, steppes, mountain ranges and desert savannah. The hawk-eagles being the exception and mainly inhabiting primary forest.

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1.3 General Behaviour

Activity/locomotion/migration

Most but not all of this diverse group are diurnal. Some like the Bat Hawk Machaerhamphus alcinus, hunt at twilight or even after dark. But generally this group of raptors hunts in full daylight. Those who do not require the heat of the day to give them lift will tend to hunt at first light and towards the end of the day, particularly if from hot countries. Others, inhabiting inhospitable northern climates hunt when they can. Apart from hunting or migrating, most raptors are very sedentary, especially those that catch quarry over half their own body weight. Those reliant on small prey items such as insects are more active. All and particularly the males, are very active when attempting to feed and rear young.

Social Behaviour.

There is very little social behaviour in any of the raptors. Despite certain species of vulture that colony nest and others, like some harriers that roost together, they are relativity unsociable. They usually hunt alone, and are very protective of their nesting areas during breeding. Vultures do observe other vultures to see if carrion has been spotted and will gather to feed in large numbers. Many of the smaller species socialise only during the breeding season and become solitary once the young have gained independence. The Harris Hawk Parabuteo unicinctus is rare among raptors, in that it does appear to live and hunt in groups or extended families, often working together co-operatively.

Voice.

It is not possible to describe all the voices of the Accipitridae in these Guidelines. They exhibit a considerable range of vocalisation and can be very noisy particularly during the breeding season.

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1.4 Diet and feeding behaviour

Most of the Old World vultures, like the New World vultures, have specialised in feeding on carrion and so do not have feet designed to catch and kill. However a few species of these vultures, such as the Palmnut Vulture Gypohierax angolensis the Egyptian Vulture Neophron percnopterus and a few others, have some power in their feet and do take small live prey on occasion. Almost all other raptors catch their food using their feet. The size and strength of those feet will depend entirely on the species of quarry normally caught. Most eagles have feet that are very powerful and in some cases are capable of catching and holding small antelope, medium sized monkeys and geese.

Many of the very small raptors have small feet suitable for catching the insects and small reptiles, which constitute their diet. Others, like the Snail Kite Rostrhamus sociabilis only need their feet for picking up, carrying and holding the Apple Snails Pomacea that they eat with their specially adapted beak. However the sparrowhawks have long legs, and long very narrow toes suitable for grabbing the small birds that they hunt and feed on.

The fish eagles have developed especially rough and scaly feet for grasping slippery fish. Red Kites Milvus milvus, although large birds have small feet and catch relatively small prey or scavenge.

All the Accipitridae eat meat or fish of some description: ranging from tiny insects, amphibians, reptiles, small to medium sized mammals, small to large birds and carrion, crabs, surface fish, and including dead and dying spawning fish and washed up carrion fish. A very few will eat vegetable matter such as palm fruits.

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1.5 Reproduction

The age of sexual maturity varies tremendously and is related mainly to the size and longevity of the species. Tiny birds such as the sparrowhawks and some of the small kites breed in their first year. This means they are breeding before they are a year old themselves. It is not that uncommon for many species to breed whilst still in juvenile plumage. Some will also produce more than one clutch of young per year, depending on the abundance of the food. At the other extreme some of the very large birds don’t reach breeding age until 6 - 8 years old and may, where the young take many months to gain independence, have a two year breeding cycle.

Raptors have a complex set behaviours for finding suitable mates and breeding. In many species the females are larger than the males so they signify their willingness to allow mating by letting males bring them food, feed them and by mutual preening. This lets the male know he is relatively safe in the proximity of the larger female. By supplying food frequently he illustrates to her that he will be efficient enough to feed her and subsequent young.

Some males will attempt to hold particularly food abundant territories in order to attract females; some will build several nests. Some species bond for life and so the male once he has paired, does not have to overtly demonstrate suitability. Some species remain together for the breeding season only and have no pair fidelity. There are also species that will participate in polyandry.

Females will signal their readiness to mate by certain postures and stances, accepting food, dropping the head, wailing for food, dropping their wings, all of these are signals to the males. Some, however can also be signs of aggression such as the head dropping. Some species are very noisy during mating, others silent.

All of this diverse group build a nest, although the size and structure can vary from 3 metres deep, to an insubstantial platform that is see-through. Some birds will use the nest for so many years that eventually the weight of the nest destroys the branch or tree that it occupies. Others build a new nest every year. Some males will build several nests to give the prospective female a choice.

Laying times vary considerably in the wild. Even within members of the same species breeding can occur at very different times. In such a large group as this breeding is inevitably diverse.

The size of eggs and of the clutch is also very variable. Here there is no set pattern, some eagles, such as the Steppes Eagle Aquila nipalensis may lay up to five eggs (more normally 2 - 3) whereas the Martial Eagle Polemaetus bellicosus lays only one. Again the Steppes Eagle Aquila nipalensis may quite commonly rear two or three young when the prey base is high, but the Verreaux’s Eagle Aquila verreauxii only rears one, with the second hatched young almost invariably being killed by its older sibling, regardless of the food supply. The Rough-legged Buzzard Buteo lagopus will lay up to seven eggs in abundant vole or lemming years.

Incubation periods differ widely with the smallest birds hatching the quickest and the largest birds taking the longest to develop. The incubation times vary from 30 - 32 days for the smallest of the sparrowhawks to 50 - 56 for the large Old World vultures and 60 - 61 days for the Philippine Eagle Pithecophaga jefferyi

Fledging follows the same pattern – the smallest raptors fledge in 26 - 30 days and the huge raptors 4 - 6 months with parent dependency after fledging much longer in the larger species. All the Accipitridae young are semi altricial and remain helpless, needing to be actively fed for at least half of the time spent in the nest.

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1.6 Survival

Longevity

As might be expected when the genera in this group vary so much, the longevity is highly varied. The larger birds - the huge vultures and eagles can live 20-30 years in the wild and upwards of 40 years in captivity, whereas the smaller species such as the Eurasian Sparrowhawk Accipiter nisus may only survive 4 years or so. Most have a high mortality rate of between 40 - 70% in the first year. Once past the critical first year the chances of survival increase with experience.

Factors of Mortality

The smaller raptors are often taken as food by larger avian, mammal and reptilian predators. In addition to this, hunting or foraging accidents result some deaths either directly or as a result of subsequent performance impairment. Starvation accounts for many of this group particularly in the first year. Degradation of the environment or direct persecution makes man the most significant factor in mortality.

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1.7 Conservation status

The populations of the Accipitridae vary tremendously, some such as the Madagascar Serpent Eagle Eutriorchis astur is so rare that it was thought to be extinct, although recently a bird has been found and photographed. Others like the Black Kite Milvus migrans is one of the commonest and most widely spread.

Threats are most commonly habitat destruction, so island species tend to be vulnerable. The Mauritius Kestrel Falco punctatus was brought close to extinction by destruction of natural forest, mainly due to clearing for crops, invasion of non-indigenous plants and a high human population. The Philippine Eagle Pithecophaga jefferyi again at dangerously low numbers through habitat destruction, but in their case the forests are being over-used for hard wood timber extraction and substance farming. This felling of timber threatens most species indigenous to primary rain forest. For many of the species there is little or no information available on the habits, breeding rates or population.

Pollution and pesticides are increasingly dangerous, particularly in third world countries where the priorities are not conservation, but survival of the human population. Birds of prey being ‘indicator species’ are amongst the first to show the effects of a poisoned environment.

To an extent human persecution threatens raptors, particularly migrating species. Malta, at the time of writing, is responsible for the deaths by shooting of up to 5,000,000 migratory birds each year. Up to 100,000 of these are raptors and owls.

All the Accipitridae have CITES status II or I.

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