A Vulnerable White-chinned Petrel at sea; photgraph by Petre Ryan

The Conservation Services Program of New Zealand’s Department of Conservation has released a report by Kalinka Rexer-Huber (Parker Conservation, Dunedin, New Zealand) and colleagues on the White-chinned Petrel Procellaria aequinoctialis population of the Antipodes Island. 

The report’s Summary follows:

This study provides an updated estimate of the white-chinned petrel (Procellaria aequinoctialis) breeding population size on Antipodes Island. We also detail the setup of a mark-recapture study suitable for estimating key vital rates and detecting population change, adult survival in particular. Lastly, we document blood and feather collection for a wider study on mercury contamination, and deployment and recovery of time-depth recorders for data on dive depth of white-chinned petrels. 

Population size estimate. Burrow density is estimated from a representative sample of burrowed areas then corrected for burrow occupancy and extrapolated to the available area of nesting habitat to estimate the breeding population of white-chinned petrels. For an estimate as accurate and precise as possible we built on previous efforts in 2009–11 and 2021–22 (Thompson 2019; Elliott & Walker 2022). To estimate burrow density we used the distance sampling dataset from 2021–22 and expanded the sampling coverage across the whole island, adding 93 transects to a new total of 248 island-wide sampling locations. Distance sampling enabled burrow density estimates that explicitly account for burrow detectability. Occupancy was assessed by inspecting 293 burrows just after laying, calculating rates and corrections using the approach developed for the 2009–11 study (burrow numbers corrected for entrances that are not in fact burrows, and for other species using white-chinned petrel burrows). The area used by white-chinned petrels, with two habitat types distinguishable, was drawn from comprehensive habitat mapping 2021–22. Antipodes Island had an estimated 26,400 (95% CI: 22,200–31,600) white-chinned petrel pairs breeding in Dec 2022 during early incubation. Burrow detectability was different in the two habitat types and occupancy rates differed, so for accuracy the estimate used burrow density, area and occupancy specific to each habitat type. These refinements to 2009–11 and 2021–22 methods result in a population size estimate here that is smaller but more accurate and precise. 

Demographic study setup. Population change is more readily detected via intensive study of birds in a representative study population, so we established a mark-recapture study to estimate vital rates, survival in particular. Marked burrows in two study areas contain 169 banded white-chinned petrels. For accurate, precise survival estimates this marked population needs building further, along with recaptures at existing marked burrows for a minimum of three years. 

Recommendations. An efficient and effective long-term monitoring strategy could combine annual intensive monitoring effort in a representative study population, as set up here, supplemented by occasional whole- island population size estimates (5–10-year intervals). Ongoing mark-recapture will enable robust trend estimation over time, with whole-island estimates providing occasional more-general overview of breeding numbers. 

Reference:

Rexer-Huber K., Parker G.C., Elliott G., Walker K. 2023. Antipodes white-chinned petrel population size and survival study setup. Final report to the Department of Conservation. Parker Conservation, Dunedin. 18 p. 

13 September 2023

Not a cool situation. An albatross chick is near buried among flowering Verbesina on Midway, photograph from the US Fish and Wildlife Service

Following the failure of the House Mouse Mus musculus eradication effort on Midway Atoll in the North Pacific this year as recently reported, more positive news is to hand on another eradication effort, to rid both Sand and Eastern Islands within the atoll of the introduced Golden Crownbeard Verbesina encelioides. This invasive plant forms “chest-high, impenetrable thickets” in which breeding Black-footed Phoebastria nigripes and Laysan P. immutabilis Albatrosses have difficulty reaching and departing from their nest sites, become entangled, and their well-insulated, downy chicks overheat due the plants' sheltering effect against cooling sea breezes.

Before (2011) and after (2023) views on Eastern Island from the same spot. The dense Verbesina has been replaced with “outplanted” native grass Eragrostis variabilis, photographs by Pete Leary (top) and Jon Brack (bottom)

In May 2000 I spent a week on Midway following the Second International Conference on the Biology and Conservation of Albatrosses and other Petrels, held in Honolulu, Hawaii. Along with other conference delegates (we filled a whole plane to get there). I experienced the dense Verbesina stands with albatrosses breeding among them on both Sand and Eastern Islands. As the before and after photographs taken over a decade apart show, a concerted effort since my visit to remove plants and exhaust the seed load within the sandy soil shows remarkable differences. Study plots on both islands have demonstrated the value of clearing away the daisy-like plant with breeding success almost doubling in treated areas, compared to untreated controls. With atoll-wide eradicatioin hopefully approaching the last remaining one percent of Verbesina is being targeted by cutting paths through the native vegetation to access the remaining mature plants to remove their flower heads before they set seed and to find seedlings which are then sprayed with herbicide (click here).

This Laysan Albatross on its nest is covered with a tangle of collapsed Verbesina stems, photograph by Matt Brown

Read an earlier article on the eradication effort in ACAP Latest News here.

John Cooper, Emeritus Information Officer, Agreement on the Conservation of Albatrosses and Petrels, 12 September 2023

 A fledgling Black Petrel; photograph by Elizabeth (Biz) Bell, WMIL

A report by Elizabeth Bell (Wildlife Management International Ltd, New Zealand) and colleagues on the tākoketai/Black Petrel, Procellaria parkinsoni of Aotea/Great Barrier Island has been released by New Zealand’s Department of Conservation (NZDOC). Research for the report, Key demographic parameters and population trends of black petrels (Procellaria parkinsoni) – 2022/23, was carried out over the 2022/2023 breeding season.

The summary from the NZDOC website follows: 

"During the 2022/23 breeding season 480 tākoketai/black petrel study burrows were intensively monitored within the Mt Hobson/Hirakimata study area on Aotea/Great Barrier Island. 

There were 313 (65.2%) burrows occupied by breeding pairs, 64 (13.3%) occupied by non-breeding birds, and 103 (21.5%) were unoccupied. Overall, 191 chicks were produced from the study burrows representing a fledgling success rate of 61%, but 13 chicks were found to be below weight and smaller in size during the May chick banding trip, and most of these chicks were not expected to survive to fledging. This would further reduce breeding success to 56.9%. 

Breeding success was impacted by weather events, specifically the Auckland flood event on 27 January 2023 and Cyclone Gabrielle between 12-16 February 2023. A number of burrows flooded, causing eggs to fail and small chicks to drown or chill and die, and foraging success of parents appeared to be reduced with 13 chicks being in poor condition by May prior to fledging. 

Nine census grids were monitored within the study area and accounted for 197 of the inspected study burrows. Of these, 119 were occupied by breeding pairs (60.4%) and 68 chicks were produced representing a fledging success rate of 57.1%. Again 7 of these chicks were in poor condition and were not expected to fledge, reducing breeding success to 52.1%. 

A total of 664 adults and 129 fledgling chicks were captured during the 2022/23 field season with 174 adults banded this season (including 52 from study burrows). Of the 129 fledgling chicks banded during the 2022/23 field season, 119 were banded in study burrows; 72 could not be banded due to torrential rain over the chick banding trip, and one had already fledged prior to the banding visit in May 2023. 

There have been a total of 420 returned chicks recaptured at the colony since they were banded prior to fledging. Of these, 117 returned chicks were identified during the 2022/23 breeding season; 28 of which were caught for the first time at the colony. The majority of all 420 returned chicks were from the 2016/17 breeding season, followed by the 2013/14 cohort. Not all cohorts were represented as no returned chicks from the 1995/96, 1996/97 and 1997/98 cohorts were recaptured this season. Understanding the factors affecting return rates of chicks within the 35-ha study site is vital. It is important to determine whether it is related to low juvenile survival and/or recruitment or if it is simply due to a lack of detection. Understanding juvenile survival and recruitment is necessary for accurate demographic modelling and for species risk assessment modelling. Therefore, it is recommended that effort to obtain this data is completed with urgency. 

Additional monitoring of pig and other predator occurrence and impact on black petrels on Cooper’s Castle was undertaken this season. Eighteen black petrel burrows were identified within the boundaries of this study area; three were breeding sites and four sites were being visited by non- breeding birds. All other burrows were empty. Trail cameras were placed along pig pathways, walking tracks and outside active black petrel burrows. Footage confirmed feral pig, rat, and feral cat presence. While no interactions with black petrels were caught on camera at Cooper’s Castle, there was one cat predation of an unbanded adult and one chick from a random, non-monitored burrow. There was one rat predation event at the study colony on Hirakimata this season. Introduced species still pose a threat to the black petrel population and it is imperative pest control measures continue."

Reference:

Bell, E.A., Lamb, S. & Maclean, C. 2023. Key demographic parameters and population trends of tākoketai/black petrels (Procellaria parkinsoni) on Aotea/Great Barrier Island: 2022/23. POP2022-01 final report prepared by Wildlife Management International Ltd for the Conservation Services Programme, Department of Conservation, Wellington. 41 p.

07 September 2023

Southern Buller's Albatross, Snares Islands, April 2007, photograph by Paul Sagar

The Albatross and Petrel Agreement recognizes 22 species of albatrosses, all of which it lists under its Annex 1. Distinct breeding populations of two of these species continue to be variously treated in the professional and popular literature (and on social media) either at the subspecific or specific level; a third albatross, hitherto thought not to vary taxonomically (“monophyletic”) has recently been proposed to consist of two species. The question thus arises should there be 22 or 25 species of albatrosses? In this Monthly Missive I consider the taxonomic status of these three albatross species, primarily based on reviews summarized by ACAP’s Taxonomy Working Group (TWG) in its reports to meetings of the ACAP Advisory Committee.

Buller’s Albatross

New Zealand’s endemic Buller’s Albatross Thalassarche bulleri occurs in two distinct populations. These have been treated either as subspecies or as distinct species in the literature. The northern population T. (b.) platei (sometimes referred to as the Pacific Albatross) breeds in the Chatham Island group (Rangitatahi/Three Sisters and Motuhara/Forty-Fours) and on Rosemary Rock, Manawatāwhi/Three Kings Islands. The southern population T. (b.) bulleri breeds on the Solander and Snares Islands. The two populations breed around two months apart with the northern population laying eggs in October-November and the southern birds over January and February. At least some field guides consider they can be identified by plumage and other differences. According to New Zealand Birds Online “the two subspecies are separated by bill size and colour and head plumage. Southern Buller’s mollymawk has a silvery-white forehead with black extending over about 70% of the sides of the bill. Northern Buller’s mollymawk has a silvery-grey forehead with black extending over about 80% of the sides of the bill. In addition, the bill of northern Buller’s mollymawk is more robust (longer and deeper) than that of the southern Buller’s mollymawk”.

In 2006 the TWG evaluated the taxonomic status of Buller’s Albatross and in its report (AC2 Doc 11 to the 2nd Meeting of the ACAP Advisory Committee, recommended the northern and southern populations be recognized as subspecies, this then being supported by the committee. This year the TWG reevaluated the situation following new genetic evidence, recommending to the 13th Meeting of the Advisory Committee that the two populations’ subspecific status should be retained (AC13 Doc 10 Rev 1). It commented that “no statistical analyses of morphometric data have been published for these taxa”, suggesting the need for a study. MSc anyone?

Antipodean Albatross

The Albatross and Petrel Agreement recognizes four species within the “wandering” group of great albatrosses in the genus Diomedea. These are the Amsterdam D. amsterdamensis, the Tristan D. dabbenena, the Wandering D. exulans and the Antipodean D. antipodensis. The first three species are regarded as monophyletic by ACAP and most authorities. The Antipodean Albatross, a New Zealand endemic, is recognized by ACAP as having two subspecies, the nominate D. a. antipodensis, which breeds on Antipodes Island, and the “Gibson’s” race D. a. gibsoni, which breeds on the Auckland Islands. However, this view is not held by all authorities, with some awarding full species status to the two subspecies, as set out in detail on the TWG’s 2006 Report (AC2 Doc 11) to the Second Meeting of the ACAP Advisory Committee. Following its literature review the working group recommended that the two subspecies did not warrant specific status. It did, however, recognize that little or no gene flow occurs between the two taxa; that D. a. antipodensis tends to be darker than D. a. gibsoni, and that it is likely D. a. antipodensis forages more frequently in the eastern Pacific whereas D. a. gibsoni tends to forage in the Tasman Sea. The TWG concluded that these two taxa be recognised as subspecies, which accords with the current situation within the Agreement.

Short-tailed Albatross

Males of the two proposed cryptic species of the Short-tailed Albatross, photographs by Satoshi Konno

The Short-tailed Albatross Phoebastria albatrus breeds primarily on two island groups in the North Pacific: Japan’s Torishima and to the west on the disputed Senkaku/Tiaoyutai/Diaoyu Islands. The species has long been considered monophyletic, but recent research by Masaki Eda and colleagues has shown genetic and mensural differences between the populations breeding on the two island groups, leading to their proposal that they constitute two cryptic species – but not providing scientific or common names for them (click here). Hybridisation between the two populations is thought to occur.

The TWG considered the available evidence this year and noted that there “were some significant differences in morphological characteristics between males of the two taxa. In general, Torishima-type birds were larger than western-most current breeding site-type birds, whereas western-most current breeding site -type birds had relatively longer beaks. Sample sizes were small however and insufficient to analyse female differences statistically.” The TWG went on to say “Assessment of the two types of Short-tailed Albatross is undoubtedly hampered by low sample sizes and the inability to visit the [disputed] western-most current breeding site. It remains possible that further research might demonstrate that the two types represent two sub-species, but the morphometric discrimination is not great and the assortative mating is incomplete and likely reflects the known differences in timing of courtship/breeding in the two populations.” The working group therefore recommended that these taxa do not warrant specific status. Collecting new evidence will surely need a ground visit to the disputed islands, but this seems to be unlikely any time soon, given the geopolitical tensions that exist in the region (click here).

Considerations by the 13th Meeting of the Advisory Committee

Following the report from the TWG, the Advisory Committee at its meeting in 2023 stated in its own report that:

“10.1.3 Based on recommendations from the TWG, AC13 agreed that the taxonomic treatment of both Buller’s Thalassarche bulleri and Short-tailed Phoebastria albatrus Albatrosses should not change despite additions to the evidence on the taxonomy of the two species.

10.1.4 New Zealand advised that data had been collected on the morphometrics of T. bulleri and on the plumage of Antipodean Albatross Diomedea antipodensis breeding on the Antipodean and Auckland Islands. A whole-genome analysis for Antipodean Albatross was also reported to be underway. This information will further inform the taxonomic treatment of these species.”

So, for the time being, and until new evidence is to hand, there remain 22 species of albatrosses, at least from the perspective of the Albatross and Petrel Agreement.

References:

Brothers, N., Bone, C. & Wellbelove, A. 2022. Albatross population monitoring using satellite imagery, a case study. Marine Ornithology 50: 7-12.

Eda, M., Yamasaki, T., Izumi, H., Tomita, N., Konno, S., Konno, M., Murakami, H. & Sato, F. 2020. Cryptic species in a Vulnerable seabird: short-tailed albatross consists of two species. Endangered Species Research 43: 375-386.

Taxonomy Working Group 2006. Taxonomy Working Group Report to the Second Advisory Committee Meeting - Annex 5 to AC2 Meeting Report. AC2 Doc 11. 21 pp.

Taxonomy Working Group 2023. Report of the Taxonomy Working Group.  Thirteenth Meeting of the Advisory Committee, Edinburgh, United Kingdom, 22 – 26 May 2023.  AC13 Doc 10 Rev 1. 12 pp.

John Cooper, Emeritus Information Officer, Agreement on the Conservation of Albatrosses and Petrels, 07 September 2023