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Secretarybird Sagittarius serpentarius Scientific name definitions

Alan C. Kemp, Guy M. Kirwan, David Christie, Jeffrey S. Marks, and Peter F. D. Boesman
Version: 1.1 — Published December 11, 2020
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The Secretarybird is an iconic member of sub-Saharan savanna habitats. Secretarybirds are unmistakable and elegant, with long legs, long central tail feathers, and mostly gray plumage accented with black wings and thighs. Named for their elongated head plumes, which resemble writing quills, Secretarybirds stride through the savanna, hunting for a wide variety of prey items, including insects, small vertebrates, and perhaps most famously, snakes. When prey is located, they subdue it with swift kicks from their feet, which have relatively short toes. They are a mostly solitary species, although sometimes pairs will forage close to each other. While Secretarybirds are mostly sedentary, they can be nomadic at times, following changes in rainfall, grazing conditions, and fires.

Identification

125–150 cm; c. 2300–4270 g; wingspan 191–215 cm (1). Unmistakable , terrestrial raptor , with long pink legs, long black crest feathers, bare orange face , hooked aquiline bill and long central tail feathers . Grey above, white below with black flight feathers , abdomen and thighs. Female is probably slightly smaller and less bluish than male (1). Juvenile is similar to adult, but has shorter tail and crest (1), with grey barring on white underwing-coverts and undertail-coverts; also paler face; brown edges to grey dorsal feathers, especially in juvenile female. Eye changes from grey to brown and bill from black to blue-grey when adult. Confusion with other raptors impossible, but at long range or in brief view might be momentarily mistaken for a bustard or crane, especially Blue Crane (Anthropoides paradiseus) (1).

Systematics History

Birds of W Africa have occasionally been awarded subspecific status as gambiensis. Monotypic.

Subspecies

Monotypic.

Distribution

Senegambia E to Eritrea and Somalia, and S to South Africa.

Habitat

Steppe or tree and grass savanna, favouring short grass with scattered acacia (Acacia) thorn trees to provide sites for roosting and nesting, but found also in large-scale cereal farmland and subdesert areas (1). Rarely, visits clearings in woodland or forest. Recorded from sea-level (1) to 3150 m (2).

Movement

Sedentary (with regular seasonal breeding) in some areas, but nomadic in most areas in response to changes in rainfall, grazing and fires. Adult males usually last to forsake territories; juveniles wander widely in search of places unoccupied by mated pairs. May enter and breed regularly in an area for several years and then be absent, or present only in much-reduced numbers.

Diet and Foraging

Mostly arthropods, especially grasshoppers (Orthoptera) and beetles (Coleoptera), but devours most small animals, including frogs, lizards, small tortoises, snakes  (including venomous species) (1), domestic chickens and other birds (1), including migrant Marsh Warblers (Acrocephalus palustris) (3), as well as small rodents, hedgehogs, mongooses, squirrels, hares and even freshwater crabs (1); eggs and young of birds also taken. Crop and stomach of a salvaged adult female contained 13 grasshoppers and eight snakes (4). Usually kills prey by fast kicks with the long legs and stout toes ; swallows it whole (has wide gape), and tears only larger prey while holding it down with the inner toes. Seizes snakes with bill and drops them from high in the air; stamps on other mobile or dangerous prey by using stubby toes (1). Sometimes caches prey under bush (1). Usually hunts alone or with mate in close proximity. Regularly hunts around grass fires, taking dead prey, but shuns large carrion (1).

Sounds and Vocal Behavior

Secretarybird is a silent bird, and one will rarely hear any vocalization when birds are seen feeding. In several situations of excitement however, it utters loud roaring calls which sound quite surprising.

Vocalizations

Vocal development

Small chicks beg with soft cheeping calls. As the birds become older, calls evolve into insisting clucking, mewing, squealing, and eventually braying notes (5). Braying calls are similar to adult's Croak call, but more stuttering and slightly higher-pitched. They are also used by older chicks to threaten intruders. Young in the nest may also call at night.

Vocal Array

Croak. A very low-pitched guttural croak or roaring groan urrrrrrh repeated several times (reminiscent of a mammal or e.g. a cormorant). Duration of croak ⁓0.7-1.5s.

Kee-uk. A repeated kee-uk...kee-uk...kee-uk sounding like a gull-like nasal laughter (recording in 6). Presumably the same vocalization is also described as a rapid ou-ook..ou-ook (7) or fast, high-pitched ko-ko-ko-ko-ka or louder kowaaaaa (8).

Other. A full-throated oo-or-kok is said to be a usual call (7). Softer clucking calls and low whistles are given by the mates on the nest (5). Mewing cries are said to be given when roosting at night (9).

Geographic variation

None documented.

Phenology

Croak calls may be uttered occasionally all year, but at the onset of the breeding period, an increase in calling while soaring high above the nest area can be noted (5). Equally so, one or both members of a pair may perform pendulum display flights while calling.

Daily Pattern of Vocalizing

There is no clear daily pattern of vocalizing, and vocal activity is mainly determined by the events during the day, such as alarming for intruders or breeding activities.

Places of Vocalizing

Croak calls are uttered either on the ground, in flight, or on the nest in the canopy of a tree (very often a dense flat-topped acacia).

Gender differences

No differences have been documented between males and females.

Social Content and Presumed Functions of Vocalizations

The Croak call is the main call, uttered in a variety of situations. It is uttered in flight during pendulum displays above its territory, at the nest by mates during a bowing greeting display, and on the ground during fights among rivaling birds or when signaling danger. A single croak indicts alarm, while deeper louder croaks are used in threat (5). The kee-uk call has been noted on the nest (6). It is not entirely clear if the kee-uk call is exclusively an adult vocalization used in alarm or contact (6), a call uttered in surprise or fear (7), or also uttered by chicks said to make 'a sharp sound heard as chee-uk-chee-uk-chee-uk for their first 30 days' (9).

Nonvocal Sounds

During territorial disputes, encounters frequently involve, leaping and kicking with wings or legs, making clapping noises, but these obviously don't have a communicative function.

Breeding

Nests at any time of year, whenever food abundant (nests recorded in virtually all months in Ethiopia (2) and S Africa) (10), usually to fledge chicks in period of food abundance in summer rainy season (e.g. in Aug–Mar S from Zambia) (1). Territory of 25–45 km². Each pair places large, saucer-shaped (10) nest platform (1·5–2·5 m wide and 20–30 cm thick) (10) of sticks, densely lined with grass, wool and mammal dung (1), usually 3·0–7·5 m above ground, sometimes up to 36 m up (1), on top of low tree, often a flat-topped Acacia (2), but exotic trees (e.g., wattles, pines and pyracanthas) also used (10); nest may be reused, but usually a new one is constructed for separate breeding attempt; nest-building may sometimes continue indefinitely, without laying (10). Clutch 1–3 eggs (rarely four) (10), normally two, pale white with very sparse dark markings (10), mean size 78 mm × 56 mm (10), laid at intervals of 2–3 days (10); incubation by both sexes, period 42–46 days, change-over made up to six times per day (10); chicks hatch in pale grey down with short straight bill, second dark grey down by three weeks, well feathered by six weeks; nestling period variable, 64 (1)–106 days, usually 75–90 days (1); young can remain dependent for 62–105 days (1). Only rarely three chicks raised, but pair may have successive broods with intervals of less than a month between them. Infanticide recently documented in Tanzania, but reasons unknown (11). In study in Kgalagadi Transfrontier Park, straddling NW South Africa and SW Botswana, in 1988–1990, total of 26 chicks hatched, of which almost all (23) fledged successfully, and productivity was 2·2 young fledged per breeding attempt per year (12).

VULNERABLE. Recently uplisted (13). CITES II. Variously common to rare and localized; recent evidence suggests rapid decline across its huge range. Often locally common, both in protected natural areas and in various forms of extensive agriculture; apparently always uncommon in Malawi (14), and never common in Uganda, where now largely confined to national parks in N (15). According to BirdLife, no reliable estimates of global population available, but surveys suggest that total does not exceed five figures. Has not been seen anywhere in West Africa in recent years and is now considered the most threatened raptor in that region (16, 17). Pertinent records, local surveys and other observations appear to indicate decreases in many areas, suggesting that this species is undergoing rapid decline; this particularly evident in Tanzania since late 1990s and in South Africa between 1987–1991 and 2007–2010 (18). In 1990s, more than 1000 breeding pairs thought to occur in former Transvaal Province of NE South Africa alone, and in E Karoo  densities apparently increased during mid 1990s from 0·71 birds/100 km to 1·9 birds/100 km, possibly owing to changes in farming and locust-control practices (19). Although this species may benefit from deforestation, any such effects may be outweighed by adverse impacts of spreading cultivation and urbanization (1, 20); similarly, excessive burning of grasslands can reduce populations of prey species, and intensive livestock grazing probably results in degradation of habitat (18). Human disturbance, e.g. by herders, likely to have negative impact on breeding. Other potential causes of declines include collisions with fences and power lines (20), poisoning by insecticides (20), direct hunting and nest-robbing. Although this raptor is captured and traded in apparently small numbers, it is unknown how many individuals die in captivity or in transit. Effects of severe droughts in some areas are exacerbated by aforementioned anthropogenic threats. Has been recorded as drowning in steep-sided farm reservoirs in S Africa (21). Often protected in recognition of snake- and rodent-killing abilities, but sometimes persecuted at low, accessible nest-sites. Proposed conservation actions include establishment of a co-ordinated continent-wide monitoring programme to obtain accurate and up-to-date estimate of this raptor's population and to determine its current trends. In areas where it is declining, it is important to raise awareness among local inhabitants, especially livestock-herders, of threats facing this species. Equally, it is essential to monitor the capture and trade of the species and to make efforts to prevent such activities. Occurs in a number of national parks and other protected areas across its very large range; alarmingly, however, recently reported to be declining in Kruger National Park, South Africa (20). Has been bred several times in captivity.

Distribution of the Secretarybird
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  • Year-round
  • Migration
  • Breeding
  • Non-Breeding
Distribution of the Secretarybird

Recommended Citation

Kemp, A. C., G. M. Kirwan, D. A. Christie, J. S. Marks, and P. F. D. Boesman (2020). Secretarybird (Sagittarius serpentarius), version 1.1. In Birds of the World (S. M. Billerman and B. K. Keeney, Editors). Cornell Lab of Ornithology, Ithaca, NY, USA. https://doi.org/10.2173/bow.secret2.01.1