Bensch, S., H. Källander, and R. Lager. “Mass and Wing Length of Young Black-Headed Gulls Larus Ridibundus As Predictors of Age and Survival”. Ornis Svecica, vol. 6, no. 1–2, Apr. 1996, pp. 57-66, doi:10.34080/os.v6.22995.