Cavities in trees are important nesting sites for a wide variety of wildlife, including the white-breasted nuthatch shown on the first page of this chapter.

Cavities in trees are much more common in old-growth forests than in recently logged forests. A recent survey in Missouri found that 45 out of 273 trees in an old-growth area had cavities, while the rest did not (Fan et al. 2005). What is the probability that a randomly chosen tree in this area has a cavity?