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Vol. 57, 2018 (update: 2018.01.16; 01.25) Weather Conditions Influence Egg Volume Repeatability in Clutches of the Red-backed Shrike Lanius collurioArtur Golawski1 and Cezary Mitrus2,* doi:10.6620/ZS.2018.57-02
1University
of Natural Sciences and Humanities in Siedlce, Faculty of Natural
Science, Department of Zoology, Prusa 12, 08-110 Siedlce, Poland,
E-mail: artur.golawski@uph.edu.pl (Received 6 December 2016; Accepted 29 December 2017; Published 25 January 2018; Communicated by Chih-Ming Hung) Artur Golawski and Cezary Mitrus (2018) Birds show considerable variation in egg size, both within and between clutches. There are many factors affecting egg dimensions including features of the birds themselves, territory quality, food abundance and weather conditions. One feature that varies in clutches is repeatability of egg dimensions within a clutch. We studied variation in egg size in clutches of the Red-backed Shrike Lanius collurio in east-central Poland and examined the effects of territory quality and weather conditions on egg size repeatability. Repeatability of egg size was low and ranged from 0.51 to 0.55. No significant differences in egg dimensions were found between clutch size classes (3 to 7 eggs, modal clutch size of 6). Weather conditions only influenced repeatability of egg volume. This parameter was affected by the year and one environmental factor - total rainfall immediately before egg laying. With increasing rainfall, the repeatability of egg volume decreased. Weather conditions can influence food availability and in this way also affect egg size. The Red-backed Shrike diet consists mainly of insects, the activity of which significantly decreased during rainfall. In such conditions, birds have to spend more energy to gain food, which could consequently lead to differences in egg size. Key words: Egg dimensions, Farmland, Repeatability, Rainfall, Territory quality, Weather. *Correspondence: Tel: +48177855459. E-mail: mitrus@univ.rzeszow.pl
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