Chick-kidnapping Behavior in Emperor Penguins
Emily Kam and Garon Coriz Biology 342 Fall 06
Adaptive ValueBenefits of Prolactin
Prolactin is usually present in female birds during their gestation period, but these levels fall after they give birth to their chicks. However, in emperor penguins, prolactin levels remain high even after the chick hatches. Scientists believe that this mechanism provides an incentive for the mothers to come back to take care of their offspring after feeding themselves. This is the primary adaptive value of prolactin, as it ensures the survival of the chicks. However, prolactin also poses another problem for some unfortunate mothers whose chicks do not survive to see their return. The high levels of prolactin still present in these penguins, which have lost their chicks but still have the urge to display maternal behaviour, cause them to resort to kidnapping.
Costs of Prolactin In Penguins
It is a strange puzzle as to why chick-kidnapping behavior continues to be displayed by female emperor penguins when it has no apparent adaptive value. This is because the parents of the kidnapped chick often lose interest in fighting for their young quickly. The kidnapper, also loses interest in the kidnapped chick usually within an hour, leaving the helpless chick to later fend for itself. These chicks usually have not developed skills necessary for adulthood and are left open to predation, leading to a very low survival rates for kidnapped chicks. In the end, this behavior would seem to have no adaptive value because the chicks of the penguins involved die and fail to pass on their genes.
However, it appears as though kidnapping behavior remains in the populations mainly because the benefits of prolactin, e.g., higher chick survival rates, outweigh its costs, e.g., chick-kidnapping and the deaths attributed to the behavior.