I’ve been reading about flight initiation distance in birds – an issue of concern to wildlife managers as they try to reduce human disturbance by using FID to develop set back distances for paths and viewing areas in bird sanctuaries. And an area of interest for bird photographers.
While the benefits of leaving in the face of a predation threat are fairly obvious, there are also costs in leaving and benefits in staying (the energy costs in flight, the benefits in remaining in a good foraging spot or continuing an activity such as courtship), so birds could be expected to vary their FID on the basis of an assessment of the relative costs and benefits of leaving or staying.
In one study, observers walked towards a bird at a constant pace of approximately 1.0 metre per second, while maintaining eye contact, and recorded the distance at which the bird initiated flight. Each flush was conducted using one of three different treatments: one person directly approached a bird; two people side–by–side approached a bird; and two people directly behind one another approached a bird. The study found that invariably the bird flushed sooner when there were two observers, but that there was little difference in the FID whether the observers walked side-by-side or directly behind one another.
Another study found that for 64 of 68 species of Australian birds, the starting point of the observer had a significant impact on the FID. The further away the observer was when spotted by the bird, the greater the flight initiation distance. The researchers hypothesised that this may have been because of the energy costs of continually monitoring an approaching predator. They also noted that a range of factors such as time of day, season of the year, and acclimatization to humans affected FID.