Densities of individually marked migrants away from the marking site to estimate population sizes: a test with three wader populations

Abstract

Capsule Population estimates based on the mark-resighting method can be a useful alternative to population-wide counts. Aims To investigate whether the mark-resighting method can be used as an alternative to counts to estimate the size of wader populations. Methods Individual colour-marking and subsequent resightings allowed accurate estimates of annual survival for three populations of waders, on which basis we could estimate the actual number of marked birds alive. Densities of marked birds were determined on sites away (2000-4300 km) from the ringing locations expecting marked birds to be randomly distributed among non-marked conspecifics. Population sizes are estimated by combining these densities with the number of marked birds alive. Results We found indications that the distribution of marked birds was indeed random in the locations away from the site of marking. The estimated population size of Red Knot Calidris canutus canutus was in accordance with the most recent estimates based on counts. Our estimate of the Calidris c. islandica population was somewhat lower, and that of the Bar-tailed Godwit Limosa lapponica taymyrensis population was considerably lower than the latest estimates based on counts. Conclusion Population estimates based on the mark-resighting method can be a useful alternative for, or addition to, population-wide counts, as long as the assumption of random distribution of marked birds at the reading sites is taken into account. We conclude that the Afro-Siberian Bar-tailed Godwit population has recently decreased in size or has been substantially overestimated during the counts.

Fuelling conditions at staging sites can mitigate Arctic warming effects in a migratory bird

“…To estimate effects of departure fuel load on subsequent survival, we individually colour-marked and resighted godwits in the Wadden Sea from 2001 9 , 52 . We used data from adult birds captured in April–May in The Netherlands in 2002–2016 (3995 individuals).…”

Mortality within the annual cycle: seasonal survival patterns in Afro-Siberian Red Knots Calidris canutus canutus

“…For a shorebird the size of the Red Knot, the survival estimates found are relatively high (Sandercock 2003), and establish that Red Knots both show strong site fidelity to non-breeding sites and generally have high survival rates (Brochard et al 2002;Baker et al 2004;Leyrer et al 2006Leyrer et al , 2012Spaans et al 2011). The 9 % decline in annual apparent survival detected between the time spans of 2002-2005 and 2006-2009 The goodness of fit was tested for the starting model / studies.…”

Field measurements give biased estimates of functional response parameters, but help explain foraging distributions

“…After the experiment, in order to increase body mass before release, the birds were fed ad libitum for 2 days. On 5 July 2012, they were tagged with unique colour-coded ring combinations placed around their legs to allow for individual identification in the field (Spaans et al 2011) and released near the catching site. The experiment was in full compliance with Dutch law regarding animal experiments under permits issued by the DEC-KNAW (NIOZ 12.01).…”