Rachel Buxton (Department of Zoology, University of Otago, Dunedin, New Zealand) and colleagues have published in the journal Biological Invasions on what happens with breeding burrowing petrels when Pacific Rats Rattus exulans are eradicated from their breeding islands.  The species considered are Flesh-footed Shearwater Puffinus carneipes, Fluttering Shearwater P. gavia, Little Shearwater P. assimilis, Sooty Shearwater P. griseus, Grey-faced Petrel Pterodroma macroptera gouldi, Pycroft’s Petrel P. pycrofti and Common Diving Petrel Pelecanoides urinatrix.

The paper’s abstract follows:

“Introduced mammals have been eradicated from many offshore islands around the world, removing predation pressure from burrow-nesting seabirds and other affected wildlife.  Nest-site selection in procellariiform seabirds is mediated by nesting habitat characteristics and social information, although it is unclear if, or how, nest-site selection will affect post-eradication colony growth.  Using a Bayesian hierarchical modeling approach we assessed how nest-site selection differs among burrow-nesting seabird colonies at different stages of recovery after Pacific rat (Rattus exulans) eradication.  We compared nest-site selection in a community of seven procellariiform species among six offshore islands in northeastern New Zealand: four designated rat-free over a continuum within the last 26 years, an island which never had rats, and an island with rats present.  We hypothesized that, immediately after eradication, birds would be constrained to nesting habitat where they were less vulnerable to predation, and as time since eradication increased birds would eventually spread to new habitat.  We found a positive relationship between mean burrow density and time since rat eradication.  Soil depth was the most important predictor of burrow presence, abundance, and occupancy in plots among islands, with more burrows found in deeper soil.  We found that the relationships between habitat covariates and nest-site selection decreased with increasing time since eradication.  The probability of a covariate having a significant effect on nest-site selection decreased with increasing time since eradication and decreasing variability in the covariate across an island.  Our results suggest that the eradication of rodents reduced constraints on petrel nesting distribution and that nest-site selection in burrow-nesting petrels may be influenced by burrow density, where selection of particular nesting habitat characteristics may be relatively more important in small recovering populations.  We conclude that colony expansion immediately after predator removal is complex, influenced by numerous interacting factors, but may be partly limited by the availability of suitable nesting habitat.”

Pycroft's Petrel

With thanks to Barry Baker and Rachel Buxton for information.

Reference:

Buxton, R.T., Anderson, D., Moller, H., Jones, C.J. & Lyver, P.O'B. 2014.  Release of constraints on nest-site selection in burrow-nesting petrels following invasive rat eradication.  Biological Invasions 17: 1453-1470.

John Cooper, ACAP Information Officer, 13 April 2015

Susan Waugh (Museum of New Zealand Te Papa Tongarewa, Wellington, New Zealand) and colleagues have published in the journal The Condor Ornithological Applications on aspects of the ecology of the ACAP-listed and New Zealand endemic Westland Petrel Procellaria westlandica.

The paper’s abstract follows:

“The use of long-term ecological datasets to explore the importance of the effects of environmental variability on higher predator populations has been focused mainly on high-latitude areas.  We modeled the population dynamics of the Westland Petrel (Procellaria westlandica), which spends its time mostly in subtropical waters during both breeding and the interbreeding migration across the Pacific Ocean.  We found that the population has slowly increased since the early 1970s, a result of high adult survival, high fecundity (0.6 of all eggs laid survived to fledge) and moderate mean age at first return to the colony (7.7 yr; a recruitment age typical for this genus), strong recruitment rate of juveniles, and negligible emigration.  The modeled population trends were supported by similar rates of increase in nest occupancy since 2001 and nest density since 2007.  Annual adult survival for breeders was the same for both sexes (0.954, 95% CI: 0.918–0.975) and constant across years.  However, nonbreeders had lower survival rates than breeders, and, among nonbreeders, males tended to survive better (0.926, 95% CI: 0.917–0.934) than females (0.917, 95% CI: 0.900–0.931).  Breeders transitioned to the nonbreeding state at a rate of 0.232 and nonbreeders to the breeding state at a rate of 0.295.  Sea-surface temperature anomalies had a negative effect on adult survival during the breeding period and a positive effect on survival outside the breeding season.  Local marine productivity as measured by fishery catches was strongly correlated with adult survival: Years with a greater fish catch were also years of higher adult survival.  Despite many threats operating throughout the breeding and foraging range of Westland Petrels, it appears that marine environmental change is a strongly influential factor for the species, with uncertainty in population growth due to predicted increases in sea-surface temperature in the future.”

Westland Petrel at its breeding site, photograph by Sue Waugh

With thanks to Barry Baker for information.

Reference:

Waugh, S.M., Barbraud, C., Adams, L., Freeman, A.N.D., Wilson, K.-J., Wood, G., Landers, T.J. & Baker, G.B. 2015.  Modeling the demography and population dynamics of a subtropical seabird, and the influence of environmental factors.  The Condor Ornithological Applications 117: 147-164.

John Cooper, ACAP Information Officer, 12 April 2015

Ruth Brown (Ecosystems Programme, British Antarctic Survey, Cambridge, United Kingdom) and colleagues discuss hybridization in giant petrels Macronectes spp. in the open-access online journal PLoS ONE.

The paper’s abstract follows:

“Hybridization in natural populations provides an opportunity to study the evolutionary processes that shape divergence and genetic isolation of species. The emergence of pre-mating barriers is often the precursor to complete reproductive isolation.  However, in recently diverged species, pre-mating barriers may be incomplete, leading to hybridization between seemingly distinct taxa.  Here we report results of a long-term study at Bird Island, South Georgia, of the extent of hybridization, mate fidelity, timing of breeding and breeding success in mixed and conspecific pairs of the sibling species,Macronectes halli (northern giant petrel) and M.giganteus (southern giant petrel).  The proportion of mixed-species pairs varied annually from 0.4–2.4% (mean of 1.5%), and showed no linear trend with time.  Mean laying date in mixed-species pairs tended to be later than in northern giant petrel, and always earlier than in southern giant petrel pairs, and their breeding success (15.6%) was lower than that of conspecific pairs.  By comparison, mixed-species pairs at both Marion and Macquarie islands always failed before hatching.  Histories of birds in mixed-species pairs at Bird Island were variable; some bred previously or subsequently with a conspecific partner, others subsequently with a different allospecific partner, and some mixed-species pairs remained together for multiple seasons.  We also report the first verified back-crossing of a hybrid giant petrel with a female northern giant petrel.  We discuss the potential causes and evolutionary consequences of hybridization and back-crossing in giant petrels and summarize the incidence of back-crossing in other seabird species.”

Northern Giant Petrel on Marion Island, photograph by Marienne de Villiers

With thanks to Richard Phillips for information.

Reference:

Brown, R.M., Techow, N.M.S.M., Wood, A.G. & Phillips, R.A. 2015.  Hybridization and back-crossing in giant petrels (Macronectes giganteus and M. halli) at Bird Island, South Georgia, and a summary of hybridization in seabirds.  PLoS ONE 10(3): e0121688. doi:10.1371/journal.pone.0121688.

John Cooper, ACAP Information Officer, 11 April 2015

Marion Island, the larger of South Africa’s Prince Edward Islands in the southern Indian Ocean, has been overrun by introduced House Mice Mus musculus since the early 19th Century.  In the absence of rats and following the successful eradication of feral Domestic Cats Felis catus in 1991 the mice are now the only introduced terrestrial mammal on the island.

Long thought to be having little effect on the island’s birds more recent observations have shown that mice on Marion attack chicks of several species, including the ACAP-listed Wandering Albatross Diomedea exulans and Sooty Albatross Phoebetria fusca, with some attacks leading to fatalities (click here).

A Wandering Albatross and its chick on Marion Island: at risk to alien House Mice

Previous to these observations the South African Department of Environment Affairs’ then Prince Edward Islands Management Committee (PEIMC) had requested that a review be undertaken of the impacts of mice on Marion Island.  Among its recommendations, the 2011 review called for a study of the feasibility of eradicating Marion’s mice.  A newly constituted Prince Edward Islands Advisory Committee that replaced the PEIMC was established in 2014.  Following a proposal from BirdLife South Africa support from the new committee was forthcoming this year and a berth for an expert has been found on the annual relief expedition which sailed to the island from Cape Town yesterday.

Ready to board: John Parkes on the first step of the ship's gangway

Aboard the S.A. Agulhas II to undertake the feasibility study is John Parkes (a collaborator with Invasive Species International, Landcare Research, New Zealand) who is an internationally respected invasive species ecologist with 35 years’ experience of applied research on vertebrate pests.  John has had a long interest in restoring island ecosystems by eradicating invasive species and specialises in studies to determine whether this is feasible.  He previously undertook a similar feasibility study for Gough Island’s alien House Mice.

ACAP Latest News hopes to report on progress with the feasibility study after the annual relief returns to Cape Town next month.

Selected Literature:

Angel, A. & Cooper, J. 2011.  A Review of the Impacts of the House Mouse Mus musculus on sub-Antarctic Marion Island, Prince Edward Islands.  Report to the Prince Edward Islands Management Committee, South African National Antarctic Programme.  Rondebosch: CORE Initiatives.  57 pp.

Angel, A., Wanless, R.M. & Cooper, J. 2008.  Review of impacts of the introduced House Mouse on islands in the Southern Ocean: are mice equivalent to rats?  Biological Invasions 11: 1743-1754.

Bester, M.N., Bloomer J.P., van Aarde, R.J., Erasmus, D.G., van Rensburg, P.J.J., Skinner, J.D., Howell, P.G. & Naude, T.W. 2002.  A review of the successful eradication of feral cats from sub-Antarctic Marion Island, southern Indian Ocean.  South African Journal of Wildlife Research 32: 65-73.

Jones, M.G.W. & Ryan, P.G. 2010.  Evidence of mouse attacks on albatross chicks on sub-Antarctic Marion Island.  Antarctic Science 22: 39-42.

Parkes, J. 2008.  A Feasibility Study for the Eradication of House Mice from Gough Island.  RSPB Research Report No. 34.  Sandy: Royal Society for the Protection of Birds.  51 pp.

Wanless, R.M., Cooper, J., Slabber, M.J. & Ryan, P.G. 2010.  Risk assessment of birds foraging terrestrially at Marion and Gough Islands to primary and secondary poisoning.  Wildlife Research 37: 524-530.

John Cooper, ACAP Information Officer, 10 April 2015