Some aspects of the ecology of the fairy penguin Eudyptula minor novaehollandiae (Forster) in southern Tasmania

Abstract

Observations of the fairy penguin commenced in 1958 and are continuing intermittently at three sites in Southern Tasmania. Graphs and tables of weights were useful in interpreting the behaviour of breeding birds. Departure weights of fledglings were used as criteria for breeding success. Birds were sexed by cloacal examination, confirmed by dissection when possible. Provisional sexing by accurate measurements and comparisons of bill depths proved 97% reliable with adults and was applied to fledglings. Between 1959 and 1963 at the intensive study area on the Neck connecting North and South Bruny Island, a surplus of females, not evident among fledglings, adversely affected the breeding of many birds. Juveniles displayed, kept company and occupied nests without breeding. Two- and three-year-old birds bred unsuccessfully. Young birds not banded as fledglings were detected by bill size or growth and irregularities in behaviour causing breeding failure. Recoveries from Victoria, Cape Barren Island and South Australia of birds banded as fledglings or suspected juveniles, included one which had bred unsuccessfully seven years earlier on Bruny Island. Four males and eleven females, returning here when over ten years old, included two females which were established breeders thirteen years earlier and therefore aged at least sixteen years. From May t o July the few birds that came ashore collected nesting material, displayed and copulated promiscuously, often in the open. From August onwards displays increased in intensity prior to egg-laying, both sexes participating in fighting and nests being occupied by successive pairs with frequent exchanges of partners. Eggs were laid from September to December and daily observations were essential to determine the birds responsible. Clutches of two eggs were produced within 45 to 96 hours. Most eggs laid late in the season and all second clutches were unsuccessful. No second clutch was produced following breeding success. Successful parents alternated in incubating eggs for 31 .5 to 38.5 days and in guarding chicks for a further 16 to 28 days, then combined to feed them regularly until they departed. Chick mortality was high at 77%. Males delivered more food, but deserted more readily. Feathering necessitated abundant food, shortage causing immediate retardation. The critical period was after banding, when chicks were over 5 to 6 weeks old. Rare cases of adoption of a young chick and feeding of alien fledglings were recorded. Onset of breeding and moulting were correlated. Irrespective of condition, moulting could not be unduly delayed. The process took 15 to 20 days. Breeding pairs often moulted together. Small groups of separate east and west populations occupied different localities on the east and west sides of the Neck study area, with some overlapping and a few east-west matings. The total population gradually declined, due to natural losses, mainly from the pod-chick to the pre-egg period and losses of breeding and non-breeding birds attributable to human agency. The resulting disturbances affected breeding in subsequent seasons and few young west side birds became established, so that by 1972 the west population was nearly non-existent.