Effects of spring weather on laying dates, clutch size, and nest survival of ground-nesting passerines in abandoned fields

Abstract

Weather conditions have a significant impact on the life-history strategies of birds. The mechanisms by which weather variability drives demographic processes in boreal passerines have been investigated insufficiently. We examined the effects of spring weather on first egg-laying dates, clutch size, and nest survival of Booted Warbler (<em>Iduna caligata</em>) and Whinchat (<em>Saxicola rubetra</em>) breeding in abandoned agricultural fields in the north of European Russia in 2005–2019. We used general linear models to express first egg-laying dates and clutch size and program MARK to model nest survival as a function of weather variables. Our results demonstrated that variability of May precipitation and averaged daily temperature are important drivers of first egg dates, clutch size, and nest survival in both species. The first egg dates of Booted Warblers and Whinchats were determined primarily by the May temperature: the warmer the weather in May, the earlier the laying dates. Taking into account the effect of the first egg date, the clutch size of Booted Warblers strongly depended on the May averaged daily temperatures, whereas the clutch size of Whinchats was weakly affected by May precipitation. The spring weather had a strong impact on Booted Warbler and Whinchat nest survival, potentially by influencing the activity of nest predators. We suggest that years with a coincidence of low spring precipitation and temperature are the