Reliability of animal counts and implications for the interpretation of trends.

Accordingly, we found that it is most challenging to detect the direction of a slight trend (sensu Wauchope et al., 2019 ) when temporal changes in observers occur (Table S1 ).

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Indeed, a greater frequency of observer change gradually increased the period necessary to detect a significant trend, and decreased the precision of estimated trends for a given monitoring duration, although the direction of the trend was generally adequately detected (See also supporting 1).

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