Timing of Breeding and Breeding Performance in a Population of Greenshanks (Tringa nebularia)

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Abstract
(1) The paper examines data from a 19-year study of a greenshank population in north-west Scotland [UK]. (2) Greenshanks completed clutches earlier, and laid heavier eggs, in years when early spring was warm. Laying date was independent of weather conditions around the time when chicks hatched. Fresh egg weight was heaviest in years when the laying season was early. (3) Fewer chicks hatched, and they were likely to be lighter, when weather conditions during the incubation period were cold and wet. (4) Fewer birds (of both sexes) returned to breed and fewer new territories were established when the 2 preceeding years were characterized by (a) harsh weather around the period of chick growth and (b) a low estimate of population potential breeding success. (5) Three factors, in addition to weather conditions, were associated with laying date: (i) individual differences between females (every year some laid early and others laid late), (ii) female age (older females laid earlier in the spring), and (iii) territory type (territories which included a river produced earlier clutches than those including only lochs). (6) There was a negative correlation between the annual average fresh clutch weight and the number of breeding females. However, total number of chicks hatched and an estimate of population potential breeding success were positively correlated with female number. (7) The paper concludes that a range of climatic and female-specific factors appear to shape breeding performance throughout spring and summer. Year-to-year fluctuations in population size are attributed to these factors and it is suggested that population regulation does not occur.