The vast majority of animals have been relinquished to us by their owner. The underlying reason for most relinquishments is a lack of commitment on the part of the owner. People often buy a cute puppy who grows up to be a rowdy adolescent because of lack of training and attention. Most of the dogs relinquished to us are at that stage...1 - 2 years of age.
Some animals have been strays who were not reclaimed at the Animal Control facility. Some were cared for temporarily by those who found them, but eventually relinquished them to us. Others may be strays or perhaps they had a great home but their owner is unable to care for them any longer.