Male fiddler crabs wave their greatly enlarged major claw to attract females into the burrow. Claw size appears to be a target of a female choice that increases the likelihood a female will initially approach a male. Here I show that a behavioral display trait, the maximum height that the tip of the claw reached during a courtship wave is a strong correlate of the subsequent likelihood that a female will visit a male’s burrow.

I studied U. perplexa on an intertidal mudflat on the Okukubi River, Okinawa. The crabs live individual burrows in mixed colonies and are surface active during the diurnal low tide. I followed mate-searching females as they wandered through the population. For each female I captured the first male that she passed without visiting and the first male that she visited. I measured their carapace width and major claw length.

I again located mate searching females and either for the first male that she passed without visiting or for the first male that she visited, I filmed the male’s claw waving display. I captured and measured the passed or visited males. The waving was analyzed to give maximum height of the top-most point of the dactyl from the surface of the sediment.

The size of passed males did not differ from that of the visited males. The wave height relative to crab size differed between passed and visited males (F=13.97, P<0.01).