A Female-Specific Color Signal? Black-Mottled Bills Indicate Breeding in Female Common Waxbills.

Area of Science:

• * Evolutionary biology
• * Animal behavior
• * Ornithology

Background:

• * Female birds often display ornamentation, typically mirroring male traits.
• * The common waxbill (Estrilda astrild) presents a deviation from this pattern.

Purpose of the Study:

• * To investigate the unique bill color change in female common waxbills during the breeding season.
• * To determine the pigmentary basis and potential adaptive significance of this coloration.

Main Methods:

• * Observation of wild adult common waxbills during breeding.
• * Analysis of bill coloration and pigment composition (carotenoids vs. melanin).

Main Results:

• * Adult female common waxbills' red bills become mottled with black during breeding.
• * This change is due to melanin deposition, not carotenoid reallocation.
• * The black-mottled bill visually resembles the bill of nestlings and fledglings.

Conclusions:

• * The female bill coloration is derived from a nestling trait, not a male trait.
• * This unique signal may exploit male responses, shifting behavior from mating to parental care.
• * The findings support the theory that color signals evolve via pre-existing developmental pathways.