A biologist in Australia has discovered what may be the world's pickiest mates: a species of bird that will only reproduce if their partner has a certain type of feather.

The birds, called superb fairy-wrens, are found in the rainforests of eastern Australia. They are small, brightly colored birds that live in monogamous pairs.

For years, biologists have been puzzled by the fact that superb fairy-wrens seem to be very selective about their mates. They often spend hours inspecting each other's feathers before they decide to mate.

Now, a biologist named Megan Head has discovered what the birds are looking for: a specific type of feather called a "spangle." Spangles are small, iridescent feathers that are found on the backs of male superb fairy-wrens.

Head found that males with more spangles were more likely to attract females. In fact, females were only interested in males with at least 10 spangles.

Head believes that the spangles may be a way for males to show off their health and fitness. Birds with more spangles may be more likely to survive and reproduce, so females may be choosing males with more spangles in order to increase their chances of producing healthy offspring.

The discovery of the superb fairy-wren's picky mating habits sheds light on the evolution of sexual selection. Sexual selection is the process by which certain traits become more common in a population because they increase an individual's chances of finding a mate.

The superb fairy-wren's picky mating habits show that sexual selection can be a very strong force in evolution. Even a small difference in a trait, such as the number of spangles on a bird's back, can make a big difference in an individual's chances of reproducing.

The superb fairy-wren's picky mating habits are also a reminder of the diversity of the animal kingdom. There are many different ways for animals to find mates, and the superb fairy-wren is just one example of the many fascinating ways that animals have evolved to reproduce.