In a 1999 study Dr. Patronek, professor Tufts University defined animal hoarders:

People who accumulate a large number of animals; fail to provide minimal standards of nutrition, sanitation and veterinary care; and fail to act on the deteriorating condition of the animals, the environment, and their own health.

Hoarders justify their behavior with the view that the animals are surrogate children and that no one else can care for them. They harbor a fear that if they seek help the animals will be euthanized.

More recently, in a publication from the Hoarding of Animals Research Consortium, Animal Hoarding: Structuring interdisciplinary responses to help people, animals and communities at risk, Patronek and his cohorts list four key characteristics:

• Failure to provide minimal standards of sanitation, space, nutrition, and veterinary care for the animals
• Inability to recognize the effects of this failure on the welfare of the animals, human members of the household, and the environment
• Obsessive attempts to accumulate or maintain a collection of animals in the face of progressively deteriorating conditions
• Denial or minimization of problems and living conditions for people and animals