their pups developed slightly faster (Wang 1991). In still
other species, such as naked mole-rats, it is not known
whether alloparental experience affects subsequent paren-
tal behavior and success in rearing young (Lacey and Sher-
man 1997).
Reproductive experience can influence neuroendocrine
physiology of female rodents. For example, experience
causes changes in the endogenous opioid system that medi-
ates olfactory-based interactions between mother and off-
spring (Kinsley 1994). Parity also can influence maternal
behaviors, although effects range greatly. No effect of par-
ity is reported for captive female wild house mice (König
and Markl 1987), deer mice, or white-footed mice (Har-
tung and Dewsbury 1979). Social environment may deter-
mine whether parity affects maternal behavior in Norway
rats. When rearing young in the absence of males, multi-
parous and primiparous females did not differ in nursing,
nest building, and retrieving (Moltz and Robbins 1965), or
in the overall time spent with litters (Grota 1973). How-
ever, when rearing young in the presence of males, multi-
parous females more effectively switched between neonatal
care and mating during postpartum estrus; such females
also more effectively retrieved pups (Gilbert et al. 1984). Ex-
perience also enhances pup retrieval in other species (house
mice; Cohen-Salmon 1987; golden hamsters; Swanson and
Campbell 1979). In a particularly striking example, multi-
parous female prairie voles spend more time caring for off-
spring than do primiparous females, yielding more rapid
physical development and a higher survival rate of young
(Wang and Novak 1994).
Few studies examine the effects of parity on paternal be-
havior. Prior parenting experience had no effect on paternal
behavior in prairie voles (Wang and Novak 1994) or white-
footed mice (Hartung and Dewsbury 1979). Minor changes
in a few behaviors are reported for other species, such as
deer mice (Hartung and Dewsbury 1979) and Norway rats
(Brown 1986a). Thus at this time, previous experience as a
male caregiver appears to have little or no effect on pater-
nal care of rodents.
Physical environment
Most rodents care for young in underground burrows or
covered nests, making it difficult to observe parent-offspring
interactions in the field, particularly before weaning. Direct
field observations are available for some relatively large di-
urnal species (hoary marmots; Barash, 1975a; black-tailed
prairie dogs, Hoogland 1995) and for at least one small
diurnal rodent, the striped mouse (Rhabdomys pumilio;
Schradin and Pillay 2003). Even though observations in-
side the nests of striped mice are not reported from the field,
time spent at the nest by parents has been recorded, and
parental interactions with offspring have been studied once
young are old enough to venture from the nest (Schradin
and Pillay 2003). Other field studies of parent-offspring
interactions involve indirect measures such as trap associa-
tions and patterns of space use revealed by radiotelemetry
(Schug et al. 1992).
Testing environments in laboratory studies range from
small cages with little or no cover to seminatural environ-
ments with extensive space and cover. Patterns of nesting
and parental care can vary with the size and complexity
of the testing environment. For example, when families of
meadow and montane voles were studied in small cages in
which nesting material was the only source of cover, no sex
differences were apparent in the amount of time parents
spent in the nest with pups (fig. 20.1a; Hartung and Dews-
bury 1979). In contrast, when these same species were stud-
ied in seminatural environments that provided substantial
space and hay cover, females of both species aggressively
excluded males from natal nests; males nested separately
and spent very little time with young pups (fig. 20.1b; Mc-
Guire and Novak 1984, 1986; Oliveras and Novak 1986).
The latter results are consistent with reports from natural
populations of female-only care of young and separate nest-
ing by adult males and females during most of the breeding
season (Madison 1980b; Jannett 1980). Studies on parent-
offspring interactions in white-footed mice reveal a very
similar pattern; whereas males in small cages show sub-
stantial pup care (Hartung and Dewsbury 1979), males in
larger enclosures are excluded from nests by females (Xia
and Millar 1988), and the latter pattern is more consistent
with what is known about nesting and space use by males
and females in natural populations (Wolff and Cicirello
1991). Female aggression toward strange males might be
interpreted as defense of young, but the reasons why fe-
males aggressively exclude mates from the natal nest remain
unclear.
Conflicting findings, such as those described previously,
may indicate that the pup care reported for some species
in small cages is a laboratory artifact (McGuire and Novak
1984, 1986; Wolff 2003c). Alternatively, males of these spe-
cies have the potential to display paternal behavior, and
may do so under certain conditions (Dewsbury 1985). For
example, free-living male and female meadow voles some-
times nest together during colder months (Madison et al.
1984), and thus paternal care is possible under conditions
of late autumn or winter breeding. Indeed, male meadow
voles housed under short day lengths displayed longer
grooming and huddling bouts with young than did males
housed under long day lengths (Parker and Lee 2001). Ad-
ditional data on parent-offspring interactions at low tem-
peratures are needed from field or seminatural environ-
ments to confirm facultative paternal care in this species.238 Chapter Twenty