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Chris Perrins (Edward Grey Institute of Field Ornithology, University of Oxford, UK) and colleagues writing in the annual journal Seabird of the [UK] Seabird Group have used tape playback in sample plots to estimate the breeding population of Manx Shearwaters Puffinus puffinus on the Welsh island of Skomer in 2011.

The paper’s abstract follows:

“Skomer Island, Pembrokeshire, Wales is believed to have one of the largest colonies of Manx Shearwaters Puffinus puffinus in the World.  In 1998 a census was made of the whole island, and the adjacent islands of Skokholm and Middleholm, in order to try to establish the size of the breeding population; the Skomer population was estimated to be just over 101,000 breeding pairs.  A second census was carried out in 2011.  First, a set of study burrows was opened and a tape of the male call (normally only males respond to these) was played down each burrow several times during the course of incubation in order to establish the male response rate.  Then the same tape was played down all the burrows in each of 288 randomly selected plots across the island and the number of responses recorded.  Extrapolating response form census plots to the whole island yielded an estimate of 1125,112 (CI ± 16,445) responses.  Adjusting this figure to take account of the response yielded an estimate of 316,070 (SE ± 41,767) breeding pairs.  This figure is greatly in excess of the estimate made just 13 years earlier. Possible reasons for this are discussed.”

Reference:

Perrins, C.M., Wood, M.J., Garroway, C.J., Boyle, D., Oakes, N., Revera, R., Collins, P. & Taylor, C. 2012.  A whole-island census of the Manx Shearwaters breeding on Skomer Island in 2011.  Seabird 25: 1-13.

Note Volume 25 of Seabird is not yet available on line. Click here to access most of the earlier earlier volumes of the journal.

John Cooper, ACAP Information Officer, 5 January 2013