McClellan, R. K.; Habraken, A. (2017) [2013]. "Black-billed gull". New Zealand Birds Online. Archived from the original on 3 June 2019. Retrieved 5 January 2019.
nzgeo.com
Morris, Bill (January–February 2019). "Tending the Flock". New Zealand Geographic. Vol. 155.
McClellan, Rachel Katherine (2009). The Ecology and Management of Southland's Black-billed Gulls (PhD). University of Otago. Nonetheless, different counting methods and the various limitations of these methods mean that "estimates must be treated with caution".
McClellan, R. K.; Habraken, A. (2017) [2013]. "Black-billed gull". New Zealand Birds Online. Archived from the original on 3 June 2019. Retrieved 5 January 2019.