Vet Felicity Bradshaw extracting the liver of a Masked Owl Photo B Wykes

Vet Felicity Bradshaw extracting the liver of a Masked Owl Photo B Wykes

LOCAL RESEARCH

Prompted by Mike Lohr’s revelations from Boobook analysis, the Owl Friendly team have forwarded to the Edith Cowan University team as many fresh corpses of owls and other wildlife as possible, sourced from members of the public, wildlife carers and vets.

Analysis of their livers is helping to determine which species are at high risk from rodenticide poisoning.  We also need to understand how the poisons get taken up by the various wildlife species, both through various means of directly accessing baits and through a range of potential secondary food pathways.

A vibrant Masked Owl population is enabling a unique capacity to investigate potential poisoning of this Priority 3 listed species. A treasure trove of pellets containing remnants of bone and hair are being analysed to determine the diet of local Masked Owls and half a dozen corpses have been obtained to date for liver analysis.

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CLUES TO THE OWLS’ DIET
CAUSES OF DEATH

CLUES TO THE OWLS’ DIET

Fresh and dried Masked Owl pellet Photos B Wykes

Local research has shown that the prey eaten during a night by a Masked Owl – small animals such as mice swallowed whole, larger prey in chunks – is digested through the day and coughed up, first thing on waking, at the roost or a nearby perch. Masked and Barn Owl pellets have a distinctive, glossy black coating. Hundreds of regurgitated pellets containing the fur and bones of prey have now been collected at hard-won locations of adult and fledgling roosts high in dense tree foliage.

Initial drying and sorting of the contents shows that the Masked Owls of the Margaret River region are primarily feeding on rats and mice, likely obtained where abundant around human homes and enterprises. Plus occasional rabbits and the odd morsel of their original diet of native mammals including phascogale, mardo and western ringtail possum.

Rat skull ready for ID

Rat skull ready for ID Photo B Wykes

bush rat reference corpses
bush rat reference skeleton

Prey specimens and derived reference skeleton of a native bush rat Photo B Wykes

Systematic, accurate analysis of pellet contents is a skilled, time-consuming task being undertaken with support from professionals at the WA Museum and Edith Cowan University. Their expert advice and reference skeleton collections are being used to tackle a first batch, with ID based on distinguishing features of skulls, jaws and leg bones. Once skills are gained, our team will complete the work independently using a reference collection prepared from local specimens.

CAUSES OF DEATH

With little research previously conducted on rodenticide poisoning of wildlife in Australia, a wide range of species is being tested for levels of rodenticide by ECU and allied research bodies around Australia, funded by concerned government agencies.

Masked Owl - primary cause of death electrocution

Masked Owl – primary cause of death electrocution Photo B Wykes

The first place to look for rodenticide poisoning of wildlife is veterinarian clinics and wildlife care facilities where the most likely victims will be animals found debilitated and dying without obvious causes of physical trauma such as road collisions and attack by animals.  However, Mike Lohr’s finding of rodenticides in livers of many Boobooks for which cause of death was apparently a clear cut case of trauma reveals the insidious nature of anticoagulant poisons – non-lethal levels of internal haemorrhaging are debilitating, leading to poor condition, susceptibility to disease, poor capacity to compete for territory and diminished feeding skills.  On this basis, the Owl Friendly team have been freezing and forwarding fresh dead wildlife that comes their way.  Key sources are members of the team – veterinarian Felicity Bradshaw, raptor champion Phil Pain and wildlife carer Linda Moyle. Many have also been provided by contacts in the wider community on an opportunistic basis.

Testing is being conducted on potential victims of primary poisoning. In addition to introduced black rats and house mice, native mammals and marsupials that may be directly poisoned by eating baits include native Bush Rats, Quenda, Brushtail Possums, perhaps Western Ringtails. However many bait stations are readily accessed and attractive to insects and other invertebrates which are not harmed by anticoagulants but can pass these on to their predators.

Bait-attracted reptiles such as Kings Skinks and Bobtails are a special case – they seem to have a high degree tolerance to anticoagulant rodenticides and as such may pass on high doses of poison to their predators.

Potential victims of secondary poisoning that are being tested are wildlife that eat all of the above. The most obvious groups are nocturnal birds – owls, frogmouths and Owlet-nightjars – and nocturnal predatory marsupials – Dunnart, Mardo, Brushtail Phascogale, Chuditch.  However, many diurnal (day) birds may obtain nocturnal rodent and other wildlife prey, particularly individuals that are dead and dying.  Add to that the many bird species that may feed on reptiles, insects and other invertebrates that access bait stations.

phascogale corpse

Phascogale – primary cause of death unknown Photo B Wykes

liver extracted from Phascogale

Vet Felicity Bradshaw extracting the liver of a phascogale Photo B Wykes

It’s early days for pulling together the full picture on rodenticide poisoning of wildlife in our region – what species are being impacted, the degree of impact, the sources and the locations within our landscape. However, in addition to presence in the three Masked Owls for which results are back, rodenticides were found in an Osprey from Busselton, a diurnal fish-eating bird of prey, which is very concerning.

Meanwhile there is a simple message to take on board:

poison is poison and why would you let that loose in our environment knowing what we already know?

This clip of a roadkill Masked Owl being examined by wildlife specialist veterinarian Felicity Bradshaw provides a sad but fascinating insight into the science behind a campaign to protect these enigmatic, charismatic forest owls. Just when Margaret River owl enthusiasts, retired ornithologist Boyd Wykes and lawyer/photographer Steve Castan, aka estabanthenatureman, were discovering Masked Owls living ‘in plain sight’ on our town outskirts, feeding on introduced rats and mice, liver testing was showing that Boobooks and likely other owls are being poisoned by widely used anticoagulant rat baits.

This second clip of a roadkill Masked Owl being examined by wildlife specialist veterinarian Felicity Bradshaw, showing the internal examination, provides a sad but fascinating insight into the science behind a campaign to protect these enigmatic, charismatic forest owls. Just when Margaret River owl enthusiasts, retired ornithologist Boyd Wykes and lawyer/photographer Steve Castan, aka estabanthenatureman, were discovering Masked Owls living ‘in plain sight’ on our town outskirts, feeding on introduced rats and mice, liver testing was showing that Boobooks and likely other owls are being poisoned by widely used anticoagulant rat baits.