Secretary Bird

Secretary Bird
In Kalahari, South Africa
In Kalahari, South Africa
Conservation status
Status iucn3.1 LC.svg
Least Concern (IUCN 3.1)[1]
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Aves
Order: Accipitriformes
Family: Sagittariidae
R. Grandori & L. Grandori, 1935
Genus: Sagittarius
Hermann, 1783
Species: S. serpentarius
Binomial name
Sagittarius serpentarius
(J. F. Miller, 1779)

The Secretary Bird, Sagittarius serpentarius, is a large, mostly terrestrial bird of prey. Endemic to Africa, it is usually found in the open grasslands and savannah of the sub-Sahara.[2] Although a member of the order Accipitriformes, which also includes many other diurnal raptors such as kites, buzzards, vultures, and harriers, it is so distinctive that it was given its own family, Sagittariidae.

It enjoys a certain fame in Africa, specifically Sudan and South Africa, serving as a prominent emblem on both nations' coats of arms.

Contents

Etymology

Showing the feather crest.

Its common name is popularly thought to derive from the crest of long quill-like feathers, lending the bird the appearance of a secretary with quill pens tucked behind his or her ear, as was once the practice. A more recent hypothesis is that "secretary" is borrowed from a French corruption of the Arabic saqr-et-tair or "hunter-bird."[3]

The generic name "Sagittarius" is Latin for "archer," perhaps likening the Secretary Bird's "quills" to a quiver of arrows. Its specific epithet - "serpentarius" - recalls the bird's skill as a hunter of reptiles.

Characteristics

Closeup of head
Secretary bird in natural habitat
Secretary bird, Kruger National Park

Description

The Secretary Bird is instantly recognizable as having an eagle-like body on crane-like legs which increases the bird’s height to around 1.3 m (4 ft) tall. This 140 cm (4.5 ft) long bird has an eagle-like head with a hooked bill, but has rounded wings.[4] Body weight averages at about 3.3 kg (7.3 lbs) and the wingspan is over 2 m (6.6 ft).[5]

From a distance or in flight it resembles a crane more than a bird of prey. The tail has two elongated central feathers that extend beyond the feet during flight, as well as long flat plumage creating a posterior crest.[4] Secretary Bird flight feathers and thighs are black, while most of the coverts are grey with some being white.[6] Sexes look similar to one another as the species exhibits very little sexual dimorphism, although the male has longer head plumes and tail feathers. Adults have a featherless red face as opposed to the yellow facial skin of the young.[4]

Habitat

Secretary Birds are endemic to Sub-Saharan Africa and are non-migratory (although they may follow food sources).[7] Their range is from Senegal to Somalia and south to the Cape of Good Hope.[4] These birds are also found at a variety of elevations, from the coastal plains to the highlands. Secretary Birds prefer open grasslands and savannas rather than forests and dense shrubbery which may impede their cursorial existence. While the birds roost on the local Acacia trees at night, they spend much of the day on the ground, returning to roosting sites just before dark.[8]

Threats

Young are preyed upon by crows and kites as they are vulnerable in Acacia tree tops.[4] As a population, the Secretary Bird is mainly threatened by loss of habitat and deforestation.[9] In 1968 the species became protected under the Africa Convention on the Conservation of Nature and Natural Resources.[4]

Diet

The Secretary Bird is largely terrestrial, hunting its prey on foot, and other than the caracara (such as Polyborus plancus), is the only bird of prey to do so habitually. Adults hunt in pairs and sometimes as loose familial flocks, stalking through the habitat with long strides.[10] Prey consists of insects, small mammals, lizards, snakes, young birds, bird eggs, and sometimes dead animals killed in brush fires. Larger herbivores are not hunted, although there are some reports of Secretary Birds killing young gazelles.[10]

Young are fed liquefied and regurgitated insects directly by the male or female parent and are eventually weaned to small mammals and reptile fragments regurgitated onto the nest itself. The above foodstuffs are originally stored in the crop of the adults.[4]

Secretary Birds have two distinct feeding strategies that are both executed on land. They can either catch prey by chasing it and striking with the bill, or stamping on prey until it is rendered stunned or unconscious enough to swallow.[4] Studies of this latter strategy have helped construct the possible feeding mechanisms employed by dinosaur-like 'terror birds' that once walked the earth five million years ago.[11]

Reproduction

Mating

In flight

Secretary Birds associate in monogamous pairs. During courtship, they exhibit a nuptial display by soaring high with undulating flight patterns and calling with guttural croaking. Males and females can also perform a grounded display by chasing each other with their wings up and back, much like the way they chase prey. They usually mate on the ground, although some do so in Acacia trees.

Rearing

Nests are built on top of acacia trees, and are usually 5-7 m (15-20 feet) high. Both the male and female visit the nest site for almost half a year before egg laying takes place. The nest is around 2.5 m (eight feet) wide and 30 cm (one foot) deep, and is constructed as a relatively flat basin of sticks.

Secretary birds lay two to three oval, pale-green eggs over the course of two to three days, although the third egg is most often unfertilised. These eggs are incubated primarily by the female for 45 days until they hatch. The Secretary Birds are facultatively fratricidal.[12]

The downy young can feed autonomously after 40 days, although the parents still feed the young after that time. At 60 days, the young start to flap their wings, and by day 65-80 are able to fledge. Fledging is accomplished by jumping out of the nest or using a semi-controlled fall via fervent wing flapping to the ground. After this time, the young are quickly taught how to hunt through expeditions with their parents and are considered independent soon after.[4]

Evolution

Recent cladistic analysis has shown Sagittariidae to be an older group than Accipitridae and Falconidae, but a younger divergence than Cathartidae.[13] Studies are still being conducted due to the peculiarity of the single species group and recent molecular biology techniques in taxonomic organization.

Cultural significance

The Secretary Bird is the national emblem of Sudan as well as a prominent feature on the Coat of arms of South Africa.

In Sudan, It is featured in the middle white strip of the Presidential Flag; it is the main object on the Presidential Seal, and features heavily in Sudanese military insignia. The Secretary Bird on the Presidential Flag and Seal has its head turned to the right, with its distinctive crest clearly visible and its wings spread out with a white banner between its outstretched wings reading "Victory is Ours".

In South Africa, the Secretary Bird, while not the official bird, is featured as a symbol on the national coat of arms, representing vigilance and military might, as well as the rise and pride of modern South Africa.

References

  1. ↑ BirdLife International (2004). Sagittarius serpentarius. 2006 IUCN Red List of Threatened Species. IUCN 2006. Retrieved on 8 May 2006. (database entry includes justification for 'least concern')
  2. ↑ Illustrated Guide to the Birds of Southern Africa - Sinclair, I., Hockey, P., & Tarboton, J., Princeton: Princeton University Press (1993)
  3. ↑ Family Sagittariidae (Secretarybird), Handbook of the Birds of the World, Volume 2 - Kemp, A.C.; Eds. del Hoyo, J., A. Elliott, & J. Sargatal. Lynx Edicions, Barcelona. 206-215 (1994)
  4. ↑ 4.0 4.1 4.2 4.3 4.4 4.5 4.6 4.7 4.8 Eagles, Hawks, and Falcons of the World, Volume 2 - Brown, L. & Amadon, D. New York: McGraw-Hill Book Company (1968)
  5. ↑ Raptors of the World - Ferguson-Lees, J.; Houghton Mifflin, New York. 978-0618127627 (2001)
  6. ↑ Birds of Africa: South of the Sahara - Sinclair, I. & Ryan, P., Princeton and Oxford: Princeton University Press (2003)
  7. ↑ Bird Migration in Africa: Movements between six continents, Volume 2 - Curry-Lindahl, K., New York: Academic Press (1981)
  8. ↑ Large trees, fertile islands, and birds in arid savanna - Dean, W.R.J., Milton, SJ., & Jeltsch, F., Journal of Arid Environments, 41, 61-78 (1999)
  9. ↑ The Impact of Commercial Afforestation on Bird Population in Mpumalanga Province, South Africa - Insights from Bird-Atlas Data - Allan, D.G., Harrison, J.A., Navarro, R.A., van Wilgen, B.W., & Thompson, M.W.; Biological Conservation, 79, 173-185 (1997)
  10. ↑ 10.0 10.1 The Depression of Reptile Biomass by Large Herbivores - Janzen, D.H., American Naturalist, 110, 71-400 (1976)
  11. ↑ The Terror Birds of South America - Marshall, L.G., Scientific American, 82-89 (Mnday 1 March 2001)
  12. ↑ Evolution of Growth Rates in Eagles: Sibling Competition Vs. Energy Considerations - Bortolotti, B.R., Ecology, 67, 182-194. (1986)
  13. ↑ The deep divergences of neornithine birds: a phylogenetic analysis of morphological characters - Mayr, G. & Clarke, J., Cladistics, 19, 527–553 (2003)

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