European Storm-petrels are pelagic, returning to land only to breed, and choose to nest on remote offshore islands where nocturnal access is often difficult and dangerous. They nest below ground, appearing above ground only during darkness and are much more widespread in Britain and Ireland than Manx Shearwaters and Leach's Storm-petrels. These characteristics of European Storm-petrel behaviour and distribution have meant that obtaining accurate estimates of breeding numbers has been virtually impossible. Consequently, both Operation Seafarer and the SCR Census had largely to guess at the location of many colonies, let alone make an accurate estimate of size.

 

The results of Seabird 2000 represent the first accurate baseline estimate of the number of European Storm-petrels breeding in Britain and Ireland. A method called tape playback was used to survey apparently occupied sites (AOS) of breeding European Storm-petrels. The method involves playing calls of European Storm-petrels to elicit a response from adults hidden in burrows during the day whilst incubating. Unfortunately not all Storm-petrels present at a colony will respond to taped calls, thus counts of responses underestimate the number of AOSs and have to be adjusted by a response rate measured at the colony.

 

Evidence of possible or probable breeding obtained during Operation Seafarer and SCR Census and from other sources was used as a basis for selection of sites to survey during Seabird 2000. However of the 164 islands that were surveyed for European Storm-petrels during Seabird 2000, breeding had not previously been confirmed or suspected on 98 islands. Surveys were not possible on 17 islands where breeding was either confirmed or suspected during the last 30 years and on a further eight where breeding had been suggested from historical records prior to 1969. It is highly unlikely that any substantial colonies (i.e. greater than 100 pairs) were missed. In Ireland, 16 island colonies were surveyed and breeding was confirmed on a further four islands where a rough estimate of AOS was made, based on the density of AOS on nearby islands and the area of suitable habitat. There are a further 31 sites where Storm-petrels were either proved or strongly suspected to be breeding in the past but not surveyed during Seabird 2000. Breeding had previously been confirmed at 16 of these and rough population estimates were available for ten, which were added to the Seabird 2000 playback survey results to provide a total estimate of AOS for Ireland. The estimated colonies accounted for 40% of the total population in Ireland. It is highly unlikely that any other substantial colonies (i.e. greater than 100 pairs) were missed.

 

Census Methods     Data Processing and Analysis     References     Seabird 2000