Tree hollows

By Gayle Osborne

Where does much of our wildlife live and breed? Hollows in trees provide homes and nests for 17% of bird species, 42% of mammals and 28% of reptiles in Australia (Gibbons and Lindenmayer 1977).

The formation of hollows is a slow process. Hollows can take up to 100 years to form and it is estimated that large hollows can take 250 years. As trees age, storm and fire cause damage to the protective coating of the tree allowing termites and fungi access to the heartwood. Branches are lost and eventually decay (microbial activity) will create a home for many species. Gum species, such as Manna Gum and Candlebark, tend to produce more hollows in a shorter period of time than Stringybarks, such as Messmate.

In the Wombat Forest logging has reduced much of the forest to vast areas of regrowth and is probably one of the reasons for low densities of some birds and mammals. Fire also helps to create new hollows, but destroys existing hollows by entering at the base of the tree and burning through the already damaged heartwood.

Who needs these hollows? In the Wombat Forest the list includes Greater Gliders, Sugar Gliders, Feathertail Gliders, Common Brushtail Possums, Mountain Brushtail Possums, Common Ringtail Possums and Brush-tailed Phascogales. Some bat species use hollows and others roost under peeling bark or in caves.

Throughout Australia birds are the major users of hollows. In the Wombat they include Kookaburras and Sacred Kingfishers, Powerful Owls, Boobooks and Owlet-nightjars, Sulphur Crested Cockatoos, Gang Gangs and Crimson Rosellas, Treecreepers and Dusky Woodswallows.

Hollow logs on the ground are also used by many native fauna species. These include the Spotted Tail Quoll, a native cat which is rare in Victoria, but we believe still exists in the Wombat. Many other small mammals use hollows in fallen timber and Echidnas rest in ground hollows, often in the burnt base of a tree. Some species of native fish use submerged hollows for shelter and to attach their eggs. Everyone needs just the right size home. The Sugar Glider will choose a hollow with a narrow entrance to deter predators, the White Throated Treecreeper prefers knot holes in tree trunks whereas the less common Red Browed treecreeper prefers to nest in sloping dead hollow spouts. The size of the entrance, the size of the hollow, degree of insulation and position on the tree determines which species will use the hollow.

Many species, particularly gliders use a number of hollows so that their predators cannot predict where they will emerge from to feed. Water also catches in some hollows and provides a drinking source. The protection of hollow bearing trees and those with immediate potential for hollows is very important for our wildlife. Hollow users play a large role in the pollination of plant species. Managing your own property to protect habitat should be a priority. When walking in the forest, take the time to look for tree hollows. It’s not uncommon to see a parrot popping in a hollow to feed its young in Spring. It is a great delight to spot hollows and guess who may live there.