Koala birth seasonally and sex ratios across multiple sites in Queensland, Australia
William Ellis,* Fred Bercovitch, Sean Fitz Gibbon, Alistair Melzer, Diedre de Villiers, and David Dique
San Diego Zoo's Institute for Conservation Research, Zoological Society of San Diego, 15600 San Pasqual Valley Road, Escondido, CA 92027-7000, USA (WE, FB)
Centre for Mined Land Rehabilitation, The University of Queensland, St. Lucia, Queensland, 4072, Australia (WE, SF)
School of Integrative Biology, The University of Queensland, St. Lucia, Queensland, 4072, Australia (WE, SF)
Koala Research Centre of Central Queensland, Central Queensland University, Rockhampton, Queensland, 4702, Australia (WE, AM)
Koala Research Unit, Queensland Environmental Protection Agency, Brisbane, Queensland, 4000, Australia (DDV) GHD Pty. Ltd., G.P.O. Box 668, Brisbane, Queensland, 4000, Australia (DD)
Establishing accurate demographic information for free-ranging populations of animals is difficult without knowledge of individual chronological age. We estimated the birth dates of 743 koala (Phascolarctos cinereus) joeys at 3 sites in Queensland, Australia, using body mass obtained from a reference population with known birth dates. From these age estimates we compared the annual distribution of births across calendar months. At all 3 locations about 60% of births occurred between December and March. The annual pattern of births was identical for males and females within locations, but overall annual patterns of births differed between the southern and northern sites. We conclude that koalas can bear offspring in every month of the year, but breed seasonally across Australia, and that a sex bias in the timing of births is absent from most regions.