Female Birds Sacrifice Health During Egg Production

Bright blue eggs made by female birds, such as those created by flycatchers, do not come at no cost. Females sacrifice a portion of their own health in an attempt to make their eggs as colorful as possible. Males of these species do not always stay with the female to tend to the young. The brighter the eggs, the more likely the male will stay with the female. The male is able to gauge the health of the female according to how bright and colorful the eggs are.

The blue cue of the eggs comes from bilverdin, a compound created from the breakdown of hemoglobin. The function of bilverdin is not only being blue dye for the eggs but it is also an antioxidant which prevents cellular damage. The female bird trades off her own health and resources in an attempt to persuade the male that he should help with the young . The brighter the eggs are, the healthier the young is likely to be, and the more likely the male will stay.

A study conducted by Judith Morales and the University of Viog tested the levels of bilverdin in the blood of female pied flycatchers. The sample they were testing were located in one hundred boxes in central Spain. In order to stress the females, the researchers removed the nests once they were almost complete and allowed the female to create a new nest. After building their second nest, the females then began to lay their eggs. The researchers then recorded the color of the eggs and took a blood sample from the female one week after they had laid the eggs. Neither the stress of having to rebuild a nest nor having vibrant blue eggs alone indicated a large decrease of bilverdin in blood, but when combined there was a noticeable difference. The levels of bilverdin in the blood become measurable when birds are under the effects of stress.

Click here for the original article, "Female Birds Sacrifice Health to Create More Colourful Eggs," by Matt Kaplin.

Rob Lubenow (3)

Update 10-07-08:
This one of the first studies as well as the first proof that female birds sacrifice their own health to help keep the males around. This sacrifice of the female's health to turn her eggs bright blue does have serious benefits. By increasing the chances of keeping the male around, there is an increase of the chance of survival of the young chicks. Offspring will have two parents caring for them instead of one, more protection from other birds or predators, and for some species a guaranteed father there during critical periods for song development. The male flycatchers mate with different females throughout the different mating seasons. Since this is a relatively new study the evolution of the trait has not yet been defined. In the future they will most likely have an even greater understanding concerning this female health sacrifice.