By looking at their stomach contents, it was found that they had recently eaten leaves and seeds of an English yew (Taxus baccata) plant.
The English yew has lance-shaped leaves and a red, berry-like cupped structure called an “aril” with a single brown seed. It’s widely grown in eastern North America as an ornamental shrub and is common in urban areas.
Every type of yew contains the alkaloid compound taxine, which is poisonous to most animals and humans if eaten. In winter, the toxicity of the yew rises and it affects the heart’s ability to beat properly.