An interest in innate behaviors arose again in the 1950s with Konrad Lorenz and Nikolaas Tinbergen, who made the distinction between instinct and learned behaviors. Our modern understanding of instinctual behavior in animals owes much to their work. For instance, there exists a sensitive period for a bird in which it learns the identity of its mother. Konrad Lorenz famously had a goose imprint on his boots. Thereafter the goose would follow whoever wore the boots. This suggests that the identity of the goose's mother was learned, but the goose's behavior towards what it perceived as its mother was instinctive.