Sub-populations within species can exhibit differing population growth trajectories in relation to one another depending on various environmental factors. In threatened species, negative population growth in some sub-populations can ultimately cause the demise of the species; therefore, understanding causal factors of population change is critical to inform management aimed at reversing population declines. Feral house cats Felis catus are potential predators of Endangered yellow-eyed penguins Megadyptes antipodes and were considered the principal causal factor in the species' decline on Stewart Island/Rakiura, New Zealand. The number of yellow-eyed penguins breeding on Stewart Island is low relative to the number on close outlying islands, where cats are absent, and a census had recorded few juveniles on Stewart Island, suggesting poor reproductive success. Yellow-eyed penguin breeding attempts on the northern coast of Stewart Island and outlying islands were monitored for 5 yr, but predation by cats was not evident. Instead, disease, probably aggravated by starvation and poor dietary provisioning, was found to be a significant cause of chick mortality on Stewart Island. Reproductive success was consistently low there (0−33%), in contrast to outlying islands (27−76%). Little recruitment was recorded on Stewart Island, and the number of breeding pairs on the northern coast of Stewart Island declined by 27% between 1999 and 2008. Factors unique to the north coast of Stewart Island are believed to be adversely affecting nesting yellow-eyed penguins, as a similar decline was not recorded elsewhere on the island or on outlying islands.KEY WORDS: Megadyptes antipodes · Feral cat · Population decline · Breeding success · Chick mortality · Starvation · Disease · 'Junk-food' hypothesis Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 467: [233][234][235][236][237][238][239][240][241][242][243][244] 2012 ited distribution (IUCN 2008) and decreasing numbers (ca. 1600 to 1800 pairs, D. Houston pers. comm.). It is a tall, distinctive, penguin of a monotypic genus and species, endemic to the southern South Island and Stewart Island/Rakiura, New Zealand, and its sub-Antarctic islands (Marchant & Higgins 1990; our Fig. 1). Approximately 600 to 700 pairs breed in loose colonies around southern New Zealand, which are both geographically and genetically distinct from their sub-Antarctic conspecifics (Boessenkool et al. 2009). Most breeding areas in the southern South Island are monitored each year, and the population estimate for these areas (470 pairs) is considered reasonably accurate. Historical estimates for Stewart Island have varied from 470 to 600 pairs (McKinlay 2001) to 220 to 392 pairs (Darby 2003), while a recent survey found 178 pairs (Massaro & Blair 2003), suggesting a decline. Factors known to contribute to population decline in yelloweyed penguins include fishery by-catch (Darby & Dawson 2000) and human disturbance (Ellenberg et al. 2007), although dise...

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1. Understanding the ecological and evolutionary processes that occur during range shift or (re-)colonization is of critical importance for species whose ranges are changing due to human-induced climate change or species such as New Zealand sea lions where their established colonies are significantly declining due to human impacts.2. The mechanisms underlying colonization are poorly understood. Observations are required to determine the processes that change individual's behaviour associated with colonization, but such observations are rare.3. Here, the establishment of a new breeding colony of New Zealand sea lions, Phocarctos hookeri, as they recolonized mainland New Zealand, an area from which they had been absent for 200 years was investigated.4. There are differences in breeding location behaviour and population connectivity between established and establishing colonies of New Zealand sea lions. The recolonizing population is more dispersed with breeding locations that change annually and have more connections with other populations compared with established colonies and populations.5. The establishment of a new colony and the greater numbers of resightings between colonies means that for species' management, considerably more public education, habitat management, and protection is needed to ensure the safe return of New Zealand sea lions back on to mainland New Zealand.