EPOW - Ecology Picture of the Week

Pigeon Seed-Disperser

Torresian Imperial Pigeon (Ducula spilorrhoa), Family Columbidae
Northern Territory, Australia

Explanation:  This avian denizen of the forest canopy is a Torresian Imperial Pigeon that also goes by the Torres Strait Pigeon as well as quite a list of other common names.  

We are in the area of Palmerston, Northern Territory, in the "Top End" of Australia, in the tropics.  From August to January, the birds will migrate from Papua New Guinea to tropical northern Australia where they nest and raise their chicks.  

Torresian Imperial Pigeons play key ecological roles of seed-dispersal.  One of their primary foods in Australia is the seeds of Carpentaria palm trees (Carpentaria acuminanta) which is endemic to Northern Territory and is grown widely in Australian tropical gardens, according to a local information sign.  The palms produce profusions of bright red berries during the rainy season that are eaten copiously by the pigeons that then widely disperse the seeds as they pass through their gut.  The seeds can then readily germinate, making the pigeon an important ecological agent to maintain the health and distribution of the palm populations.  

  
But the pigeons are not doing well.  The IUCN Red List has marked their populations as Decreasing, even though they are also rated as Least Concern.  Their justification is that populations are suspected to be declining from habitat destruction and from overexploitation for use as food and for the pet trade.  

The local information sign also quotes Ranger Julie Trembath as saying "Some Torres Strait Pigeons [Torresian Imperial Pigeons] no longer migrate because watered gardens provide fruit throughout the Dry [Season]" (also see Noske and Lilleyman 2016).  How this change in migration strategy affects seed dispersal in Australia and in Papua New Guinea as well does not seem to have been studied.  

It is yet another interesting case of how human activities affect wildlife behavior, with unknown secondary effects on the wildlife's key ecological functions.  

    

Information:
     Brothers, N., and C. Bone.  2011.  Torresian Imperial Pigeon Ducula spilorrhoa monitoring, population trends and species suitability as an indicator of environmental changes.  Corella 36(3):69-75.
     Noske, R.A. and A. Lilleyman.  2016.  Partial loss of migratory behaviour by Torresian Imperial-Pigeons 'Ducula spilorrhoa' in Darwin, Northern Territory.  Australian Field Ornithology 33:206-210.