6.3.2Mobile tracking
When tracking on foot, it is important to have lightweight, robust receivers with
simple controls. Many receivers are not waterproof, in which case it must be
possible to operate them through plastic bags during rain. A light source is useful
at night, and headphones or an ear-plug make it easier to detect faint signals and
changes in signal strength. For directional tracking at short range, it should be easy
to reduce the signal reception gain to a level at which signals from nearby tags are
only just detected. Power supplies should last for at least the length of a tracking
day, with reserve power sources available (e.g. plug in battery packs in case an
overnight recharge has failed). Antennas should be light and not cumbersome.
Yagi antennas with 3–4 elements are very suitable, to give optimal gain and
directionality, and can now be obtained with flexible elements that do not impede
passage through brush.
When tracking from vehicles, it is important that other equipment does not
interfere with the very sensitive receiver reception. Diesel or thoroughly sup-
pressed engines are important, and the effect of communications equipment,
GPS receivers and computers should be checked before starting a journey. The
plasma in strip lighting can give a lot of interference. On boats and road vehicles,
a pneumatic mast is ideal for raising antennas (www.clarkmasts.co.uk, http://www.
aoaqps.com/hilomast.htm), which can be longer than for hand-held work. A
5–6 element Yagi on a 3–5-m mast more than doubles the reception range
compared with a 3-element hand-held antenna. A compass repeater from the
mast to the cabin is often indispensable (e.g. at night), and accurate GPS is
invaluable in boats and for all off-road work.
Antennas give optimal gain on aircraft if mounted externally; high-wing
Cessnas have very convenient struts. Obtaining aviation authority approval can
be problematic, but mounts must in any case always be firm, fail-safe, and approved
by the pilot. Selecting an understanding and cautious pilot is important too.
6.3.3Software
Conservation questions may appear to be very simple, such as “do they survive if
we release them here”? However, if data are collected in the right way, they can be
used to answer further questions like “do they survive here significantly better
than there” or “why didn’t they stay here” or “what do these animals really need”?
Alas, all too many projects look only at the simple questions. They invest
much effort in setting up an experiment, yet omit to record information that
could later explain why one treatment fails while another succeeds. However,
a decision to use radio-tags is a good start toward discovering what really happens.
150 |Radio-tagging