taken conservatively. Higher population sizes in the 1950s and 1960s were potentially the result of increased agricultural activity, but the correlation is tenuous. Populations at this time were of legendary proportions, with anecdotes telling of farmers who “were forced to wear raincoats so as not to be coated in droppings". Due to "very rapid decline over three generations" the IUCN has rated the species as Near Threatened. The gull had earlier received a Least Concern rating in 1994, and a Vulnerable rating in 2000. The New Zealand Department of Conservation listed the gull as Nationally Critical in 2016. It has been referred to in other publications as “critically endangered”, and James Westrip proposed in August 2018 that the gull's status be uplisted to Critically Endangered in the next BirdLife International Red List report, though it was eventually downlisted in 2020. Bill Morris calls the bird “the world’s rarest gull”. Threats In her study of Southland colonies of black-billed gulls, Rachel McClellan found that eighty per cent of observed chick deaths resulted from predation. Introduced mammals, namely ferrets, stoats, cats, and hedgehogs, constitute the “primary factor influencing productivity,” that is, nest success, in the colonies. Chick predation from the indigenous black-backed gull (Larus dominicanus) also threatens the black-billed gull population. 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. McClellan suggests that climate change could have a positive impact on black-billed gull populations, such as in encouraging earlier or extended breeding seasons, but also a negative impact in increasing food availability,