Long-term patterns in egg mortality during incubation and chick mortality during rearing in three species of tits in an English woodland

Abstract

Capsule: Mortality from egg-laying to fledging is species-dependent with Great Tits exhibiting greater losses of chicks, Coal Tits greater losses of eggs and Blue Tits exhibiting comparable rates of mortality of eggs and chicks. Aims: To determine whether reproductive losses during incubation and chick-rearing were different and to ascertain whether there were different effects in three closely related songbirds. Methods: Breeding success of Great Tits Parus major, Blue Tits Cyanistes caeruleus and Coal Tits Periparus ater at Treswell Wood, Nottinghamshire, England was examined, selecting only those nests which fledged at least one chick. Mortality during incubation (i.e. loss of eggs) or rearing (i.e. loss of chicks) was recorded per nest and annual means were calculated and used in the analysis, which examined relationships between year, first-egg date and species. Key factor analysis was used to investigate the relative effects of egg or chick losses on the total breeding mortality. Results: Timing of reproduction showed a long-term trend to earlier nesting, but there was considerable variation from year to year in first-egg date. In this location there has been a long-term decline in clutch size in all three species. Previously unseen differences between these three species of tit are shown for mortality at different stages of the reproductive process. Coal Tits suffer the greatest losses through unhatched eggs, whereas Great Tit failures are greater during chick-rearing. Blue Tits exhibited problems in achieving success in both incubation and rearing. Conclusion: Closely related tit species living in close proximity exhibit different patterns of reproductive mortality during breeding. © 2011 British Trust for Ornithology.