Variations in Egg Characteristics of the House Wren

Abstract

THERE are scattered records in the literature showing that the weights of consecutively laid fresh eggs or their measured lengths and maximum diameters may either decrease or increase in different species. In a statistical analysis of 20 clutches in the Laughing Gull (Larus atricilla), Preston and Preston (1953) showed that the length measurement did not differ significantly either among the eggs of the same clutch or between the eggs of different clutches. On the other hand, in three-egg clutches the third egg laid had a significantly smaller diameter than the first two. In two-egg clutches, the second egg appeared to resemble the third more than the second in the three-egg clutches, but the small number of measurements available did not permit definite conclusions. Since a large series of data had been collected at the Baldwin Bird Research Laboratory, near Cleveland, Ohio, between 1925 and 1938, on the eggs of the House Wren (Troglodytes aedon), we decided to determine whether or not there were any consistent changes in dimensions and weight with sequence of laying in this passerine species.