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Counting the Emperor

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Population biology has always been a heavy user of statistics. One of its primary assumptions is that we cannot count everything, so we have to select a smaller sample population and extrapolate, using carefully selected parameters, to estimate larger populations. But what if we could count everything? What would this mean in statistical terms and how would we have to change our thinking to accommodate such information?

In 2012 we published the first census of a species from space. Our aim was to estimate the population of emperor penguins (Aptenodytes fosteri) using a single synoptic survey. We examined the whole continental coastline of Antarctica using a combination of medium resolution and Very High Resolution (VHR) satellite imagery to identify emperor penguin colony locations. Where colonies were identified, VHR imagery was obtained in the 2009 breeding season. The remotely-sensed images were then analysed using a supervised classification method to separate penguins from snow, shadow and guano. Actual counts of penguins from eleven ground truthing sites were used to convert these classified areas into numbers of penguins using a robust regression algorithm. We found four new colonies and confirmed the location of three previously suspected sites giving a total number of emperor penguin breeding colonies of 46. We estimated the breeding population of emperor penguins at each colony during 2009 and provide a population estimate of approx. 238,000 breeding pairs (compared with the last previously published count of 135,000–175,000 pairs). Based on published values of the relationship between breeders and nonbreeders, this translates to a total population of ~595,000 adult birds. There is a growing consensus in the literature that global and regional emperor penguin populations will be affected by changing climate, a driver thought to be critical to their future survival. However, a complete understanding is severely limited by the lack of detailed knowledge about much of their ecology, and importantly a poor understanding of their total breeding population. To address the second of these issues, our work now provides a comprehensive, consistent and robust estimate of the total breeding population. Since this survey we have continued to monitor each colony and hope that over the next few years we can publish a total population trend for the species. Most previous studies on emperor penguins have been taken from a single accessible site, our studies of the whole population have led to a number of other important observations about emperor penguins that lead us to question the suitablity of single site studies for this and possibly other species.

This talk is part of the Cambridge Statistics Discussion Group (CSDG) series.

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