Females prefer nests with pizzazz. (Fish That Decorate).

Biology has met home-decorating TV.

In spring, some male fish build nests of algae where females visit and occasionally deposit eggs. In the wild, a nest's murky mass looks to human eyes as if it would be perfect for camouflaging the eggs. Yet, when scientists offered some males bits of shiny foil, the fish went wild, taking home the bright strips and placing them around the entrance to the nests. Even though the strips hardly looked like camouflage, the fish were making a canny decorating choice, researchers report in the March Behavioral Ecology and Sociobiology. In tests, females preferred the gaudy nests.

It's the first modern, controlled test showing that nest decor matters when female fish pick their mates, says coauthor Sara Ostlund-Nilsson of the University of Oslo in Norway.

Three-spined sticklebacks (Gasterosteous aculeatus) live in temperate waters worldwide and build nests with varied architecture. On the Swedish coast, Ostlund-Nilsson and Mikael Holmlund of Stockholm saw males tending nests of greenish algae that often had around the entrance several strands of red algae or of dead algae that had turned orange. The researchers had planned to study camouflage but became interested in learning why males incorporate bright accent colors if given the chance.

By cutting up the shiny foil from a Christmas candy, the researchers created 15-millimeter-long strips. When male sticklebacks in aquariums were ready to build nests, the researchers offered them foil in five colors as well as a choice of sequins.

The sequins weren't of much interest to the fish, but the nest builders added plenty of strips, especially red ones. The males themselves turn red in breeding season, so Ostlund-Nilsson now wonders whether that color choice has special significance. She imagines the fish's message as: "I'm red, but my nest is even redder."

To set up a test of female response, the researchers replaced the decorators with other males and then compared foil-decorated and unadorned nests held at the time by males of similar size. When offered a choice, the females clearly preferred the nest bedecked with shiny strips.

The finding makes an intriguing fit with an earlier study, says Felicity Huntingford of the University of Glasgow. She and Iain Barber of the University of Wales in Aberystwyth found that most desirable males, those with robust immune systems and high androgens, made the tidiest, most compact nests. This result suggested that nest architecture could tip off females to the appeal of the builder, but that study didn't test females' choice. "It's a nice precursor to the new study" says Huntingford.

The findings on shiny strips remind Huntingford of bowerbirds. Males display collected ornaments, such as colorful feathers and plastic objects, around twig structures. Females prefer males whose bowers have lots of decorator touches (SN: 12/2/00, p. 362). The female thereby chooses a top-quality male "who's good at getting and fighting for stuff," Huntingford says.

The Scandinavian test may have documented an underwater version of the bowerbird strategy, in which females go for the glitter to find the best guy.