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Sagittarius serpentariussecretary bird(Also: secretarybird)

By Patrick Sherman

Geographic Range

Sagittarius serpentarius is found throughout Africa south of the Sahara, except the extreme deserts of the Namib coast and the forested region around the equator in western Africa. Secretary birds do not occur in the southern areas of Guinea, Cote d'Ivoire, Ghana and Nigeria, and are entirely absent from the sub-Saharan countries of Sierra Leone and Liberia. (Ferguson-Lees and Christie, 2001; Mackworth-Praed and Grant, 1980; Steyn, 1983)

Habitat

Secretary birds prefer open savannahs and grasslands, although they also live in semi-deserts and lightly wooded or scrub areas. In grasslands, secretary birds choose areas where the grass is one meter or less in height so their view is not obstructed. They are common near agricultural areas that offer hunting opportunities. Secretary birds are never found in true deserts with extreme aridity, or heavily wooded areas. These birds are found from sea-level to around 3,000 m. (Ferguson-Lees and Christie, 2001; Hosking, et al., 1988; Steyn, 1983)

  • Range elevation
    3,000 (high) m
    ft

Physical Description

Secretary birds stand around 0.9 to 1.2 meters tall and weigh between 2.3 to 4.27 kg. Females tend to be slightly smaller than males. Wingspans of females range from 1.2 to 1.32 m, while those of males range between 1.26 to 1.35 m. (Ferguson-Lees and Christie, 2001; Mackworth-Praed and Grant, 1980)

These large raptors have very distinctive morphology. The plumage is generally gray in color, perhaps with some white feathers. They have black flight feathers on the wings and a crest of black-tipped feathers on the back of the head. The bare face is orange to red in color. They have a relatively small head, a gray-white beak, a long neck, and an eagle-like body. Unlike an eagle, however, the bare, pinkish legs are very long and end in stubby toes with blunt claws. The tibial portions of the legs are covered in black plumage that give the bird the appearance that it is wearing shorts. The long tail has especially long central rectrices that are often tipped with black. (Ferguson-Lees and Christie, 2001; Hosking, et al., 1988; Mackworth-Praed and Grant, 1980; Steyn, 1983)

Juvenile Sagittarius serpentarius are similar in appearance to adults with a few exceptions. First, the bare skin on the face is yellow rather than orange or red. Second, juveniles show black coloration on the tips of the wing shoulder feathers, as well as brown to black barring on the underwing coverts. Lastly, juveniles also tend to have shorter central tail feathers and crests than adults. (Ferguson-Lees and Christie, 2001; Mackworth-Praed and Grant, 1980; Steyn, 1983)

It would be hard to confuse Sagittarius serpentarius with any other bird of prey, mainly due to their very long legs. From a distance secretary birds are mistaken for bustards or cranes. They are perhaps most commonly mistaken for blue cranes (Anthropoides paradiseus). (Ferguson-Lees and Christie, 2001; Hosking, et al., 1988; Steyn, 1983)

  • Sexual Dimorphism
  • male larger
  • Range mass
    2300 to 4270 g
    81.06 to 150.48 oz
  • Range wingspan
    1.2 to 1.35 m
    3.94 to 4.43 ft

Reproduction

Secretary birds are monogamous and are thought to pair for life. In courtship, they give a croaking call while displaying in the air and on the ground. Aerial displays consist of high soaring and diving performed by a single individual (usually the male), or by the pair when the male will dive toward the female and she will half-turn to present her claws. This courtship behavior is very similar to that of other birds of prey. On the ground, their displays are very crane-like with the two birds dancing around with their wings outstretched. Sometimes small groups of secretary birds will all join in this ground display behavior. After courtship displays, mating will usually take place on the ground, although some pairs mate in trees. (Ferguson-Lees and Christie, 2001; Hosking, et al., 1988; Steyn, 1983)

Sagittarius serpentarius may breed throughout the year, although there are peaks in breeding from August to March. Both the male and female will construct a large nest on a flat-topped tree (usually an acacia tree or some other thorny tree). The nest is usually a saucer-shaped platform made of sticks and lined with a thick layer of grass, wool, dung, and other such materials. A pair of secretary birds will usually reuse the same nest for many years, adding to the structure each year to create a nest that can range from 1.5 to 2.5 meters in diameter. A frequently reused nest will be abandoned if the structure becomes too large and heavy to be supported by the tree and seems likely to collapse. (Ferguson-Lees and Christie, 2001; Hosking, et al., 1988; Mackworth-Praed and Grant, 1980; Steyn, 1983)

The female lays a clutch of 1 to 3 eggs, with each egg laid two to three days apart. The eggs are chalky-white with reddish-brown streaks and are pyriform in shape. Eggs are variable in size and can range from 68 to 92 mm in length and 52 to 61 mm in width. Incubation of the eggs begins as soon as the first egg is laid. Incubation duties are shared by both the male and female, although more frequently by the female. The male brings food to the nest for the female during this time. In 42 to 46 days, the semi-altricial young hatch. Young generally hatch 2 to 3 days apart, but no siblicide has been observed. However, in a clutch of three eggs, the smallest chick usually dies of starvation because it cannot compete with its larger nest mates. (Ferguson-Lees and Christie, 2001; Mackworth-Praed and Grant, 1980; Steyn, 1983)

Hatchlings are covered in off-white down and have large heads that seem too heavy for their bodies. At two weeks of age, they attain a thick coat of gray down, and in three weeks the crest begins to appear. Development is slow in secretary birds and it takes six weeks before the hatchlings can stand on their own. At this stage, they learn to feed themselves from prey brought to the nest. By seven weeks, nestlings are fully feathered. Around 60 days, the young begin flexing their wings, often flapping and lifting small distances into the air before dropping back to the nest. In 64 to 106 days, the offspring will fledge. The offspring remain around the nest tree for an additional 62 to 105 days, during which time they are dependent upon the parents for food and training in foraging techniques. (Ferguson-Lees and Christie, 2001; Steyn, 1983)

  • Breeding interval
    Secretary birds can raise two broods within ten months under desirable conditions.
  • Breeding season
    Breeding can occur throughout the year.
  • Range eggs per season
    1 to 3
  • Range time to hatching
    42 to 46 days
  • Range fledging age
    64 to 106 days
  • Range time to independence
    62 to 105 days

Both male and female secretary birds invest heavily in the young. Both sexes share incubation duties. After the eggs hatch, parental care is constant. Both the male and female feed the young via regurgitation, although the female mostly regurgitates food that the male has brought back to the nest for her. After about a month, parental care drops significantly, with the parents only returning to the nest to feed the chicks. After six weeks, the parents stop feeding via regurgitation and bring larger prey items that they give the chicks to eat directly. When the chicks fledge and leave the nest, the parents will teach the chicks how to hunt for prey. Once the offspring know how to provide for themselves and are independent, they generally head off on their own, leaving the parents’ territory. However, in some circumstances the parents will still tolerate having the juveniles in their territory and even allow the now-independent offspring to join in their hunts and share the nest tree as a roost. It is important to note that juveniles are not dependent on the parents during this time. They are just temporarily sharing a territory. Two months is the average amount of time that independent juveniles are allowed to remain in the parents’ territory before being chased away so that the parents can breed again. (Hosking, et al., 1988; Steyn, 1983)

  • Parental Investment
  • pre-fertilization
    • provisioning
    • protecting
      • female
  • pre-hatching/birth
    • provisioning
      • female
    • protecting
      • male
      • female
  • pre-weaning/fledging
    • provisioning
      • male
      • female
    • protecting
      • male
      • female
  • pre-independence
    • provisioning
      • male
      • female
    • protecting
      • male
      • female
  • post-independence association with parents
  • extended period of juvenile learning

Lifespan/Longevity

The lifespan of Sagittarius serpentarius is currently unknown and further study is required.

Behavior

Sagittarius serpentarius is sometimes solitary, but is more often found in pairs or family groups consisting of up to five individuals. Larger aggregations of secretary birds may form near an abundant food source or a watering hole, but these groups do not remain together long. Secretary birds become active about two hours after the sun has risen, when the grass is no longer wet with morning dew. These birds spend the day walking around and feeding until late afternoon, at which point they return to their roosts. Secretary birds prefer to walk rather than fly, and average about 20 to 30 km a day on foot. When hurried or confronted with a threat they run before taking flight. When they do fly, they fly well and often at great heights. (Ferguson-Lees and Christie, 2001; Steyn, 1983)

  • Range territory size
    20 to 500 km^2

Home Range

A pair of secretary birds defends an area that can range from 20 to 500 square kilometers depending on the density of secretary birds and food resources in the area. Any conspecifics caught intruding in a pair's territory will be chased out forcefully. Sagittarius serpentarius is generally sedentary and will remain in its own territory, but they are sometimes nomadic. In most cases, these nomadic tendencies are caused by a search for food. (Ferguson-Lees and Christie, 2001; Steyn, 1983)

Communication and Perception

Secretary birds are generally silent. When they do call, they typically give a deep, trisyllabic croaking wail that can be heard for quite some distance. This call, along with a drawn-out growling sound, is used in conjunction with aerial and ground displays during the courtship process. A softer version of the main call is used when feeding young. An occasional whistle is given from time to time. The young have their own calls to solicit food from their parents, which start off as a quiet squealing, then becoming a loud 'chok-a-chok-a-chok-a-chok'. (Ferguson-Lees and Christie, 2001; Hosking, et al., 1988; Mackworth-Praed and Grant, 1980; Steyn, 1983)

Food Habits

Sagittarius serpentarius is an opportunistic predator with a broad prey base. The majority of the diet is made up of arthropods (including grasshoppers, beetles, spiders, scorpions, wasps, etc.) and small mammals (including mice, rats, hedgehogs, hares, mongooses, etc.). Other recorded prey of secretary birds includes small and young birds, eggs, amphibians, freshwater crabs, lizards, small tortoises, chameleons and snakes. Although this species is famed for killing and eating snakes, these reptiles are not eaten as often as is generally believed. However, the snakes taken as prey are often adders, cobras, and other venomous species. (Ferguson-Lees and Christie, 2001; Hosking, et al., 1988; Mackworth-Praed and Grant, 1980; Steyn, 1983)

Secretary birds hunt exclusively on the ground, either alone or in pairs (usually with their mate). The birds will set out across a grassy area at a steady pace searching for movement. If a particularly thick tuft of grass is encountered, the bird will stamp on it to flush out any potential prey. Once prey is spotted, the bird quickens its pace to take the prey by surprise. If a chase commences, the bird will flap its wings and run after the prey until catching up to it. With small prey, the bird will merely bend down and capture it in its bill. Larger prey, especially snakes, are stamped to death with the bird's blunt feet. A secretary bird will strike a snake just behind its head to snap its neck or stun it. Secretary birds are said to pick up a stunned snake, fly high into the air and drop the snake to its death, but this behavior has not been well documented. Once the prey is stunned or killed, the bird will swallow it whole through its large gape. If the prey proves too large, then the bird will tear it apart much like an eagle, using its feet to hold the prey down. (Ferguson-Lees and Christie, 2001; Hosking, et al., 1988; Steyn, 1983)

Secretary birds regurgitate pellets after the prey is digested. The pellets consist of fur, bones, and invertebrate exoskeletons. Sometimes grass is found in the pellets. It is unknown whether the birds swallow grass incidentally along with the prey, or if they swallow it intentionally to help hold the pellet together when there is little fur present. Stones, which are swallowed to help in breaking up the exoskeletons of larger invertebrates, have also been found in the pellets. Secretary bird pellets are found around and in the nest and are especially helpful to researchers in analyzing the diet of birds in that area. (Steyn, 1983)

  • Animal Foods
  • birds
  • mammals
  • amphibians
  • reptiles
  • eggs
  • insects
  • terrestrial non-insect arthropods
  • aquatic crustaceans

Predation

Secretary birds are generally only vulnerable to predation as eggs and young birds in the nest. Their large, open nests leave the nestlings vulnerable to predation by crows, ravens, ground hornbills and birds of prey, such as kites or eagle-owls. (Steyn, 1983)

Ecosystem Roles

These birds prey on a wide range of large invertebrates and small to medium-sized vertebrates, but do not seem to have a great overall effect on these populations in the wild. Smaller, localized populations may be affected by predation from this species if hunting increases, especially during breeding season.

The vulnerable nestlings of secretary birds are occasionally taken as food by a number of predators. However, the low density of secretary bird nests means they are not vital to the predators' diets, and they have little effect on their survival. (Ferguson-Lees and Christie, 2001; Steyn, 1983)

Economic Importance for Humans: Positive

Perhaps the most beneficial action that Sagittarius serpentarius performs for humans is eating rodent and insect pests that feed on the crops of the local peoples. Secretary birds also hunt the snakes that are attracted to the fields to eat the rodents. (Ferguson-Lees and Christie, 2001; Steyn, 1983)

  • Positive Impacts
  • controls pest population

Economic Importance for Humans: Negative

There are no known adverse effects of Sagittarius serpentarius on humans.

Conservation Status

Sagittarius serpentarius is common throughout its range, although its numbers have been reduced in historic times. Since it is in no immediate danger, the IUCN Red List gives it a Lower Risk/Least Concern status. However, as human populations increase and more land is converted, there is likely to be a further reduction in secretary bird numbers. As a bird of prey in the order Falconiformes, Sagittarius serpentarius is protected under Appendix II of CITES, meaning that trade of this species is controlled. (Ferguson-Lees and Christie, 2001; Steyn, 1983)

Other Comments

The etymology behind both the common and scientific name of this species is quite interesting. The scientific name Sagittarius serpentarius means "bowman" and "interest in snakes" in Latin. The generic name may have arisen because the crest may resemble arrows sticking out of an archer's quiver. The specific epithet reflects the fact that this species often feeds on snakes. (Ferguson-Lees and Christie, 2001; Steyn, 1983)

The origin of the common name may come from the fact that their crest feathers made these birds look like old-time secretaries who used to keep their quill pens tucked behind their ears. In recent years, however, this has been challenged. It is instead thought by some that the name comes from the Arabic 'saqr et-tair'. 'Saqr' means "hunter" or "hawk" and 'et-tair' means "flight" or, in general, "bird". Thus, 'saqr et-tair' might mean "hunter bird", which would be an appropriate name for this species given its feeding behavior. (Ferguson-Lees and Christie, 2001; Hosking, et al., 1988; Mackworth-Praed and Grant, 1980; Steyn, 1983)

Contributors

Tanya Dewey (editor), Animal Diversity Web.

Patrick Sherman (author), Michigan State University, Pamela Rasmussen (editor, instructor), Michigan State University.

Glossary

Ethiopian

living in sub-Saharan Africa (south of 30 degrees north) and Madagascar.

World Map

acoustic

uses sound to communicate

agricultural

living in landscapes dominated by human agriculture.

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

carnivore

an animal that mainly eats meat

chemical

uses smells or other chemicals to communicate

diurnal
  1. active during the day, 2. lasting for one day.
endothermic

animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.

fertilization

union of egg and spermatozoan

insectivore

An animal that eats mainly insects or spiders.

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

monogamous

Having one mate at a time.

motile

having the capacity to move from one place to another.

native range

the area in which the animal is naturally found, the region in which it is endemic.

nomadic

generally wanders from place to place, usually within a well-defined range.

oviparous

reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.

scrub forest

scrub forests develop in areas that experience dry seasons.

sedentary

remains in the same area

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

solitary

lives alone

tactile

uses touch to communicate

terrestrial

Living on the ground.

territorial

defends an area within the home range, occupied by a single animals or group of animals of the same species and held through overt defense, display, or advertisement

tropical

the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.

tropical savanna and grassland

A terrestrial biome. Savannas are grasslands with scattered individual trees that do not form a closed canopy. Extensive savannas are found in parts of subtropical and tropical Africa and South America, and in Australia.

savanna

A grassland with scattered trees or scattered clumps of trees, a type of community intermediate between grassland and forest. See also Tropical savanna and grassland biome.

temperate grassland

A terrestrial biome found in temperate latitudes (>23.5° N or S latitude). Vegetation is made up mostly of grasses, the height and species diversity of which depend largely on the amount of moisture available. Fire and grazing are important in the long-term maintenance of grasslands.

visual

uses sight to communicate

year-round breeding

breeding takes place throughout the year

References

Ferguson-Lees, J., D. Christie. 2001. Raptors of the World. New York: Houghton Mifflin Company.

Hosking, E., D. Hosking, J. Flegg. 1988. Birds of Prey of the World. Lexington, Massachusetts: The Stephen Greene Press.

Mackworth-Praed, C., C. Grant. 1980. Birds of Eastern and North Eastern Africa, Volume 1. New York: Longman Inc..

Steyn, P. 1983. Birds of Prey of Southern Africa: Their Identification & Life Histories. Dover, New Hampshire: Tanager Books, Inc..

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