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Breeding success and foraging ranges of blue penguins from Motuara Island/Marlborough Sounds and Oamaru/North Otago were examined during the breeding season 2000/2001. We examined 64 nests on Motuara Island and 87 nests at Oamaru. Breeding success parameters and chick growth were determined. Breeding success differed significantly between sites. Oamaru penguins raised 1.44 fledged chicks per pair compared with 0.71 on Motuara Island. Breeding failure on Motuara Island was generally related to chick starvation and nest desertions by adults, whereas at Oamaru, predation was the main mortality factor. Differences between the two sites were directly related to adult foraging strategies. We used VHF-telemetry to determine foraging routes and ranges of penguins equipped with streamlined transmitter packs. On Motuara Island we tracked penguins on 11 one-day-trips and five partial long-term trips (>2 days). At Oamaru penguins were tracked on 16 one-day trips and four longterm trips. Differences in foraging patterns between the populations were apparent. Motuara penguins rarely left the Queen Charlotte Sound on one-daytrips, stayed close to the Island (mean foraging range <6 km). Birds leaving the Sound on longterm trips generally stayed away for at least 2 days. Some adults undertook long-term trips during chick rearing. The main factors influencing the foraging behaviour of Motuara Island penguins seemed to be time dependent variations in prey availability and foraging restrictions by topographic features of Queen Charlotte Sound.