Communal roosting in Potamarcha congener (Rambur) and its possible functions (Anisoptera: Libellulidae)
Odonatologica , Volume 18 - Issue 2 p. 179- 194
Communal roosting is described at 9 sites all close to a temporary pond on the campus of Madurai Kamaraj University, south India, observed between November. 1987, and the end of January, 1988. Up to 100 males and females, all sexually inactive, were found at one roosting site whereas others normally contained smaller numbers. Some sites were in regular use for at least 70 days. Communally roosting females had immature ovaries whereas males contained apparently mature sperm. Over 400 dragonflies were individually marked and this showed that many of them returned to the same roosting sites for up to at least 23 successive nights. The sites were dead twigs on trees which offered good fields of view. By using pinned, dead individuals and by altering the positions of roosting twigs, evidence was obtained to suggest that the locations of sites are learnt visually and that they do not provide any special microclimatic benefit. The possibility that communal roosting serves an anti-predator function in a species which may remain reproductively inactive throughout a long dry season is considered.
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