Observing Animals at Night
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, which is the reflection of light from the retina.
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 I occasionally 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 others, as word will quickly spread and the owl is sure to be harassed ("loose lips sink ships").
The eye contains two fundamental types of light receptors called cones and rods. Diurnal (day active) birds and mammals including humans, have high densities of cone cells of two to four different types depending on the animal species, each having a peak sensitivity to a different spectral colour. The brain combines the signals from each cone type to enable colour vision. Unfortunately, cones are insensitive at low light intensity, which is why we cannot see colour outside at night.
Human Cone sensitivity
Rods can detect very low light intensities and enable vision in near darkness, however rods are only sensitive to one spectral colour, which is why we only see in shades of grey 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 at night but very poor colour perception. Rod cells are sensitive to light around 500nm wavelength (cyan) and are insensitive to wavelengths longer than 650nm (deep red). From this it follows that for watching nocturnal animals deep red light causes minimum disturbance.
For nocturnal observation red light has several advantages over white light. I have used home-made red headlamps made with 630nm and 660nm 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 3.6 volt lithium battery . It can be attached to a tripod and the beam can be spread to vary the brightness. The main disadvantage of using red light is that you cannot see other colours.
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 have observed this nest for many years with the aid of red light and the birds 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 chick. If I had used white light it probably would not have returned whilst I was watching or if this was earlier in the season, 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 the true colour of an animals eyeshine. During a holiday in Sabah (Malaysian Borneo) I heard this animal in the forest just outside my hotel and with the aid of a 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 and spare battery. On other occasions I may take a map, GPS, photographic gear and sound recorder. If I am watching an nesting owl, I may include tripod, binoculars, special lighting or an Infrared viewer. With all this gear a casual walk can soon become a 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. Being 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 if you are not prepared and careful it is easy to become disoriented, lost of fall and injure yourself on something you didn't see. Each of these experiences has happened to me and now when I venture 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, I stop until I have worked out where I am
· Stay on the track or the intended route unless I have navigation equipment or am very familiar with the area
· When I venture off-track I always watch where I place every footstep to avoid a fall.