Australia's smallest and most common species of owl is in decline, and a Perth researcher is determined to find out why.

The boobook owl, named after its distinctive call, is not listed as endangered, but its population has been falling for the past 10 years.

Michael Lohr from Edith Cowan University is collecting samples from live and dead boobook owls across Perth and the Wheatbelt to investigate what is threatening the species.

"The basic purpose of this study is to understand some of the factors that are causing the decline in boobooks that might be associated with habitat fragmentation in urban areas and agricultural areas," he said.

Australia's smallest and most common species of owl, the boobook owl, is in decline ( ABC News: Irena Ceranic )

The study will look at a number of possible causes for the decline, including a loss of nest hollows because of land development, and inbreeding as a result of that reduced habitat, as they have less area to disperse to.

It will also examine secondary consumption of rat poison, by eating poisoned rats, and toxoplasmosis, a disease spread by feral cats which can affect the owls' reaction time.

It is hoped the findings will help identify why some other less common raptors are also diminishing.

"Potentially it has applications outside of just boobooks, and might help us to understand some of the reasons why other, rarer species have declined to the point that they are, but unfortunately they're more difficult to study at this point," Mr Lohr said.

The project is relying on the public to report live or dead boobooks so they can be sampled.