DISCUSSION
Homing behavior. — The experiments conducted in this study
confirm the Pancake tortoise to exhibit excellent homing abilities. This
was attested by the fact that 69.23% of the radio-tracked tortoises
that had been displaced from their original home crevices successfully
homed. The successful homing again of the first two already homed
tortoises when recaptured and re-translocated to a different compass
orientation clears any doubt on the existence of homing in the species.
Further, the fascinating scenario whereby two pairs of tortoises,
collected from and translocated to crevices opposite in direction,
crossed paths each journeying home is an allusion to the genius of the
homing ability of the Pancake tortoise.
The homing patterns and trajectories imply a response to some cue(s)
which at the present cannot be explained with certainty and therefore
need further testing. The supposed response to certain cue(s) is evoked
by the observation of some distinct movement patterns whereby homing
tortoises that had been displaced from the same crevice tended initially
to follow the same or nearing paths, only in some cases diverging when
nearing their home crevices. We suppose this observed divergence could
be as a result of the existence of a wider home range, a delimited area
freely traversed by the individual (tortoise) during its normal
activities such as feeding, mating, oviposition (Burt 1943).
A number of hypotheses however have been put forward for the mechanisms
that make homing possible in animals. Painter and Plachocka (2019)
inferring from Mouritsen (2018) and Putman (2018) suggest that for
animals to achieve migration, they detect various cues to formulate a
map and compass, with the map providing position relative to a target
and the compass giving a heading. Such cues include geomagnetic field
responses (Brothers and Lohmann 2015), odour plumes (Koch et al. 1969)
and celestial bodies (sun, moon) (Foster et al. 2018).
Even though homing has only been investigated in a few tortoise species,
the use of such cues certainly has been documented. Chelazzi and Delfino
(1986) state that the Herman’s tortoise (Tesudo hermanni ) makes
use of olfaction during homing. Cannor (1996) records that vision and
olfaction appear to be important senses for the orientation and
movements of Gopher tortoises. Gourley (1974) also records that the
Gopher tortoise (Gopherus Polyphemus ) is capable of making use of
sun compass orientation, albeit secondarily to visual landmarks (Cannor
1996). In Pancake tortoise it appears that the response to whichever
cue(s) is more perfected in adults than juveniles although it was only
one juvenile that was tested. Also, despite our study not investigating
further on the cues utilized during the homing, we nonetheless feel that
since our tortoises were translocated in closed boxes, the use of visual
landmarks by the species may play a lesser role when homing.
Although traveling in incomparable medium with tortoises, Gould (2015)
states that Sea turtles memorize the magnetic coordinates of their natal
beach, returning to that combination of parameters to lay eggs decades
later. To accomplish this feat, Gould (2015) reiterates that the young
animal is hypothesized to ‘imprint’ on the nest site, storing
navigational information for later use. Lohmann et al (2001, 2004)
explain the global cues used during the homing of Loggerhead sea
turtles, as well as juvenile orientation to the initial feeding area, to
be unambiguously magnetic.
Site fidelity. — The successful homing of the displaced Pancake
tortoises over vast and heterogeneous landscapes is indisputable proof
of strong site fidelity in the species. The explanation for the results
showing a significantly decreasing trend (Mann-Kendall) is that there
were translocations into stations 1, 2 and 4 and consequently the
decreasing trend is attributable to the homing movement out of the
crevices. Also occasional tortoise dispersals from station 3 to station
4 and back is assumed to have led to decreasing trends in both the
stations. The reason as to why there was no statistically significant
trend in station 6 despite tortoises having been removed from there is
that the tortoises homed within a period (3-5 days) short for a trend to
be detected in the long term. ‘No trend’ in the other stations implied
that since there were no translocations out of them, the tortoises
initially present remained in the crevices throughout the study period.
Considering that reproduction rate in the species is low (Spawls et al.
2002; Schmidt 2006; Mwaya et al. 2018), and our observations that the
few hatchlings/juveniles which are reprod uced always find refuge
farther away from the adult tortoise crevices, the tortoise numbers in
the short term were unlikely to increase hence the constant number in
the crevices over the study duration. Our results ultimately show that
the tortoises always abided by their crevices and if displaced returned
home alluding to strong site fidelity.
These findings agree with Malonza (2003), Wood and MacKay (1997) and
Moll and Klemens (1996) who also documented that the Pancake tortoise
resides in well-defined home ranges over long periods of time. We
believe that such fidelity to the specific crevice and associated
habitats certainly confers special survival advantages to the species.
For instance, as animals become familiar with a site, site fidelity can
help them know where to find good food, nesting sites as well as help
them avoid predators (Merkle et al. 2022).
Territoriality. — The camera trap events and ad libitum
observations that showed events of aggressive behavior with resident
males fighting and chasing away other visiting males add to our
knowledge, not only of site fidelity, but also of territoriality. A
study by Wood and MacKay (1997) notes that adult males and females of
Pancake tortoises may be territorial with respect to other members of
their own sex but not to members of the opposite gender. Their
observation, further showed that a male may exclude all the other males
and a female may do likewise with all other mature females. Our study
however did not observe females fighting other females as up to five
females were found residing in the same crevice harmoniously for over
two years. Since the general habitats surrounding the crevices seem to
have comparable vegetation structure and composition, mate
territorialism becomes the only reasonable candidate for the aggressive
behavior observed.