A Grey Petrel chick starts to shed its down on Macquarie Island; photograph by ‘Jez’ Bird

Jeremy ‘Jez’ Bird (School of Biological Sciences, University of Queensland, St Lucia, Australia) and colleagues have published open access in the journal Ecography on estimating populations of burrowing seabirds ion Australia’s Macquarie Island, including that of the ACAP-listed and Near Threatened Grey Petrel Procellaria cinerea.  “Species [such as the Grey Petrel] with low abundance that occur patchily across large islands are likely to be best estimated using targeted surveys …”.

Steep!  ‘Jez’ Bird surveys burrowing petrels on Macquarie Island; photograph by Melissa Houghton

The paper’s abstract follows:

“Maximising survey efficiency can help reduce the tradeoff between spending limited conservation resources on identifying population changes and responding to those changes through management. Burrow-nesting seabirds are particularly challenging to survey because nests cannot be counted directly. We evaluated a stratified random survey design for generating unbiased population estimates simultaneously for four petrel species nesting on Macquarie Island, Australia, where the survey cue, burrow entrances, is similar for all species. We also compared the use of design-based and model-based analyses for minimising uncertainty in estimates. We recorded 2845 Antarctic prion burrows, 306 white-headed petrel burrows and two blue petrel burrows while distance-sampling along 154 km of transects. For blue petrels and grey petrels, we completed nocturnal searches along a further 71 km and searched 249 km of tracks during follow-up ground searches. We failed to generate unbiased population estimates for two rare and localised species, blue and grey petrels, from our stratified random survey. Only for the most widespread and abundant species, Antarctic prion, did the estimate have reasonable power to detect a rapid population change. Model-based analyses of the stratified random survey data did not improve upon traditional design-based analyses in terms of uncertainty in population estimates, but they did provide useful spatial representation of current populations. Models that used the targeted survey data did not reflect current population sizes and distributions of the two rare and localised species. We found that when species ecologies, distributions and abundances vary, a multi-method approach to surveys is needed. Species with low abundance that occur patchily across large islands are likely to be best estimated using targeted surveys, whereas widespread and abundant species can be accurately and precisely estimated from randomised surveys using informative model-based analyses.”

Read Jez Bird’s photo essay for the Grey Petrels of ‘Macca’ here.

With thanks to Jeremy Bird and Justine Shaw.

Reference:

Bird, J., Terauds, A., Fuller, R.A., Pascoe, P.P., Travers, T.D., McInnes, J.C., Alderman, R. & Shaw, J.D. 2022.  Generating unbiased estimates of burrowing seabird populations.  Ecography doi: 10.1111/ecog.06204.

John Cooper, ACAP Information Officer, 02 May 2022

 
Like most burrow-nesting petrels, White-chinned Petrels are largely nocturnal at their colonies. However, their large size gives them a degree of bravado when it comes to dealing with Brown Skuas, and they occasionally sit outside their burrow entrances during the day

The White-chinned Petrel Procellaria aequinoctialis is the largest member of the petrel family after the two giant petrels Macronectes spp. It breeds at sub-Antarctic islands, with three regional populations: the nominate subspecies breeds at South Georgia and locally on the Falklands in the south-west Atlantic Ocean, and at the Prince Edward, Crozet and Kerguelen Islands in the south-west Indian Ocean, whereas P. a. steadi breeds at islands south of New Zealand.

Peter Ryan scans for seabirds, including White-chinned Petrels,  on a Southern Ocean voyage

White-chinned Petrels are the seabird most often caught on longlines in the Southern Ocean. Since I started checking the age and sex of hooked seabirds returned to South African ports by fishery observers, I have examined nearly 4000 White-chinned Petrels. They are competent divers, occasionally reaching depths of up to 16 m, which allows them to retrieve baited hooks for some distance behind vessels. Indeed, they are thought to facilitate the bycatch of albatrosses by bringing hooks to the surface, only to be displaced by larger albatrosses.

The White-chinned Petrel is the largest burrow-nesting petrel, and their burrows tend to be fairly obvious; most have an entrance moat

The large, distinctive burrow nests of White-chinned Petrels make it possible to attempt a complete survey of their breeding distribution on Marion Island. Most colonies are close to the coast, but nests occur up to 420 m above sea level below Spitskop (map from Ryan et al. 2012). They favour well-drained sites with deep soils for burrowing, avoiding more recent black lava flows

Given concerns about their population status – the species is listed a Vulnerable globally – it was the first burrowing petrel for which we attempted to estimate the breeding population at the Prince Edward Islands. Genevieve Jones, Ben Dilley and I conducted a systematic survey of all burrows in April 2009, and Ben followed up with occupancy checks the following breeding season. This indicated a total population of some 30 000 pairs on Marion Island and at least another 10 000 pairs on Prince Edward Island. Subsequent randomized transects conducted around Marion Island in 2015 by Ben, Stefan Schoombie, Alexis Osborne and I indicated that this initial estimate was too low, with an extrapolated 40 000 pairs breeding on the island. This makes the Prince Edward Islands the third most important breeding site for the nominate subspecies after South Georgia and Kerguelen.

In March and April at Marion Island, White-chinned Petrel chicks exercise their wings outside their burrows at night in preparation for fledging. A few fail to make it back to the safety of their burrows by day break, and typically fall prey to Brown Skuas

Despite their frequent mortality on long-lines, White-chinned Petrel numbers have shown the greatest recovery among burrow-nesting petrels on Marion Island following the eradication of cats in 1991. Their breeding success is generally quite high (average 59% of attempts fledge a chick), suggesting that their chicks are seldom attacked by the introduced House Mice. In this regard, they are probably helped by their large size and by breeding in summer, when mice have a greater range of other food options than in winter. Surprisingly, large chicks may occasionally be killed by Grey Petrels if they find a White-chinned Petrel chick in their burrow when they return to breed in autumn.

A White-chinned Petrel glides by the photographer in the Southern Ocean

At sea, White-chinned Petrels are among the most vocal of petrels, often giving their characteristic chittering call during squabbles over food
All photographs by Peter Ryan

References:

Dilley, B.J., Davies, D., Schoombie, S., Schoombie, J. & Ryan, P.G. 2019. Burrow wars and sinister behaviour among burrow-nesting petrels at sub-Antarctic Marion Island. Ardea 107: 97-102.

Dilley, B.J., Hedding, D.W., Henry, D.A.W., Rexer-Huber, K, Parker, G.C., Schoombie, S., Osborne, A. & Ryan, P.G. 2019. Clustered or dispersed: testing the effect of sampling strategy to census burrow-nesting petrels with varied distributions at sub-Antarctic Marion Island. Antarctic Science 31: 231-242.

Dilley, B.J., Schoombie, S., Stevens, K., Davies, D., Perold, V., Osborne, A., Schoombie, J., Brink, C.W., Carpenter-Kling, T. & Ryan, P.G. 2018. Mouse predation affects breeding success of burrow-nesting petrels at sub-Antarctic Marion Island. Antarctic Science 30: 93-104.

Dilley, B.J., Schramm, M. & Ryan, P.G. 2016. Modest increases in densities of burrow-nesting petrels following the removal of cats (Felis catus) from Marion Island. Polar Biology 40: 625-637.

Rollinson, D.P., Dilley, B.J. & Ryan, P.G. 2014. Diving behaviour of white-chinned petrels and its relevance for mitigating longline bycatch. Polar Biology 37: 1301-1308.

Ryan, P.G. 2001. Partial leucism in Whitechinned Petrels. Bird Numbers 10(2): 6-7.

Ryan, P.G., Dilley, B.J. & Jones, M.G.W. 2012. The distribution and abundance of White-chinned Petrels (Procellaria aequinoctialis) breeding at the sub-Antarctic Prince Edward Islands. Polar Biology  35: 1851-1859.

Peter Ryan, FitzPatrick Institute of African Ornithology, University of Cape Town, 29 April 2022

NOTE: First published on the Mouse-Free Marion website on 26 April 2022.

A Streaked Shearwater at night in a breeding colony

Junco Nagata (Forestry and Forest Products Research Institute, Ibaraki, Japan) and colleagues have published in the journal Mammal Study on identifying predators of Streaked Shearwaters Calonectris leucomelas by genetic analysis.

"The conditions of the Streaked Shearwater carcasses found in this study"; from the publication

The paper’s abstract follows:

“The domestic cat Felis silvestris catus is known to be one of the most notorious invasive alien predators. Seabirds are typical taxonomic groups that have been impacted by free-ranging cats on islands, and their headless carcasses are frequently observed. We conducted genetic predator identification of the carcasses of streaked shearwater Calonectris leucomelas and described their characteristics on Mikura Island, Japan, where free-ranging cats were blamed for the recent rapid decline of the shearwater population. Eight carcasses of streaked shearwaters were found in the survey. Genetic analysis of swab samples from scarred tissues of the carcasses detected cat DNA and identified cat predation on six out of eight carcasses. All six cat-positive carcasses were headless or almost headless with the head and body faintly connected by esophagus and trachea, several of which were missing their intestines. We describe the conditions of these headless carcasses, noting the main characteristics that could lead to suspicion of cat predation. To the best of our knowledge, this is the first genetic predator identification using seabirds, and may make more stakeholders aware of the reality of cat predation worldwide. On Mikura Island, we expect that this evidence will contribute to the development of systematic cat management.”

Reference:

Nagata, J., Haga, A., Kusachi, Y., Tokuyoshi, M., Endo, H. & Watari, Y. 2022. Cats were responsible for the headless carcasses of shearwaters: evidence from genetic predator identification.  Mammal Study 47(3) : 1-8. doi:10.3106/MS2021-0047.

Control and experimental hooks, the weighted hook is on the left; from the publication.

Eric Gilman (The Safina Center, Honolulu, Hawaii, USA) and colleagues have published open access in the journal Scientific Reports on researching weighting longliner hooks tor reduce seabird bycatch.

The paper’s abstract follows:

“Fisheries bycatch threatens the viability of some seabird populations and reduces fishing efficiency. Albatross bycatch in a US North Pacific tuna longline fishery has increased over the past decade and now exceeds 1000 annual captures. Seabirds interacting with this fishery reach hooks at depths up to 1 m. A branchline weight’s mass and distance from the hook affect seabird catch rates. We conducted experimental fishing to compare the commercial viability of a weighted hook relative to conventional gear with weights attached 0.75 m from the hook. We used a Bayesian random effects meta-analytic regression modelling approach to estimate pooled expected species-specific log relative risk of capture on conventional versus experimental gear. There was a significant 53% (95% HDI: − 75 to − 25%) decrease in retained species’ catch rates on experimental hooks, indicating an unacceptable economic cost, and no significant effect for discarded species. Using a Bayesian general linear mixed regression modelling approach, experimental hooks sank to 85 cm ca. 1.4 times (95% HDI: 1.37–1.48) faster than control hooks. Given their potential to reduce seabird catch rates, eliminate safety risks from bite-offs and facilitate robust compliance monitoring, it is a priority to find a weighted hook design with acceptable catch rates.”

Reference:

Gilman, E., Musyl, M., Wild, M., Rong, H. & Chaloupka, M. 2022.  Investigating weighted fishing hooks for seabird bycatch mitigation.  Scientific Reports doi.org/10.1038/s41598-022-06875-4.

John Cooper, ACAP Information Officer, 27 April 2022