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Tuatara: Volume 13, Issue 3, November 1965

A Portable Time Interval Indicator for Animal Behaviour Studies

page 190

A Portable Time Interval Indicator for Animal Behaviour Studies

Any Set of Observations of animal behaviour is enhanced by correct information about the temporal sequence of events. This is particularly so when information is being sought on the status of internal factors (e.g. ‘drive’ or ‘motivation’) using speed of arousal or waning as an indicator of these factors. Often the time lags are of importance, e.g. between stimulus and response, or attack and escape. Indeed almost any behaviour pattern study requires reference to time intervals.

Many devices are available which apprise the observer of time intervals, usually by means of an audible signal. These usually suffer from one or more disadvantages such as expense, non-portability, damage by dust or sand, need for constant re-setting, and the fact that the audio signal may disturb the behaviour of the animal under study. The device described here is relatively cheap. The total cost of the components, which are readily available, is about five pounds. The device combines portability and reliability, and can be used in such a way that only the observer can hear the signal. Time intervals between successive signals of 3 to 100 seconds are possible. (Modification of this range is simply achieved by changing only one component.) Thus the device should prove useful to researchers making field observations of animal behaviour, especially when compactness and ruggedness of equipment are essential.

The prototype was designed to use four pencells as the source of power. The drain on these is very low, being 2.2 milliamps for the duration of a time ‘pip’ and only 6 microamps between ‘pips’. The pips have a duration of about ¼ second which is found to be ample.

The pips may be heard by means of a small loudspeaker or an earphone. The speaker used can be any cheap, small diameter model. The connection of the earphone cuts out the loudspeaker via a telephone jack, as indicated in the diagram. The 5-ohm resistor in parallel with the earphone was necessary in the prototype to provide an acceptable sound intensity. The resistor was built into the handle of the phone plug.

The time interval between signals is governed by the rate of discharge of C2; i.e. by the resistance shunted across it. For the time intervals involved this is necessarily a large value, hence the leakage currents in T1 and C2 also play a considerable part in the discharge. Thus the selection of the shunt resistors has to be determined experimentally and the values given in the diagram are only a rough guide. In the prototype, these values gave time page 191
Fig. 1: Circuit Diagram

Fig. 1: Circuit Diagram

intervals of 60, 30, 20 and 10 seconds. As already stated, the range of 3 to 100 seconds is easily altered. This is achieved by changing the value of C2—a lower capacitance gives shorter intervals. The value of C1 governs the pitch of the note; 0.25 microfarad gives about 4.000 c.p.s.

Although the device is temperature-sensitive, it is not unduly so for the purposes of most behaviour studies in the field. A fall in temperature from 20°C to 12°C causes the time intervals to be decreased by about 5%. At a particular temperature, the intervals are reproduced to within ½.