As warmer winter temperatures become more common, one way for some animals to adjust is to shift their ranges northward. But a new study of North American bird species indicates that doing so is not easy or quick — it took about 35 years for many birds to move far enough north for winter temperatures to match where they historically lived.

For example, black vultures have spread northward in the last 35 years and now winter as far north as Massachusetts, where the minimum winter temperature is similar to what it was in Maryland in 1975. On the other hand, the endangered red-cockaded woodpecker did not alter its range at all despite the warming trend, possibly because it’s very specific habitat requirements precluded a range shift. Warmer winters are also affecting the fruits and vegetables that California sends around the country. The state produces the majority of the country's supply of almonds, wine grapes, walnuts, pistachios and peaches.

Both of these scenarios could represent problems for birds, La Sorte said. Species that do not track changes in climate may wind up at the limits of their physiological tolerance, or they may lose important habitat qualities, such as favoured food types, as those species pass them by. But they also can't move their ranges too fast if the habitat conditions they depend on also tend to lag behind climate.