For bird-watchers, winter is the time for caliology – that’s the study of birds’ nests in case you are wondering.
During this time of year with trees and shrubs stripped of leaves, nests are easy to find. The nests of bigger sticks built by ravens and currawongs are also blown from trees in winter storms.
The subject of nests came up when I was invited to appear on ABC Radio’s Afternoons with Joel Rheinberger recently, in their current daily segment devoted to “ologies”.
As I explained, my interest in bird nests stemmed from my schooldays when I collected birds’ eggs with my friends, a practice that is now not only discouraged but outlawed.
I never felt comfortable taking the eggs and instead concentrated on viewing the nests.
I was amazed at their complex construction. The nests were also exceedingly beautiful. To this day I call nests the gems of the hedgerows.
Nests come in all shapes and sizes – cups, platforms, domes and hanging constructions. There are also floating nests, built by grebes. As with the variety of shapes, there is a variety of building materials – sticks, twigs, leaves, grasses, mosses, mud and even saliva used as cement.
The goal is to keep eggs and chicks safe but in the process the birds build marvels of engineering, which can withstand the stresses and strain of gravity, winds and rain and even attempts by predators on some occasions to pull them apart.
Birds are really intelligent animals. They use their intelligence, along with their beaks and feet, to find the most clever ways to make nests with whatever materials are available.
Instead of actually building nests, about a quarter of Australian bird species use tree hollows or dig burrows. The beautiful spotted pardalote, for example, digs a tunnel.
For the cavity nesters, not all holes suit all birds. Some species are very fussy about what holes they choose. The endangered swift parrot needs a hole with a very long drop and the bigger parrots, like yellow-tailed black cockatoos, needs large holes that are only formed in old-growth trees at least 80 years old.
Not all birds build nests. Shorebirds simply lay their beautifully camouflaged eggs amid sand, shells and pebbles. And some seabirds lay eggs on the bare rock of cliff faces.
I was not the only one to talk birds on the “ologies” segment. A few days previously avian ecologist Dr Jennifer Lavers described how plastic pollution was impacting birds, especially seabirds which were eating plastic items and feeding them to their young.
Caliology has also not escaped the plastic menace. Birds are increasingly using the material to build their nests, as evidenced by the sight of kelp gulls in spring towing long sheets of plastic across the Hobart sky. They are travelling from the tip to offshore islands, where they build DIY homes.