Using physiology to infer the reproductive status and breeding performance of cryptic or at-risk bird species

Historically, the estimation of breeding parameters for most bird populations has relied on conventional methods where researchers locate nests and count the numbers of eggs or chicks produced. However, for cryptic, rare, and at-risk populations these simple methods can be problematic if such species are difficult to locate and study, or are sensitive to disturbance. The measurement of yolk precursors in the plasma of breeding birds can provide a useful means for assessing the reproductive status of threatened and endangered birds, which can provide those tasked with the conservation and management of rare and cryptic bird species important information about their phenology and population dynamics. Through the use of yolk precursor analysis, researchers can also infer the sex of individual birds that lack clear differences in morphological characters (sexual dimorphism), as determination of breeding status can facilitate estimates of breeding phenology and effective population size.