Owl-Friendly Margaret River Region

Main Club 4 November 2022

Dr Boyd Wykes started his career early, as a child, banding birds. During his studies, he did a PhD on the Helmeted Honeyeater, then had a career as an ornithologist, which brought him to WA. In retirement, he indulged his passion for birds by investigating Masked Owls (Tyto novaehollandiae) in the Margaret River region. Boyd showed a fascinating video about Masked Owls that can be seen at Boola Bardip WA Museum.

Initially, not much was known about the population, and their screeches could be mistaken for a Brushtail Possum – but on steroids! They were first seen in the Margaret River region in 2017. Ninety per cent of their diet is rats, which leads to them suffering impacts from the secondary effects of rat poison. This led to the forming of the group Owl Friendly Margaret River Region covering the Wadani lands. Boyd played a number of calls for us, and examples can be found on the website.

The Masked Owl is a large barn owl with dark dorsal and pale ventral feathers. It has an unbroken dark rim on the facial disc. There are eight bars on its primary feathers compared to three on a Barn Owl. Females with heftier legs and talons are around 900g compared to males, which weigh about 530g. Females often have chevron markings, and males have dots. When nesting, females will sit on the nest and not directly hunt for food; the male will feed her and the brood. Female vocalisations tend to be deeper than males. They catch prey using a ‘perch and drop’ method, whereas a barn owl typically flies around. Photo: 1

Five years of research have revealed a vibrant population in the Margaret River region. Its current status is enigmatic/threatened and shows it can shift its diet from native mammals or birds to rats and rabbits, depending on habitat and availability. Home ranges are 1000-3000 ha with an approximate diameter of 6 km from a suitable roosting tree or hollow. Nesting in southwest WA had not been described until Boyd began this study.

The study used sound recorders to determine presence and document nightly and seasonal vocalisations with activity, age, and gender. Mapping has been ongoing since 2017, using playback and subsequent response, roadkill, and wounded animals. Margaret River is surrounded by breeding Masked Owl pairs, and these were the first records for the southwest of WA of them nesting in trees and hollows. Records have also been made of roosting in foliage, compared to the east coast, which mainly uses hollows.

Once roosts were determined, a collection of pellets was conducted, and then a diet was determined, primarily feral rodents: 49% black rats & 33% house mice. This means that how we manage pest rodents can affect owls. Mike Lohr spoke at Club’s meeting some time ago on the effects of second-generation anticoagulant rodenticides (SGAR) and their impact on Boobook Owls and released a key paper. It was also found that there were high levels of rodenticide in the livers of Masked Owl corpses in the Margaret River region.

Boyd shared how rat poison = wildlife poison. We should control rodents with alternative methods and use first-generation poisons as a last resort since these are blood thinners and require multiple feeds but have a short half-life and minimal toxicity in secondary pathways. SGAR-affected rodents can take weeks to die, and they stagger around looking for water – hence becoming easy prey for owls – and have a long half-life. Typically, they are marketed as ‘one-dose kill’, and it can be hard to select the poison with the least secondary impact.

As part of Owl Friendly’s mission, the group raises community awareness of the owls and the impact of rodent poison. It’s making a difference, but it requires national regulation. The group made submissions to the Australian pesticides and veterinary medicines regulator in 2020, but an outcome is not likely until 2025.

Ry Beaver

1. [Photo: Northern Masked Owl
P Barden, CC BY 4.0 https://creativecommons.org/licenses/by/4.0, via Wikimedia Commons]