Game Ranging / Field Guiding Course. Eagles. There are seventeen eagle species in Southern Africa. The group is subdivided into two groups:

Transcription

1 1 Module # 6 Component # 6 Eagles Introduction There are seventeen eagle species in Southern Africa. The group is subdivided into two groups: The snake eagles are characterised by having unfeathered legs, and except for the Bateleur, are all classed in a single genus: Genus Circaetus. There are five members of the snake eagle group in the region. Snake eagles generally still hunt from a perch, except for the Bateleur. The true eagles have feathered legs. Only five of the true eagle species are found in the same Genus - Aquila. There are twelve true eagle species in the region. The true eagles have large claws and heavy bills and usually hunt from the air. The more common of the species are: Bateleur (Terathopius ecaudatus) Short-toed Snake Eagle (Circaetus gallicus) Brown Snake Eagle (Circaetus cinereus) Wahlberg's Eagle (Hieraaetus wahlbergi) Tawny Eagle (Aquila rapax) African Fish Eagle (Haliaeetus vocifer) Martial Eagle (Polemaetus bellicosus) Verreauxs' Eagle (Aquila verreauxii) The other less commonly seen species include: Western Banded Snake Eagle (Circaetus cinerascens) Southern Banded Snake Eagle (Circaetus fasciolatus) Booted Eagle (Hieraaetus pennatus) Lesser Spotted Eagle (Aquila pomarina) Longcrested Eagle (Lophaetus occipitalis) Steppe Eagle (Aquila nipalensis) Ayres's Hawk Eagle (Hieraaetus ayresii) African Hawk Eagle (Aquila spilogaster) Crowned Eagle (Stephanoaetus coronatus)

2 2 Bateleur - Terathopius ecaudatus Vital Statistics Wingspan Weight Preferred prey Incubation period Clutch size IUCN Status Nesting site Nestling period Habitat 180 cm [72 in] 2 3 kg [ 4 ½ - 6 ½ lbs.] 66% = Carrion, 33% = generalist hunter 55 days 1 egg Vulnerable Tree tops, usually Acacia Spp. or other thorn trees days Open Grassland and Savanna Woodland

3 3 Description The Bateleur is arguably one of the most striking of the greater group of eagles. It is difficult to wrongly identify it, with its red face, legs and feet. This bulky looking eagle is mostly black with grey wing coverlets. It also has a creamy white patch on its upper back. Its eyes are a deep honey brown and its bill grey tipped, merging to yellow at its base. The bird is also very distinctive in flight, appearing almost tailless. The juvenile of the species is very different, being mostly light brown. Its face is a pale greenish - blue, and legs and feet whitish - grey. These characteristics often lead to it being mistaken for the Brown Snake eagle. Progression from first juvenile plumage to full adulthood is a lengthy period, taking seven to eight years, as it passes through a succession of gradual moults. From the few complete records kept, only about 10 % of juveniles reach adulthood. The reason for this very high mortality is unknown. The bird was first described by the French naturalist and explorer, Le Vaillant. Bateleur in French describes an acrobat or tumbler, a possible allusion to its remarkable flight. Its scientific name is a mixture of Greek and Latin and is translated as marvellous face ; "without tail".

4 4 Courtship and Reproduction Courtship within the species involves some spectacular flight displays. In these flights, the males chase the females. The male who can reach up to 80 Kph [50 mph] in flight dives at the female, who rolls and presents her talons at him. He may then execute several 360º rolls, and start off for her again. This is all accompanied by loud calling by the male, and an odd sound made by his wings that sounds like a loose sail flapping in the wind. Nests are situated in large trees, usually 10 to 15 m [33 50 ft] above the ground. They are built within the canopy, and thus are shaded for most of the day. Although a variety of trees may be used, thorny acacias are favoured. A single egg is laid from January to April (Southern Hemisphere Summer). Several studies indicate that both sexes incubate the egg. The male will also vigorously defend the nest if an egg or nestling is present by frequently dive bombing any intruders. If the intruder is still not dislodged, he will settle on the tree between the intruder and nest and make threatening postures by raising his wings. Incubation generally lasts 55 days, and nestling periods have been observed between 95 and 195 days. Once the young begin flying, they still stay around the nest for about three months, where they are still fed by the adults. Juvenile Bateleur

5 5 Flight and Hunting Although the Bateleur is capable of rigorous powered flight, like most birds of prey, they prefer to slowly soar. Also like many of the other raptors, they wait for warm thermals to gain their lift into the air. Thus, they may be considered late risers, only taking to wing in mid to late morning. On rainy or overcast days, they in fact remain grounded, and do not hunt. Bateleurs are undoubtedly accomplished hunters, and have been found to take a very wide variety of prey species, ranging from other birds, to mammals up to 4 Kg [9 lbs.] in weight. An assortment of reptiles, including the very venomous snakes to which the bird is not immune, is also taken. With all this said however, two thirds of its diet consist of carrion. It is this bird s high dependence on carrion that has almost confined it to the status of a game reserve species, having totally disappeared from most other regions of the country. This is due to the diminishing number of carcasses and the poisoning of many others. In many ways, it has suffered the same plight as the vultures in this regard. Ironically the pest species that the poisoning was meant to quell, the jackal, remains in undiminished numbers after decades of poisoning. Within the conservation areas, the birds have reached quite high densities, and may remain in the same territory with the same mate throughout their lives.

6 6 African Fish Eagle - Haliaeetus vocifer Vital Statistics Wingspan Weight Preferred prey Incubation period Clutch size Status Nesting site Nestling period Hunting success Habitat 2.15 m [ 7 ft] 3-4 Kg [6 ½ - 9 lbs.] Fish specialist, will hunt other vertebrates and take carrion days 2 eggs Common resident species Trees that are difficult to climb, Acacias, Euphorbias days 13 % (of each attempt) Near water. Natural or artificial

7 7 Description This raptor is one of the best known of all the birds of prey. This is due in part to the wide usage of footage of the bird catching fish from water. This bird is also the easiest to identify. It has a distinctive white head, breast and mantle, which is offset by a chestnut brown abdomen and shoulders and black wings. It also has a short white tail that is often concealed by its folded wings. Its face and legs are a dull yellow, and its beak is grey. Females can be distinguished from males, being 10 to 15 % larger when seen perched together, and have a squarer bib, which is not as deep as the males. Some may confuse it with the American Bald Eagle but these birds are not African residents. The juveniles of the species are a drab brown, with a whitish head. Their bib is also whitish, but streaked with brown. They also have a white tail that is longer than that of the adults. However, the tail has a conspicuous black terminal band which is a clear diagnostic character that can be seen in flight. Transition from the immature plumage to adult takes about five years, but individuals may breed before they reach full adult plumage.

8 8 Courtship and Reproduction Fish eagles form a bond-pair to mate, and the pair can often be seen duetting. This not only strengthens the bond-pair, but is an integral part of their nuptial display. When their vocalisation increase, the start of their breeding season is initiated. This also stimulates other pairs in the vicinity. The calling is accompanied by aerial displays, where they perform undulating dives and upward swoops. This is intensified when the male rises high above his mate and dives toward her. As he reaches her, she turns on her back presenting her talons to his. Occasionally the pair may lock claws and fall hundreds of metres in whirling flight. Nests are built in tall trees, which are usually difficult to climb. Thorny acacias, smooth barked trees and euphorbias are commonly used; the nests are built within the canopy or on top of it. The size and shape of nests vary, depending on their duration of use. Both sexes help in its construction and a new nest may be built in about two months or an old one repaired in a few weeks. Regularly used nests may persist for ten years, and one studied site had the nest being used annually for 21 years. In Southern Africa, eggs are laid during April through to June, and a normal clutch consists of two plain white eggs. Incubation is undertaken exclusively by the female, while the male feeds her. Eggs hatch after 42 to 45 days, and the nestlings begin flying at 70 to 75 days. They become fully independent of the adults about two months after leaving the nest. Due to the already mentioned high mortality of juveniles (around 94 % die before reaching adulthood), adults must live at least between 16 and 24 years in order that enough breeding adults will replace them.

9 9 Feeding and Fishing The African Fish Eagle is not unique in utilising fish as a food resource, but it is the most majestic in its mode of obtaining it. These birds have long claws with spicules (tiny hooks) on the pads of their feet to aid in the grasping of their favoured prey. Its broad wings enable this eagle to soar even in light breezes, and give maximum lift when rising off the water with a fish. It hunts from either a perch or on the wing. Fish are caught in a shallow dive, both feet being thrown forward just prior to the strike, and the bird usually maintains momentum and swoops up gracefully clutching the fish. Fish are usually caught 15 cm [6 in] below the water, and never below 30 cm [12 in], so the birds don't immerse themselves during a kill. Prey is normally located by sight, although recent evidence suggests that the sound of splashing fish may be used in prey detection. They are also able to catch fish in choppy or murky water. Occasionally the eagle may literally bite off more than they can chew. In these cases, these large fish will be killed by the gripping talons prior to take off. However, if the fish is too large to carry off, the bird may paddle to shore using its wings, while dragging the fish a far less graceful sight to its usual modus operandi. Although considered quite accomplished hunters, an average of seven and a half strikes is attempted for every successful capture. The African Fish Eagle is also quite a skilled pirate, capable of considerable speed and dexterity on the wing and taking prey from a variety of other avian species. Their prey resource base is also far from being limited to fish, as they hunt other birds, reptiles and amphibians. Mammalian prey is rarely taken, but this species is not above scavenging on carrion and is occasionally seen in the company of vultures at a carcass.

10 10 Home Range Adult African Fish eagles, are generally sedentary, and stay within a relatively small territory if conditions suit them. The juveniles are however prone to wandering before they settle. One ringed immature individual was found 200 Km's [80 miles] from the nest where it had been ringed some two and a half years earlier.

11 11 Martial Eagle - Polemaetus bellicosus Vital Statistics Wingspan 2.6 m [8 ½ ft] Weight 6 Kg [ 13 lbs.] Preferred prey Rodent specialist Incubation period 49 days Clutch size 1 egg every two years IUCN Status Vulnerable (2016) Nesting site Tree tops or electricity pylons Nestling period days Hunting success 20 % (of each attempt) Habitat Open Grassland and Savanna Woodland

12 12 Description This species is the largest of all the eagles. It is most distinctive, although the inexperienced observer may confuse it with the Black Breasted Snake Eagle. Martial Eagles have a dark brown head and upper breast. This contrasts with white underparts which are spotted with light brown. The species has a broad flat head, with a short crest at the back. Its eyes are a deep yellow, and they have a greyishblack beak. This eagle has a bold stance when perched, which is accentuated with long, white feathered legs. The sexes are essentially very similar in plumage, with the females being slightly larger and more heavily built. The juveniles have grey upper parts, with white edges to the feathers, and immaculate white below. Their eyes are also a dark brown. Transition to the adult plumage takes between six to seven years, and only begins when these immature birds are at least two years old.

13 13 Courtship and Reproduction Martial eagles are not known for any special courtship behaviour, which basically consists of the pair flying around and calling to each other. Breeding only takes place every two years, and when it does occur, eggs are laid from March through to August. The species normally nests in trees, but a considerable number have been found on high tension electricity pylons, a habit that seems to be increasing. The nests themselves are quite sturdy constructions made from stout sticks and branches. Because nests may be continually repaired and reused year after year, some old ones have reached massive proportions of 2 m [6 ½ ft] across and just as deep. Only one white egg is laid at a time and the female is responsible for 90 % of the incubation. The male feeds her and she hunts when having the opportunity. The incubation period is sketchy at present but seems to average at 49 days. The development of the eaglet is also not well documented, although nestling periods have been recorded between 90 and 109 days. Juveniles may persist at the nest anywhere from 3 to 8 months while still being fed by their parents. However, one aspect of their development that is noteworthy is that just after one day after their first flight, most eaglets can soar quite competently.

14 14 Hunting and Feeding Being the largest of the raptors has given the species the opportunity to become the most revered of all the avian hunters. This great bird can soar kilometres up, and they frequently do in their search of prey. They also have incredible eyesight, at least ten times more acute than our own. Thus, their combination of such power and superior vision makes them master killers. Martial eagles capture a very wide variety of prey, including animals from all the vertebrate classes. Large avian species recorded caught include the African Spoonbill, Black Headed Heron, White bellied Stork and Spurwing Goose, these in the same weight range as, or larger than, the 6 Kg [13 lbs.] of the eagle. More impressive are the mammal species that it can catch and kill. These include many of the small antelope up to the 20 Kg range [44 lbs.], and a spectacular example includes an adult Martial Eagle killing a 37 Kg [82 lbs.] Red Duiker, which it grasped around the neck and strangled. They have also been credited with killing young baboons, vervet monkeys, Black - Backed Jackals, Dassies, Springhares, Warthogs, Wild Cats, Servals, Caracals, Striped polecats, Genets, Suricates, Mongoose, Squirrels and even Pangolins. Although this bird will take snakes, including the venomous ones, its preferred reptilian prey is large monitor lizards or leguaans. Also, like all the other large eagles, the Martial will eat carrion on occasion when available. Its actual mode of hunting consists of a long shallow swoop as its target is sighted, frequently beginning its descent onto its prey from miles away. When closer to its quarry, it dives at a steeper angle and at this point it may be flying more than 60 Kph [38 mph]. At the point of kill, it shoots its long legs forward grabbing its victim, most often killing it on impact.

15 15 Status They maintain a low population density even in optimal conditions, with one pair every 100 to 150 square kilometres [38 57 miles]. Because of persecution by farmers blaming them for domestic stock kills, which is an unfounded accusation, the birds remain scarce outside of the larger conservation areas.