Shape can influence the rate of colony fragmentation in ground nesting seabirds

There have been catastrophic population declines at a number of rockhopper penguin Eudyptes chrysocome rookeries over the past 50 years or so. At Campbell Island, New Zealand, large contiguous rookeries have fragmented into much smaller subcolonies and although the underlying cause of the major part decline was possibly diet related, it seems likely that predation may be having an increasingly important impact. In an extension of selfish herd ideas, we hypothesised that since predation and colony contraction are edge related, the initial shape of the colony may play an important role in how quickly it might fragment and in turn how long it might persist. Intuition tells us that fragmentation is likely to occur on these smaller subcolonies and that their shape will likely affect their rate of fragmentation. We provide the first quantitative assessment of this qualitative theory of fragmentation risk as a function of colony shape for a range of hypothetical colonies.