Our meeting topic in June was Hollows as Habitat and was presented by Club Member John Gregurke. Here are some notes from his talk and the photos are by another club member.
If you mention hollows many people immediately think of the ones in standing trees but they are also found in fallen timber, in the trunks that fall into rivers, rock crevices, burrows and caves. All sorts of fauna require hollows for breeding and or shelter including mammals, reptiles, birds and frogs and fish. The list of birds for the Ballarat area includes 30 birds that need access to hollows. Across Australia 114 of the 700 species of birds need hollows.
Different animals have different requirements for hollows particularly in relation to the size of the entrance and the depth, width or angle of the hollow. River Red Gums have the best hollows of those trees utilized around Ballarat and form them readily when limbs break off.
Peppermints to a lesser extent, as they struggle to reach more than 30cm in diameter and you don’t often see hollows in the trunk. Like stringybarks, many hollows occur near the base, especially where trees have been cut off and regrow. These hollows are good for antechinus but are also the ones most often lost in fires. Manna gums have useful hollows as do candlebark.
Silver banksias often reach a size to develop hollows but more often it is small mammals or bees that take up residence rather than birds. Large hollow trunks of many eucalypts on the ground provide very useful habitat, foraging areas and protection for a range of species. As the wood rots, nutrients are returned to the soil and organic matter is added.
The ‘Loss of hollow bearing trees from Victorian native forests’ is listed as a Potentially Threatening Process under the Flora and Fauna Guarantee Act 1988. There are many threats to hollows including land clearing, logging, firewood collection and fire. Dead trees are often cut before they have a chance to develop into hollows.
John referred to an interesting example of the decline in old trees from a website by Ian Lunt. Ian studied aerial photos from the 1940s from an area near Dunkeld and overlaid the image from Google Earth. Much to his surprise over the past 65 years, the Dunkeld woodlands haven’t shrunk but they haven’t expanded either. The boundary between the grasslands and the woodlands hadn’t changed. What is worrying is there isn’t a single new tree in the big paddock. About 7% (approximately 31 of 428 trees) had died since 1948. All of the paddock trees are old and the only new trees are along the roads.
Given the continuing loss of hollows there is interest in building and installation nest boxes as replacements. In many area they are an important aspect of wildlife conservation where natural hollows are not available. Threatened species such as the Powerful Owl, the Barking Owl, Red-tailed Black Cockatoos and the Brush-Tailed Phascogale all use nestboxes where provided. Nestboxes are not a long term substitute and we should be managing the land to protect hollows. Here is a link to some nest box designs