Could chainsaws fix our animal habitat problem?
The plywood nest box is a familiar sight in woodlands, parks and backyards across Australia.
Many thousands have been installed over the past decades as homes for birds, bats, marsupials and other native animals to replace hollows in old trees that have been chopped down.
But what if, under certain circumstances, those artificial homes do more harm than good? And what if the very tool used to fell forests – the chainsaw – could be the key to providing better shelter?
Those are some of the questions raised by a group of Melbourne researchers who have spent several years comparing naturally occurring tree hollows to their artificial replacements.
The team from La Trobe University, the University of Melbourne and the Arthur Rylah Institute released a scientific paper last month comparing natural tree hollows to nest boxes – as well as another artificial alternative: hollows carved directly into living trees with chainsaws.
Lead author Steve Griffiths said the paper was part of a growing body of research into chainsaw-hollows, but the first in the world to provide evidence that they make well-insulated homes.
Which could not only make for healthier animals but, in times of extreme weather, be the difference between life and death.
“Natural tree hollows, as a general rule, are very well insulated,” Mr Griffiths said.
“So they are quite well buffered from large variations in day-to-day ambient temperatures – they provide relatively constant and stable microclimates.
“In comparison, nest boxes often have very thin walls and they heat up and cool down a lot over a 24-hour cycle so, particularly in summer, you end up with nest boxes getting much hotter during the day than tree hollows and at night they often get much colder.”
The researchers found nest boxes could be both five degrees hotter and colder than tree hollows.
Co-author Pia Lentini, from the University of Melbourne School of Biosciences, was most concerned about how the animals and birds in the nest boxes reacted to heat waves and cold snaps.
During periods of extreme heat, for example, nocturnal animals sleeping in hot nest boxes may become stressed and abandon their boxes in desperation, entering the bright light of day where they become easy prey.
For newborn animals, the potentially fatal effects of extreme temperatures are even more immediate.
“We’ve got over 200 species in Australia that rely on tree hollows for shelter from predators and the elements – and these structures are only going to become more important as extreme weather events become more common,” Dr Lentini said.