Suggestions for Calculating Nest Success

Abstract

In field studies of nesting birds, many nests are not found at the very beginning or are not followed to a conclusion. When nests are not under observation for their full dura- tion, the observed loss rates are less than the actual rates of the species. The amount of error varies according to the total exposure of all nests not spanned by human ob- servation in the sample. A way of incorporating the time span of observations is to mea- sure the exposure in nest-days, and calculate mortality and survival rates in these units at each stage of the nesting cycle. This method allows pieces of data to be used that would be discarded in customary analyses. A suggested worksheet simplifies analysis, and illustrations answer some questions that troubled users of this method.