Romantic display gets tree planted.

A three-wattled bellbird waggling and booming to impress a female may be the best friend a tropical fruit ever had.

Male bellbirds pick conspicuous perches to strut their stuff, often in gaps in the forest canopy. Such sunny spots make the perfect nursery for certain tree seedlings, notes Daniel G. Wenny of the Illinois Natural History Survey in Mount Carroll. One such tree species, an avocado relative called Ocotea endresiana, produces fruit that attracts bellbirds, which then drop a high percentage of the seeds on the ground beneath these gaps in the canopy.

Scientists have long discussed the notion that vertebrates might in some cases disperse seeds to a prime location instead of just dropping them at random. However, researchers rarely manage to demonstrate such directed dispersal, observes Douglas J. Levey of University of Florida in Gainesville. A study of bellbirds that he and Wenny published in the May 26 Proceedings of the National Academy of Sciences represents the first documented example of directed dispersal for tropical trees, Levey says.

Wenny and his colleagues trailed birds that had just eaten Ocotea fruit through the cloud forest in Monteverde, Costa Rica. When the birds finally spit up or excreted the seed, the researchers combed the forest floor to find it. "That was the really frustrating part," Wenny says.

The team compared the success of seed planting by five bird species. "A seed that's dispersed by a bellbird has a better chance of surviving as a seedling," says Wenny These seedlings were only half as likely to catch a fungus disease, perhaps because bellbirds perch in relatively sunny spots.

The finding intrigued another bellbird researcher, Nat Wheelwright of Bowdoin College in Brunswick, Maine. "What makes it doubly fascinating is that it's driven by the peculiar mating system of a polygamous tropical bird species that dashes off of its perch for maybe 10 or 20 percent of the day, grabs a little fast food, and hustles back," he says.

When a female shows up, the male waggles his wattles, three stringy growths dangling from his bill. During the shaking display, the wattles engorge with blood and triple in length.

The males "do kind of a `dry heave' behavior where they open their gape and gasp," Wheelwright explains. "They swell up larger and larger, and then they let out this thunderous call." The sound carries several kilometers, yet males call right into the ear of the female. "She'll actually recoil--it will blow her back."