May 13, 2014
Post by guest student blogger Julia Brokaw. Just in time for all the bluebird nesting that will be starting this month! Thanks for an excellent post, Julia.
Both bluebirds and tree swallows are cavity-nesting birds that aggressively defend their territory from each other, often seen dive-bombing, swooping, and tumbling in our backyards. But just like us, not all birds have the same personality type. Some are highly aggressive and easily agitated while others are not. But do different personality types affect the health of the newly hatched chicks? Is there the care-taking mom and serious dad? Or two competitive parents pushing for healthy dinners and straight A’s?
In a recent paper published in PLOS ONE, researchers from Appalachian State University demonstrated that when bluebirds mate “assortatively” (with a partner that shares similar personality traits), they are better able to take care of nestlings while defending their territory from tree swallows.
We might think that when “opposites attract”, one bird could spend all its time defending the nest, while the other takes care of the nestlings. However, the results showed that when two parents have opposite personality types (one aggressive, one non-aggressive), the nestling mass after two weeks was lower than nestlings of parents with similar personality types. Conversely, offspring of pairs with similar personalities, showed increased mass.
The researchers believe that when parents have similar personalities, they are better able to coordinate duties for taking care of the nestlings. So, for example, when a tree swallow attacks the nest of two aggressive parents, the tree swallow is driven off much quicker than defense by one bluebird alone. This means that the bluebirds can spend more time feeding their babies. The more the chicks are fed, the heavier and healthier they will be.
This study took place at a site where tree swallows are extending their natural range southward. The results are especially relevant to understand the impacts of range expansion to less aggressive species, like bluebirds. Personality studies are often overlooked in range expansion or invasion studies, so this research provides a new perspective on the consequences of overlap zones.
Harris MR, Siefferman L (2014) Interspecific Competition Influences Fitness Benefits of Assortative Mating for Territorial Aggression in Eastern Bluebirds (Sialia sialis). PLoS ONE, 9(2): e88668.