Concealed ovulation

Concealed ovulation or hidden estrus in a species is the lack of any perceptible change in an adult female (for instance, a change in appearance or scent) when she is fertile and near ovulation. Some examples of perceptible changes are swelling and redness of the vulva in baboons and bonobos, and pheromone release in the feline family. In contrast, the females of humans and a few other species^[1] that undergo hidden estrus have few external signs of fecundity, making it difficult for a mate to consciously deduce, by means of external signs only, whether or not a female is near ovulation.