A survey of Leach’s Petrel Oceanodroma leucorhoa on North Rona, Western Isles, Scotland in 2015

Abstract

Comparable surveys have been made of the Leach’s Storm-petrel Oceanodroma leucorhoa colony on North Rona, Western Isles, Scotland in 2001, 2009 and 2015 using responses to tape recordings played at burrow entrances. Response rates estimated from a calibration plot were used to correct the total number of responses to tape playback from an island-wide survey. A ‘simple arithmetic’ method of calculating the population estimate suggested 606 apparently occupied burrows (AOB) for 2015, which is the lowest number to date and represents a c.15% decline since the last survey in 2009, when 713 AOB were found. In 2001 there were 1,084 AOB, giving an overall decline of 44% since this first survey. The ‘first response’ method, which only makes use of the first response from each burrow in the calibration plot, is designed to avoid potential bias, caused either by habituation or by very vocal individuals. As this suggests a population of 805 AOB there is a need to be cautious about inferring a further island wide decline since 2009.