Raptors and Rodenticide

Birds of Prey or “Raptors” are fascinating birds of our skies, or in the case of Owls, of the night.

Many of us would have experienced the exhilaration of watching raptors like Wedge-tailed Eagles and their total command of flight.  Or an Osprey diving to superbly scoop a fish out of the water.  Or an Owl floating silently across the road caught in our vehicle headlights.  Or a Kestrel hovering in expectation over an open field

Powerful as they are, raptors suffer many threats to their survival.  These increasingly include the dangers of feeding on rodents such as rats and mice which have been poisoned by anticoagulant rodenticide (ARs) set in the home or on the farm.  Owls in particular take poisoned rats or mice because they are nocturnal (mainly Barn and Southern Boobook). Kestrels, Swamp Harriers, Kites (Black–shouldered and Whistling) and Goshawks (Brown and Collared Sparrow Hawk) are also affected.

Research here in WA has found 73% of samples tested from Boobook Owls had detectable exposure levels to ARs and 18% had levels high enough to kill them directly. Most of the toxins were second generation anticoagulants (SGARs) which take longer to break down in the body and can ultimately cause the death of the raptor. First generation ARs (FGARs) break down more quickly in the body and although harmful are not as lethal for raptors as SGARs.

There are alternatives to bait, including traps of various types but if you really do have to use bait, choose the less harmful rodenticide with the FGAR compounds “Warfarin” or “Coumatetralyl”.  Avoid the more harmful SGARs containing “Brodifacoum” or “Bromadiolone”.

Raptors such as the Boobook and the Barn Owl are in decline and the evidence indicates that rodenticide is one of the main culprits. By poisoning these raptors indirectly in this way we are reducing the very predators that would help to control the rodent numbers in the first place.

Southern Boobook Owl
Eastern Barn Owl
Nankeen Kestrel