Results from a long-term radio-tracking study of pteropodid fruit-bats are reported. Grey-headed fruit
bats (Pteropus poliocephalus) captured from seven colonies in eastern New South Wales, Australia, were
fitted with collar-mounted radio transmitters to permit their movements to be monitored over the
following year. The sheepskin-lined leather collars were well tolerated by the bats over periods of
6-18 months. Bats moved between major colony sites for distances of up to 750 km, with movements
occurring in both northerly and southerly directions. One bat from Lismore had a feeding range of
25 km, whereas in Sydney bats flew up to 17 km each night to feeding sites. There was considerable
interchange between bats in adjacent colonies.
The roosting and foraging behaviour of Nyctimene robinsoni (Chiroptera : Pteropodidae) was studied
at Cape Tribulation, far north Queensland, in November and December 1987 using radio-tracking
techniques. Bats under and around fruiting sourcop (Annona muricata) trees in a fruit orchard and
under cluster fig trees (Ficus spp.) in abandoned pastures were captured with mist nets. Females
dominated the captures in the orchard, but the sex ratio was 1 : 1 under cluster fig trees (their presumed
normal food). Distances between day-roosting sites and places of capture ranged from 63 to 1012 m.
During the day, bats roosted solitarily in the foliage of canopy or understorey trees, usually in primary
forest, and most individuals roosted in the same small area for several consecutive days. Except for
occasional visits to isolated fruiting trees, individuals foraged at night within 200m of their day roost.
The high density of fruiting cluster fig trees in November and December could account for the sedentary
behaviour ot this bat at this time of year.
A remotely switched null-peak network for combining RF signals from dual antenna arrays used for
radio direction finding and animal tracking is described. The design is based on a balanced 50-Ohm coaxial
bridge, which provides a difference (null) and summed (peak) output from two parallel antennas to the
receiver. Reed relays activated through the receiver cable permit the network to be switched between
peak or null modes of operation from the receiver, without the need for long dual cable runs from the
antenna. The bridge presents a nominal 50-Ohm impedance at all terminals.
For a recently initiated large-scale study of the biology of pferopid fruit bats in eastern Australia to be
economically feasible, all radio-tracking equipment had to be designed and constructed as part of the project.
A compact and lightweight receiver, operating in the 150-2 MHz frequency range, which combines a simple
and radically novel design with high performance, was developed following a thorough re-evaluation of the
requirements for radio-tagging and tracking these animals. The receiver uses a frequency synthesiser to
provide 200 channels at 10 kHz spacing. Some initial findings obtained from the project are discussed.
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