The reproductive ecology of Palm Cockatoos, Pesquets Parrots, and Eclectus Parrots in the southern Watershed of Papua New Guinea
A project undertaken at the Centre for Resource and Environmental Studies, Australian National University, and implemented by R Heinsohn
Paul Igag, a Papuan from Madang province, has worked on the conservation biology of various species at Crater Mountain, PNG, since 1999 with the support of the Wildlife Conservation Society (New York). With generous support from the Pacific Biological Foundation, he came to the Australian National University in 2001 to study for a Masters degree under the supervision of Rob Heinsohn and Sarah Legge. The aim of Pauls research was to outline the breeding biology and likely causes of threat to three species of large parrot found in the New Guinea rainforest. Palm Cockatoos (Probosciger aterrimus) and Pesquets Parrots (Psittrichus fulgidus) are threatened by over-exploitation for food and the thriving trade in their feathers, and along with Eclectus Parrots (Eclectus roratus) are threatened by loss of habitat. Eclectus Parrots are more abundant and less threatened from hunting, and provide a good comparison for the other two species.
Pauls research had the additional interest of the close involvement of traditional people whose life-styles have changed dramatically in recent times. By training 23 traditional land-owners as research assistants, Paul was able to monitor the breeding efforts and reproductive success at 51 Palm Cockatoo, 71 Eclectus Parrot and 34 Pesquets Parrot nest trees for 28 months over his 2645 ha study site. Some retrospective information was also attained from local people who knew about nest trees prior to the study. Only Palm Cockatoos and Pesquet's Parrots showed overlap in the types of trees they used for nesting (3/10 tree families). The three parrot species differed significantly in every quantitative physical characteristic of the nest trees and hollows measured. Palm Cockatoo hollows tended to be in the skywards-facing end of a broken, dead trunk. Pesquet's parrots were the only species to entirely excavate their own hollows; they used the trunks of dead trees, but their hollows had entrances that opened horizontally. Eclectus parrot hollows were in taller live trees and had entrance sites and aspects that were more varied than the other two species.
The density of Palm Cockatoo nest trees averaged 0.06 nest trees/ha, but the annual density of active nests was only 0.008/ha. The density of Eclectus Parrot nest hollows averaged 0.069/ha, but the density of active hollows each year was 0.023/ha. Pesquet's Parrots create new nests each year and the annual density of these was 0.017 nests/ha. Eclectus Parrots tended to nest closer to human settlements than either palm cockatoos or Pesquets Parrots. Palm Cockatoos appear to breed seasonally, with eggs being laid between June and October. Pesquet's Parrots showed similar seasonality. In contrast, Eclectus Parrots occupied their nests and bred all year. In any one year one-sixth of all potential Palm Cockatoo nest trees were actually used for breeding, whereas Eclectus Parrot nests were active more than once per year on average. Similar figures for Pesquet's Parrots were not available.
Palm Cockatoos always lay one egg, Pesquets Parrots lay one or two eggs, and Eclectus Parrots usually lay two eggs. Eclectus Parrots were the most successful at fledging young - 54% of all eggs laid (in 66% of broods) resulted in a fledgling. This compares to 40% in Palm Cockatoos and 17% (in 20% of broods) in Pesquet's Parrots. Whereas most losses in Palm Cockatoos and Eclectus Parrots were due to predation, Pesquets Parrots appeared to continue to lose even large chicks through starvation. Paul concluded that the major life-history traits that render Palm Cockatoos vulnerable are their low density of nest trees and infrequent breeding, whereas Pesquet's Parrots appear to be most affected by low reproductive success per breeding attempt.
Paul Igags research is presently in the form of a Masters thesis in the Faculty of Science, Australian National University, but is also being prepared for publication. For further information contact Rob Heinsohn, CRES, ANU, email: Robert.Heinsohn@anu.edu.au, http://cres.anu.edu.au/~heinsohn/