BACK TO NATURE - Rainbows and Roosts

By Jamie Walker

Last year, as the chill of winter increased, I noticed parties of Sulphur-crested Cockatoos passing over our house in early evening and heading in the same direction. In May, there were six or seven in each party: by July there were two dozen. I believe they were making for a night roost at The Narrows, where the Obi Obi Creek flows out of Baroon Dam.

Over the same period, I noticed more and more Welcome Swallows dropping into the Maleny Wetland’s rush tussocks as the light faded.

Communal roosting is a well-known bird habit. In the suburbs, people are accustomed to noisy congregations of Rainbow Lorikeets and Little Corellas, flighting to the same trees each evening.  

It’s not only birds that gather together to rest and sleep. Microbats of many species use daytime roosts in caves, tree hollows, mine shafts, tunnels, deserted birds’ nests and under bridges. And the daytime ”camps” of Flying Foxes are, in effect, roosts.

Butterflies on migration also roost together in sheltered places – each insect often passing the night concealed under a leaf.

It seems obvious that roosts provide safety in numbers, but there are many other reasons why these assemblies have developed as a chosen system. Mutual co-operation is very important to some birds (as is mutual warmth). Energy is conserved, and body-heat is maintained, when the tension of vigilance is shared with others and when the day’s last meal can be digested in an atmosphere of comparative safety. An individual’s risk of being predated reduces if each bird is lost in a crowd; and the young benefit from choices made by the more experienced.

In late autumn, North Maleny witnessed a magnificent roosting event. Up to one thousand Rainbow Bee-eaters gathered at dusk to spend the night in a single, thickly leaved tree (ironically a Camphor Laurel) growing in an open meadow. When we first arrived at the site, there were only a handful of birds present; but, as the sky darkened, hundreds more (making their signature trilling call) began to arrive.

Birds flew in from every direction. (Those coming from the Wetlands had no doubt been feasting on the last of the season’s dragonflies). At first, they lined up on the telephone wires before rising to become a loud swarm. Individuals then began to dive into the roost tree, as one or two appeared to stand sentinel on its top. Finally, there was a mass descent into the foliage as darkness fell, and then an abrupt hush, as though each bird felt a signal, and the performance was ‘switched off’.

Shelter, safety, warmth, the shared awareness of companions – so simple, so sensible and, as a life support system, so effective.