Aviary use, supplementary food use, and
use of the natural environment
The aviary remained open to the bats following release,
with mealworms and honey water provided ad libitum
in the same manner as pre-release. Aviary use was
monitored by nightly entry / exit counts, and weights
of mealworms and honey water consumed each night
were recorded to monitor supplementary food use.
Radiotracking at night provided individual level
information on aviary use and on movements outside
the aviary, while daytime radiotracking was used
to locate roosts. Roost boxes placed outside the
aviary were monitored for use.
Aviary use
The number of bats day-roosting in the aviary has
fluctuated between zero and seven bats since release,
although recently there has been a tendency for
no bats to use the aviary (figure 1). It is unknown
whether only a subset of the same seven bats is
using the aviary as a day-roost.
Supplementary food use;Supplementary
food consumption has declined since release to roughly
one third the pre-release means (figure 2). However
since the absolute number of bats using the aviary
is unknown it cannot be determined if the amount consumed
is a reflection of many bats foraging for wild food
and eating a small amount of supplementary food, or
if it is a small number of bats relying heavily on
supplementary food.
This should be elucidated by analysis of faecal samples
collected daily from the aviary, where insect parts
will be identified to determine the proportions of
different orders present in the faeces. This will
indicate the proportion of wild food consumed by the
bats.
Nightly
movements; Five bats have been fitted with
transmitters since release, with the last signal
lost 21st May. Four of these bats have been radiotracked
at night for 2 – 7 nights each. Due to the
rugged terrain and speed of flying bats it was not
possible to follow bats throughout their nightly
ranges. Radiotracking was confined to the area of
flat ground surrounding the aviary. Transmitters
placed in known locations suggested bats could be
detected up to a distance of ca. 500 m from the
aviary.
Three bats commuted quickly into
and out of the aviary area, with telemetry signals
rapidly being lost when bats left the aviary. Vanishing
bearings for individual bats were similar each night,
suggesting individuals were visiting the same areas
each night, however each bat seemed to commute to
a different area.
It is uncertain whether these bats were commuting
to foraging areas or to night roosts.
The fourth bat remained in the area
of signal reception for most of the time, with the
majority of fixes successfully obtained over the
seven nights he was followed. Many of these fixes
showed fluctuations in signal strength characteristic
of the rapid turning of foraging flight.
Day
roosts ; Telemetry was also used to follow
bats to roosts during the day. Bats roosted out
of the aviary on 19 occasions, and were successfully
tracked to roost trees on 10 of these. Five individual
roost trees were found. These trees are yet to be
characterized, but will be compared with trees sampled
in the pre-release habitat assessment to identify
elements of roost tree selection.
Four
roost boxes that had been in the aviary during the
captive period were placed on trees ca. 10 –
40 m from the aviary prior to release. No roost
boxes have shown any evidence of use since release,
although it should be noted that (1) bats did not
roost in these particular boxes during captivity,
and (2) bird roost boxes are common throughout the
forested parts of the island, and these may have
been used instead. No bats fitted with transmitters
were tracked to roost boxes.
Post
release condition
Few bats have been caught and weighed
since release to minimise stress, so little information
is available on their current condition. Bats that
have been caught have either been taken directly
from the aviary or harp trapped near the aviary
(see above). Weights are summarised in Table 1.
Post-release weights were similar to pre-release,
although one bat weighed on April 17th and two on
May 11th were lighter than the lightest bat weighed
on April 1st, showing some bats have lost weight
since release.
In two cases it was possible to track the weight
changes of bats fitted with transmitters, as these
individuals could be identified by shaved backs.
A female weighing 15 g on release night decreased
to 14 g on April 17th and 11 g on May 11th. A male
weighing 13.5 g on May 11th may have been either
a 16g male tagged on release night or a 15.5 g male
tagged on April 17th. It seems likely that transmitters
contributed to weight loss in these cases. If so,
weights taken on May 11th were skewed by this, as
two of the three bats had been tagged.
Future plans
The objective from now on is to
assess the success of the translocation beyond confirming
that the bats remained on the island, by measuring
bodyweight changes through time and if possible
getting an indication of reproduction.
If the bats continue to visit the
aviary throughout the year this will provide an
opportunity for capture, either by harp trapping
outside the aviary or by taking day roosting bats
from the aviary. This will probably occur once every
two months until December. If bats do not use the
aviary harp trapping or mist netting may be attempted
in the forest, however judging by the success of
harp trapping so far this is unlikely to be successful.
Captured bats will be weighed and
the reproductive condition of the females classified,
although short-tailed bats may not breed in their
first year. Male reproductive singing may still
occur, and may be an indicator of reproductive condition.
Singing begins in September (Lloyd, 2001), and will
be surveyed for by walking the forest at night.
Lastly,
insects will be sampled for a final two week period
in August
