Use of individual colour-ringing to estimate annual survival in male and female Red Knot Calidris canutus islandica: a progress report for 1998–2001

In relatively long-lived birds like shorebirds, even small changes in adult mortality may affect population size. However, annual survival estimates based on metal-ringing and accumulating recoveries by the general public take at least a decade to materialise. To try and obtain faster and more sensitive estimates of annual survival, we started an individual colour-ringing project on Red Knots Calidris canutus in 1998, focusing on the islandica-subspecies that spends part of the non-breeding season in the Dutch Wadden Sea. By using molecular sex determination techniques we were able to distinguish males and females. A total of 1805 birds was colour-marked in the study period from August 1998 to late 2001. Of these, 1603 were adult birds (52% were female, 39% male and 9% undetermined). Based on a total of 850 individual observations, 486 different adults were resighted at least once over this period. Using the software MARK, we estimated average annual survival in adult birds as 0.841 (SE = 0.066). Compared with previous studies this is a great improvement in the time over which a survival estimate can be obtained with such precision. No differences between sexes and years were apparent.