Bateleur (Terathopius ecaudatus) Fact Sheet: Reproduction & Development

Monogamous (from Watson 1990b)

• Breeding pair holds an exclusive territory (Steyn 1980; Watson 1990b)
• Partners reproduce together in consecutive years

Courtship flights (from Ferguson-Lees and Christie 2001)

• Male and female perform aerial maneuvers
• Male dives at female
• At times dangling outstretched legs
• Birds make short, mock dives at one another (Steyn 1965)
• Female rolls over to present her claws
• Both individuals with heavy (audible) wing beats
• Sound similar to that of a flapping sail

Extensive reproductive investment (from Smeenk 1974; Watson 1988)

• Parental care lasts 8-9 months
• Period from nesting to post-fledge
• Development time of egg and nestling “unusually long” (Watson 1988)

Seasonal reproduction

• Annual interval of egg laying
• Timing highly variable within and between years
• Kruger National Park (KNP), South Africa (from Watson 1990b)
• Lay eggs January to mid-June
• Zimbabwe (from Steyn 1980)
• Lay eggs December to June
• An apparent peak February-March
• East Africa (from Smeenk 1974)
• Lay eggs January to June
• Higher rainfall associated with reductions in egg laying (Watson 1990b)

Nests characteristics

• Location (from Steyn 1980 unless otherwise noted)
• Set within the canopy where shaded most of the day (Osborne 1982; Steyn 1980)
• Location likely provides concealment (Watson 1988)
• Set at a point c. 73% of the height of the tree
• c. 7-10 m (23-33 ft) above the ground, in one Zambian study (Osborne 1982)
• Atypically in full sun
• Positioned on a main fork or on a lateral tree branch (Osborne 1982; Steyn 1980)
• Support branches > 90 mm thick (3.5 in) (Watson 1988)
• Most often in the 5^th or 6^th fork of a tree (Watson 1988)
• Nest most commonly supported by three branches (Watson 1988)
• Placement often mid-way between the trunk and the tree’s periphery (Watson 1988)
• Frequently within the northern-facing side of the tree (Watson 1988)
• Tree species preferences
• Often in Acacia spp, in Zimbabwe
• Prefer Acacia nigrescens and Diospyros mespiliformis, in KNP (Watson 1988)
• Dimensions (from Watson 1988)
• No well defined parameters
• Overall (outer-most) dimensions
• Diameter 400-1,500 mm (1.3-4.9 ft)
• Depth 250-800 mm (0.8-2.6 ft)
• Cup dimensions
• Diameter 300-800 mm (1.0-2.6 ft)
• Depth 30-170 mm (1.2-6.7 in)
• Construction (from Watson 1990b)
• Built primarily by the male
• Male spends >50% of daylight hours assembling the nest
• May spend long periods building a nest; a minimum of 38 days taken to construct one nest in KNP
• Female often perches nearby
• Nesting materials
• Sturdy nests made of larger sticks (Brown 1955; Steyn 1980)
• Lined with green leaves (Ferguson-Lees and Christie 2001)
• Inter-annual use (from Steyn 1980)
• Re-use the same nest in consecutive years
• Same nest used for up to three years, in Zimbabwe
• Partners may return to a nest following a year of disuse

Clutch characteristics (from Watson 1990b unless otherwise noted)

• Clutch size
• A single large egg (Steyn 1980; Watson 1990b)
• Appearance of eggs
• White (Steyn 1980)
• A few red marks appearing on some
• "Nest stained” by the end of incubation
• Egg size
• Mass c. 160 g (c. 5.6 oz)
• May weight more
• c. 8% of adult’s weight
• Mean dimensions
• 79.1 mm x 62.7 mm (3.1 in x 2.5 in) (Steyn 1980)

Incubation (from Watson 1990b unless otherwise noted)

• Both parents incubate
• Male and female spend roughly equal amounts of time at the nest
• Older studies suggest only females incubate (Brown 1955)
• Duration
• c. 55 days (Steyn 1980)
• Possibly for shorter periods; 42-43 days (Brown 1955)
• Egg uncommonly left unattended
• Eggs left unattended <10% of the time, one study
• Most often occurring between 10:00 and 13:00, when ambient temperatures are similar to that of the egg

Hatching

• Appearance at hatch (from Brown 1955 unless otherwise noted)
• Feeble
• The head exceptionally large in proportion to the body
• Eyes
• Large and dark (Moreau 1945)
• Bill
• Black overall
• Cere (base of upper beak) creamy white and heavily wrinkled
• Wrinkles disappear and color turns pale blue-green c. 2 weeks
• Legs
• Grayish-white
• First down
• Buff on the head, neck and underside
• Dark brown on the back and wings
• Mass (from Steyn 1965)
• Weigh c. 110 g (3.9 oz) by 2 days of age, one description of a single chick
• Body mass may more than double within a week of birth
• Weight may more than quadruple within 2 weeks of birth

Interclutch interval

• Yearly breeding (from Watson 1990b)
• Uncommonly produce two clutches in a single year
• Disturbance by other birds or humans may induce parents to abandon clutches
• Replacement clutches uncommonly observed in the wild (Osborne 1992; Watson 1990b)
• A single replacement clutch observed in one multi-year study in KNP (Watson 1990b)
• Loss of reproductive effort also due to addled or crushed eggs
• Previous year’s success does not affect attempts to breed the following year

Nestling (from Watson 1990b unless otherwise noted)

• Nestling period
• Highly variable
• 101-213 days
• Care
• Both parents provide care and food (Brown 1955; Watson 1990b)
• Parents brood nestlings c. 20 day after hatch
• Nest attendance declines significantly as eaglets age
• Young birds are left alone for much of the nestling period
• Adults shade older eaglets with their bodies
• Feeding rate and timing, observations from one study in KNP
• Younger nestling is fed c. 4 times/day (Watson 1990b)
• Provisioned by regurgitation (Brown 1955)
• Provisioning typically occurs between 8:00-14:00 and between 16:00-17:00 (Watson 1990b)
• Nest may accumulate bits of food items (Brown 1955)
• Older nestling receives food 2-3 times/day
• Provisioning typically occurs around mid-day
• Eaglet begins to feed itself
• Minimal active guarding of nests (Watson 1988)
• Protection provided through the concealment of the nest (Watson 1988)
• Feeding response
• Nestling calls or crouches low in the nest when a parent approaches
• Typically produces a soliciting call only when the parent approaches without vocalizing
• Development (from Brown 1955)
• Nestling gains strength by c. 14 days
• May sit up and take active interest in its surroundings
• Black feathers grow through down c. 25 days
• Head, neck, wing-coverts, and primaries feathered by 32 days
• Feathers on the forepart of the body rapidly develop thereafter
• Immature plumage appears near the time of fledging
• Mortality
• Nest depredation may account for 50% of mortality
• Accidental injury
• Heavy rainfall may increase mortality risk
• Sensitive to human disturbance at the nest

Fledgling

• Plumage development (from Brown 1955)
• First immature plumage
• Body feathers brown; sometimes dark
• Flight quills black
• Feet grayish-white
• Tail markedly longer than in the adult
• Fledging (from Brown 1955)
• Fledgling exercises wings by flapping prior to fledge
• May walk short distances along branches near the nest
• First flight c. 93-194 days (Ferguson-Lees and Christie 2001)
• Post-fledging dependence (from Watson 1990b unless otherwise noted)
• A flighted fledgling continues to receive parental care
• Early portions of the day may be spent in exploratory flight;
• Youth spends longer periods near the nest site as the day progresses
• Remains near the nest 31-120 days after fledge (Steyn 1980; Watson 1990b)
• Low-end estimates of post-fledging dependence may be due to mortality
• Mortality likely high during this time (Brown and Amadon 1968)
• Fledging success rate (from Watson 1990b)
• 0.36-0.57 per year, one study in KNP

Juveniles

• Non-breeding individuals
• May migrate over short distances (from Watson 1990a)
• Move between areas in the dry winter (breeding) season and the wet summer (non-breeding) season
• Pattern inferred from changes in relative abundance in KNP through the year

Adults (from Brown and Cade 1972)

• Adults outnumber immature within a population
• Equal numbers of males and females; sex ratio roughly 1:1
• Adult plumage
• Comes in c. 7 years of age

Wild populations

• Not reported

Managed care

• Commonly live 30–40 years (ZIMS 2015)

Bateleur pairs perform complex aerial maneuvers during courtship.

Image credit: © San Diego Zoo Wildlife Alliance. All rights reserved. (Note: This is a cropped image.)

Brown (1955)
Brown and Amadon (1968)
Brown and Cade (1972)
Ferguson-Lees and Christie (2001)
Moreau (1945)
Osborne (1992)
Smeenk (1974)
Steyn (1965)
Steyn (1980)
Watson (1988)
Watson (1990a, b)
(ZIMS 2015)