No, emotional support animal (ESA) letters are not limited to therapy dogs alone. A wide range of animals can be ESAs, including cats, rabbits, birds, and even miniature pigs, among others. The primary function of an ESA is to provide emotional comfort and support, rather than perform specific tasks or therapies that service animals are trained for. So, when you apply for an ESA online, you have the flexibility to choose an animal that best suits your emotional and psychological needs. Make sure your choice is reasonable and within the guidelines of any applicable housing regulations.