Seasonal Decline in Clutch Size of the Marsh Tit (Parus palustris) in Relation to Date-Specific Survival of Offspring

Smith, Henrik G.Lund University,Lunds universitet,Biodiversitet,Biologiska institutionen,Naturvetenskapliga fakulteten,Biodiversity,Department of Biology,Faculty of Science (author)

This paper documents and evaluates seasonal trends in reproductive performance in the Marsh Tit (Parus palustris) in southern Sweden. Clutch size decreased for nests started later in the season. This pattern held true both for second-year and older females when analyzed separately. Individual females adjusted clutch size in relation to the relative time of season they produced a clutch a particular year. The seasonal decline in clutch size was also evident for clutches produced in the same territory at different parts of the season in different years. Females breeding for several years demonstrated a high consistency in relative laying date and clutch size. The same was not true for males or for territories. The length of the incubation period normally decreased with season. Nestling mass and survival did not show any systematic seasonal trend. Nest predation was probably more prevalent late in the season. Fledglings that hatched later had poorer survival until autumn. This effect was evident for males, but not for females. Hatching date did not influence fledglings' survival to the next breeding season, but sample sizes were small. I suggest that the Marsh Tit adjusts clutch size to the survival probability of nestlings, this being affected by the probability of nest predation and by fledgling survival. Hence, late-laying females are not prepared to accept as large reproductive costs as early laying females.

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