Hollows as Homes

This is a guest post by Dr Adrian Davis, Hollows as Homes coordinator and Research Associate at the University of Sydney. 

In urban and agricultural areas large, hollow-bearing trees are in decline, but many species of animal rely on them. In Victoria, hollow-using species include at least 31 mammals, 60 birds, 38 reptiles, 15 frogs and many insects (such as bees). Of these, at least 33 species are listed as threatened with extinction. This is why the ‘loss of hollow-bearing trees’ has been listed as a key threatening process nationally.  Hollows as Homes is a citizen science program asking you to report hollows in your local area, and the wildlife using the hollows – but more on that later.

Farms and agricultural areas are often characterised by large, old, isolated trees, or small clusters of trees. These clusters often act as ‘stepping stones’ and can be vital in linking up other small patches of trees on adjacent farms, allowing wildlife to more easily move throughout the landscape. Even a single standing tree with a hollow can provide valuable habitat and provide a nest or roost for an animal that would otherwise not be able to live on that farm. A good example of an animal that depends on clusters of trees on farms is the superb parrot, listed as vulnerable to extinction, which uses paddock trees for nesting, feeding, perching and protection. Retaining existing hollow-bearing paddock trees, ensuring that younger paddock trees are maintained so that they form hollows, and gaining a greater understanding of how wildlife use paddock trees is vital to maintaining wildlife in our agricultural areas.

Cut in hollow for small bird. Photo: John Martin.

Cut in hollow for small bird. Photo: John Martin.

 It’s not just on our farms that hollow-bearing trees play an important role, but within the bush and urban regions as well. Large, old trees - those most likely to contain hollows - are rare in urban areas. If you’re lucky, your local park or street may contain one of these trees; a grandparent of the bush. If you’re even luckier, this tree will contain hollows, although this isn’t guaranteed. In general, our urban areas contain young trees; however, it is likely that many of the species planted will never form hollows, or be allowed to form hollows for reasons of public safety (in case the tree falls). Urban bushland typically contains only half the number of hollows that are present in bushland outside metropolitan areas, and there are fewer hollows in urban parks and streets.

Importantly, not all hollows are the same, and some species prefer particular types of hollows (for example, a deep hollow, a hollow with a small entrance, or a ‘pipe’ style hollow). When we lose the hollow-bearing trees, we also reduce the number of different types of hollows, which can result in competition between wildlife, with some species losing out to more dominant species, such as the rainbow lorikeet taking a hollow from the eastern rosella. It has been shown that there are more aggressive interactions at hollows in urban areas than there are in natural bushland.

Hollows as Homes aims to increase the knowledge and understanding that we have about tree hollows: the distribution of tree hollows, the types of hollows available and how wildlife use tree hollows, including nest boxes and cut-in hollows. In areas lacking natural tree hollows, supplementary hollows, in the form of nest boxes or cut-in hollows, are often provided. However, the effectiveness of these alternatives is still not entirely understood. To help us understand more about how wildlife use tree hollows, nest boxes and cut-in hollows, we are asking people join in the Hollows as Homes program.

Choose a tree in your garden, street, park, bush or paddock that has a hollow or a nest box and report it through the website (this also works as a web-app on your phone). You can provide details about the tree and hollow, such as tree height and the direction the hollow is facing. Ideally, the hollow is in a location that you periodically encounter, such as while walking the dog or sitting in your garden. This provides occasional opportunities for you to observe wildlife using the hollow. If you see that any animals or insects are using the hollow, you can add these observations to your original report of the hollow through the website.

Galah at nest in tree hollow. Photo: J Turbill (OEH)

Galah at nest in tree hollow. Photo: J Turbill (OEH)

In addition, people can participate as a group, designating an area that they regularly visit and collectively assessing the trees for hollows and adding wildlife observations. The group option is ideal for bushcare sites, landcare programs, parks, schools, golf clubs, community gardens, and many more. An unlimited number of people can participate in a group, and, importantly, anyone who is part of the group is able to both view and add wildlife sightings to any of the reported tree hollows or nest boxes within the group boundary.

The information reported through Hollows as Homes will be accessible to the public, especially to land managers. Ideally, this information will inform conservation planning to conserve habitat trees and the provision of supplementary habitat, as well as our understanding of exactly which species are inhabiting our own backyards.

For information on how you can be a part of this program, visit the Hollows as Homes website or Facebook page. Alternatively, you can email Dr Adrian Davis for more information.

Hollows as Homes is a collaborative project between the University of Sydney, the Royal Botanic Garden Sydney and the Australian Museum. It is supported by funding from the Australian Government.

Cover image by Simone Cottrell.