13 First northern giant petrel (Macronectes halli) breeding population survey and estimate for the Auckland Islands, New Zealand GRAHAM C. PARKER* GRAEME A. TAYLOR Parker Conservation, 126 Maryhill Terrace, Department of Conservation, PO Box 10420, Dunedin 9011, New Zealand Wellington 6143, New Zealand REBECCA K. FRENCH KALINKA REXER-HUBER CHRIS G. MULLER Parker Conservation, 126 Maryhill Terrace, Wildbase, School of Veterinary Science, Dunedin 9011, New Zealand Massey University, Private Bag 11222, Palmerston North 4442, New Zealand ABSTRACT: This first breeding population estimate of northern giant petrels (Macronectes halli) in the Auckland Islands group involved whole-island censuses, apart from the main Auckland Island, in the 2015-16 breeding season, and multi-year repeat visits to a subset of island colonies. Parallel line-transects in giant petrel habitat were used to survey the number and spatial distribution of pre-fledging chicks. The Auckland Islands 2015-16 whole-island census resulted in a count of 216 northern giant petrel chicks on eight of the 15 islands in the group. Applying a simple correction factor, the breeding population in 2015 is estimated as c. 340 breeding pairs (range 310–390). This estimate is higher than historical non-quantitative records of 50–200 breeding pairs. Multi-year counts on Enderby, Rose, Frenchs, Ocean, Disappointment, and Adams Islands showed some inter- annual variability, but other island colonies remained more stable. The northern giant petrel colony on Enderby Island has increased from two chicks in 1988 to 96–123 chicks in 2015–18 (four annual counts undertaken). Parker, G.C.; French, R.K.; Muller, C.G.; Taylor, G.A.; Rexer-Huber, K. 2020. First northern giant petrel (Macronectes halli) breeding population survey and estimate for the Auckland Islands, New Zealand. Notornis 67(1): 357–368. KEYWORDS: population estimate, subantarctic, procellariiform, seabird, breeding pairs Received 26 April 2019; accepted 7 August 2019 *Correspondence: [email protected] Introduction on large ground-nesting southern royal albatross (Diomedea epomophora) (R.H. Taylor 1971) and Robust estimates of the size of breeding popu- likely also nesting giant petrels. Giant petrels are lations are critical to inform conservation man- also prone to human disturbance (Brooke 2004) agement for species of conservation concern. and secondary, non-target poisoning in operations Determining the conservation status of many to eradicate introduced mammals (Alderman et species of albatross and petrel is important al. 2019). Northern giant petrels were recorded as because these taxa are subject to threats such by-catch mortality by fisheries observers in New as incidental by-catch resulting in declines in Zealand commercial trawl, surface, and bottom breeding populations, competition for resources longline fisheries during 2002–17, at an average of with commercial fisheries, the impacts of intro- less than one bird per year (Abraham & Thompson duced mammals at breeding sites, and suscepti- 2015). This does not account for mortalities in bility to climate change and pollution (Croxall et unobserved fisheries, nor for cryptic mortality in al. 2012; Phillips et al. 2016). commercial fishing operations. Giant petrels are Northern giant petrels (Macronectes halli; Fig. 1) recorded as mortalities in commercial fisheries are large, southern hemisphere fulmarine petrels in other areas of the Southern Ocean (Petersen that face conservation threats in both their ter- et al. 2008; Parker 2012, 2013), with fatal captures restrial and marine environments (Shirihai in Patagonian toothfish fisheries of particular 2008). Along with the closely related southern concern in the past (Nel et al. 2002). giant petrel (M. giganteus), northern giant petrels Northern giant petrels exhibit strong site are the most common avian scavengers in sub- fidelity, and pairs generally show long-term pair antarctic and Antarctic waters (Brooke 2004), and bonds (from a long-term study during 1966–80 are also predators of large birds such as great alba- at Île de la Possession, Crozet archipelago; Voisin trosses and penguins (Cox 1977; Hunter & Brooke 1988). The species is surface-nesting, with the age 358 1992; Ryan et al. 2008; Dilley et al. 2013). at first breeding averagingc . 10 years (Woehler & Northern giant petrels forage between 30°S Johnstone 1988). A single egg is laid mid-Aug to and 64°S (Marchant & Higgins 1990). The species late-Sep (Brooke 2004). Chicks fledge at 110–120 breeds on nine island groups between 44°S and days of age ( Johnstone 1977), and females fledge 54°S (ACAP 2010). Over one-third of the total esti- 5–6 days earlier than males (Hunter 1984; Cooper mated breeding population is on South Georgia, in et al. 2001). Breeding sabbaticals are common; at the South Atlantic (ACAP 2010). In the southern Île de la Possession 15–40% of adults did not breed Indian Ocean, breeding takes place on the Prince each year (Voisin 1988), and at South Georgia Edward Islands (Ryan et al. 2003) and the Crozet 27–57% took breeding sabbaticals (1978–81; and Kerguelen archipelagos (Weimerskirch et al. Hunter 1984). 1989; Shirihai 2008). In the southern Pacific region, The worldwide northern giant petrel breeding northern giant petrels breed on the Chatham population is estimated to be c. 11,800 pairs (ACAP Islands group, Macquarie Island, Campbell Island, 2010). However, recent quantitative population the Auckland Islands group, and the Antipodes estimates exist for only four of the nine island Islands (Marchant & Higgins 1990). groups where the species breeds (ACAP 2010). Introduced mammalian predators at some Local population trends show that some northern northern giant petrel breeding sites can cause giant petrel populations have been increasing and nesting failures and, in some instances, may also others decreasing (ACAP 2010). At South Georgia depredate adults. Cats (Felis catus) and ship rats the population increased by 60% during 1978– (Rattus rattus) caused egg and chick failure on 1996, apparently linked to the dramatic increase Macquarie Island (ACAP 2010) prior to cat eradica- in Antarctic fur seals (Arctocephalus gazella) and tion in 2000 and rat eradication in 2012 (Robinson the increased availability of commercial fisher- & Copson 2014; Hunt 2014). Nest trampling by live- ies discards (González-Solís et al. 2000). On Île de stock (sheep Ovis aries on Campbell Island, and la Possession the population increased between cattle Bos taurus on Enderby, Auckland Islands, 1966 and 1980 (Voisin 1988), declined during the before their respective removals) had impacts 1980s, increased in the early- to mid-1990s, and Northern giant petrel population FIGURE 1. Northern giant petrel chick, Disappointment Island, January 2016. Image: Graham Parker. 359 was reportedly decreasing from 1998 (Delord et Campbell Island (234 breeding pairs; Wiltshire al. 2008). The Marion Island population has had & Scofield 2000). These provide a baseline periods of both increase and decrease during population estimate for those islands but no 1985–2008, but overall the trend on Marion was population estimates have been conducted since, for a slight decrease of 0.5% in the breeding popu- preventing any insight into population trends at lation to 2008 (ACAP 2010), and breeding numbers Antipodes and Campbell. The Chatham Islands appear to have increased by around 30% over the are the stronghold of the species in the New past decade (P. Ryan, pers. comm., 12 Mar 2019). Zealand region. The entire Chatham Islands’ The contemporary size and trends of northern population was estimated at 2,000 breeding giant petrel populations in the New Zealand (NZ) pairs in 1993, based on extrapolation (Robertson region are not known. The Macquarie Island popu- & Sawyer 1994), and 2,150 pairs in 2017, based on lation experienced large increases from the mid- counts during the mid-chick phase and adjusted 1990s (ACAP 2010), but was reduced by approx- for breeding success with Macquarie Island imately 30% in 2010–11 due to non-target data (Bell et al. 2018). No population trend data mortality during the eradication of invasive exist for the main population in the Chatham mammals (Springer & Carmichael 2012). Statis- Islands, Motuhara/Forty-Fours, which comprises tical modelling suggests that the Macquarie approximately 92% of the northern giant petrel population has a high probability of returning population in the island group (Bell et al. 2017). to pre-poison levels over the ensuing 10 years In the Auckland Islands, northern giant petrels (Alderman et al. 2019). Single population reportedly breed throughout the group, but no estimates exist for the Antipodes Islands (230 targeted, island-wide count of breeding birds breeding pairs; Wiltshire & Hamilton 2003) and has been conducted and population estimates Lost Gold: ornithology of the subantarctic Auckland Islands for the Auckland Islands group are based predators (Miskelly et al. 2020 – Chapter 2 in this solely on anecdotal evidence. The most recent book; Russell et al. 2020 – Chapter 6 in this book). estimate of approximately 50 pairs dates from The vegetation of the Auckland Islands consists the 1980s (G.A. Taylor 2000). This work reports of southern rātā (Metrosideros umbellata)- on the first quantitative estimate of the size dominated low forest at sheltered lower altitudes, of the Auckland Islands northern giant petrel interspersed with Coprosma foetidissima, breeding population, and describes their spatial Myrsine divaricata, Pseudopanax simplex, and distribution in the group. Dracophyllum cockayneanum and D. longifolium. The rātā-dominated forest turns to Coprosma spp., Veronica elliptica, Myrsine divaricata, and Methods Dracophyllum spp. shrubland at mid-elevations, with tussock grasslands of Chionochloa antarctica, The Auckland Islands (50°44’S, 166°05’E) are located Poa litorosa, and P. foliosa followed by herb-fields c. 450 km south of the New Zealand mainland at higher elevations. (Fig. 2). The total area of the island and islets is c. To ensure that all areas on the Auckland Islands 56,800 ha with Mt Dick (705 m a.s.l) the highest with historical records of northern giant petrel point, located on Adams Island.