Holly berries are somewhat toxic and will cause vomiting and/or diarrhea when ingested by people, partly due to the ilicin content. The fatal dose is estimated to be around twenty berries for adults. However they are extremely important food for numerous species of birds, and also are eaten by other wild animals. In the fall and early winter the berries are hard and apparently unpalatable. After being frozen or frosted several times, the berries soften, and become milder in taste. During winter storms, birds often take refuge in hollies, which provide shelter, protection from predators (by the spiny leaves), and food.