Observations on the use of dummy nests by fledgling Worthington's Marsh Wrens (Cistothorus palustris griseus)

Abstract

For decades, researchers have attempted to understand why some avian species expend energy building nests that are not explicitly used for breeding (i.e., dummy nests). Most work has focused on whether dummy nests serve as indicators of male fitness or as decoys for confusing nest predators. Anecdotal observations suggest that dummy nests may also be used as temporary shelters for adults and fledglings, but the frequency with which this occurs is unknown. While trapping Cistothorus palustris griseus (Worthington's Marsh Wren) nestlings as part of a larger study in the saltmarshes of northeast Florida, we observed newly fledged young using dummy nests on 8 of 45 occasions (18%) during which one or more nestlings were absent from the natal nest. It is likely that the actual frequency of dummy nest use by fledglings is greater than what we observed because our efforts to locate fledglings were infrequent and opportunistic, and because depredation may account for a significant proportion of the occasions when no fledglings were found. Dummy nests may play a larger role in post-fledging survival than previously thought and warrant further investigation.