CHARACTERISTICS AND POSSIBLE FUNCTIONS OF TRADITIONAL NIGHT ROOSTING AGGREGATIONS IN RUBYSPOT DAMSELFLIES

Abstract

Summary Many species of animals congregate into groups when roosting. While studies exploring roosting behavior are common, relatively few detailed, quantitative studies have been done on the roosting behavior of insects, and the adaptive value of roosting aggregations are still unclear for most edible (non-distasteful) species of any taxon. We investigated night roosting aggregations of the rubyspot damsele y, Hetaerina americana, along a creek in the Coastal Range Mountains of California. Both male and female rubyspots were found in roosting aggregations, although the aggregations tended to be male-biased relative to the population sex ratio. Rubyspots roosted on the west side of slow moving sections of the creek; within this habitat they were highly aggregated but were not associated with any particular habitat features. The spatial pattern of site use tended to change gradually over time and sites with a relatively large number of individuals were more likely to be used on subsequent nights. These results suggest that within suitable habitat, the specie c locations of roosting aggregations were traditional (socially learned). Rubyspot roosting patterns, when taken in combination with other aspects of this species’ biology, do not support habitat limitation, thermal or desiccation benee t, foraging, and aposematic hypotheses for the function of rubyspot roosting aggregations. Rather, the roosting aggregations most likely serve an antipredator function or are the result of using conspecie cs to choose safe sites.