National Red-Billed Gull Survey 2014-2017

In 2014, Birds New Zealand, working with the Department of Conservation, initiated a national survey of the red-billed gull, with the objective of establishing more precisely its current population status. Information collected over the past few decades, much of it anecdotal, suggests that the species has experienced overall a substantial population decline, notwithstanding an apparent regional increase in Otago. Because of this, and despite its seemingly still-large population, the red-billed is now classified as Nationally Vulnerable, with an expected ongoing population decline of 50–70 % over the next three generations.

Phase 1, carried out during the 2014/15 breeding season, was a scoping survey, designed to check all 166 colony sites listed by Lou Gurr and Fred Kinsky in a paper published in Notornis in 1965, and locate any new sites. In the end, only 99 (60 %) of the pre-1965 sites were resurveyed, just under half of which (47 %) were still active. Most of the unsurveyed sites were on offshore islands, which are more difficult for the public to reach. Overall, active colonies were reported at 162 sites across mainland New Zealand with a further 19 in the Chatham Islands. Whether any of the ‘new’ sites were active in the past, but had been overlooked, or whether they reflect a shift in the locus of breeding is an open question at this stage. A report on the results of Phase 1 of this study is available below.

Of the sites listed in 1965 that are still active today, just over 40% appeared to support fewer pairs than before, while 30 % are marginally bigger. Interpreting these changes in colony size is complicated, however, because we only asked for order-of-magnitude estimates of the number of breeding pairs (although more precise figures were sometimes provided). It is also unclear if the estimates excluded or included the number of non-breeding birds at a colony. The same shortcoming almost certainly applied to the figures reported by Gurr and Kinsky (1965). This is one problem that we want to overcome in this year’s survey by providing everyone with clear guidelines on what to count and how best to do it.

Phase 2 was carried out in 2015/16 and extended into 2017. The aim was to obtain an overall estimate of the size of the red-billed gull population breeding in New Zealand. It will also incidentally establish the location and size of active colonies, allowing us to set up a more systematic monitoring programme to determine what long-term population changes, if any, are occurring. Read the final report here.

Displaying red-billed gulls, here giving oblique (L) and head-toss (R) threat displays, can be useful indicators of breeding, even if actual nests are not seen (Taiaroa Head colony, Otago Peninsula) 

Distribution and abundance of Red-billed Gull, Gannet, w/f Tern – Aerial Survey November 2017 – Report 2019 
Frost & Taylor, Status of Red-billed Gull – Notornis 2018
Aerial Survey Red-billed Gull and Gannet November 2017 – Report
National Red-billed Gull Survey 2014-16 – Report
National Red-billed Gull Survey 2015-2016 – Overview Article
Guidelines to count Red-billed Gulls
List of known Red-billed Gull Colonies 2015
Red-billed Gull Survey – Scoping Phase 2014-15 – Report
Flyer Red-billed Gull Survey