「Reliability of egg candling for the estimation of hatching date: an example using Common Goldeneye (Bucephala clangula) eggs」

Mayumi Satoh

A portable candler has been widely used for determining incubation stage and estimating hatching date, but the predictive ability of the technique based on different incubation stages has not been assessed. Using Common Goldeneye eggs, we evaluated the predictive ability of the candling technique for estimating hatching date. Based on the characteristics viewed through the candler, all eggs were categorized into seven incubation stages. A strong negative correlation was found between the stages and the number of days from each stage to hatching (r = -0.93, p < 0.001). Difference in the mean number of days to hatching was statistically significant between all pairwise incubation stages (p < 0.05) except between stage 4 and 5 (p = 0.990), indicating that two different characteristics of eggs would be expected at the incubation around 10 days to hatching. The estimate was more reliable at later incubation stages. Our results indicate that, by knowing its accuracy of each incubation stage, the candling technique should be useful to determine incubation stage and estimate hatching date in the field.