Sexual Identity Issues in Male Red-backed Fairy-Wrens
January 1, 2008 by Gregory Gough
There are 3 distinct types of male red-backed fairy-wrens (a bird that lives in northern Australia): brightly-colored breeders, dull-colored breeders, and dull-colored helpers.
The brightly-colored males are a deep jet black with bright crimson patches. The dull-colored breeders are brown and white, like the females, with a black bill (like brightly-colored males). The helpers are also colored like the females and have a pale bill (like females). Helper males stay on the territory where they were raised and assist the resident pair in raising young.
These 3 types of males occur in young birds. Young males that are the most robust and healthy typically molt into the brightly-colored plumage. Less healthy males retain a female-like plumage and the least aggressive males became the helpers.
Even though the dull-colored males look like females, tests in the aviary confirmed that the brightly-colored males were not deceived but were not as aggressive to them as they were to other brightly-colored males.
So, the dull coloration of some males appears to give them respite from brightly-colored male bullies.
There does not appear to be a cost to having a brightly-colored plumage as all 3 types of males had similar lifespans.
Females appear to prefer brightly-colored males when cheating on their mate so if a brightly-colored male vacates a territory, dull-colored males will change their bill or plumage color to move up on the male social ladder.
This article summarizes the information in this scientific paper:
Karubian, Jordan, Sillett, Terence Scott and Webster, Michael S. 2008. The effects of delayed plumage maturation on aggression and survival in male red-backed fairy-wrens. Behavioral Ecology, 3: 508-516.