Shining a light on bird behaviour
13 September 2006
Current lighting systems used in the housing of many captive birds may not enable the animals to make reliable assessments of potential partners.
Captive birds are normally housed under conventional fluorescent lights. These lights work by flickering at twice the mains supply frequency, which in Britain is 50 Hz. Therefore, they flicker at 100 Hz or 100 times every second. Most humans are unable to detect this flicker since our visual systems do not work at a fast enough speed. However, it is hypothesised that avian visual systems ‘refresh’ at a quicker rate than those of humans, meaning that birds may be able to perceive the flicker. Even if the lights don’t actually appear as ‘stroboscopic’ to birds, the flicker could quite plausibly have an effect on their general welfare and behaviours dependent upon vision.
The flicker emitted had a negative effect on the females’ ability to inspect the males visually.
We decided to examine the mate choice preferences of European starlings under conventional fluorescent lights versus special high frequency fluorescent lights that do not emit perceptible flicker. With all other aspects of the lighting identical between treatments, we tested whether the flicker would affect the choices made by female birds. We let each female view a selection of four males and recorded which male she chose to spend the most time close to. We found that under high frequency lights, females concurred in their choices, all preferring the males with longer iridescent throat feathers, as is found with wild starlings. However, under the conventional low frequency lights, females did not agree on which male they preferred. In addition, individual females chose to spend the most time with different males under the two lighting types.
So why did females rank males consistently under high frequency, but not under conventional fluorescent light? It is possible that the flicker emitted by the conventional lights had a negative effect on the females’ ability to inspect the males visually. Background flicker impairs our own discrimination abilities and, in humans, conventional fluorescent lights can cause abnormal firing rates in the neurons leading from the eye to the brain, even though most people cannot consciously detect the flicker. We hypothesise that a similar response may also occur in birds. In addition, being placed under lighting with perceptible flicker may cause low-level stress. This could lead to a reduction in the birds’ attention and motivation levels under the conventional lights or cause them to become less ‘choosy’ with regards to mates. However, we need to conduct further work to establish which, if any, of these possibilities is correct.
Behavioural responses of starlings can alter under high frequency fluorescent light.
While this experiment shows that starlings differ in their choice of mates under the two types of fluorescent light, we cannot draw any definite conclusions from this study about their welfare status under these lights. However, both this experiment and other work by our group show that the behavioural responses of starlings can alter under high frequency as opposed to conventional fluorescent light. Previous results also indicate that groups of starlings choose to spend more time under high frequency rather than normal lights when given a choice. At the moment, we don’t know if normal fluorescent lighting appears as stroboscopic to the birds or if the flicker is only detected subconsciously, as is the case in humans. For example, humans experience more headaches, eyestrain and reduced performance on visual tasks under conventional fluorescent lights (which are commonly found in offices), even though most people are not consciously aware of the flicker.
Our findings suggest that the flicker rate of fluorescent light can have an effect on the behaviour of birds and that researchers need to be aware of the implications of the lighting type under which experiments are conducted. At the very least, they should report fully the lighting conditions that have been used in any research papers published. Looking towards the future, we now need to carry out more work looking both at a broader range of species and at a wide variety of welfare indicators before we can make any firm recommendations about the lighting arrangements used for the housing of captive birds in farms and zoos.
This article summarises: Evans, J.E., Cuthill, I.C. & Bennett, A.T.D. 2006. The effect of flicker on mate choice in captive birds. Animal Behaviour, 72, 393-400.