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Radjah Shelduck (Rajah rajah) Fact Sheet: Reproduction & Development

Courtship

Mating system

  • Thought to be monogamous (Frith 1967; Carboneras and Kirwan 2018)
    • Probably form life-long pair bonds

Courtship behavior and copulation

  • Male defends female, not allowing “intruders” to approach (Frith 1967)
  • Male displays to female by dipping head into water (Johnsgard 1965; Marchant and Higgins 1990)
  • Copulation occurs on water (Marchant and Higgins 1990)
  • Courtship and postcopulatory behaviors not well known (Marchant and Higgins 1990)

Reproduction

Sexual maturity

  • Not reported for Radjah Shelduck
    • Most likely similar to other shelducks—at about 2 years of age (Johnsgard 2010b)

Breeding range

  • Assumed to breed throughout main range but not well known (Marchant and Higgins 1990)

Breeding season

(observations from Northern Territory)

  • Breeding coincides with end of wet season/early dry season (as floodwaters recede and mudflats become exposed) (Johnsgard 2010a)
    • Increased sexual activity early in wet season (Frith 1967)
    • “Timing and duration…may depend on extent and intensity of wet season” (Marchant and Higgins 1990)
  • Breeding territories established January to February (Frith 1967; Marchant and Higgins 1990)
    • See Breeding habitat, below
  • Clutches laid February to July or later, depending on seasonal rainfall (Frith 1967; Shurcliff and McKean 1990)
    • Peak in May and June (late wet season/early dry season), when more food available (Frith 1967)

Breeding habitat

  • Pair defends a breeding territory (Marchant and Higgins 1990)
    • Contains a nesting site and a feeding area (Johnsgard 2010a)
  • Use freshwater pools, lagoons, and river banks (Marchant and Higgins 1990)
  • Territory size
    • Up to 2.5 to 3.0 km (1.6 to 1.9 mi) long (on rivers) (Royal Australasian Ornithologists Union 1984; Carboneras and Kirwan 2018)
  • May remain in breeding territory during dry season (Marchant and Higgins 1990)

Nesting Behavior

Australia

  • Single pairs nest in hollow cavities of trees, usually in or near water (Le Souëf 1902; Frith 1967; Marchant and Higgins 1990; Pizzey 2012; Carboneras and Kirwan 2018)
    • Both sexes select nest site
    • Nest solitarily, away from other pairs
    • Eggs laid on wood
      • No nest materials, except some down

New Guinea

  • Not yet described (Coates 1985)

Incubation and Hatching

Egg description

  • Shape
    • Oval (Marchant and Higgins 1990)
  • Size
    • 55-61 mm x 39-45 mm (2.2-2.4 in x 1.5-1.8 in) (Frith 1967)
  • Weight
    • About 49.5 g (1.75 oz) (observation from managed care) (Carboneras and Kirwan 2018)
  • Shell (Le Souëf 1902; Frith 1967; Carboneras and Kirwan 2018)
    • Creamy white
    • Smooth
    • Glossy

Incubation and laying

  • Incubation period
    • About 30 days (Phillips 1922)
  • Clutch size
    • About 9 eggs, on average (Carboneras and Kirwan 2018)
    • Precise range unclear
      • 6 to 15 eggs: Carboneras and Kirwan (2018), noting that largest reported clutches may result from “egg dumping” (when a female lays eggs in another pair’s nest)
      • 6 to 12 eggs: Frith (1967)
      • 4 to 11 eggs: Le Souëf (1902)
  • Timing of laying influenced by geography and seasonal rainfall (Carboneras and Kirwan 2018)
    • Western Australia (e.g., Northern Territory): February to March
    • Eastern Australia (e.g., northern Queensland): November to January
    • Near Darwin: March to July

Duckling description

  • Distinctive appearance (compared to other shelduck young) (Johnsgard 1965)
  • Plumage (Marchant and Higgins 1990; Carboneras and Kirwan 2018)
    • Head
      • Crown chestnut brown
      • Areas below eye white
    • Neck
      • Foreneck white
      • Nape of neck brown
    • Upperbody
      • Dark brown with white patches
    • Underbody
      • White, except for backs of thighs
  • Bill, legs, and feet (Carboneras and Kirwan 2018)
    • Pink

Parental Care

Prior to hatching

  • Female incubates eggs (Marchant and Higgins 1990; Carboneras and Kirwan 2018)
  • Male guards female and nest (Carboneras and Kirwan 2018)

After hatching

  • Both parents defend young (Marchant and Higgins 1990)
  • If water present in breeding territory during dry season, family group remains there until the next breeding season (Frith 1967)
  • If water sources in breeding territory dry up during the dry season, family group moves to remaining bodies of water (Frith 1967)
    • Broods of several families may join together (Carboneras and Kirwan 2018)
      • Observations of adults with up to 23 young (Marchant and Higgins 1990)
      • May remain together at start of the following wet season (Carboneras and Kirwan 2018)
  • Parents remain with young until fully fledged (Marchant and Higgins 1990)
    • Age at fledging not reported (Marchant and Higgins 1990; Carboneras and Kirwan 2018)

Longevity

In the wild

  • Not reported (Carboneras and Kirwan 2018)
    • Common Shelduck (Tadorna tadorna) reported to live up to 25 years (Fransson et al. 2017)
      • Based on European bird ringing studies

In managed care

  • About 12 to 15 years in clean conditions (ZIMS 2018; Phoebe Vaughan, personal communication, 2018)

Mortality and Health

Survival rates

  • Breeding success
    • Not reported (Carboneras and Kirwan 2018)
  • Adult survival
    • Not reported (Carboneras and Kirwan 2018)

Predators

  • Reported
    • Crocodile, Crocodilus porosus (northern Australia) (Carboneras and Kirwan 2018)
    • Dingo, Canis dingo (northern Australia) (Carboneras and Kirwan 2018)
  • Other likely predators (John McEvoy, personal communication, 2019)
    • Red fox, Vulpes vulpes (eastern/northeastern Australia)
    • Feral cats

Family Group

Radjah Shelduck with ducklings

Breeding Radjah Shelducks are thought to form strong lifelong pair-bonds.

Both parents care for and defend their young until fledging.

Image credit: © Hayley Alexander via Macaulay Library at the Cornell Lab of Ornithology (asset #ML108129611). Some rights reserved.

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