By Lara Pacillo
A one-millimetre difference in the size of a nest box entrance could help rare little pygmy-possums recover after bushfire, according to new research by Adelaide University, Kangaroo Island Research Station, and Kangaroo Island Dance School.
Two species of pygmy-possum are found on Kangaroo Island: the common western pygmy-possum and the rare little pygmy-possum. The little pygmy-possum is known to be strongly affected by fire and lost 88 per cent of its recorded range on the island during the 2019-20 Black Summer bushfires.
The study, published in Australian Zoologist, examined whether smaller nest box entrances could be used to exclude the western pygmy-possum from boxes intended for little pygmy-possums on Kangaroo Island.
Lead researcher Associate Professor Sophie Petit, from Adelaide University’s School of Biological Sciences, said the study forms part of the Kangaroo Island Nest Box Project, a community-supported bushfire recovery project investigating the role nest boxes can play in supporting wildlife after fire. Kangaroo Island Dance School assisted with the construction of the nest boxes.
“The Nest Box Project was set up to determine scientifically the role of nest boxes in bushfire recovery after the Black Summer Bushfires, with the help of the community,” Dr Petit said.
“Volunteers have been involved since day one and we are very grateful to all who participated in building, deploying, and monitoring boxes, and supporting in other ways.”
Monitoring at several sites on the island found nest boxes with 20-millimetre openings were used by western pygmy-possums, but not little pygmy-possums, raising the possibility that the slightly larger and more common species could be outcompeting little pygmy-possums for boxes.
Western pygmy-possums were also recorded using 16-millimetre entrances, although they preferred larger openings.
Researchers then trialled 13 nest boxes with different opening sizes at an unburnt Kangaroo Island site known to have little pygmy-possums. The only two boxes with 15-millimetre entrances were occupied by little pygmy-possums, while boxes with 20-millimetre entrances were occupied by western pygmy-possums.
Dr Petit said the observations suggest nest box design could be refined to support rare species, but more work is needed before the design can be widely applied.
“The findings mean that technically it may be possible to exclude western pygmy-possums to benefit little pygmy-possums using boxes with entrances just one millimetre smaller, but more research is needed with larger sample sizes, which is always difficult to achieve when one works with rare species,” Dr Petit said.
“In addition, we do not know whether little pygmy-possums can reproduce in boxes with 15-millimetre entrances and how different species interact at nest boxes. Are they able to defend their box, for example.”
In a previous study, Dr Petit and her team discovered that carnivorous Kangaroo Island dunnart used nest boxes with 20-millimetre openings.
“An encounter between dunnarts and pygmy-possums could create fireworks, and the dunnarts would probably be the ones enjoying them,” warned co-author Peter Hammond from Kangaroo Island Research Station.
Dr Petit said the research shows wildlife interventions need to be tested carefully, particularly when they may benefit one species over another.
“Any wildlife intervention can have risks. In this case, a difference of one millimetre for a nest box entrance hole was significant for small animals,” Dr Petit said.
“We must not think of nest boxes as toys or fun little houses for little animals. The role of nest boxes must be examined scientifically.
“They can have implications for genetic selection if breeding sites are limiting, conservation, ecological research, and animal welfare.”