Observation

Category: Pages
Published: Monday, 11 January 2016 23:11

Night observation

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 animals have acute senses compared to us and they are usually aware of our presence long before we see them. Often I find an animal by its call or the noise it makes as it moves, then I locate it by eye-shine.

 

Attraction aids

Many animals can be attracted by playing their calls and sometimes the calls of other species. Recorded calls are often used during owl surveys, by photographers and I  use them when looking for owls at new locations. Call playback 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 locations to other photographers and twitchers, as the owls are sure to be harassed.

 

Vision

Vision is a complex sense which involves signals from the eyes which are interpreted by the brain. The retina at the back of the eye contains two fundamental types of light receptor cells, called cones and rods. Cones only work in bright light and rods only work in dim light. Diurnal animals including humans have cone dominated vision which enables excellent perception of colour with high visual acuity in daylight. Most nocturnal animals have eyes with relatively few cones and an abundance of rods which makes for excellent night vision but comparatively poor daylight vision. 

There are several cone types, each having a peak sensitivity to a different light wavelength. The brain 'sees' colour; not the eyes and it does this by combining the signals from each cone type, analogous to mixing primary paint colours to achieve all the colours of the rainbow. The more cone types a species has, the better its ability to distinguish colours. Mammals have either two or three cone types whilst birds, reptiles and fish have four, which provides them with superior colour perception and the ability to see ultraviolet light.

The graph below shows the colour sensitivity of the three types of cone cells in the human eye.

In very dim light cone cells don't function and the brain receives signals from the rod cells only. Rod cells in the human eye enable low light vision with poor visual acuity and no perception of colour. The images below are of a bioluminescent fungus. The upper view  shows how our eyes see the fungus at night and the lower view shows the true colour and high sharpness as seen by the camera.

 

 

Rod cells in the human eye and nocturnal animals have a spectral sensitivity of 400-600nm (see graph below) and are completely insensitive to red light (620-680nm). The significance of this is that you can observe most nocturnal animals with a dim red light without causing them excessive disturbance. Most animals can can see a red lamp, because their eyes also contain low concentrations of red sensitive cones.

 

White light

Intense white light torches and spotlights are great for finding animals but are not well suited to studying nocturnal behaviour or watching nesting owls. White light has the advantage that we can see the true colour of an animal's eye-shine, which can be useful for identification at distance. During a holiday in Sabah, Borneo, I heard a creature on the forest floor in the grounds of the hotel I was staying at. With the aid of a LED torch, I located it by its beautiful blue eye-shine (below) and it was a Mouse deer, not much larger than a rabbit. Bright white light can cause temporary night blindness lasting at least 10 minutes, during which time the animal may become susceptible to predation.

 

 

Red light

Rods don't see red, so for observing animals at night, headlamps that use red LED's are ideal. Dim red light does not disrupt an animal's night vision or your own. My favourite headlamp below, comprises a lens, a 3 watt red LED, a resistor to limit the current, a switch and a 3.7 volt rechargeable battery. It can be attached to a tripod and the beam can be focused or spread to control the width and brightness. The main disadvantage of using red light is that everything appears red.

 

 

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 using 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 white light was used, it probably would not have returned whilst I was watching or it may have abandoned its nest.

 

 

 

Walking at night

Long-sleeved shirt, long pants and sturdy boots are essential  to protect yourself from cuts, scratches and bites when walking in the bush at night. I prefer to walk along tracks rather than through bush because you can move quietly and are likely to see more animals. Depending on the weather and where I am, I may also take extra clothing, food, water, insect repellent, first aid kit and something to sit on. Unnecessary gear can turn a casual walk into a hard slog so I try to carry only the essentials.

Being in the bush by yourself can be very rewarding and you usually locate more animals when you are alone because your senses are heightened, however you need to be better prepared. In the dark your vision and sense of direction is poor and it is easy to become disoriented or fall on something you didn't see. 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 it out

·     Stay on the intended route unless I am familiar with the area or am carrying  navigation aids

·     When I venture off-track I always watch where I place my footsteps to avoid falling.