Biased sampling of birds by mist nets

A review of the literature identified 21 causes of bias in mist-net catches of birds. In some cases there is strong evidence of the existence of bias and some quantification of its magnitude, but most causes of bias have not been investigated in detail. Researchers using mist nets as a tool to sample birds should assume that catch data they obtain will be subject to biases and should evaluate these effects carefully to avoid misinterpretation of results. Particular consideration should be given to birds learning to avoid mist nets after experience of capture, to effects of lures, species-specific flight-height distributions, net type, bird size and morphology, net-visiting protocol and influences of artificial feeding. There is considerable scope, and an urgent need, for studies that identify these biases, the extent to which they are species-specific, and their magnitude. Such studies would greatly help in the interpretation of mist-net catch data, which is of key importance in many ornithological research programmes.