A. Trespassing animals: The English common law rule has apparently always been that the owner of livestock or other animals is liable for property damage caused by them if they trespass upon another’s land. This liability existed even though the owner exercised utmost care to prevent the animals from escaping. However, the rule applied only to animals of a sort likely to roam and do substantial damage. Thus cattle, horses, sheep and goats were included but “household” animals like dogs and cats were not. See P,W&S, p. 683.
1. American rule: In most American jurisdictions, this English rule of strict liability (with its exception for dogs and cats) applies. P&K, p. 539. This is particularly likely to be the rule in the populous eastern states.
a. Western states: A number of western states, however, whose economy still depends on raising of livestock, have never adopted a broad rule of strict liability. “Fencing in” statutes in some states provide that an animal owner is not strictly liable if he attempts to fence in his animals, but that he is strictly liable if he does not. Conversely, “fencing out” statutes provide that if the plaintiff properly fences his land, he has a strict liability claim against one whose animals break in. P&K, p. 540.
b. Use of highway: Even in the eastern states, if the defendant is using a public road to transport his animals to market, he will not be strictly liable if they wander onto the land immediately adjoining the road. P&K, ibid.
B. Non-trespass liability: Strict liability also sometimes exists for damage other than trespass (e.g. personal injury). There is strict liability for harm done by “dangerous animals” kept by the defendant. But the definition of a “dangerous animal” depends in turn upon whether the animal is of a species that is regarded as “wild” or “domesticated”.
1. Wild animals: A person who keeps a “wild” animal is strictly liable for all damage done by it, provided that the damage results from a “dangerous propensity” that is typical of the species in question (or stems from a dangerous tendency of the particular animal in question of which the owner is or should be aware). Rest. 2d, §507.
Example: D keeps a lion cub, which has never shown any violent tendencies. One day, the cub runs out on the street and attacks P. Even if D used all possible care to prevent the cub from escaping, he is liable for P’s injuries, because lions are wild animals, and the damage resulted from a dangerous propensity typical of lions, that they can attack without warning.