Abstract
Despite the threats faced by seabirds in both terrestrial and marine habitats, even basic knowledge of the locations of colonies, population sizes and trends is lacking for many remote areas of the world. Recent studies have shown that the guano of Adelie penguins can be identified from Landsat Enhanced Thematic Mapper (ETM) imagery and used to map colonies on coasts around continental Antarctica. Our study highlights a new technique based on the unique spectral signature of guano that can be used to discriminate seabird colonies from background geology and vegetation in a wider range of natural environments, including the vegetated and zoologically-diverse region of the Antarctic Peninsula; moreover, the method was effective for all densely colonial, surface-nesting seabirds. Using Landsat ETM imagery, we correctly identified all known seabird colonies of over 50 pairs in the area of Marguerite Bay. Almost all other areas with a similar spectral signature that were outside known breeding areas were single pixels that were readily distinguishable from genuine colonies. If these were excluded, only 4.1% of pixels appeared to represent unknown breeding or roosting sites, and warrant further investigation. The spatial extent of the guano provided a general guide to the number of individuals present, but further work would be required to determine the accuracy of this method for estimating population size. Spectral profiles of guano collected by satellite and hand-held spectrometers were compared with available data in spectral libraries and did not match with any known geological profile. There may also be potential for discriminating colonies of different species that differ in phenology and show seasonal changes in diet by the carefully-timed acquisition of suitable satellite imagery. We conclude that the remotely-sensed guano signature is a good indicator of the location of seabird breeding or roosting sites, with potentially wide application to other areas of the world.
Highlights
According to the Red List index compiled by the World Conservation Union (IUCN), the conservation status of seabirds has deteriorated more rapidly than any other species group since 1988, with 28% of species currently listed as Threatened, of which 5% are considered to be Critically Endangered (Croxall et al, 2012)
Our results show a close match between the location of known seabird breeding colonies or, in a few cases, probable roosting aggregations, and the pixels highlighted by the SAM analysis
The two colonies that were not identified in our analysis were both of Antarctic shags. This species feed predominantly on fish rather than krill and it may be that the different diet affects the spectral profile of the guano
Summary
According to the Red List index compiled by the World Conservation Union (IUCN), the conservation status of seabirds has deteriorated more rapidly than any other species group since 1988, with 28% of species currently listed as Threatened, of which 5% are considered to be Critically Endangered (Croxall et al, 2012). Of the world even basic knowledge of breeding site locations, population sizes and trends of many seabird species is sparse (Brooke, 2001). This includes Antarctica where projected changes in sea ice extent and duration are predicted to have major impacts on food webs (Ainley et al, 2010; Barbraud et al, 2011), potentially exacerbated by an increase in fisheries for Antarctic krill Euphausia superba, which is a key prey for many seabirds, including penguins and petrels (Watters, Hill, Hinke, Matthews, & Reid, 2013). The breeding locations of only around 500,000 pairs (i.e. 1 million breeders) are known (van Franeker, Gavrilo, Mehlum, Veit, & Woehler, 1999), probably under a quarter of the estimated total
Sign-in/Register to view highlights & summary 
Published Version
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call