title: Limited catching bias in a wild population of birds with near-complete census information.
abstract: Animal research often relies on catching wild animals; however, individuals may have different trappability, and this can generate bias. We studied bias in mist netting, the main method for catching wild birds. The unusually high resighting rate in our study population-house sparrows (Passer domesticus) on Lundy Island (England)-allowed us to obtain accurate estimates of the population size. This unique situation enabled us to test for catching bias in mist netting using deviations from the expected Poisson distribution. There was no evidence that a fraction of the birds in the population consistently remained uncaught. However, we detected a different bias: More birds than expected were captured only once within a year. This bias probably resulted from a mixture of fieldworkers sometimes ignoring rapid recaptures and birds becoming net shy after their first capture. We had sufficient statistical power with the available data to detect a substantial uncaught fraction. Therefore, our data are probably unbiased toward catching specific individuals from our population. Our analyses demonstrate that intensively monitored natural insular populations, in which population size can be estimated precisely, provide the potential to address important unanswered questions without concerns about a fraction of the population remaining uncaught. Our approach can help researchers to test for catching bias in closely monitored wild populations for which reliable estimates of population size and dispersal are available.
authors.affiliation: Department of Animal and Plant Sciences, University of Sheffield Sheffield, S10 2TN, UK.
authors.forename: Mirre J P
authors.initials: MJ
authors.lastname: Simons
authors.affiliation: Department of Animal and Plant Sciences, University of Sheffield Sheffield, S10 2TN, UK.
authors.forename: Isabel
authors.initials: I
authors.lastname: Winney
authors.affiliation: Department of Animal and Plant Sciences, University of Sheffield Sheffield, S10 2TN, UK ; Evolution & Ecology Research Centre, School of Biological, Earth and Environmental Sciences, University of New South Wales Sydney, NSW, 2052, Australia ; Department of Zoology, University of Otago PO Box 56, Dunedin, 9054, New Zealand.
authors.forename: Shinichi
authors.initials: S
authors.lastname: Nakagawa
authors.affiliation: Department of Animal and Plant Sciences, University of Sheffield Sheffield, S10 2TN, UK.
authors.forename: Terry
authors.initials: T
authors.lastname: Burke
authors.affiliation: Evolutionary Biology, Max Planck Institute for Ornithology Seewiesen, DE-82319, Germany.
authors.forename: Julia
authors.initials: J
authors.lastname: Schroeder
keywords: Capture methods; house sparrow; island populations; methodology; ornithology; trappability