Rare Flier : '' Half male, half female '' ....... and completely stunning. Colombia's diverse ecosystems - which include mountain ranges, mangrove swamps, Caribbean beaches and Amazonian rainforests - are home to more avian species than any other country.

So when Hamish Spencer, an evolutionary biologist at the University of Otago in New Zealand booked a bird watching vacation in Colombia, he was hoping to spot some interesting creatures.

He got more than he bargained for. During one outing in January 2023, the proprietor of a local farm drew his attention to a green honeycreeper, a small songbird common in forests ranging from southern Mexico to Brazil.

But this particular green honeycreeper had highly unusual plumage. The left side of its body was covered in shimmering spring-green feathers, the classic coloring for females.

Its right side, however, was iridescent blue, the telltale marker of a male. The bird appeared to be a bilateral gynandromorphic female on one side and maleon the other.

Gynandromorphism has been documented in a variety of birds, as well as insects, crustaceans and other organisms.

The bird Dr. Spencer saw in Colombia is only the second known case of bilateral gynandromorphism in a green honeycreeper - and the first documented in the wild.

[ The only previous example was reported more than a century ago and was based on a museum specimen.]

The condition could result from an error during the production of egg cells in female birds. Female birds have two different sex chromosomes, designated W and Z, while males have two Z chromosomes. An error during egg cell production could result in two fused or incomplete separately separated cells.

If those fused cells are fertilized by two different sperm, each of which carries a Z chromosome, the result might be a bird with the WZ chromosomes of a female in some cells and the ZZ chromosomes of a male in others.

'' And so you get a bird that's half and half,'' Dr. Spencer said. [Emily Anthes]


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