Breeding habitat-choice in two closely related species of passerines, Great Tit (Parus major) and Blue Tit (Cyanistes caereleus) was studied to reveal if their habitat preferences primarily is a hereditary trait, or if they could be acquired through early learning. We performed a cross-fostering experiment by swappingeggs between nests of the two species, which entailed that a number of broods were reared by hetero-specific foster-parents. Blue Tits prefer deciduous forests as their breeding habitat, whereas Great Tits often are found breeding in habitats with a higher share of coniferous wood. If preferences for habitat primarily are based uponlearning from parents while growing up, we would expect the cross-fostered birds to settle in habitats preferred by their foster-parents. If they did not, habitat preferences would most probably be ahereditary trait. We detected no significant differences in choice ofnesting habitat in coniferous or deciduous forests between cross-fostered birds raised by hetero-specific parents and control-birds raised by con-specific parents. Cross-fostered birds did not choose habitats according to the preferences of their hetero-specific foster-parents though there was a slight tendency in that direction. We found some evidence of early learning, however. The cross-fostered Blue Tits chose large nest-boxes, which are usually preferred byGreat Tits.