In our attempts to find a nestbox design for the 40spots, we are trying out limited volume boxes.
The original design, trialed successfully by Amanda Edgeworthy (ANU) some 20 years ago, worked very well for a while, until it was noticed that Striated pardalote and Tree martins were using the boxes as well, with the striated actually usurping the nest from 40spots, breaking their eggs and driving the 40spot parents out.
This, of course, is exactly the opposite of what researchers were trying achieve.
Working with Fernanda Alves (also of Difficult Bird Research Group at the ANU), trials have included reducing the entrance hole size. This has been partially successful, but there are concerns that this will put evolutionary pressure to reduce bird size as well.
Andrew Hingston, project manager of TWBBI is thus taking a different approach, which is reducing the volume inside the box by making the boxes themselves smaller. Again, it seems that this is working, as 40spots are preferentially using these boxes.
Boxes already deployed are being retrofitted to further reduce box volume as well.
Monitoring nesting during the upcoming breeding season will tell whether this is working.
