While “the species is relatively tolerant of human disturbance,” having potentially benefitted from increasing land conversion for agricultural use since the arrival of Europeans, human activity has also had a negative impact on population size. Largescale shootings of black-billed gulls, such as a 2009 “massacre” of around 200 birds in North Canterbury, are particularly detrimental to the species’ future. A similar event was reported in December 2018, while another article tells of a gull being discovered with an arrow in it. The birds have also been targeted by people in vehicles who “occasionally plough through colonies”. Morris suggests such actions in part result from confusion with the more common and disliked red-billed gull ("Chroicocephalus novaehollandiae scopulinus"), which is nonetheless also endangered in New Zealand. Although no studies have been conducted in this area, previous DDT usage on farms may affect the breeding success of black-billed gulls and herbicides that remain in use could have consequences that are yet unknown.