Egg Weights, Egg Component Weights, and Laying Gaps in Great Tits (Parus Major) in Relation to Ambient Temperature

Abstract

We collected 328 freshly laid Great Tit (Parus major) eggs from 38 clutches in 1999 to determine the relationship of whole egg weight, wet yolk weight, wet albumen weight, dry shell weight, and the occurrence of laying gaps with mean ambient temperature in the three days preceding laying, while controlling for laying date and position in the laying sequence. We also reanalyzed existing data on whole egg weight in 1978 and 1979 in relation to temperature, controlling for the same other variables. Egg weight was correlated with temperature in 1978 and 1979, but not in 1999. None of the egg components was related to temperature preceding laying, apart from a nonsignificant tendency for albumen weights to be lower at higher temperature. Egg weight increased with laying date in 1978 and 1979 after controlling for other variables. In 1999, albumen and shell weight increased seasonally, but shell weight only did so to the extent expected on the basis of the seasonal increase in whole egg weight. Yolk weight did not increase significantly seasonally, but neither did yolk weight relative to whole egg weight decrease significantly. Whole egg weight and the weights of all components varied between clutches. Most weights also varied through the laying sequence. The probability of a laying gap occurring varied between clutches, and increased with position in the laying sequence and decreased with temperature and laying date. Eggs preceding laying gaps were lighter and contained less albumen but had higher shell weights than other eggs. Eggs following laying gaps also had heavier shells relative to the size of the egg than other eggs.