Rodent Societies: An Ecological & Evolutionary Perspective

young are dependent on their parents. In species with ex-

tended dependency on parental care, young have many op-

portunities to observe and learn from their parents’ be-

haviors (e.g., antipredator, foraging, and social behaviors)

before having to exhibit these behaviors themselves. Con-

versely, species with little or no parental care must acquire

behavior without assistance from adults. Thus the length

of dependence on parents will influence the developmental

process of offspring’s behavioral repertoires, and extended

parental care may allow for variable pathways of behav-

ioral development, including social facilitation of responses

(Heyes and Galef 1996). For example, as discussed ear-

lier, day-old garter snakes (Thamnophisspp.) that receive

virtually no parental care respond defensively to predator

models upon first exposure (Herzog and Burghardt 1986).

In contrast, experiences with their mothers may signifi-

cantly modify the responses of young vervet monkeys (Cer-

copithecus aethiops) to both predators and alarm calls, as

they maintain close proximity to their mothers for at least

2 years (Cheney and Seyfarth 1990). Brown (1984) studied

the development of antipredator behavior in two bass spe-

cies differing in the length of time the male parent guards

his young. Fry with limited paternal care (Ambloplites ru-

pestris) showed predator-avoidance behavior sooner than

those with extended care (Micropterus salmoides). Mexi-

can jays (Aphelocoma ultramarina) with prolonged associ-

ations with experienced adults exhibit mobbing behavior at

a later age than less social scrub jays (A. coerulescens) that

fledge at an earlier age (Culley and Ligon 1976). Rates of

behavioral development in rodents may also reflect varia-

tion in the length of parental care, which in turn could in-

fluence the development of offspring’s response repertoires,

while extended parental care may favor variable pathways

of behavioral development, including social facilitation of

responses (Heyes and Galef 1996). Comparisons among

animals that differ in active-season lengths, growth rates, or

periods of dependence upon mothers provide an oppor-

tunity to examine how selection has favored plasticity of

behaviors as a function of environmental influences on de-

velopmental rates, and how these resulting individual dif-

ferences relate to fitness.

Rates of development in ground-dwelling squirrels may

also impact the length of maternal care and potential for so-

cial interactions. Juveniles of some nonhibernating species,

which have slower growth rates than those that hibernate

(Clark 1970; Morton and Tung 1971; Pizzimenti and Mc-

Clenaghan 1974; Maxwell and Morton 1975; Koeppl and

Hoffmann 1981; Rickart 1986) and subsequently longer

associations with their mothers, may exhibit more social

facilitation (Heyes and Galef 1996) of behavioral devel-

opment than juveniles with limited growth periods. As an

Ontogeny of Adaptive Behaviors 203

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Figure 17.3 (continued)