A population biology of breeding redshanks (Tringa totanus L.)
A breeding population of Redshanks was studied by trapping adults at the nest and individually marking them, over a period of nine years, on part of the extensive Ribble saltmarshes. Other aspects of breeding biology were investigated over three years. The capture-recapture analysis of the breeding adults revealed an overall annual survival rate, of both sexes, of 0.77, and a population of approximately 200 pairs in 1.04km? Mate fidelity was very high, with 71% of surviving pairs remaining faithful. Nest site fidelity was extremely strong for faithful pairs and males with new mates, but significantly weaker for females with new mates. A lower nest site fidelity of young birds was regarded as a major contributing factor to their lower recapture rates. The timing of both the onset and ending of the breeding seasons varied greatly, and was determined mainly by the rainfall. High rainfall delayed onset and hastened ending of breeding. Mithin a breeding season the older birds bred throughout, while the young ones were mostly not able to breed early. The substantial losses of nests due to cattle grazing on the marsh (45%) could easily be controlled by preventing the access of cattle to the main breeding area until after the end of the nesting season. Nest predation was rare (less than 4%) in most years, but increased in a year of short vegetation (to 25%). The production of pulli was estimated under varying environmental influences and ranged from 0.73 to 2.28 pulli. pair": The variation of egg size within the population was investigated and the significant influences of laying order (within a clutch) and maternal size demonstrated. Pullus size at hatching was positively correlated with egg size and also with maternal size. The growth and development of pulli were described for weight, bill length, tarsus length and postnatal moult. For three days after hatching the weight remained below the hatching value and then rapidly increased, whereas the bill and tarsus showed a linear increase in length A tentative model of the population dynamics was produced, despite the lack of good estimates of pre- and post-fledging mortality. This model indicated a high pre-fledging mortality of 0.67 and also further highlighted the impact on the population of cattle grazing during the nesting season.