PRACTICAL INFRA-RED ILLUMINATION AND OBSERVATION TECHNIQUES FOR WILDLIFE STUDIES USING ICI-962 PERSPEX CLIVE A. MARKS, FRANK BUSANA, FRANK GIGLIOTTI AND MICHAEL LINDEMAN MAMMALS do not normally visually perceive infra- red (IR) or ultra-violet (UV) light that exists on either side of the visual spectrum from 390 to 760 nanometers (nm) (Wolken 1975). There is no evidence to suggest that nocturnal mammals have become more sensitive to long wavelength light as an adaptive response (Lythgoe 1979), although some reptiles can sense longer wavelength, thermal IR radiation (Barrett et al. 1970). Because it is not perceived, and is unlikely to affect animal behaviour, IR observation can be an invaluable tool for wildlife researchers. This paper describes the construction and use of simple IR radiation sources that can be used for non-invasive behavioural observations of captive and free-ranging mammals. Description A 12 V sealed-beam or quartz-halogen automotive lamp is an ideal source of IR. Removal of shorter, visible wavelengths, is accomplished by placing a suitable filter in front of the lamp. Black perspex 962 (ICI Ltd: Sydney) is an opaque building material which acts as a near-perfect infra-red filter. Its spectral transmission characteristics (Fig. 1) indicate that the material will greatly attenuate visible light while providing approximately 80% transmission in the ‘near infra-red’ wavelengths beyond 800 nm. It is relatively inexpensive and will tolerate prolonged heat exposure. The 3 mm thick perspex can be purchased in sheets measuring 2.0 x 2.5 m which will allow the construction of an IR floodlight of any practical size. Poly Vinyl Chloride (PVC) water-pipe can be obtained in a variety of diameters and is a convenient light tight and weather proof material with which to work. Discs of 3 mm thick 962 perspex can be cut to fit into the recess in adapter inserts, which can be obtained for most PVC water-pipe. A light-tight seal can be produced by placing a bead of black silicon Fig. 1. Spectral characteristics of ICI perspex number 962 as percentage transmission of radiation between 400 and 1000 nm. Over 80% of radiation is transmitted in the near infra- red spectrum (> 800 nm) (Source: ICI Building Products technical data, Dandenong, Victoria.). sealant (Dow Corning or equivalent) around the circumference of the joins. In spite of the relatively good heat tolerance, the perspex will distort if lamps are positioned too close to it. As a general guide for bulbs rated up to 150 W, lamps should be spaced 1 mm away from the filter for every watt of power used. Construction of an effective ‘baffle’ ensures that reflected light is not transmitted from the rear of the unit while maintaining some degree of air flow around the lamp. A 3 mm thick disc of PVC and a water-pipe end-cap is an ideal baffle if they are each drilled with a symmetrical radial cross-pattern of 10 mm holes. Upon mounting in the housing these holes should be offset, so that light transmission is effectively blocked passed the second baffle. An internal coat of flat-black paint will also assist in reducing reflected light transmission (Fig. 2). Marks C, Busana F, Gigliotti F and Lindeman M, 2003. Practical infra-red illumination and observation techniques for wildlife studies using ICI-962 perspex. Australian Mammalogy 25: 201-203. Key words: infra-red, behaviour, video, night-vision, wildlife observation. C. Marks, F. Busana, F. Gigliotti and M. Lindeman, Vertebrate Pest Research Department, Victorian Institute of Animal Science, P.O. Box 48, Frankston, Victoria 3199, Australia. Email: camarks@attglobal.net. Manuscript received 18 June 2003; accepted 26 October 2003. 0 10 20 30 40 50 60 70 80 90 100 400 500 600 700 800 900 1000 nm % relative transmission