Night length (time between sunset and sunrise) at the two sites during the breeding season and basic breeding data (mean ± SE) of the Finnish and Czech populations of Tengmalm's owls.

The statistical comparisons are done with General Linear Mixed Models (Normal distribution, identity-link) (date egg laying, fledging date), or with a Generalised Linear Mixed Model (Poisson distribution, log-link) (clutch size, number of nestlings, number of fledglings, brood reduction). All models included year as random factor. Brood reduction was calculated as the number of nestlings which disappeared from a nest box before fledgling date (ring or dead nestling found in nest box).