Steen, R., A.-M. Austad, S. Johnny, and B. A. Bjerke. “Daily Activity and Nest Attendance in a Breeding Pair of Parrot Crossbills Loxia Pytyopsittacus in Southern Norway”. Ornis Norvegica, vol. 40, Apr. 2017, pp. 24-32, doi:10.15845/on.v40i0.1206.