A Great Shearwater on the wing

Paloma Carvalho (Department of Biological Sciences, University of Manitoba, Winnipeg, Canada) and colleagues have published in Ibis International Journal of Avian Science on aspects of the moult of Great Ardenna gravis and Sooty A. grisea Shearwaters

The paper’s abstract follows:

“Moult is an energetically demanding period, during which flight may be impaired and foraging ranges may become constrained. During the non-breeding period, Great Ardenna gravis and Sooty A. grisea Shearwaters migrate from South Atlantic breeding colonies to aggregate at North Atlantic feeding grounds. We investigated whether both shearwater species used coastal Newfoundland, Canada, as a moulting area and used stable isotope ratios (δ¹⁵N, δ¹³C) of recently moulted primary feathers (P1, P5, P10) to infer moult location/diet for both species. Moult scores indicated that both species finished their moult (i.e. P6-10) in coastal Newfoundland, which was further corroborated with similar stable isotope ratios for Great (δ¹⁵N = 15.17 ±1.13 ‰; δ¹³C = -18.66 ± 0.54 ‰) and Sooty Shearwaters (15.54 ±0.74 ‰; -18.43 ± 0.78 ‰); however, Sooty Shearwater moult was more advanced relative to Great Shearwater. In contrast, isotopic ratios of P1 and P5, which were grown before arriving in coastal Newfoundland, differed between and within species, suggesting divergent locations/diet during early moult. For Great Shearwaters, P1/P5 isotopic ratios were more variable (broader niche breadth) than P10, suggesting that some individuals started moulting in the South Atlantic prior to trans-equatorial migration, while others start moulting in the North Atlantic Ocean. Sooty Shearwaters had two distinct groupings of either higher or lower δ¹⁵N in P1/P5, suggesting that individuals began moulting either on the Newfoundland Shelf or further offshore based on comparisons to reference shearwater feathers grown in known locations. These findings illustrate distinct locations and/or diets at the start of primary feather moult, both within and between species, but diets converged when aggregated together at the end of moult in coastal North America, where growing feathers of both species were sampled. More importantly, we identified an important area for both Sooty and Great Shearwaters to complete their moult in coastal Newfoundland. Protecting this moulting area would minimize disturbance and the impacts of threats (e.g., by-catch) to both species during this energetically demanding period. The area has been suggested previously to be an important candidate area for protection due to annually persistent prey aggregations that can be spatiotemporally delimited based on specific prey habitat requirements.”

Reference:

Carvalho, P.C., Ronconi, R.A., Bugoni, L., Davoren, G.K. 2022.  Moult chronology and strategies of sympatric Great (Ardenna gravis) and Sooty (A. grisea) Shearwaters based on stable isotope janalysis.  Ibis International Journal of Avian Science  doi:10.1111/ibi.13060.

John Cooper, ACAP Information Officer, 17 March 2022

"Seabird Sunset“”, White-chinned Petrels by ABUN co-founder Kitty Harvill for ACAP, acrylics, 27 x3 5 cm; after a photograph by Dimas Gianuca 

Note:  The illustrated Species Summaries have been written to help inform the general public, including school learners, of the biology and conservation needs of the 31 ACAP-listed species.  They serve to complement the more detailed and referenced ACAP Species Assessments.  To date, summaries for the 22 species of albatrosses have been produced in in all three ACAP official languages, English, French and Spanish.

Texts have also been prepared for the nine ACAP-listed petrels and shearwaters in English, but as yet have not been translated into French and Spanish.  As an interim service, the illustrated English texts are being posted to ACAP Latest News, continuing here with the White-chinned Petrel Procellaria aequinoctialis.

 
A White-chinned Petrel pair in its burrow on Marion Island; photograph by Ben Dilley

The White-chinned Petrel is one of five medium-to-large petrels within the genus Procellaria, along with the Black, Grey, Spectacled and Westland.  Among all the petrels and shearwaters in the tubenose family Procellariidae, the ‘White-chin’ is one of the largest to breed in burrows.  The species is dark brown to black, save for a white chin of varying size that is not always readily visible in flight.  The white chin is a diagnostic feature separating the species from the otherwise similar looking Black and Westland Petrels.  The legs and feet are black; the bill is pale yellow with a black saddle.

‘White-chins’ have a wide range in the Southern Ocean breeding on sub-Antarctic islands.  In the southern Indian Ocean birds breed in the Prince Edward Islands (South Africa), Crozets and Kerguelen (France), on islands south of New Zealand (Antipodes, Auckland, Campbell) and in disputed territories* in the South Atlantic (South Georgia/Islas Georgias del Sur) and in small numbers in the Falkland Islands/Islas Malvinas.  At sea it ranges widely over the whole Southern Ocean south to the Antarctic pack ice and north to the coasts of southern Africa and southern South America.  The global population has been estimated at around 1.2 million breeding pairs representing three million adults, with the largest numbers (>100 000 pairs each) breeding on South Georgia/Islas Georgias del Sur, followed by Kerguelen and Auckland Islands. At localities where trends exist populations have decreased by a quarter to a third over two decades or so, corroborated by similar declines in at-sea counts.

White-chinned Petrels breed colonially in burrows dug on vegetated peat slopes, usually with small ponds at their entrances. As for all other tubenose seabirds they lay a single white egg.  Breeding takes place in the austral summer.  Diet consists of fish, crustaceans and squid obtained by surface seizing and diving to a depth of 15 m, often feeding at night.  Scavenging behind fishing vessels is common, putting the bird at high risk to longline hooks and trawl warp collisions.

Because of population declines and fishery mortality the species has a global threat category of Vulnerable, despite its overall large population.  Introduced mammals, including predatory cats and rodents, have been removed from most breeding islands where they occurred, leading to improved breeding success where studied, but not from all.  Introduced mammals require removal from French sub-Antarctic islands and from Auckland Island.  More widespread adoption of mitigation measures (such as deploying bird scaring lines) is required on fishing vessels within the species’ wide range in both national and international waters.  The White-chinned Petrel is listed both within the Albatross and Petrel Agreement (ACAP) and the Convention on Migratory Species on Appendix II.  Nearly all breeding islands are national nature reserves with management plans or equivalents restricting landings by permit only.  Several are World Heritage Natural Sites and/or Ramsar Wetlands of International Importance.  Most are surrounded by Marine Protected Areas of varying sizes.

Sources:

ACAP 2012.  White-chinned Petrel Procellaria aequinoctialis.

Bell, E.A. 2017.  White-chinned petrel.  In: Miskelly, C.M. (Ed.)  New Zealand Birds Online.

BirdLife International 2021.  Species factsheet: Procellaria aequinoctialis

John Cooper, ACAP Information Officer, 16 March 2022

*A dispute exists between the Governments of Argentina and the United Kingdom of Great Britain and Northern Ireland concerning sovereignty over the Falkland Islands (Islas Malvinas), South Georgia and the South Sandwich Islands (Islas Georgias del Sur y Islas Sandwich del Sur) and the surrounding maritime areas.

Exposed bone on the rump of an incubating Northern Giant Petrel on Marion Island, August 2003; photograph by John Cooper

Christopher Jones (FitzPatrick Institute of African Ornithology, University of Cape Town, South Africa) and colleagues published in the journal Polar Biology in 2019 on what they considered to be the first record of an attack by introduced House Mice Mus musculus on an adult Northern Giant Petrel Macronectes halli on Marion Island.  They photographed flank wounds consistent with a mouse attack in September 2017, noting that whereas mice are significant predators of seabird chicks on islands where they are the only introduced mammal, there are very few records of attacks on adult birds.

In August 2003 John Cooper observed an incubating Northern Giant Petrel on Marion Island with a large rump wound that exposed bone.  The next day the colour-banded bird was no longer present and the abandoned egg was broken.  A long-lost photograph of this incident has recently been found in support of mice attacking an adult seabird at Marion Island 14 years earlier than the published record.

A flank wound on an incubating Northern Giant Petrel on Marion Island, September 2017; photographs by Christopher Jones

House Mice were first recorded attacking Wandering Albatross Diomedea exulans chicks on Marion Island in 2003; subsequently attacks have been recorded on chicks of the other three albatross species that breed on the island, as well as on two species of burrowing petrels.

References:

Dilley, B.J., Schoombie, S., Schoombie, J. & Ryan, P.G. 2015.  ‘Scalping’ of albatross fledglings by introduced mice spreads rapidly at Marion Island.  Antarctic Science 28: 73-80.

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.

Jones, C.W., Risi, M.M., Cleeland, J. & Ryan, P.G. 2019. First evidence of mouse attacks on adult albatrosses and petrels breeding on sub-Antarctic Marion and Gough Islands.  Polar Biology 42: 619-623.

Jones, M.G.W. & Ryan, P.G. 2009.  Evidence of mouse attacks on albatross chicks on sub-Antarctic Marion Island.  Antarctic Science 22: 39-42

John Cooper, ACAP Information Officer, 15 March 2022

Northern Giant Petrel chick by ABUN artist Andrea Siemt Schmincke for ACAP, in watercolours; after a photograph by Liezl Pretorius

Note:  The illustrated Species Summaries have been written to help inform the general public, including school learners, of the biology and conservation needs of the 31 ACAP-listed species.  They serve to complement the more detailed and referenced ACAP Species Assessments.  To date, summaries for the 22 species of albatrosses have been produced in in all three ACAP official languages, English, French and Spanish.

Texts have also been prepared for the nine ACAP-listed petrels and shearwaters in English, but as yet have not been translated into French and Spanish.  As an interim service, the illustrated English texts are being posted to ACAP Latest News, continuing here with the Northern Giant Petrel Macronectes halli.  The Photo Essay series of the 31 listed species takes a more personal approach; click here for the Northern Giant Petrel by Janine Schoombie.

After scavenging from a seal carcass, bloodied Northern Giant Petrels s are fastidious about bathing at sea
Protected from the prevailing weather by a rock face, a Northern Giant Petrel broods its downy chick on Marion Island
Photographs by Janine Schoombie

The Northern Giant Petrel is one of the two largest petrels in the family Procellariidae.  They are so large they do not need to breed in burrows to be protected from predators.  The species was only recognized as separate to the closely related and similar looking Southern Giant Petrel in the 1960s.

Unlike its sister species, which has a white phase, the Northern Giant Petrel exists in only one colour phase.  Juveniles are uniform dark brown, adults are paler, especially on the face.  The horn-coloured bill has a diagnostic reddish tip, separating it from the southern species which has a green tip.  Males are noticeably larger than females.

The species has a more restricted breeding range than the near-Southern Ocean distribution of the Southern Giant Petrel.  It breeds on sub-Antarctic islands in the Atlantic and Indian Oceans, including on islands south of New Zealand (where the Southern does not).  Unlike the Southern species it does not breed within Antarctica.  The bird breeds singly or in loose colonies, laying its single egg in nests on the ground, often made against the sides of protruding rocks.  Breeding commences about six weeks earlier than Southern Giant Petrels, although hybridisation has been reported at several breeding localities where both species coexist.  The global population is estimated at 11 800 breeding pairs; largest concentrations are found in the South Atlantic and in New Zealand waters (with an estimated 2000 pairs on tiny Forty-Fours/Motuhara Island).  At most breeding sites where studies exist, populations are increasing in numbers, leading to it being categorized as Least Concern.

Banding and tracking studies show individuals can travel over great distances within the Southern Ocean.  As for its sister species, the diet of Northern Giant Petrels comes from scavenging on carcasses from increasing seal populations and preying on seabirds, including penguins, on land and feeding on marine life (squid, fish) caught at sea, as well as from scavenging behind fishing vessels.

Threats included being killed as bycatch by longline fisheries, notably by IUU (Illegal, Unreported and Unregulated) fisheries for toothfish in the Southern Ocean in the 1990s; now largely eliminated by the adoption of mitigation measures (such as deploying bird-scaring lines) by the legal fisheries and concerted international action against the poaching vessels.  Birds have died from poisoning on several islands during introduced predator eradication programmes but have shown subsequent signs of recovery.  Human disturbance by researchers and tourists is largely controlled by management plans and guidelines on approach distances.  Most breeding sites are proclaimed nature reserves or equivalents, several with international status coming from the World Heritage and Ramsar Wetlands Conventions.  Nearly all breeding sites are surrounded by large Marine Protected Areas.  The Northern Giant Petrel is listed both within the Albatross and Petrel Agreement (ACAP) and the Convention on Migratory Species on Appendix II.

Sources:

ACAP 2012.  Northern Giant Petrel Macronectes halli.

BirdLife International 2021.  Species factsheet: Macronectes halli.

John Cooper, ACAP Information Officer, 14 March 2022