KRISTIANSEN, Jens Nyeland. Estimating the population size of breeding Greylag Geese Anser anser based on vertical aerial photographs. Wildfowl, [S. l.], p. 65–71, 1997. Disponível em: https://tidsskrift.dk/Wildfowl/article/view/154101. Acesso em: 17 dec. 2025.