Territoriality and Social Organization
As predicted under the territory defense
hypothesis
(Burt 1943, Maher and Lott 1995) and
confirming previous observations
(Vaughan 1976,
McWilliam 1987, Smarsh and Smotherman 2017), tracking Cardioderma
cor revealed that males sing on small territories containing food
sources, they return to these locations nightly, and there is minimal
overlap between neighbors. This space use strategy is consistent with
predictions for terrestrial gleaning
species
(Egert-Berg et al. 2018). Some of the ranges
we calculated from our telemetry data were larger than those estimated
from observation only
(Vaughan 1976). While C.
cor territory locations and boundaries can be reliably determined by
observations of singing perches, this method may underestimate total
space use, as demonstrated in Swainson’s warbler (Limnothlypis
swainsonii )
(Anich et al. 2009). Scaling laws and
diet can influence foraging range size
(Haskell et al.
2002). C. cor night ranges were similar in size to the congeneric
gleaning species Megaderma lyra , the greater false vampire bat,
which is a bat of similar size and diet to C.
cor(Audet et al. 1991).
The core areas of the night ranges are the focal spots for singing inC. cor males. As nights progressed and foraging activity
decreased, bats spent more time on more concentrated areas as they
increased singing output. The overlay of the singing ranges and overall
use ranges (including foraging) further supports singing as a
territorial behavior for resource defense foraging strategies inC. cor , rather than an exploded lek
(Toth and
Parsons 2013). Previous work found that song playbacks conducted within
the outermost singing perches of heart-nosed bats evokes strong
territorial response, but not beyond these perches, demonstrating
boundary maintenance demarked by singing
(Smarsh and
Smotherman 2017). Our observations of antiphonal singing when a neighbor
sang within the outer singing perches also supports this mechanism of
spatial organization. During the summer rains singing ceases and males
disperse
(Vaughan 1976), but opportunistic recapture
data from this paper and others suggests that territory fidelity of
heart-nosed bats extends across years
(Vaughan 1976,
McWilliam 1987).
Similar to the multi-use territories in songbirds and
gibbons,
(Marshall and Marshall 1976, Mitani 1984,
1987, Raemaekers and Raemaekers 1985, Ham et al. 2016) McWilliam noted
that male-female heart-nosed bat pairs hold territories, which was not
observed in this study
(McWilliam 1987). A sympatric
species, Lavia frons , the yellow-winged bat, has multi-use
territories in which male-female pairs roost in Acacia trees and forage
on the territories
(Wickler and Uhrig 1969, Vaughan
and Vaughan 1986). For C. cor, our study suggests that females
have fidelity to foraging areas that may overlap more with neighboring
males, and do not sing. On several occasions we observed a non-singing
adult producing contact calls and joining the tracked male for short
time periods, possibly for courtship, although presumably mating would
take place in the mixed-sex colonies in baobabs. A targeted tracking
study of females along with courtship observation will determine whetherC. cor females may benefit from mating outside of the roost, such
as additional access to resources, and where C. cor may fall on
the resource defense polygyny- exploded lek
continuum
(Kotrschal and Taborsky 2010, Alonso et al.
2012, Toth and Parsons 2013).