Breeding habitat: Hazel-rich deciduous woodland, mixed woods with hazel and oak, sometimes older spruce forest in the fringe zones. Decisive is the availability of hazelnuts within reasonable flight distance — without hazel, no nutcrackers.
Breeding season: Sweden: January–March — one of the earliest-breeding birds of the year. The female lays 3–4 eggs in a nest built of twigs and conifer needles high up in a spruce, and incubates for 18 days. The young are fledged after a further 23–28 days.
Early breeding is an adaptation to nut caching: the parents need to retrieve stored nuts to feed the young, and the best caches remain in March–April, when competition for fresh food is still low.