A TECHNIQUE FOR OBSERVING THE BEHAVIOUR OF 
SMALL ANIMALS UNDER FIELD CONDITIONS* 
By Michael H. Robinson and Nicholas D. E. Smythe 
Smithsonian Tropical Research Institute 
P.O. Box 2072, Balboa, Panama Canal Zone 
Small animals are difficult to observe under field conditions, 
and arthropods of less than 10 mm body length are particularly 
difficult subjects. When such animals are making complex move- 
ments with small parts of their body (mouth parts, reproductive 
organs) some device is needed to augment direct vision. One solu- 
tion to the problem is to use the zoom optics of a movie camera 
equipped with close-up devices (Robinson & Robinson, 1972). 
Recently, however, one of us (M.H.R.) studied the behaviour of 
Drosophila-sized flies that associate with orb-web spiders and 
spend long periods standing on the spider’s body. To find out what 
the flies were doing there it was essential to see them in close-up and 
be able to watch them, for long periods, under field conditions. 
Watching them through the macrosystem of a movie camera gave 
insufficient magnification. We solved the problem by adapting a 
stereo-binocular microscope for horizontal viewing. We feel that 
this adaptation has a wide variety of potential applications in field 
ethology. It may be a re-invention but is worth describing here. 
Making the Microscope Adapter 
Essentially the adaptation consists of making a mount that en- 
ables the microscope to be used on a camera tripod, for horizontal 
viewing and with a greatly extended focussing range. Any micro- 
scope can be used that consists of a subassembly comprising the 
optical and focussing systems that is clamped onto a vertical col- 
umn on the base subassembly. The optical/ focussing subassembly 
is simply detached from the conventional base and attached to a 
specially made horizontal column mounted on a tripod. All that 
is needed is a length of steel rod the same diameter as the support 
column on the original base. The rod has then to be modified to 
fit onto a tripod. This can be done in several ways depending on 
* Manuscript received by the editor September 7, 1976. 
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