Skip to main content
sdzglibrarybanner San Diego Zoo Global Library

Radjah Shelduck (Rajah rajah) Fact Sheet: Behavior & Ecology

Activity Cycle

Day–night patterns

  • During nonbreeding, flocks roost during the day (Marchant and Higgins 1990; Carboneras and Kirwan 2018)
    • Rest on sandbars, mudflats, earth banks, or in trees over water (Marchant and Higgins 1990; Pizzey 2012; Pratt and Beehler 2014)
  • Leave roost in small groups in late afternoon or at dusk; return after dawn (Frith 1967; Marchant and Higgins 1990)
  • Some nocturnal activity (Pizzey 2012)
  • Also see “Daily movements” in Movements and Dispersal

Feeding

  • Feed mainly in the early morning, evening, and at night (Johnsgard 2010a; Carboneras and Kirwan 2018)
  • Also see Feeding

Movements and Dispersal

Daily movements

  • May regularly fly up to 6 km (4 mi), from roosts to preferred feeding areas (Frith [1982] as cited by Carboneras and Kirwan [2018])

Seasonal movements

  • Mainly resident (Phillips 1922; Frith 1967; Shurcliff and McKean 1990; Pizzey 2012; Pratt and Beehler 2014; Carboneras and Kirwan 2018)
    • Not a long-distance migrator (Marchant and Higgins 1990)
    • Seasonally, likely move within, rather than among, river valley systems (Johnsgard 2010a)
  • Northern Australia
    • Wet season: disperse widely (Frith 1967)
      • At end of wet season, occupy breeding territory
    • Dry season: disperse from breeding territories to coastal areas and other habitats where water remains (e.g., coasts, large rivers, permanent inland lagoons) (Royal Australasian Ornithologists Union 1984; Marchant and Higgins 1990; Carboneras and Kirwan 2018)
      • May move southward in search of water (Pizzey 2012)
      • Disperse when seasonal rains begin (Royal Australasian Ornithologists Union 1984)
  • New Guinea (Carboneras and Kirwan 2018, and as noted)
    • Not reported far from breeding range
    • Less commonly, movements between New Guinea and northern Australia
  • Present in small numbers on islands in Torres Strait, year-round (Draffan et al. 1983; Royal Australasian Ornithologists Union 1984; Marchant and Higgins 1990)
    • May indicate nomadic or erratic movements
  • Nomadic movements to Timor and Tanimbar, west to Bali (Carboneras and Kirwan 2018)

Social Behavior

General

  • Strong pair bonds (Johnsgard 2010a)
  • Flocks consist of pairs and family units (Johnsgard 2010a)

Breeding season

  • Found in pairs or small family groups (usually 6 to 8 individuals) (Marchant and Higgins 1990)

Nonbreeding season, dry season

  • Found in pairs and small to large flocks (Marchant and Higgins 1990)
    • Family groups commonly 6 to 8 individuals (Phillips 1922; Frith 1967)
  • May gather in flocks of 20 to 60 individuals; maximum flock size possibly up to 150 to 200 birds but rarely reported (Phillips 1922; Frith 1967; Royal Australasian Ornithologists Union 1984; Marchant and Higgins 1990; Carboneras and Kirwan 2018; White 1917)
  • Flocks often form on rivers or permanent lagoons (Johnsgard 2010a)

New Guinea

  • Pairs or small groups (Pratt and Beehler 2014)
  • Small flocks of up to 40 birds (Carboneras and Kirwan 2018)
    • 150 recorded in New Guinea in 1988

Communication

Vocalizations

  • Very vocal (Carboneras and Kirwan 2018)
    • Call while on land, on water, and in flight (Frith 1967)
    • Group members call and “squabble” before leaving roost for feeding grounds (Frith 1967; Marchant and Higgins 1990)
  • Some sexual dimorphism in call characteristics (Marchant and Higgins 1990; Pratt and Beehler 2014; Carboneras and Kirwan 2018)
    • Display call of male
      • Thin, rattling, hoarse whistles
    • Female response to male’s call
      • Lower pitch
      • Harsh, rattling notes
  • Listen to audio recordings on xeno-canto.org

Visual communication

Agonistic Behavior and Defense

Defense

  • Fly a short distance away (Marchant and Higgins 1990)
    • Settle on shallow water

Aggression

  • This species is described as “quarrelsome” (Pizzey 2012) and “pugnacious” (Frith 1967; Marchant and Higgins 1990)
  • Male not tolerant of other Radjah Ducks at any time of year, according to Marchant and Higgins (1990)
    • More aggressive during breeding

Territorial Behavior

Threat display

  • Male and female codefend a breeding territory (Johnsgard 1965; Marchant and Higgins 1990)
    • Rush toward intruder with feathers raised and neck stretched high
    • Sometimes call loudly
    • May motion with head (head pumping forward and down) and raise folded wings (Inciting Display)
    • Triumph Ceremony follows
  • Also see “Breeding habitat” in Reproduction

Interspecies Interactions

Other water birds

Locomotion

Running

  • Run quickly (Frith 1967; Marchant and Higgins 1990)

Flying

  • Fly slowly (Pratt and Beehler 2014)
  • Strong, maneuverable flier (Frith 1967; Marchant and Higgins 1990)
    • In marsh woodland, often flies low through trees rather than over canopy

Swimming

  • Swims well but infrequently (Marchant and Higgins 1990)

To Fly Among Reeds

Radjah Shelduck during takeoff among green marsh reeds

Radjah Shelducks are strong, maneuverable fliers.

Their agility is most easily seen when watching this duck flying over reed beds and through marsh woodland trees.

Image credit: © Lip Kee Yap via Flickr. Some rights reserved: Creative Commons (CC BY SA 2.0).

SDZG Library Links