Why do male Columbian ground squirrels give a mating call?

Male Columbian ground squirrels, Spermophilus columbianus, give a repetitive vocalization after copulation. This 'mating call' sounds similar to certain alarm calls that are given during attacks by terrestrial predators. During 2005-2006, we investigated (1) the acoustic structure and similarity of mating calls and alarm calls; (2) the environmental context when mating calls occur; (3) whether males that are likely to benefit from mate guarding (viz., males that have sperm precedence because they are the first to copulate in a female's series of matings) give mating calls to guard oestrous females; and (4) whether mating calls advertise the caller to females that have not yet mated. Our approach was to observe mating behaviour in the field and quantify reactions of squirrels to mating calls and alarm calls, both in and out of their normal context, with playback experiments. Males that were the first to copulate with an oestrous female called during mate guarding, and guarded females experienced delays before subsequent copulations. Although sound characteristics of mating calls and alarm calls did not differ, squirrels became vigilant and sought protection upon hearing alarm calls, but continued feeding during mating calls. However, when we played recorded mating calls to squirrels after breeding season, they usually reacted as if an alarm call had been given. We conclude that (1) the male mating call is an intrasexual or intersexual signal that announces postcopulatory mate guarding, and (2) contextual information is important for assessing the message of mating calls. (C) 2007 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.