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Bateleur (Terathopius ecaudatus) Fact Sheet: Reproduction & Development

Terathopius ecaudatus, Bateleur

Courtship

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

Reproduction

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 5th or 6th 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

Gestation and Hatching

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

Life Stages

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

Longevity

In the wild

  • c. 26.9, one estimate (from Watson 1990a)
    • Extrapolated from data in one study; assumes adult plumage appears at 7 years of age
  • c. 23 years, according to an earlier estimate (Brown and Cade 1972)

In managed care (from ZIMS 2015)

  • Commonly survive 30-40 years
  • Long-lived
    • Oldest individual > 55 years of age
      • A female housed within various North American zoological facilities

Bateleur in Flight

Bateleur soaring

Bateleur pairs perform complex aerial maneuvers during courtship.

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

Page Citations

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)

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