Chinchillas are small rodents known for their soft, silky fur and constant chewing behavior. They can be kept as pets and bred, but they do not always have a friendly demeanor. Once they trust you, they will allow you to pet them, but otherwise they can be timid. Understanding your chinchillas is important, especially if you are interested in breeding them. Part of this is learning when female chinchillas are in heat. As the females do not act particularly different while in heat, aside from being more open to sexual activity with males, it is helpful to observe both the males and females to determine this.
Observe the chinchillas' behavior. Male and female chinchillas participate in a chase when the female is in heat, so if they are chasing each other this is a possible sign that your female is in heat.
Watch for a waxy plug in the cage where your male and female chinchillas are living. Male chinchillas only breed with females when they are in heat, and ejaculate a waxy substance which helps keep the semen inside the females. If you see this waxy substance, your chinchillas are breeding and your female is likely in heat.
Look at the male chinchillas to see if they are acting differently around the females. The males will begin to wag their tales more often than usual, act more aggressively and make small hiccuping noises. Usually a male will bond with one particular female and they will mate when the female is in heat.
Observe if your male and female chinchillas are engaging in sexual intercourse. If this occurs, your female chinchilla is in heat.