Abstract
Capsule Song Thrushes introduced to New Zealand differ in a number of life history traits compared to their source population in Britain.Aim To survey life history traits in an introduced population of Song Thrushes, for comparison with the source population.Methods Nests were monitored near Kaikoura, New Zealand. We recorded clutch size, egg size, length of incubation and nestling stages, hatching success, levels of brood reduction, and nest success. Data on life history traits of Song Thrushes in Britain were collated from the literature.Results Mean clutch size declined from 4.1 eggs in Britain to 3.6 eggs in New Zealand. Egg size, nestling period length, and breeding success of Song Thrushes in New Zealand also decreased, while incubation period lengthened. There were changes in six out of seven life history traits studied.Conclusion The general direction of changes in life history traits suggests that Song Thrushes in New Zealand invest less in each reproductive bout than in their native range. These changes may be the result of the warmer climate and longer breeding season in New Zealand. Understanding the fitness effects of these life history changes may provide insight into how a species adapts to a warmer environment.
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