Though it is not known which sex is responsible for picking and building the nest, the actual sites are almost always old woodpecker cavities. The trees in which these birds nest are usually coniferous, and are found within boreal and deciduous forests. Glaucidium californicum have clutch sizes that range from 3 to 7, which the female incubates for about 29 days while the male is responsible for bringing back food to the nest. He also defends it from any predators. After the fledglings hatch, they grow quickly and reach almost adult size after 2 weeks.
Courtship again shows how important vocalizations are for owls.
The Northern Pygmy Owl toot and trill in response to each other from nearby trees. When awake, these birds erect their tuft feathers as a possible mode of concealment from prey and predators. These owls inhabit open coniferous and mixed forests, but are not found in dense, continuous forests. This may have to do with the use of open spaces and clearings where they dive down at their prey. Because they rely so heavily on old woodpecker cavities for their nests, this selection of habitation may not be solely due to their preferences, but focus around where these woodpeckers reside as well.