Rodent Societies: An Ecological & Evolutionary Perspective

copulations occur underground, but aboveground court-
ship and guarding behaviors indicate which male(s) copu-
lates with each estrous female. Courting male black-tailed
prairie dogs, for example, sometimes take nest material into
a burrow before copulating there, and males of all three
species commonly give a unique mating call just before or
just after copulation. Three independent lines of evidence
indicate that my inferences of estrus and copulation are ac-
curate (Hoogland 1995, 1998b; Haynie et al. 2003). Black-
tailed and Gunnison’s prairie dogs avoid extreme inbreed-
ing, but at least 10% of matings among Utah prairie dogs
involve parent /offspring or sister/brother (Hoogland 1982,
1992, 1999, unpublished data).
Several of the costs and benefits that result from copulat-
ing with three different males also might accrue to females
that copulate three times with the same male (Dewsbury
1982b; Birkhead 2000). In this chapter I only consider the
number of different male sexual partners versus litter size,
but I recognize the importance of trying to separate the ef-
fects of total number of copulations versus number of dif-
ferent sexual partners.

Alarm Calling

Females

For all three species, females with kin in the home terri-
tory are more likely to call than females with no nearby
kin (fig. 37.1a). For Gunnison’s and Utah prairie dogs, fe-
males with juvenile offspringin the home territory are more
likely to call than females with only nondescendent adult
or juvenile kin such as siblings, nieces, or cousins nearby
(fig. 37.2a). By contrast, female black-tailed prairie dogs
call as often when nondescendent adult or juvenile kin are
in the home territory as when nearby adult or juvenile off-
spring are present (fig. 37.2a).
Why do female black-tailed prairie dogs differ from fe-
male Gunnison’s and Utah prairie dogs by calling so of-
ten for nondescendent kin? Demography, I speculate, has
played a key role in the evolution of these interspecific dif-
ferences (Sherman 1980a). For Gunnison’s and Utah prairie
dogs, 90% of adult females give birth each year (Hoog-
land 1999, 2001). Natural selection thus frequently can
favor calling by mothers, but selection for calling by (rarer)
females with only nondescendent kin within earshot can
only occur infrequently. For black-tailed prairie dogs, by
contrast, 50% of adult females give birth each year —
mainly because females usually do not copulate as year-
lings (Hoogland 1995). Adult female black-tailed prairie
dogs with only nondescendent kin in the home territory are

therefore common. Indeed, in some years such females are

as common as females with nearby offspring. Natural selec-

tion thus frequently can favor calling by females with only

nondescendent kin nearby.

Males

Breeding male black-tailed, Gunnison’s, and Utah prairie

dogs typically copulate with most or all females in the home

territory, and copulating males usually remain in the same

home territory until after the emergences of juveniles from

Alarm Calling, Multiple Mating, and Infanticide among Black-Tailed, Gunnison’s, and Utah Prairie Dogs 441

Figure 37.1 Alarm calling by prairie dogs with and without kin in the home

territory for (a) females and (b) males. Shown here are means 1 SE; the num-

ber above each SE line indicates the number of individuals observed (each ap-

proximately seven times per year). P-values are from Mann-Whitney U test. Data

are from Hoogland 1995, 1996, and unpublished data.