Predation as a cause of neurologic signs and acute mortality in a pheasant flock

A flock of approximately 15,000 ring-necked pheasants (Phasianus colchicus) was evaluated for a sudden increase in mortality and acute neurological signs after having been previously diagnosed 3 wk earlier with a chronic respiratory disease of undetermined etiology. Approximately 25 live birds were displaying neurological signs including circling, ataxia, and obtunded behavior and 50 birds were dead. Three birds with neurological signs were submitted for evaluation. Extensive subcutaneous hemorrhage over the head and penetrating puncture wounds through the skull and into the brain were found. Trauma from a wild predatory mammal, most likely the long-tailed weasel (Mustela frenata) that had invaded the pheasant house and expressed surplus killing behavior was determined to be the cause of the acute neurological signs and mortality. The relationship of the chronic respiratory disease to the predation episode was not determined but it is possible that pheasants with severe respiratory disease may have had increased susceptibility to predation.