Fish eavesdrop on nearby fights.

Much like a bunch of guys in a bar, Siamese fighting fish turn to watch a brawl and take note of who's the winner and who's the wimp.

A male who has seen a fight reveals what humans politely call resistance when it's his turn to tussle with the winner, report Peter K. McGregor at the University of Copenhagen and his colleagues.

The study of animals eavesdropping on each other's interactions is just opening up, says McGregor. Traditionally, animal communication research focuses on one signaler and one receiver, ignoring bystanders. But eavesdropping proves invaluable, he points out. Keeping track of fights offers data on dominance with no risk of bodily harm. Without such snooping "you'd wind up in bits before you had all the information," McGregor says.

Previous observations hinted that birds use clues from monitoring neighbors' territorial scraps, he notes. A red-winged blackbird who attacks with zest when researchers present a stuffed bird suffers fewer territorial intrusions afterward than the bird who attacks the dummy half-heartedly.

McGregor believes the new experiments are the first to examine rubber necking during fish fights. The results appear in the June 22 Proceeding of the Royal Society of London B.

The researchers observed nearby fish during showy clashes between Siamese males in laboratory tanks. Even males in separate compartments, away from ripples or chemical cues, seemed to watch the contest, the team reports.

McGregor and his coworkers next allowed a male to view only one of two simultaneous fights. That bystander took four times longer to approach the winner of the fight he had just seen than to swim up to the loser. However, in confronting fish from the battle he missed, the male showed no significant difference in approach.

Some mammals and highly social birds clearly keep an eye on neighbors, observes David W. Dunham, who has studied fighting fish at the University of Toronto. "When you get down to lower animals, it's much more difficult to find good evidence of that kind of thing."

The new fish findings remind him of a phenomenon called copying in guppies. Smaller females change their preferences for male colors after seeing a large, important female near a male of a particular hue.