Estimating numbers of birds by point counts: how long should counts last?

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Abstract
The results of point counts using 5, 10, 15 and 20 min periods were compared from 6 habitats in England [UK]. Relationships between length of count and total numbers of birds and species recorded were curvilinear; > 50% were frequently recorded after 5 min., 70% after 10 min. and 87% after 15 min. Registration rates varied between species and some evidence suggested that these rates are of a characteristic form for each bird. Assessed community composition was very similar, whether based on the same number of 5, 10, 15 or 20 min. counts. Count duration had no significant influence on 2 simple measures of community structure. Counts exceeding 10 min. are wasteful of field effort which could be used to improve other aspects of sampling.