A scavenging Southern Giant Petrel; photograph by Liezl Pretorius

William Mills (British Antarctic Survey, Cambridge, UK) and colleagues have published in the journal Marine Biology on diets of non-threatened (Least Concern) Northern Macronectes halli and Southern M. giganteus Giant Petrels in the South Atlantic.

The paper’s abstract follows:

“Northern Macronectes halli and southern giant petrels M. giganteus are opportunistic predators and the dominant avian scavengers in sub-Antarctic and Antarctic ecosystems. At South Georgia, there are globally important breeding populations of both species; however, no detailed diet study has been carried out at this site for > 35 years. Here, we analysed stomach contents of northern (n = 81) and southern giant petrel (n = 73) chicks at Bird Island, South Georgia (2014/15–2016/17). Specifically, we investigated: (1) interspecific and sexual dietary segregation; (2) diet changes within and among recent years; and (3) long-term diet changes since 1979/80–1980/81. Overall diet composition was similar between species, with penguins comprising approximately half the diet by mass. In both species (but more pronounced in southern giant petrels), prey delivered by female parents included higher proportions (by mass) of penguins and Antarctic krill Euphausia superba, and by male parents included more Antarctic fur seal Arctocephalus gazella carrion and seabirds other than penguins. Consumption of penguins increased, and of seal carrion declined, as chick-rearing progressed, mirroring the decreasing availability of the latter after the peak pupping period in December at South Georgia. Comparisons with data from 1979/80–1980/81 suggest some changes in giant petrel diets; however, these differences were no greater than the typical annual variation, and there were no clear links between diet and breeding allochrony or the differing population trends (more rapid increase in northern than southern giant petrels). The high diet diversity and ability of giant petrels to exploit both carrion and marine prey facilitates coexistence with other sympatric Procellariiformes and explains their favourable population status.’

Southern Giant Petrel by Marion Schön entitled "Bloody Beauty" - Pastels on Pastelmat, from a photograph by Jaimie Cleeland

With thanks to Richard Phillips.

Reference:

Mills, W.F., Morley, T.I., Votier, S.C. & Phillips, R.A. Long‑term inter‑ and intraspecific dietary variation in sibling seabird species.  Marine Biology doi.org/10.1007/s00227-021-03839-6.

John Cooper, ACAP Information Officer, 26 February 2021

Amsterdam Albatross painted by Birgit Bührlé (left) from a photograph taken at sea by Kirk Zufelt (right)

Alexandre Corbeau (Centre d’Études Biologiques de Chizé, Villiers en Bois, France) and colleagues have published in the journal Animal Conservation on at-sea tracking of Amsterdam Diomedea amsterdamensis and Wandering D. exulans Albatrosses in relation to the presence of fishing vessels in the southern Indian Ocean.

The paper’s abstract follows:

“Many seabirds are attracted to fishing boats where they exploit foraging opportunities, often involving bycatch‐related mortality. Bycatch risk is generally estimated by overlapping seabirds foraging ranges with coarse‐scale monthly maps of fishing efforts, but a more direct estimation would be the time birds actually spend attending fishing boats. Here we matched data from Automatic Identification Systems from all declared boats in the Southern Ocean, with 143 simultaneous foraging trips from all populations of large albatrosses (Diomedea amsterdamensis and Diomedea exulans) breeding in the Indian Ocean (Marion, Crozet, Kerguelen, Amsterdam islands). We quantified and compared real‐time co‐occurrence between boats and albatrosses, at different scales (100, 30 and 5 km). We also examined to what extent co‐occurrence at a large‐scale (5×5° grid cell) predicted fine‐scale attendance (5 km). Albatrosses on average spent about 3 h per trip attending fishing boats (<5 km) at both Amsterdam and Marion and about 30 h per trip at Kerguelen. In all populations, >90% of declared fishing boat attendances occurred within Economic Exclusive Zones (EEZ) where bycatch mitigation measures are enforced. Outside EEZs, birds from all populations to a large extent also attended non‐fishing boats. Fishing boat density at a large scale (5 × 5°, 100 km) was a poor predictor of time spent attending fishing boats (<5 km) across populations. Our results indicate a large variation in fishing boat densities within the foraging ranges of different populations and in the time birds spent attending boats. We discuss the pros and cons of considering bycatch risk at a large geographical scale and methods that can be implemented to improve the estimation of seabird vulnerability to fishing activities when fine‐scale data are available, particularly for the conservation of those highly threatened species.”

Reference:

Corbeau, A., Collet, J., Orgeret, F., Pistorius, P. & Weimerskirch, H. 2021.  Fine‐scale interactions between boats and large albatrosses indicate variable susceptibility to bycatch risk according to species and populations.  Animal Conservation doi.org/10.1111/acv.12676.

John Cooper, ACAP Information Officer, 25 February 2021

 Albatross translocation site in Hawaii with shaded chicks and adult decoys, photograph from Pacific Rim Conservation

Carmen Antaky (Department of Natural Resources and Environmental Management, University of Hawai'i at Mānoa, Honolulu, USA) and colleagues have published open access in the journal Marine Ornithology on a review of seabird site fidelity and dispersal, informing whether translocated chicks are likely to return to their translocation sites.  It seems albatrosses and petrels (tubenose procellariiforms) make good candidates, at least within the Hawaiian Archipelago.

The paper’s abstract follows:

“Management of avian species threatened by land use and climate change requires a thorough understanding of their site fidelity and dispersive behaviors. Among long-lived colonial seabird species, the behavior of returning to the natal colony to breed, i.e., natal philopatry, may increase the likelihood that adequate resources and mates are available, but it may also increase the potential for inbreeding, competition, and ecological traps. Successful management of seabird populations—using chick translocation to encourage colony establishment to locations having minimal threats—must also be informed by the likelihood that birds will return to the new sites. However, the extent of philopatry and the traits that dictate variation across seabirds have yet to be fully summarized. We evaluated whether seabirds returned to their natal colony at rates greater than those predicted by colony size and various dispersal variables, based on data gathered for 36 seabird species nesting in the British Isles and the Hawaiian Archipelago. We compiled long-term banding and census data across 663 colonies. A linear mixed-effects model was employed to determine the relationship between philopatry and colony demographics, wingspan (mobility), and spatial variables. Our results indicate that philopatric rates are higher in the Hawaiian Archipelago than in the British Isles. Additionally, our research suggests that seabird management using chick translocation will have the greatest success with Procellariiformes species.”

Reference:

Antaky, C.C., Young, L., Ringma, J. & Price, M.R. 2021.  Dispersal under the seabird paradox: probability, life history, or spatial attributes?  Marine Ornithology 49: 1-8.

John Cooper, ACAP Information Officer, 24 February 2021

MacGillivray’s Prion in Prion Cave, Gough Island; photograph by Chris Jones

Chris Jones (RSPB Centre for Conservation Science, Royal Society for the Protection of Birds, Cambridge, United Kingdom) and colleagues have published in the journal Animal Conservation on the very poor breeding success of MacGillivray’s Prion Pachyptila macgillivrayi on Gough Island due to depredations by introduced House Mice Mus musculus.

The paper’s abstract follows:

“Petrels (Procellariidae) are a highly diverse family of seabirds, many of which are globally threatened due to the impact of invasive species on breeding populations. While predation by invasive cats and rats has led to the extinction of petrel populations, the impact of invasive house mice Mus musculus is slower and less well documented. However, mice impact small burrow‐nesting species such as MacGillivray’s prion Pachyptila macgillivrayi, a species classified as endangered because it has been extirpated on islands in the Indian Ocean by introduced rodents. We use historic abundance data and demographic monitoring data from 2014 to 2020 to predict the population trajectory of MacGillivray’s prion on Gough Island with and without a mouse eradication using a stochastic integrated population model. Given very low annual breeding success (0.01 fledglings per breeding pair in ‘poor’ years (83%) or 0.38 in ‘good’ years (17%), n = 320 nests over 6 years) mainly due to mouse predation, our model predicted that the population collapsed from ~3.5 million pairs in 1956 to an estimated 175,000 pairs in 2020 despite reasonably high adult survival probability (ϕ = 0.901). Based on these parameters, the population is predicted to decline at a rate of 9% per year over the next 36 years without a mouse eradication, with a 31% probability that by 2057, the MacGillivray’ prion population would become extremely vulnerable to extinction. Our models predict population stability (λ = 1.01) and a lower extinction risk (<10%) if mouse eradication on Gough Island restores annual breeding success to 0.519, which is in line with that of closely related species on predator‐free islands. This study demonstrates the devastating impacts that introduced house mice can have on small burrowing petrels and highlights the urgency to eradicate invasive mammals from oceanic islands.”

 

 

Chris Jones holds a Macgillivray's Petrel and a downy chick attacked by mice

Photographs by Michelle Risi

The Gough Island Restoration Programme (GIRP) has reported on its Facebook page of the failure "of all our 50 monitored MacGillivray’s Prion nests due to mice predation” in the current 2020/21 breeding season, thus adding a further season of zero breeding success to the study and emphasizing the need for this year’s eradication attempt to succeed.

With thanks to Chris Jones and Michelle Risi.

Reference:

Jones, C.W., Risi, M.M., Osborne, A.M., Ryan, P.G. & Oppel, S. 2021.  Mouse eradication is required to prevent local extinction of an endangered seabird on an oceanic island.  Animal Conservation doi.org/10.1111/acv.12670.

John Cooper, ACAP Information Officer, 23 February 2021