Female black-tailed prairie dogs that copulated with ex-
actly two males reared (insignificantly) larger litters than fe-
males that copulated with only one male (fig. 37.5). When
I examine the number of juvenile offspring that survived
for at least 1 year, then the difference between doubly- and
singly-copulating females is almost significant (mean
SD1.00 1.20 versus 0.815 0.123; P0.069,
Mann-Whitney U test). Thus, females of all three prairie
dog species that I have studied might rear more offspring by
copulating with more than one male. If so, then why is the
frequency of multiple copulations for Gunnison’s and Utah
prairie dogs twice the frequency for black-tailed prairie
dogs? The answer, I speculate, relates to interspecific varia-
tion in the ability of males to monopolize sexual access to
females (Orians 1969; Emlen and Oring 1977).
A female might gain from copulating with second and
third males, but the first male that copulates seldom gains
by allowing the female to copulate with additional males.
The first male therefore should try to prevent copulations
with additional males, and first males of all three species
vigorously engage in such mate-guarding. Why are male
black-tailed prairie dogs more successful than male Gunni-
son’s and Utah prairie dogs at stopping a female from cop-
ulating with a second male? As explained below, the answer
might relate to visibility within the home territory, number
of entrances per mating burrow, and reproductive syn-
chrony among females.
Visibility within the home territory
Mate-guarding will be easier and more effective when males
can see females. One of the most conspicuous features of a
colony of black-tailed prairie dogs is the paucity and short-
ness of vegetation (Scheffer 1947; King 1955). During the
breeding season in February –March, for example, a typi-
cal home territory is devoid of all vegetation 15 cm tall
(fig. 37.6, top). Consequently, a male black-tailed prairie
dog easily can see an estrous female that is aboveground,
where she predictably is during daylight hours of the mat-
ing season unless she is actually copulating. In colonies of
Gunnison’s and Utah prairie dogs, by contrast, tall vegeta-
tion (30 cm) is conspicuous throughout the year (fig. 37.6,
bottom). Estrous females of the latter two species can con-
ceal themselves behind sagebrush (Artemisia), rabbitbrush
(Chrysothamnus), and other bushes /shrubs, so that watch-
ing and guarding of estrous females is probably more dif-
ficult for male Gunnison’s and Utah prairie dogs than for
male black-tailed prairie dogs. One thing is certain: visual
tracking of estrous Gunnison’s and Utah prairie dogs is more
difficult for students and me than is tracking of estrous
black-tailed prairie dogs.
Number of entrances per mating burrow
One way for the first copulating male to deter copulations
with additional males is to sequester the estrous female in
a burrow so that she cannot exit and so that other males
cannot enter (fig. 37.7). Like male Idaho ground squirrels
(S. brunneus;Sherman 1989), male black-tailed, Gunni-
son’s, and Utah prairie dogs all use this tactic to enhance
mate-guarding. Such incarceration is easy when a burrow
has only one entrance, but is more difficult when a burrow
has numerous entrances.
Because she submerges before the male (Hoogland 1995,
1998a, 1998b, unpublished data), the female is primar-
ily responsible for choosing the burrow where copulation
occurs (the mating burrow) for all three species. Mating
burrows for black-tailed prairie dogs usually have two en-
trances, and occasionally have three or four (Hoogland
1995, unpublished data; see also King 1955; Sheets et al.
1971). Mating burrows of Gunnison’s prairie dogs, by con-
trast, commonly have as many as five to six entrances
(Hoogland 1998b, unpublished data; see also Rayor 1988).
Mating burrows of Utah prairie dogs almost always have
a minimum of five to six entrances, and sometimes have
twenty entrances. Incarceration of estrous females thus is
probably easier for male black-tailed prairie dogs than for
male Gunnison’s and Utah prairie dogs.
I have argued that male ability to monopolize sexual
access to females probably varies directlywith visibility
within the home territory and inverselywith the number of
entrances per mating burrow. A key assumption here is that
the incentive for females to avoid monopolization is equal
for all three species. But, as noted previously (fig. 37.5),
perhaps the payoff for avoiding monopolization and for
copulating with additional males is higher for female Gun-
nison’s and Utah prairie dogs than for female black-tailed
prairie dogs; if so, this factor might explain the interspe-
cific differences of figure 37.4. Opposite of male ability to
monopolize, female ability to escape from mate-guarding
and to seek additional copulations probably variesinversely
with visibility within the home territory and directlywith
the number of entrances per mating burrow.Reproductive synchrony among females
The typical clan or coterie of prairie dogs usually has one
reproductive male and several reproductive females; fur-
ther, each female is sexually receptive for only several hours
on a single day each year. If only one female per coterie or
clan comes into estrus per day, then the resident reproduc-
tive male can devote all his attention to courting and guard-
ing that female — and thereby can increase the probabilityAlarm Calling, Multiple Mating, and Infanticide among Black-Tailed, Gunnison’s, and Utah Prairie Dogs 445