Manakin birds must choose between sex and good weather

The white-ruffed manakin of Costa Rica is a partially migratory bird, meaning each year it decides whether to stay in its natural habitat or fly elsewhere. But choosing to migrate can have serious consequences for their dating life back home.

The birds are generally found in the highlands of Costa Rica, which each year experiences a very heavy rainy season. The manakins can escape this by migrating to the lowland regions, where there's far less rain and, consequently, it's much easier to forage for food. The problem, according to new research by biologists at the University of Guelph and the University of Western Ontario, is that the male birds who migrate may sacrifice their best shot at mating when then they return.

The manakins that stay through the rainy season are able to secure the best breeding sites for themselves, and their continued presence in manakin society means they can improve their social standing. All of this makes them more attractive to female, leaving the migratory manakins out in the cold.

Researcher Alice Boyle explains the several factors at work in this decision:

"Birds that are younger are more likely to migrate because they still have several years of breeding opportunities ahead of them. It's often the older birds with a higher status that stay not only because there is a sense of urgency to breed but also they know staying will improve their chances of becoming an alpha [male]. These factors can change from year to year which is why we see these birds choose different options each year. They have to decide what makes the most sense for them based on their status and condition."

There are also health factors to consider, Boyle says, pointing to the fact that most of the migrating manakins wouldn't likely survive the heavy rains if they stayed. Under those circumstances, there's not much point in trying to become the alpha male if you'll be too dead to enjoy it.

Fellow researcher Ryan Norris explains that these partially migratory birds are a great window into the larger evolution of bird migration:

"The manakins are faced with the choice of boosting their chances of survival or boosting their chances of breeding. Most animals migrate because of the cold but in the tropics you see some populations that are partially migratory. These species provide a window into the evolution of migrating and a unique opportunity to examine the costs and benefits of this behaviour."

Via Biology Letters.