Evaluation of two observational methods to assess the numbers of nesting puffins (Fratercula arctica)

Accurate monitoring of population numbers is essential for conservation. Large numbers, dense flora, camouflage or inaccessible landscapes make counting individuals difficult or near impossible. This study compared two population count methods for puffins nesting in on steep cliffs. To estimate numbers in a colony, Apparently Occupied Burrows (AOB) are counted by the observation of adult birds returning with fish in their beaks and disappearing into the burrows (Joint Nature Conservation Committee, 2015). This study compared continuous counts via binoculars with the count obtained via a time-laps camera (one photo every 10 seconds) to help future estimates to be more accurate and provide a scientific method for the national census. The study was carried out on Lundy Island (51N, 04W) in the Bristol Channel, UK. Total counts of puffins present in the observation area were done at the beginning of each session, and then again every 30 minutes, both via binoculars and from still photos. The total camera bird count ranged from two to 39, for the live observation from zero to 45. The count of the AOBs via the photos ranged from five to 19, for the live count from one to 15. The camera count of the AOBs was always higher than the count via binoculars, by an average factor of 1.75. The difference between the two observers was smaller than the difference between the camera count and the observers. The differences in bird numbers between all three counts were significant. The observers’ bird counts did not show a trend to over- or underestimate total numbers. Both observational techniques were affected by weather conditions and visibility. Counting occupied nest sites by camera is more accurate than by live observation via binoculars. For overall numbers of birds the trend was inconclusive.