Egg Dimensions and Egg Weight Loss during Incubation in Five Species of Cockatoo, and the Use of Measurements to Determine the Stage o Incubation of Birds' Eggs

Abstract

The linear dimensions are presented of 302 eggs of 5 species of cockatoo (Cacatuidae : Psittaciformes) occurring in the south-west of Western Australia: red-tailed black cockatoo, white-tailed black cockatoo, long-billed corella, little corella and galah. Forty-four of the eggs were weighed throughout incubation and, by means of the calculated regression lines for loss of weight on time of incubation, the weight at laying of each of these eggs was determined. The weight constant Kw, was determined for each egg by the formula: Kw= W/LB*2; its mean value was 0.554±0.015. Weights at laying of the entire sample of eggs were calculated by use of this value of Kw, the daily loss of weight during incubation was determined, and a general formula based on linear measurements and weight derived for determining the stage of incubation of birds' eggs. This is: T = [(KwLB*2) - Wt]/[a(KwLB*2)*b], where T is the number of days of incubation; Wt is the known weight of the egg at time T; L, B are the length and diameter of the egg in centimetres; and Kw, a and b are constants which may be determined for the species studied (alternatively, general values may be substituted).