Method learning caused a first-time observer effect in a newly started breeding bird survey

摘要

Capsule A first-time observer effect in the new French breeding bird survey (BBS) was found to result from new observers learning how to use the point count method on randomly selected sites.Aims To estimate the first-year effect in a newly started BBS, to look for correlates and test for a temporal trend in learning.Methods Trends of 105 species were estimated using data from 2001-2007 obtained by I 100 observers conducting point counts over 1535 randomly selected squares. I estimated the average increase in detected numbers between the first and all subsequent years of survey at a site.Results Observers counted 4.3% more birds in subsequent years than during the initial year of survey. This first-year effect decreased from 2001 to 2007 (by an average of 2% per year). It was not related to most variables known to influence species defection probability. Only species with songs of lower sound frequencies (ranging from 0.5 to 8 kHz here) displayed a greater increase in locally detected numbers.Conclusion The detected first-year effect was the result of method learning by new observers who had not previously conducted point counts or visited randomly selected sites. The learning effect was larger for species with songs of lower sound frequency which are harder to hear during the dawn chorus.