Daily measurements of variation in weight loss of eggs of seven passerine species before and during natural incubation

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Abstract
The eggs of one or more clutches of seven passerine species were weighed each day from the day they were laid until hatching. In all seven, the rate of weight loss increased during incubation. This increase was more rapid in the early stages, leading to curvilinear regression. Linear regression was, however, highly significant and explained over 80% of the variation in four species. Curvilinear regression was significant in two other species. The weight loss curve of a single unfertilized Barn Swallow, Hirundo rustica, egg was similar to that of the rest of the clutch until they commenced to pip. The daily weight loss of five unincubated eggs also increased with time. Shell damage was suspected to be the cause of sudden increases in weight loss of individual eggs. A simultaneous drop in weight loss by six clutches was probably caused by high humidity. Other decreases in weight loss may have been caused by rain. Mean weight loss from water vapour conductance through the shell as a percentage of initial egg weight was 0.9 ± 0.08 during the laying period, 12.0 ± 0.72 during the laying period plus the incubation period prior to pipping, and an estimated 14.6 ± 0.85 for the laying period and the whole incubation period.
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