Filling In the Holes

Many birds depend on tree hollows for nesting. But these cozy cavities are disappearing as old trees are cut down, and new trees can take a long time to form hollows. If people don’t take action soon, researchers warn, birds such as Australia’s superb parrot could go extinct.

Almost one-fifth of bird species in North America, Europe, Australia, and southern Africa build nests in tree hollows. Once trees with hollows are gone, replacing them can be a slow process. A tree might have to grow for more than 120 years to generate big enough hollows for birds.

The superb parrot (Polytelis swainsonii), which lives in southeastern Australia, relies on the hollows of trees such as yellow box and red gum. Researchers studied one of the parrot’s breeding areas, where much of the forest has been reduced to patches. Using tree data from 48 sites, the team ran a computer model to predict how the number of hollow-bearing trees would change over time under different management scenarios.

Right now, about 3.9 trees per hectare have hollows large enough for superb parrots to build their nests. If people don’t change the way they are managing the forest, that number will drop to about 0.5 in the next two centuries, the team estimates. But if people take immediate steps to restore the forest, the density could reach 4.1 trees per hectare during that time.

Another possible solution is to offer the parrots artificial nest boxes. But superb parrots have so far ignored more than 3,000 nest boxes in their breeding areas. Roberta Kwok | 18 December 2012

Source: Manning, A.D. et al. 2012. Hollow futures? Tree decline, lag effects and hollow-dependent species. Animal Conservation doi: 10.1111/acv.12006.

Image © Jessmine |