that he will be the only male to copulate with her. If several
females come into estrus on the same day, however, then
monopolization of each female by the resident breeding
male inevitably will be more difficult. Reproductive syn-
chrony of females thus affects mate-guarding, and conse-
quently the frequency at which females copulate with a sec-
ond or third male (Emlen and Oring 1977; Sherman 1989).
Because they are seasonal breeders, a certain level of re-
productive synchrony occurs for all three species of prairie
dogs — probably because natural selection has favored fe-
males who wean offspring when new vegetation is available
in late spring. At my study colonies, for example, black-
tailed prairie dogs always copulate in February and March,
and Gunnison’s and Utah prairie dogs always copulate
in March and April. But do factors other than seasonal-
ity affect reproductive synchrony, and are all three species446 Chapter Thirty-Seven
Figure 37.6 Vegetation within home territory during the breeding season for (top) black-tailed prairie dogs,
and (bottom) Utah prairie dogs. Because of these differences, male black-tailed prairie dogs can guard estrous
females more easily than can male Utah prairie dogs. Top photo courtesy of Wind Cave National Park; bottom
photo by John L. Hoogland.