To count or to catch: a comparison of two methods of determining wader migration phenology

The phenology of wader migration at a stopover site can be studied using regular counts or systematic trapping, but each method may give different results. This issue is addressed by comparing daily counts and daily trapping at a study site in the mouth of the River Reda, Gulf of Gdańsk, Poland, during autumn migration 1996–2000. The discrepancies in migration patterns obtained by the two methods are not related to either the number of migrants that stopped in the study area, or to the total number of birds caught. It seems that the main drawback of using data from birds caught in walk-in traps is that trapping efficiency may differ not only between years, but also within a season. Therefore catching data, at least from walk-in traps, should only be used with caution in studies of migration phenology in waders.