Relationship between laying order and egg dimensions in the Blackcap Sylvia atricapilla

This study analyzes the influence of egg laying order on egg dimensions (especially on egg volume) and on the size of the last egg laid in a Blackcap clutch. The research was carried out in deciduous woodland in NW Croatia during 2002 and 2004. The analyses covered only clutches with five eggs (the dominant size of the first clutch in the study area), where the first eggs were laid on the same day (5 May 2002 and 11 May 2004). The present study suggests that the Blackcap may employ a strategy of increasing the egg volume of each successive egg laid, which may reduce size hierarchy between nestlings and prevent competition between them.