Progesterone is a steroid hormone secreted by female mammal ovaries. It has been shown that, through the analysis of blood, saliva, ocular secretions, faeces or the sub-cutaneous blubber layer of certain cetacean species—killer whales, minke whales, Indo-Pacific bottlenose dolphins, fin whales—it is possible to determine the stage of maturity or the period of the reproductive cycle of females. Thus, this technique may be used to determine the age at which females become sexually mature or even conduct pregnancy tests on whales! This kind of information can help biologists gain a better understanding of the state of cetacean populations.
The advantage of employing this method is that it requires but a small sample that can be easily collected from living animals in their natural environment. This relatively new technique is very promising.