Antipodes Island seabird research 2023/24

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POP2022-10 Antipodean wandering albatross and white-chinned petrels 2024 (PDF, 2,355K)

Summary

The Antipodean wandering albatross Diomedea antipodensis antipodensis has been in decline since a population crash in 2005–07. Declining numbers appear to have been largely driven by high female mortality, but low chick production—with fewer birds breeding and reduced breeding success—has compounded the problem. To tease out the causes of falling numbers of Antipodean wandering albatrosses and identify the effectiveness of potential solutions, research includes an annual visit to the breeding grounds on Antipodes Island. Alongside this core annual study, we present the first stage of a two-year whole-island survey aiming to estimate the size of the Antipodean albatross population nesting island-wide. Alongside the albatross research, we are developing a mark-recapture study for white-chinned petrels. This report describes the results of the annual field programme in the 2023/24 breeding season for both Antipodean albatrosses and white-chinned petrels.

Antipodean wandering albatross. The core annual study involves mark-recapture in an intensively monitored study area and census of the annual count areas. This season’s field programme allowed updates to the trend in nesting population size, survival, productivity and recruitment. There are some signs that the rate of decline is slowing. The number of Antipodean wandering albatrosses breeding has been roughly stable for the past four seasons, and female survival shows some suggestion of improving since 2014 (4-year rolling averages), although it is still highly variable year to year (from 97% in 2014 to 84% in 2019). Breeding success in 2023 at 71% approached the average pre-crash nesting success of 74%, although the mean 2006–2023 rate remains comparatively low at 62%. However, the actual number of chicks produced remains small, even in good breeding-success years, since numbers nesting remain low. Recruitment is starting to draw from the (much smaller) cohorts produced since the crash, so population numbers will soon no longer be supplemented by higher recruitment rates seen over the past decade.

The last whole-island count of nesting Antipodean albatross took place 1994–96. The first year of a two-year effort to update the whole-island estimate involved a combination of ground counts (27% of the 1,546-ha Antipodean albatross nesting distribution) and drone aerial photography for counts in orthomosaics (1,023 ha or 66% overflown). Drone counts were corrected for pretend-nesters (apparently-nesting birds with no egg) using data from concurrent nest-contents transects, and both count types were corrected for nest failures occurring before the date of count. Part of the Antipodean albatross breeding range could not be covered this first season (356 ha or 23% not counted). Numbers nesting in these not-counted areas were estimated by categorising nesting-habitat quality across the island, then extrapolating nest densities by habitat-quality class to uncounted areas. The number nesting island-wide in 2024 estimated from drone and ground counts (3,383 breeding pairs with 95% CI 3,182–3,585) is similar to the figure estimated from the annual ground count since 1997 of 15% of the island (3,307 breeding pairs), indicating that the 15% of the island chosen for annual counts remains representative of the whole island.

Trends in nest numbers and demographic parameters from the core annual study indicate that the population has been approximately stable for the last four years. However, there is so far no evidence of any sustained improvement in Antipodean wandering albatross demography, as required for the population to recover, with tentative improvements recorded here merely slowing the decline. Recommendations include ongoing mark-recapture monitoring of demographic and population-size trends; the second year of effort toward the island-wide population size estimate, to complete whole-island coverage; and research into causes of declines. More-targeted ongoing engagement is also needed to achieve better bycatch mitigation in line with ACAP best practice.

White-chinned petrel. A mark-recapture study to estimate vital rates, survival in particular, was established in late 2022. This first season of band resighting highlighted the importance of quality monitoring data: banded white-chinned petrels were resighted at an unexpectedly low rate of only 0.243. Indeed, fewer study burrows were reoccupied than expected, and in new burrows, occupancy was lower than last year. Without quality monitoring data, we cannot yet tell whether these breeding rates are now normal for Antipodes white-chinned petrels, having shifted over the decade since the last study, or whether it has simply been a bad year. Substantial effort to grow the mark-recapture study this year mean there are now 301 banded white-chinned petrels in 156 marked burrows in the two study areas. For accurate, precise survival estimates this marked population needs building further, along with recaptures at existing marked burrows for a minimum of three years.

Publication information

Rexer-Huber K., Whitehead E., Parker G.C., Patterson, E., Walker K., Welch, J., Elliott G. 2024. Antipodean wandering albatrosses and white-chinned petrels 2024. Final report to the Department of Conservation. Parker Conservation, Dunedin. 29 p.