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ORAL ABSTRACT Do penguins play leap-frog? Niche partitioning in Adélie and Chinstrap penguins: the roles of allochrony and phase-dependent foraging ranges Harriet Clewlow1, Norman Ratcliffe1, Mike Dunn1, Stacey Adlard1, Steve Votier2, Rod Downie3, Akinori Takahashi4 1 British Antarctic Survey, 2University of Exeter, 3WWF, 4National Institute of Polar Research Japan Ecological theory states that closely related species with similar ecological requirements, occupying the same fundamental niche will display niche partitioning in areas of overlap to reduce competition. Sympatrically breeding congeneric seabirds commonly display allochrony (differences in timing of breeding) and this, in combination with phase-dependant variability in foraging trip duration, can lead to spatiotemporal segregation of species by foraging areas. This causes birds to “leap-frog” one another in time and space to exploit distinct spatial niches as the season progresses. Seabird phenology is sensitive to temperature change but species do not always respond to the same degree. Therefore, if the timing of breeding of one species advances at a different rate to that of its competitor niche overlap may increase, leading to synchronous breeding, increased inter-specific competition and population declines in one or both species. Alternatively if both species advance their phenology at similar rates, thus preserving allochrony, then niche partitioning and the level of competition experienced will be unaffected. Adélie and Chinstrap penguins have similar foraging ecology in terms of diet, dive depths and phasedependent foraging ranges. Allochrony is therefore likely to be important in reducing competition between these species. This leads us to formulate the following hypotheses: a. Adélie and Chinstrap penguins show phase-dependent foraging distributions b. Allochrony causes “leap-frogging” of foraging areas c. Breeding synchronisation would substantially increase niche overlap d. Phenology of the two species will advance in parallel due to climate change as competition will be an important selective force in preserving allochrony Data was collected at Signy Island, South Orkneys during breeding seasons from 1999 to 2015. Penguins were fitted with rapid-acquisition GPS, (43 Adélie and 52 Chinstrap), or PTT tags, (50 Adélie and 75 Chinstrap; tag type year dependant). Phases were defined as incubation (~33days), guard (~22 days) and crèche (~25 days). Foraging paths will be modelled in the ‘R’ package CRAWL, which accounts for ARGOS errors and uncertainty in the path the bird followed between fixes. Species- and phase-specific foraging areas will be determined and overlaps assessed, both on the basis of the observed level of allochrony and on the assumption of complete synchrony due to climate change, to quantify the degree of niche partitioning that allochrony induces. ANCOVA will be used to model species-specific relationships between hatching dates and temperature to determine whether their phenology advances in parallel or interactively and quantify the change in competition future warming scenarios may produce. 9th International Penguin Congress, Cape Town, South Africa, 5th – 9th September 2016