Observing Nocturnal Animals
Night observation is very different from observation during daylight. At night we rely on our sense of hearing combined with sight and artificial light to locate animals. Nocturnal birds and mammals have very acute senses compared to ours and they are usually aware of us long before we see them. Most often I find an animal by its call or the noise it makes as it moves, then I locate it using eye-shine.
Many nocturnal animals can be attracted to the calls made by their own species and sometimes by the calls of other species. Recorded calls are often played during owl surveys and by photographers and occasionally I use them when I look for owls at new locations. Playing calls can be highly disruptive and stressful to the animal if not used judiciously and I do not encourage its general use. Playback should be avoided near nest sites during the breeding season. Owls are strongly territorial so you should resist the temptation of divulging their location to other potographers and twitchers, as word will quickly spread and the owl is sure to be harassed ("loose lips sink ships").
Eyes contains two fundamental types of light receptors called cones and rods. Day active creatures (diurnal) including us, have an abundance of cone cells of two to at least four different types depending on the species, each type having a peak sensitivity to a different spectral wavelength (colour). The brain combines the signals from each cone type to enable colour vision, analagous to mixing three primary paint colours to achieve all the colours of the rainbow. Cones in most species don't work at very low light levels and therefore they don't contribute to colour vision at night.
Rods can detect very low light intensity and enable nocturnal animals to see well at night. Rod cells in most species are sensitive to only one wavelength of light. In low light, cone cells don't work and the brain receives a single signal from the rods, which is why we humans and other diurnal animals don't see colour when it is dark. Nocturnal animals such as owls, cats and marsupials have retinas densely packed with rods and relatively few cones. This enables excellent vision in the dark but poor colour perception. The graph below shows that rods are sensitive to light around 500nm wavelength (cyan) and are insensitive to wavelengths longer than 650nm (deep red). Consequently, for watching nocturnal animals, deep red light is ideal because it causes minimum disturbance.
For observing animals at night I use home-made LED headlamps that use 630nm-660nm red LED's. As well as not disturbing the animal, red light does not spoil your own night vision. My favourite headlamp shown below, uses a 3 watt 630nm red LED and rechargeable lithium cell. It can be attached to a tripod and the beam can be spread to control the brightness. The main disadvantage of using red light is that you cannot see any other colour.
With red light, you are able to watch and photograph nocturnal animals behaving naturally. The photo below of a nesting Powerful owl was a 1/3 second exposure at f6.3 and ISO 6400 illuminated with the headlamp shown above. I observed this nest for many years with the aid of red light and the owls were always aware of my presence but were unconcerned. I watched this adult leave the hollow on dark and return a short time later with a Ringtail possum to feed its young. If I had used white light it probably would not have returned whilst I was watching or it may have abandoned the nest.
A white light is the second best option for viewing animals at night and has the advantage that you can see true colours and the colour of the animals eyeshine which can be useful for identification at a distance. During a holiday in Sabah (Malaysian Borneo) I heard this animal in the forest just outside my hotel and with the aid of a LED torch held close to my own eyes, I located it by its beautiful blue eye-shine. It was a Mouse deer, not much larger than a rabbit.
Clothing and gear
Long-sleeved shirts, long pants and sturdy boots are essential in the bush at night to protect from cuts, scratches and bites. Depending on the weather, where I am going and for how long, I may also take warm clothing, rain jacket, snacks, water, insect repellent, first aid kit and something to sit on.
For a casual walk or scouting a new location, I may take only a headlamp. On other occasions I may take a map, GPS, camera and sound recorder. If I am watching a nesting owl, I may include tripod, binoculars or an Infrared viewer. Carrying all this gear can turn a casual walk into a hard slog.
Safety at night
Being in the bush can be very rewarding and you usually locate more animals if you are alone because your senses are heightened. When alone you need to be better prepared and more careful. Your vision and sense of travel direction is poor compared to during the day and it is easy to become disoriented, lost or fall on something you didn't see. Each of these experiences has happened to me and now when I venture out alone I always:
· Tell someone where I am going and when I expect to return
· Know my exact location at all times and if unsure, stop until I have worked out where I am
· Stay on the intended route unless I have navigation equipment or am familiar with the area
· When I venture off-track I always watch where I place each footstep to avoid a fall.