Foraging strategies and breeding success in the Little Penguin, Eudyptula minor : a comparative study between different habitats
Little Penguins breeding at different locations in New Zealand exhibit great differences in breeding success which is likely to be related to different foraging strategies. During the 2000/2001 breeding season, foraging behaviour and breeding success of Little Penguins Eudyptula minor were examined at Motuara Island, Marlborough Sounds, and Oamaru, North Otago. To determine breeding success parameters and chick growth, 64 nests on Motuara Island and 87 nests at Oamaru were checked daily. On Motuara Island an average of0.71 chicks fledged per pair, which was significantly lower than the 1.44 chicks per pair recorded at Oamaru. Breeding failure on Motuara Island was generally related to weather conditions or chick starvation and appeared during two distinct periods. At Oamaru, predation was the main mortality factor. VHF-telemetry ('Radio tracking') was used to determine foraging ranges and at-sea behaviour of penguins equipped with streamlined transmitter packs. Motuara Island penguins rarely left the Queen Charlotte Sound on one-day trips, staying close to the Island (maximum distance to colony or foraging radius< 9 km) and travelling relatively short distances (mean= 24.4 km). Birds that did leave the Sound generally stayed away for at least 2 days (long-term trip). In contrast, Oamaru penguins showed a much wider foraging range (foraging radius< 30 km) and travelled greater distances (mean= 57.4 km) during one-day trips. At Motuara Island, long-term trips occurred during incubation and chick rearing, but at Oarnaru, penguins did not make long-term trips(> 1 day) after the chicks hatched. Five birds on Motuara Island and 6 birds at Oamaru were equipped with time-depth recorders (TDRs) to investigate diving performance. Compared to Oamaru, penguins from Motuara Island showed a greater number of dives per trip (mean number of dives 1165 vs. 809), dived significantly deeper (mean depth 10.1 vs. 6.0 m) and longer (mean dive duration 29.5 vs. 22.4 seconds). Comparison of dive parameters suggest that penguins from Motuara Island search for prey in greater parts of the water column (depths <26 m) than penguins at Oamaru (depths <14 m). The main factors influencing the foraging behaviour of Motuara Island penguins are probably temporary variations in prey availability and foraging restrictions by topographic features of Queen Charlotte Sound. Oamaru penguins have a much wider area in which to forage: environmental constraints (bathymetry, coastal topography) seem to have little effect on breeding success and foraging behaviour is probably determined mainly by prey distribution.
Advisor: Davis, Lloyd S. (Otago); Culik, Boris M. (Kiel)
Degree Name: Master of Science
Degree Discipline: Zoology
Publisher: University of Otago
Research Type: Thesis