They may be run by the government, by a local humane society, by private individuals, or by a combination of these. Some are funded by donations alone, while others receive tax money. Sometimes tax money comes with a stipulation that some animals must be turned over to experimenters.
Some shelters take in dogs only, but most take in dogs and cats.
Some can properly handle birds and wild animals. Usually, however, names of area naturalists or wildlife rehabilitators are kept on hand for referral when a wildlife emergency arises, and if a wildlife facility is nearby, any incoming wildlife should be transferred to it. Because of severe space limitations, most shelters kill animals who are old, seriously ill, or unfriendly, or who remain unclaimed or unadopted after a limited number of days. The ideal shelter is a haven for lost, injured, abused, or unwanted animals. It receives adequate funding from the county or city it serves, and no animal from it is ever knowingly turned over to a research laboratory, guard dog company, or unqualified or cruel guardian.