distribution, status, and conservation of bats in the fiji islands

Species accounts: Emballonura semicaudata
Roosts disturbance and destruction
Roost disturbance is a well known problem for many cave dwelling species, and is likely to
have been worsening in Fiji due to the increasing availability of electric torches, which
facilitates the access to caves. It may have affected E. semicaudata in some areas, but the
species seems to have disappeared even from colonies where disturbance appears to be low.
We did not find evidence that caves and lava tubes, the most typical roosts of E. semicaudata,
are regularly destroyed, but found a cave that had been partly blocked, presumably due to road
work. In addition, we found a number of caves that were made inaccessible to bats because
their entrances had become blocked by vegetation. When tree cover around the entrance of
caves is removed, the sunlight reaching the ground increases dramatically, promoting the
growth of shrubby vegetation that often completely blocks these entrances. This may reduce the
number of roosts available to E. semicaudata, and in fact we found a couple of caves
harbouring it which had entrances that were becoming blocked by vegetation.
Tropical storms and deforestation
Cyclones Val and Ofa have been blamed for the precipitous decline of this species in both
Samoa and American Samoa in the early nineties, although there is evidence that the decline of
the species in that region started well before those cyclones (Grant et al. 1994, Tarburton 2002).
Fiji is also affected by such storms, and they are likely to cause high mortality in E.
semicaudata. The shallow caves that this species often uses may not provide sufficient
protection against very strong winds, and some coastal caves may be inundated by very rough
seas, as occurred in the past in some American Samoa caves (Grant et al. 1994). In addition, it
has been suggested that the abundance of flying insects remains low for weeks after cyclones
(Tarburton 2002), and that individuals may be unable to survive if storms prevent them from
feeding for several days in a row (Grant et al. 1994).
It is certain that E. semicaudata endured the impact of very strong storms throughout most of its
range in the Pacific for millennia, so one could expect its populations to cope well with the
mortality that is associated to storms. However, there are reasons to believe that deforestation
may be worsening the effect of storms on this bat. Under the protection of canopies of well
developed forests, such as those where we observed E. semicaudata foraging on Yaqeta, bats
are able to forage even at times of fairly strong winds. Consequently, deforestation may
increase the frequency of occurrence of periods in which the bats are unable to forage due to
high winds, and lengthen the period of deprivation caused by individual storms.
Due to deforestation, storms are now likely to have a greater negative impact on E. semicaudata
than in the past, but we believe that they are not the most serious threat to the species in the Fiji
islands. This because storms are more likely to affect vertebrate populations on small and flat
islands (McNab 2002), but E. semicaudata seems to be faring better on small than large islands.
The persistence of this species on the small and flat, but well forested, islets of Aiwa is
particularly telling. Storms may cause very substantial mortality, which can have dramatic
consequences on small or weakened populations, as observed in Samoa and American Samoa.
But in the presence of good forest, storms alone do not appear to have dramatic long term
consequences for healthy populations of this species.
As referred above E. semicaudata has the capacity to forage in a variety of habitats, but in the
only site where habitat use was studied it showed a clear preference for forest (Esselstyn et al.
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