The bright blue plumage of the Western Bluebird is a key identifying characteristic for these birds. This plumage also helps the males to find their female partner. One study, performed by Anne Jacobs, Jeanne Fair, and Marlene Zuk, looked at the effect of this colouration on mate selection.  They tested whether birds with brightly coloured feathers would mate with partners of similar appearance (assortative mating), along with determining if colouration is involved in the formation of extra-pair partners – an individual outside of the original pair bond.

Through their experiment, they observed that pair bonded birds mated assortatively according to plumage colouring as they had brightly coloured males mate with brightly coloured females but this colouring was limited to the bright blue feathers, as they noticed that no assortative mating occurred with a brightly coloured breast. With the formation of extra-pair bonds, they observed that plumage had no effect on the assortative mating between a female and her extra mate and a male and his extra mate. It seemed that the only thing that had any effect on assortative mating was the age of the male; it seemed that older males in extra-pair pairings had success in rearing offspring in comparison to their younger counterpart.

The end result was they concluded that in the formation of pair bonds, colouration played a role while there was no observable effect on the formation of extra-pair pairings.

Read the original paper here.

 

References
Jacobs, A.C., Fair, J.M., and Zuk, M. 2015. Coloration, Paternity, and Assortative    Mating in Western Bluebirds. International Journal of Behavioural Biology. 121(2): 176-186