The Eastern Bluebird Mating Habits
Avian ecologists have found that eastern bluebirds display unusual mating habits which may explain the social behavior of many songbirds. They have also confirmed that the eastern bluebird is among the North American birds known to be socially monogamous but genetically polyandrous and polygynous.
Eastern bluebirds were once believed to be monogamous birds. But many scientists have discovered that they no longer stick to just one mate. The females may be socially monogamous but they are capable of mating with more than one male bird. Sometimes, they even have several broods from different mates. In fact, broods sired by different males are said to grow healthier and therefore, have a good chance of surviving.
DNA testing has confirmed that female bluebirds tend to multiply their mate. A research showed that 19 percent of bluebird chicks were not related to their supposedly fathers and 30 to 60 percent of individual nests contain babies from more than one male mate. Studies have also found that male bluebirds may have more than one nest and one mate. Eggs in one nest may not necessarily mean that they had the same father.
The female eastern bluebird’s habit of multiplying her mates is said to be beneficial rather than detrimental in many situations. One reason points to the fact that females normally do not have a chance of seeing all available mates before picking a mate. So if a female selects a mate from a limited group, a better mate might come by the following day. Another reason for multiply mating is that the chosen mate may not have the best territory or the best site to build a nest. Or the male that is most helpful may not have the best genes for battling parasites. Other studies have different explanations like the female bluebirds mate with other males in the hope of finding a responsible partner to care for her young notably when her original mate leaves the nest for a long time.
As for the males, they practice various strategies especially the floaters or those males that do not have their own territory. The options of these male bluebirds are to share a female with another male, challenge a male for his territory or replace a male that has died or left the nest for good. The adult survival rate is said to be low among bluebirds thus, many females become widowed or deserted by their mates early on.
A female eastern bluebird may produce two broods in one breeding season. In this case, the first nest usually starts in the early part of spring while the second nest starts in summer.