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POP2022-08 White-capped albatross population study: February 2023 (PDF 2,336K)
Summary
These reports detail population monitoring and surveys conducted for Gibson's albatross at Adams Island and white-capped albatross at Disappointment Island in 2022/23.
Gibson's albatross
Gibson’s wandering albatross (Diomedea antipodensis gibsoni) has been in decline since 2005. Research into the causes of and solutions to the falling numbers of Gibson’s wandering albatross includes an annual visit to the main breeding grounds on Adams Island, and this report describes the results of the field programme in the 2022/2023 breeding season.
The survival and productivity of Gibson’s wandering albatross has recovered from the dramatically low rates recorded during 2006–08, but the average survival rate for both sexes remain lower than before the population crash in 2005, and nest success has only just recovered to pre-crash levels. Recent increases in the number of nesting birds are almost certainly attributable to a higher proportion of the population choosing to breed and mark-recapture models estimates of population size still show a decline. The data missed because of the late cancellation of the 2021 season field trip precludes better estimates of population size until next year.
Twenty-two juvenile Gibson’s wandering albatrosses were fitted with satellite transmitters and dataloggers before they fledged in late December 2022. In the subsequent seven months juveniles spent more time foraging north-east of New Zealand than previously tracked adult birds. No information has previously been collected on the at-sea distribution of juvenile Gibson’s wandering albatross, so this data filled a major data gap.
For investigation into diet and mercury pollution in Gibson’s wandering albatross, work additional to the CSP annual plan, feather and blood samples were collected from 20 juvenile and 58 adult birds outside the main albatross study area.
Drone census techniques were refined, allowing a more reliable estimate of the effort required for a whole-island drone-assisted count of the number of Gibson’s wandering albatross nesting on Adams Island. High variability in the number of birds sitting on nests but not incubating eggs (loafing birds) is a large source of error when trying to count breeding birds from the air, which would require substantial concurrent ground-truthing to ameliorate. The costs and benefits of undertaking whole-island nest counts using a variety of methods including drones are explored. The island’s large size, height and persistent bad weather mean a large amount of time and resources are required to obtain a reliable whole-island count using any method. It would be a major undertaking, requiring its own dedicated effort, best done after the regular field programme to ensure the vital mark-recapture trend monitoring dataset is not compromised.
White-capped albatross
White-capped albatross (Thalassarche steadi) are a significant bycatch in commercial fisheries in New Zealand and off South Africa and, to an unknown extent, in the high seas. To determine the impact this is having on the species, a mark/recapture study was established on Disappointment Island, the main breeding ground for white-capped albatross, in 2015. Subsequent brief annual visits to the island focussed on banding and re-sighting banded birds to measure survival and productivity, and recently, to investigate the potential to census the population using drones. This report describes the results of the field programme in 11–15 February 2023.
Banded white-capped albatross were re-sighted at a rate of 0.25 in the study colony of 643 banded birds. Adult survival was 0.92, a little higher than estimated last year. Nine of ten trail cameras monitoring the last half of the 2022 breeding season and the start of the 2023 breeding season gave some data, and seven cameras continued functioning for the full 12 months, though only two stayed upright long enough for the outcome of all the nests in the frame to be determined. Seven of the nine 2022 season cameras drooped over time, probably because the island’s soft peat was so wet it was not strong enough to support the waratahs the cameras were attached to.
Chick success, or the survival of a chick from hatching to fledging, was 66% (22 out of 33 nests). Chicks fledged ~26 July (range 17 June–20 August), and adults returned to the colony from around 10 October (earliest 20 September). Camera images supported earlier findings that white capped albatross is predominantly a biennially-breeding species. This means cameras placed to capture clear views of a cluster of nests being used one season seldom capture many in the next, at least when chick success is reasonably high and nest density only moderate. Reliable information on nest failure rates between laying and hatching will be difficult to obtain without a late November visit to Disappointment Island to position cameras on clusters of nests with confirmed eggs.
An additional 24 unbanded birds were banded and darvic bands were added to three already metal-banded birds. A few feathers were collected from each of these birds for determination of sex, andGLS dataloggers were attached to the leg bands of 26 of them to follow their movements at sea. Blood samples were collected from 20 of these birds for analysis of the levels of mercury pollution.
A comprehensive ground count was made of birds nesting in part of the eastern Castaway Bay colony. The eastern and the western Castaway Bay colony were then photographed from the air by drone twice. There was great variability in the number of non-breeding birds present on the ground between counts (36-106), depending on conditions, which would make it difficult to get an accurate count of breeding birds from drone photographs. Any whole island drone-based census of nests will need to be accompanied with simultaneous ground truthing.
Before a reliable drone-based whole island census can be made, the following is required:
- Trials to determine whether the vertical orthomosaics which have so far only been tested on gentle ground, will work on the steep cliffs and narrow gullies which characterise the western and northern colonies, or whether more complicated 3D models of the steep slopes need to be constructed.
- Purchase of ~25 batteries and possibly 2 drones (if batteries no longer available for existing drones).
- Purchase of an improved digital elevation model.
Publication information
Walker K, Elliott G, Parker GC, Rexer-Huber K. 2023. Gibson’s wandering albatross: population study and potential for drone-based whole-island census. POP2022-08 final report prepared for New Zealand Department of Conservation. 28 p.
Elliott G, Walker K, Rexer-Huber K, Parker GC. 2023. White-capped albatross population study: Disappointment Island 2023. POP2022-08 final report prepared for the New Zealand Department of Conservation. 26 p.