Objects in Flux - RMIT Research Repository - RMIT University

lar use of ultrasonic detectors to detect, record and identify
microbat echolocation calls. Yes, only microbats use ultrasonic
echolocation but fear not, there are heaps of microbats
cruising around the urban areas eating insects (although
obviously there are greater numbers out bush). You may well
have been hearing microbats via your detector. Through the
detector speaker you can hear the calls as a series of rapid
clicks. These clicks become more rapid and rise in frequency
into what is called a ‘feeding buzz’ when the animal is closely
tracking its insect prey. These clicks then usually suddenly
stop when the animal has either missed the final stage of the
inflight interception, or … it suddenly has its mouth full!!
Most bats call in the range of about 20-70kHz in Victoria.
Most adult humans can only hear up to about 15-16kHz,
children up to about 20. Dogs can hear higher – prob. up
to about 40kHz I think. I have held a microbat in my hand
when there was a dog nearby and although I couldn’t hear
anything the dog pricked up its ears and wouldn’t take its
eyes off the bat!! There is one bat species in Victoria that
calls within our hearing range (down to about 10kHz) - we
hear it as a regular, high frequency (high for us but low for
bats) pinging noise above the trees and roofs. Most people
just assume it is an insect but it is the White-striped Freetail
Bat, so named because it has a white stripe through its
brown fur down either side of its body. No-one has worked
out what the stripes are for and both sexes have them.
One of the cheapest commercial bat detectors is available
from Titley Electronics, the Anabat Detection system. See
http://www.titley.com.au
Eva,
I am not an expert on megabats but there is a device for
keeping birds and flying foxes out of fruit orchards called
The Phoenix Wailer, which makes use of a series of speakers
which emit irregular sounds. The speakers are a certain
distance apart so that the sound waves end up colliding
over the orchard and creating a sound that some animals
find disturbing apparently. It has been trialled at the Melb
Botanic Gardens without much success. Perhaps someone is
directing something similar at your colony?
As for your flying fox, it may be that she is hearing the high
frequency noises from your car engine. Grey Headed Flying
foxes can actually hear up to about 54kHz, however high
frequency sound doesn’t usually travel as far as lower frequencies
so it would have to be pretty intense sound for her
to pick it up at that range, or else she has great ears!!
Cheers, Ryan
Telling Stories
Although access to knowledge is often readily
available, the selection and deployment of this
knowledge may require a high degree of judge-
ment and skill. For the novice practitioner, guid-
ance may be obtained from community forums
and other online resources. This information
may be accessed through search results on a
particular topic or via direct responses to ques-
tions posed by the practitioner. This learning-
on-demand approach worked particularly well
for practices that could adopt a trial-and-error
approach (such as software development), how-
ever, I found it was less suited to outcome-crit-
ical activities where errors could cause financial
or personal loss. In these situations, accounts
from practitioners who had successfully com-
pleted the procedure being attempted were par-
ticularly reassuring; generally, the more difficult
or risky the procedure, the greater the number
of personal accounts I sought out and read.
While writing software for the B&O MP3 Mod
project, information from online sources was
invaluable. At the commencement of the project
I had no knowledge of Objective-C, the pro-
gramming language I used to write the control
interface. Through the use of Apple’s official
development pages, community forums and in-
dividual’s personal pages, I was able to develop
a functioning user interface. I supplemented
this online knowledge with two printed texts,
Learning Cocoa with Objective-C (Davidson
and Apple Computer Inc., 2002) and Core Mac
OS X and Unix Programming (Dalrymple and
Hillegrass, 2003). While the online resources
were well suited to solving specific problems,
the printed texts were better structured to
provide a general introduction to programming
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