Death by dinner…
Barred Owl vs. Rough-skinned Newt
In April, three owls were found dead over a couple weeks on Protection Island, a small island near Nanaimo, BC. One of these, a Barred Owl (Strix varia) was submitted to the BC Animal Health Centre, home of the BC node of the CWHC. The owl was emaciated and had a mostly-intact rough-skinned newt (Taricha granulosa) in its proventriculus (the avian equivalent of a stomach). No other gross or microscopic lesions were apparent, resulting in a diagnosis of suspect tetrodotoxin toxicity.
Rough-skinned newts are extremely toxic, producing a type of tetrodotoxin. Toxin production varies between individuals and throughout the range, but most newts can produce enough toxin to kill 25,000 mice, earning them the title of the most toxic amphibian in the Pacific Northwest.
Tetrodotoxin is a very potent neurotoxin; 1-2 mg is lethal for an adult human. It is most famous as the cause of death in gourmands eating poorly-prepared fugu, a Japanese delicacy prepared from pufferfish, but is found in several other species including sunfish, triggerfish, blue-ringed octopuses, moon snails and, of course, rough-skinned newts. Tetrodotoxin kills by binding the voltage-gated sodium channels in nerve cell membranes blocking the passage of sodium into the nerve cell and therefore inhibiting nerve firing resulting in paralysis and death. Because of this mechanism of action, there are no microscopic or macroscopic lesions associated with this toxin so diagnosis is based on history or finding a probable source of the toxin in the gastrointestinal tract.
Because they are so toxic, rough-skinned newts are highly unusual prey for most animals. In this case, the owl was severely emaciated, so perhaps starvation drove it to eat this highly unusual prey-item.
Submitted by Glenna McGregor – CWHC BC