Female group mates forage together (Wilkinson and Boughman 1998),
which results in faster food finding and better defense of food resources
(Wilkinson and Boughman 1999; Boughman unpublished). Group living
and group foraging enhance reproductive success (Boughman unpublished). Reproduction is synchronous within a group (Porter and Wilkinson
2001), which may facilitate thermoregulation by young pups and allomaternal care (Porter unpublished).
Females use vocalizations, termed screech calls (Fig. 4.6A,B), to coordinate group foraging (Wilkinson and Boughman 1998), and these vocalizations differ among social groups (Boughman 1997). Screech calls differ
among groups in a number of frequency and temporal features, yet calls
from individuals within social groups are not statistically distinguishable.
Such group-distinctive calls provide an effective mechanism for finding
group mates outside the roost cave (Wilkinson and Boughman 1998). In
addition to the variation among social groups within caves, variation exists
between cave populations (Boughman and Wilkinson 1998). Little migration between caves occurs (McCracken et al. unpublished), yet this does not
result in genetic differences between cave populations (McCracken 1987).
Thus, geographical variation in screech calls is more likely to result from
social modification than from population substructure.
Screech calls convey group membership (Boughman and Wilkinson
1998). Bats discriminate between calls given by group mates and other bats.
Bats also differentiate between calls from their own cave and other caves.
However, bats reveal no ability to discriminate among calls given by individuals within their group (Boughman and Wilkinson 1998). Screech calls
function as contact calls that enable group mates to find one another
outside the roost cave. Bats give them when departing on foraging flights,
en route to, and at feeding sites (Wilkinson and Boughman 1998). Bats
approach when hearing familiar calls but fly away when hearing unfamiliar
calls (Boughman and Wilkinson 1998). This result and a lab experiment
suggest that screech calls may facilitate group defense of resources. Bats
increase their rate of calling when a large number of intruders are present
(Boughman unpublished).
Unrelated females give acoustically similar calls (Boughman 1997).
Genetics cannot explain this pattern, because group mates are not close relatives. Ontogeny of screech calls has not been studied, but because females
join social groups as adults, ontogenetic change is unlikely to give rise to
group-distinctive calls. Experimental evidence demonstrated that convergence within groups results from social modification (Boughman 1998).
Juvenile and adult bats were transferred reciprocally between social groups
that initially differed in call characteristics. Bats gradually changed calls
(Fig. 4.6C–F). The first changes occurred within one month, and by five
months calls given by transfers and residents showed strong convergence
in both frequency and temporal characteristics. Both residents and transfers changed calls. Results showed that the social environment was the
primary determinant of acoustic change. Comparisons with age-matched
4. Comparative Vocal Learning
175
which results in faster food finding and better defense of food resources
(Wilkinson and Boughman 1999; Boughman unpublished). Group living
and group foraging enhance reproductive success (Boughman unpublished). Reproduction is synchronous within a group (Porter and Wilkinson
2001), which may facilitate thermoregulation by young pups and allomaternal care (Porter unpublished).
Females use vocalizations, termed screech calls (Fig. 4.6A,B), to coordinate group foraging (Wilkinson and Boughman 1998), and these vocalizations differ among social groups (Boughman 1997). Screech calls differ
among groups in a number of frequency and temporal features, yet calls
from individuals within social groups are not statistically distinguishable.
Such group-distinctive calls provide an effective mechanism for finding
group mates outside the roost cave (Wilkinson and Boughman 1998). In
addition to the variation among social groups within caves, variation exists
between cave populations (Boughman and Wilkinson 1998). Little migration between caves occurs (McCracken et al. unpublished), yet this does not
result in genetic differences between cave populations (McCracken 1987).
Thus, geographical variation in screech calls is more likely to result from
social modification than from population substructure.
Screech calls convey group membership (Boughman and Wilkinson
1998). Bats discriminate between calls given by group mates and other bats.
Bats also differentiate between calls from their own cave and other caves.
However, bats reveal no ability to discriminate among calls given by individuals within their group (Boughman and Wilkinson 1998). Screech calls
function as contact calls that enable group mates to find one another
outside the roost cave. Bats give them when departing on foraging flights,
en route to, and at feeding sites (Wilkinson and Boughman 1998). Bats
approach when hearing familiar calls but fly away when hearing unfamiliar
calls (Boughman and Wilkinson 1998). This result and a lab experiment
suggest that screech calls may facilitate group defense of resources. Bats
increase their rate of calling when a large number of intruders are present
(Boughman unpublished).
Unrelated females give acoustically similar calls (Boughman 1997).
Genetics cannot explain this pattern, because group mates are not close relatives. Ontogeny of screech calls has not been studied, but because females
join social groups as adults, ontogenetic change is unlikely to give rise to
group-distinctive calls. Experimental evidence demonstrated that convergence within groups results from social modification (Boughman 1998).
Juvenile and adult bats were transferred reciprocally between social groups
that initially differed in call characteristics. Bats gradually changed calls
(Fig. 4.6C–F). The first changes occurred within one month, and by five
months calls given by transfers and residents showed strong convergence
in both frequency and temporal characteristics. Both residents and transfers changed calls. Results showed that the social environment was the
primary determinant of acoustic change. Comparisons with age-matched
4. Comparative Vocal Learning
175