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Persatuan Amerika Syarikat untuk Pencegahan Kekejaman terhadap Haiwan (ASPCA)

Orang untuk Rawatan Etika Haiwan (PETA)

Donahue, Jesse, and Erik Trump, The Politics of Zoos: Exotic Animals and their Protectors (2006).

Hoyt, John A., Animals in Peril  1994.

Irwin, Paul, Losing Paradise: The Growing Threat to Our Animals, Our Environment, and Ourselves (2000).

Unti, Bernard. Protecting All Animals: A Fifty-Year History of The Humane Society of the United States (2004).

Unti, Bernard, and Andrew Rowan. "A Social History of Animal Protection in the Post–World War Two Period." In State of the Animals 2001, edited by Deborah J. Salem and Andrew N. Rowan. Washington, D.C.: Humane Society of the United States, 2001.