Gestational length in the koala, Phascolarctos cinereus.

We report a possible case of extended gestation in the koala, Phascolarctos cinereus. Birth of a pouch young was first observed 127 days after the removal of the male from a multi-female colony at Taronga Zoo. No other males were present at that time or had access to the facility. Head measurements and other growth data collected at the time of detection and over the period of pouch life indicates the time from removal of the male and the date of birth to be between 50 and 77 days. DNA fingerprinting using microsatellite loci unambiguously assigned paternity of the pouch young to this male. These observations suggest either an extended period of gestation of at least 50 days, or activation of a dormant blastocyst from the previous breeding season, as the female entered the period of seasonal oestrus.