Buller's Shearwater off Mercury Islands, New Zealand; photograph by Kirk Zufelt

 Megan Friesen (Northern New Zealand Seabird Trust, Auckland, New Zealand) and colleagues have published in the journal Emu – Austral Ornithology on a breeding census of the globally Vulnerable and nationally Naturally Uncommon Buller’s Shearwaters Ardenna bulleri.

The paper’s abstract follows:

“Accurate and repeatable population estimates are key to establishing population trends and conservation status. Rako, or Buller’s Shearwater (Ardenna bulleri) is a seabird endemic to New Zealand that breeds only on the Poor Knights Islands, but forages throughout wider areas of the Pacific Ocean during the non-breeding season. The lack of threats on the breeding grounds and the wide foraging range of Buller’s Shearwaters makes them ideal sentinels of ocean health. Although they are commonly seen at sea and the population in the 1980s was thought to be around 2.5 million birds, other rapid land-based surveys suggested a much lower figure (~100,000 pairs on Aorangi), and no thorough population estimate has been undertaken to date. We calculated a population estimate for Buller’s Shearwater based on burrow counts and state of occupancy conducted at the Poor Knights during either the 2016–2017 or the 2017–2018 breeding seasons. We incorporated information on habitat availability and preference in population models. Our estimate of 78,645 (95% confidence interval 67,176–89,178) active burrows, broadly representing breeding pairs, is lower than some previously published assessments. This is a repeatable quantitative study of the Buller’s Shearwater breeding population, including breeding activity, and provides critical baseline data to determine population trends for this potentially important marine indicator species.”

Reference:

Friesen, M.R., Simpkins, C.E., Ross, J., Anderson, S.H., Ismzar-Rebitz, S.M.H., Tennyson, A.J.D., Taylor,G.A., Baird, K.A. & Gaskin, C.P. 2021.  New population estimate for an abundant marine indicator species, Rako or Buller’s Shearwater (Ardenna bulleri).  Emu – Austral Ornithologydoi.org/10.1080/01584197.2021.1924066.

John Cooper, ACAP Information Officer, 02 September 2021

 
An incubating Grey Petrel in its burrow on Macquarie.  Burrows were visited throughout the season to estimate population size and breeding success, photograph by Jeremy Bird

NOTE: This is the third in an occasional series that aims to feature photographs of the 31 ACAP-listed species, along with information from their photographers.  Here, Jeremy ‘Jez’ Bird writes about the ACAP-listed and globally Near-Threatened Grey Petrel Procellaria cinerea, a species he studied for his recently awarded PhD.

 Their burrow-nesting habit makes Grey Petrels difficult to survey.  Here Jez uses a dedicated ‘burrowscope’ on Macquarie’s steep slopes

The Southern Ocean islands are out of sight and out of mind for most of us, but they support some amazing wildlife and I’ve been passionate about the region since visiting on a travel scholarship as an 18-year-old.  Twenty years later, still inspired by that first experience, I’ve just completed a PhD studying the recovery of threatened seabirds on Macquarie Island, Australia.  This sub-Antarctic island is currently responding to the removal of invasive predators.  Pest management began with the eradication in 1998 of the Weka Gallirallus australis , a globally Vulnerable species of rail native to New Zealand which was originally introduced as a food source for sealers, followed by feral cats in 2000 and rabbits, rats and mice in 2011.

 
A Grey Petrel chick starts to lose its down, photograph by Jeremy Bird

Among the birds I studied was the Grey Petrel.  Found on a number of sub-Antarctic islands, the largest recorded population is on Antipodes Island south of New Zealand.  Grey Petrels were reported historically on Macquarie Island, but there was no evidence of breeding after the early 1900s.  In the 1990s, when the cat population was under control and on its way to eradication, Grey Petrels recolonised.  No island-wide surveys of the population had been undertaken since 2003 although the Tasmania Parks and Wildlife Service has continued monitoring at some core breeding sites.  I completed a whole-island survey and found the population has increased to c. 250 breeding pairs today.  Based upon the current population size and trajectory we expect them to warrant removal from Australian state and federal threatened species lists within the next few years.

A camera trap positioned at a burrow entrance records an entering Grey Petrel

Petrels are notoriously difficult to study.  They typically breed on remote islands, often in rugged terrain.  Birds only frequent colonies in certain seasons, and they with few exceptions only visit their nesting burrows at night to avoid native avian predators such as skuas.  They mostly nest in underground burrows whose entrances can be obscured under dense vegetation.  As a result, much of my year was spent searching for and counting burrows, and then trying to figure out what was in them.  I used a dedicated ‘burrowscope’ to help with this and used camera traps to record activity at individual nests.  By following nests through the season I found that almost 80% of nesting attempts were successful – way higher than when invasive species are present, as for example on Macquarie in the past and currently on South Africa’s Marion Island where Grey Petrels remain at risk to House Mice (click here).

We also deployed geolocator tags on a number of birds.  These tags were attached to the legs and retrieved the next season when the birds returned to their breeding burrows.  Using an internal clock, each day the tag logs sunrise and sunset whose timings tell us longitude, whereas day length tells us latitude.  We are now using this information to illustrate potential overlap of Macquarie’s Grey Petrels with fisheries throughout their at-sea range, and to understand better their population structure.  For example, we know the recolonizing Grey Petrels have arrived from Macquarie from elsewhere and the rate at which the island population is growing suggests immigration is still occurring, but we don’t know where the source population is.  As the impact of climate change in the Southern Ocean intensifies understanding how connected species’ populations are and what capacity they have to move help decisions over island management to be made.

I spent most of my year on Macquarie Island searching for seabird burrows and trying to figure out what was in them, photograph by Toby Travers

I loved immersing myself in the lives of these birds for a year.  Learning from remote recording devices when they first arrived back at their colonies. Reading how males sit atop tussock heads and ‘hose’ their staccato calls at the night, before waiting after dark to see it for myself.  Watching hatching chicks, still wet and complete with egg tooth, gradually grow and transform into sleek fledglings, seen disappearing for the last time as I flicked through camera trap photos.  Following the annual cycle of Grey Petrels on Macquarie has given me immense enjoyment and respect for the hardships they endure year in year out.

Much of my work reported here can be found in my two recent papers and in my thesis which has just been published online.

References:

Bird, J.P. 2021.  The Conservation Ecology of Burrowing Petrels on Macquarie Island.  PhD Thesis.  Brisbane, Australia: School of Biological Sciences, The University of Queensland.  216 pp. [click here].

Bird, J.P., Fuller, R.A., Pascoe, P.P. & Shaw, J.D.S. 2021.  Trialling camera traps to determine occupancy and breeding in burrowing seabirds.  Remote Sensing in Ecology and Conservation doi.org/10.1002/rse2.235. [click here]

Bird, J.P., Woodworth, B.K., Fuller, R.A. & Shaw, J.D. 2021.  Uncertainty in population estimates: a meta-analysis for petrels.  Ecological Solutions and Evidence doi.org/10.1002/2688-8319.12077.

Jeremy Bird, School of Biological Sciences, The University of Queensland, Brisbane, Australia, 01 September 2021

 
Preening Light-mantled Albatross, watercolour for ACAP by Andrea Siemt; after a photograph by Oli Prince

 As for nearly all international meetings affected by COVID-19, the Twelfth Meeting of ACAP’s Advisory Committee (AC12) and of two of its working groups are being held virtually; a first for ACAP.  This year’s meetings - delayed from last year by the pandemic - are now being held from 16/17 August to 1/2 September (depending on where one is in the world).  Meetings of the Seabird Bycatch Working Group (SBWG10) and the Population and Conservation Status Working Group (PaCSWG6) preceded AC12, from 16/17 to 18/19 August and 23/24 to 24/25 August, respectively.  These two working groups (and the Taxonomy Working Group) will give their reports to AC12.

AC12 is meeting from 30/31 August to 1/2 September, preceded by a one-hour closed Heads of Delegation Meeting.  The meeting is being chaired by Nathan Walker (Ministry for Primary Industries, New Zealand), with the support of Vice-Chair Tatiana Neves (Projeto Albatroz, Brazil).  The Advisory Committee’s current membership may be viewed by scrolling down from here.

Nineteen Documents (including AC12 Doc 02: Annotated Meeting Agenda and work programmes for the next several years) and nine Information Papers (including 2021 Implementation Reports from six Parties) have been tabled for consideration, leading to an expected busy meeting over the three days allotted.  All these documents can be downloaded from this website.

Further information on the virtual meeting of AC12 is available in AC12 Circular 5 in the three official ACAP languages of English, French and Spanish, giving information on timing at different localities around the world.  Congress Rental has been chosen to manage the technical aspects of the meeting, using the Interprefy platform.  Interprefy enables “relay interpretation” (involving multiple languages – three in the case of ACAP).  Congress Rental has been providing technical advice to Chairs, Secretariat, interpreters and to other participants.

John Cooper, ACAP Information Officer, 31 September 2021

Jeremy Bird on Macquarie, photograph by Andrea Turbott

Jeremy ‘Jez’ Bird has been awarded his PhD by the University of Queensland for a study of burrowing petrels, including the ACAP-listed and globally Near Threatened Grey Petrel Procellaria cinerea, on Australia’s Macquarie Island.

A Grey Petrel chick in its burrow on Macquarie Island, photograph by Jeremy Bird

The thesis abstract follows:

“Many seabird populations are of conservation significance, either because they are rare and threatened with extinction, or because they are abundant and play an integral role in island-ocean systems. Procellariiform petrels in the families Procellariidae, Hydrobatidae and Oceanitidae are especially vulnerable to the impacts of alien invasive species on islands and as a result 45 of 97 species globally are threatened with extinction, a higher proportion than comparable bird groups. In their natural state petrels are also the most abundant seabirds, consuming prey volumes commensurate with commercial fisheries, and transferring nutrients from pelagic to terrestrial and coastal ecosystems on a scale equivalent to other global geochemical fluxes. Seabird nutrient inputs ramify to influence whole-island food-webs. To prevent seabird extinctions, and to restore nutrient pathways the whole-island eradication of invasive species has been developed as an effective conservation tool. In this thesis I explore the conservation ecology of a diverse group of petrels following the World’s largest multi-species eradication to date—the staged removals of Wekas Gallirallus australis, Feral Cats Felis catus, European Rabbits Oryctolagus cuniculus, Black Rats Rattus rattus and House Mice Mus musculus from subantarctic Macquarie Island.

Petrels are particularly challenging to study, and few quantitative data on their responses to invasive species eradication are available. Petrels nest discontinuously across rugged terrain on remote islands. Their nests are in under-ground burrows, the entrances to which are often obscured under dense vegetation. Birds are not present year-round, and only return to or leave from colonies at night. Given these inherent challenges, I review in Chapter 1 what motivates people to collect and report population estimates for petrels. Because these species are cryptic and challenging to study I undertook a meta-analysis of uncertainty in published estimates to assess overall levels and drivers of uncertainty. I concluded that the primary motivation for estimating populations is to inform species status and trend assessments, but uncertainty in generated estimates is an impediment to reliable trend detection.

The findings of the review provide the rationale for testing field methods that measure two key metrics that underpin population estimates: the proportion of burrows occupied by breeding pairs (Chapter 2), and the total number of burrows on an island (Chapter 3). Chapter 2 compares traditional techniques for estimating burrow occupancy and breeding status with my novel application of camera traps positioned at burrow entrances. I found that (i) camera traps are effective at collecting season-long activity patterns, with evidence that these can be used to distinguish breeding from non-breeding burrows, and (ii) cameras provide higher resolution data on breeding success than repeat visits to inspect burrows manually and are a low impact approach.

To understand the current size and distributions of a diverse assemblage of petrels that includes common widespread species (Antarctic Prion Pachyptila desolata) and rare localised species (Blue Petrel Halobaena caerulea and Grey Petrel Procellaria cinerea) a multi-method approach to surveys and analysis is required (Chapter 3).  I found that a model-based analysis of stratified randomised whole-island survey data was most effective for estimating Antarctic Prions, less effective for scarcer White-headed Petrels Pterodroma lessonii, but did not yield useful data for Blue or Grey Petrels, which required a targeted approach.

In the final chapters I evaluate the outcomes that invasive species management has achieved for petrels to date (Chapter 4) and projected into the future (Chapter 5). The current distribution of petrels on Macquarie Island reflects the legacy of invasive species impacts and the removal of this threat. The two established species, Antarctic Prion and White-headed Petrel are confined largely to refugial habitat, while the recolonising species Blue and Grey Petrel are occupying optimal habitat on the island’s coastal slopes. While all four species occur in superficially similar habitats in terms of vegetation type, their realized niches defined by other environmental variables including slope, elevation, and aspect are starkly different. Each species is now increasing, but the two recolonising species are increasing much more rapidly than the two established ones, at rates suggesting immigration is an important mechanism facilitating initial population recovery.

The eradication of invasive predators from Macquarie Island has achieved a major short-term goal: to prevent further seabird extinctions and facilitate threatened species recovery. I present a case for downlisting three species from state or federal threatened species lists. However, suitable habitat is currently under-utilised. Using habitat suitability modelling and inter-island inference I illustrate how the current size and distribution of petrel populations is well short of plausible carrying capacities. Full recovery of populations, and restoration of the ecological and societal benefits that they bring is decades away, but no long-term targets for population recovery exist. I present a future scenario based upon plausible model-derived population estimates to highlight the potential advantages of establishing long-term targets. The thesis concludes with my own narrative vision of a future Macquarie Island when the full post-eradication recovery has occurred in coming decades.”

See also a recent publication by Jeremy Bird from his thesis.

With thanks to Jez Bird.

Reference:

Bird, J.P. 2021.  The Conservation Ecology of Burrowing Petrels on Macquarie Island.  PhD Thesis.  Brisbane, Australia: School of Biological Sciences, The University of Queensland.  216 pp.

John Cooper, ACAP Information Officer, 30 August 2021