Zanzibar red bishop, Euplectes nigroventris, also known as the Zanzibar bishop, photographed at Udzungwa Mountains National Park, Tanzania.
Image: Dan Logen, 10 January 2010 (with binoculars).
Nikon D300, 200-400mm lens at 400 ISO 1000, f/5.6, 1/640 sec.
Question: This spectacular African mystery bird owes its dramatic colouring to what aspect of its natural history?
Response: This is a young male Zanzibar red bishop, Euplectes nigroventris, in a heavy moult. The black throat rules out other Bishop species.
This bird owes its spectacular plumage to the evolutionary power of female choice.
During the non-breeding season, male and female Zanzibar red bishops are visually indistinguishable. However in breeding season, this species is strongly dimorphic. The males' dramatic plumage evolved because the birds are polygynous (this is the natural history trait I was asking about) and the females select their mates based on their plumage colour. Often, all of the females in a particular location will end up selecting one or a very few males as their mates in each breeding season.
There are several reasons for the females' choice: illnesses and infections are indicated by the quality of a bird's plumage. The brightest males are healthiest, and thus have better genes than those with dull plumage. This is known among biologists as an honest signal, because the male cannot fake it.
Another reason for the females' choice is that bright plumage is a maladaptive trait that makes males more conspicuous to predators. Females perceive brightly plumaged males that survive as being fittest, and thus most desirable as mates.
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