Improving census methods for nocturnal burrow nesting seabirds

Britain and Ireland are home to the most of the world’s Manx shearwaters and European storm petrels, so we have a huge international responsibility to safeguard the future of these species. However, they breed on islands, nest in holes and only come out at night, which mean that obtaining accurate assessments of the size of breeding populations in challenging. We have limited ability to detect declines, or to chart recovery following our island restoration work.

Current census methods rely on detecting birds calling from their burrows in response to playback of recordings of the species’ calls. Concern has been expressed over the accuracy, precision and efficiency of these “playback” methods. Even when nests are known to be occupied, response rates are typically low, gender specific and are known to vary among colonies and years. The method is very labour intensive, and for colonies with large areas of nesting habitat, a sampling approach is necessary, which often leads to large confidence limits and low power to detect changes in population size.

This project seeks to improve existing playback methods and evaluate novel approaches emerging from advances in technology such as infra-red imaging, which may offer more cost-efficient and precise approaches.

• Improve existing playback methods for Manx shearwater.
• Develop a novel method based on infra-red filming of nocturnal flight activity for European storm-petrels. 
• Conduct field trials to assess the precision and accuracy of the new techniques in direct comparison with existing methods.
• Make recommendations on the methods to be implemented for the upcoming seabird census, ensuring that backwards compatibility is maintained.

 

• 2014: Project start - storm petrel fieldwork.
• 2015: Fieldwork on Manx shearwaters.
• 2016: Data analysis and writing of papers.
• 2017: Publication of papers with recommendation for future census methods.

The results are soon to be published and recommendations will be fed into the Seabird Monitoring Programme.

The research project is now completed.

Experiments carried out in Manx shearwater colonies on Rum and on Ramsey conclusively demonstrated a simple modification to the playback procedure substantially increased the response rate from breeding birds. Whilst it has been known for many years that response rates are gender specific, playback surveys to date have used recordings of males only, to which females seldom respond. The use of recordings which contained calls of both males and females did not take any longer to conduct, but generated significantly higher levels of response. As a result, the precision of survey estimates was increased by up to 50 per cent.

The use of infra-red (IR) imaging to monitor flight activity and nest visits by storm petrels at RSPB Mousa reserve showed IR filming was more reliable than conventional playback methods for sub-colonies where birds breed in natural habitat such as boulder fields. However, IR filming did not work as well where birds were nesting in stone walls. IR filming may offer significant advantages over playback methods where birds are nesting solely in natural habitat, especially where direct access problematical due to safety concerns, such as steep unstable slopes. However, the equipment used for this project proved heavy and cumbersome.

• Scottish Natural Heritage

• Scottish Natural Heritage