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

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)

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)

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)

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

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)

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)

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

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.