Hoarding is considered a mental disorder where people collect various things to excessive points. Their collecting reaches uncontrollable levels and impacts their daily lives. Often their homes are overrun with whatever they collect.
People will form strong emotional attachments to seemingly useless items such as newspapers and have stacks of them all over their house impeding the use of their home.
In pet hoarding typically a person picks one type of animal and begins collecting them. They soon find themselves in an out of control situation, especially when some of the pets are not spayed or neutered and begin reproducing. The hoarder thinks they are doing the pets a favor, and often consider themselves as rescuers.
The hoarders are seldom able to feed the pets correctly, provide proper medical care, or even to provide proper social interaction and affection. Despite the fact that the animals are often suffering, the hoarder generally thinks they are doing a good job of providing care for their pets and will refuse to get rid of them on the grounds they may feel nobody else can care for, or love, the pets, as much as they can.
It is not uncommon for the person to keep the bodies of deceased animals, hiding them in freezers or around their home. Other times, due to the hunger in other pets, cannibalism occurs.
Pets are acquire through legal and illegal means. Some pet hoarders will steal pets they think are living in unsuitable situations. It is not uncommon for them to justify taking a pet out of a car because they feel it should not be left alone.
Many cities have by-laws controlling the number of animals a person can keep. This enables law enforcement to step in when somebody makes a complaint about a hoarder. However pet hoarding is easily hidden by reclusive people, some of whom may live rurally.
When actual rescuers are able to either convince the hoarder to surrender their pets, or have law enforcement remove them, the pets are typically in terrible shape. Often covered in feces and painful hair mats. Many of the pets in these situations suffer from neglected medical problems.
Often a lot of the female animals will be pregnant or with litters. The animals generally have poor social skills to humans, having formed tight bonds with the other animals.
In the case of dogs they may not be house trained, as some hoarders never let the dogs outside. In the case of cats because the homes were so overrun, many of the cats will not use litterboxes.
Studies have suggested ties to animal hoarding and early childhood trauma. Often animal hoarders find themselves living in squaller, collecting other things too.
If you know of somebody who has become a hoarder, either of junk or animals, it is important to get them the mental help they need. Try talking to them about surrendering some of their pets (preferably those who are not spayed or neutered to prevent on going population growth).
There are many no-kill pet rescues where a hoarder could trust surrendering their pets to.
This is a better option than waiting for law enforcement to confiscate some of the pets with the hoarder having no control at all.