Breeding biology and feeding ecology of little penguins Eudyptula minor at Phillip Island – a basis for a monitoring program

This research examined the breeding performance of little penguins (Eudyptula minor) at Phillip Island in south east Australia. A major goal was to relate breeding success to fluctuations in food availability within and between seasons. Data was collected on nest attendance patterns, pair bonding, chick growth rates, chick meal mass, adult time budget and diet. Sampling extended over two reproductive seasons, one with good and other with poor reproductive success. Implanted identification transponders combined with an automated penguin monitoring system were used to determine daily nest attendance. Successful breeders had shorter incubation shifts and undertook more foraging trips than failed breeders during both incubation and chick guard periods. The later a little penguin started to breed the poorer was its breeding performance. Males guarded their partners throughout the pre-egg periods but left their females as soon as the first egg was laid. Observations of the penguin pairs in their burrows showed that they had different partners on 33% of the recorded occasions. This was used as an indication of extra-pair copulation during the pre-egg period. Changing partners and burrows between seasons decreased reproductive success. Inter-seasonal divorce rate was 28%, one of the highest amongst penguins, even though evidence suggests that divorce behaviour has no obvious benefit for little penguins. During chick rearing, four fish species comprised 93% of the penguins’ diet. These species were red cod Pseudophycis bachus, barracouta Thyrsites atun, warehou Seriolella brama and anchovy Engraulis australis. Mean meal mass decreased as the breeding season progressed while foraging trip duration increased. Birds kept the length of their foraging trips below two days during the good season. During the bad season birds foraged longer than two days right from the beginning of the post guard. Compared with successful breeders from the bad season, successful breeders from the good season guarded their chicks for 6 days longer, had a post-guard that was 9 days shorter and their chicks grew faster. Little penguins exhibited substantial temporal and seasonal variation in their time budget and foraging performance. The variation was used to identify whether differences in breeding performance and food availability were related to natural causes or to commercial fishing activities. As the stock biomass is unknown for most of the commercial fishery in Victorian waters, it is difficult to prove the existence of detrimental effects of fishery on the food supply for the penguins. There was evidence, however, that fishery may impact on the penguin foraging performance. The little penguins from Phillip Island consumed almost the same amount of fish as was caught by commercial fisheries in Victoria. Pilchards and anchovies have decreased dramatically in importance in the penguin diet while the commercial catches of these fish have increased progressively. This suggests that there might be competition between penguin feeding and commercial fishing