Hybridisation between House and Tree Sparrows is reported from islands
off the coast of Northern Norway, including observed mating attempts
in two different mixed pairs, and the breeding success in a third mixe
d pair. The biometrics of hybrid offsprings were intermediate between
the parents. The hybridisation probably involve only inexperienced ind
ividuals and may have been facilitated by the spatially division of th
e population into small island subpopulations.