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Introduced house mice Mus musculus have recently been discovered to be significant predators of chicks of Tristan albatrosses Diomedea dabbenena and several burrowing petrels at Gough Island. We summarize evidence for mouse attacks on albatross chicks at sub-Antarctic Marion Island, where mice are also the only introduced mammal following the eradication of feral cats Felis catus in the early 1990s. Wounds consistent with mouse attacks have been found on wandering albatrosses Diomedea exulans since 2003 and dark-mantled sooty albatrosses Phoebetria fusca in 2009. To date, attacks on wandering albatross chicks have been infrequent, affecting <1% of chicks in study colonies, and only about half of the attacks have been fatal. Small chicks may also die when mouse burrows collapse under chicks, trapping them. Mouse attacks appear to be a recent phenomenon, supporting the contention that mice pose a significant threat when they are the only introduced mammal species. Ongoing monitoring is needed to assess whether the impacts of mice increase over time. Our observations add impetus to calls for the eradication of mice from Marion Island.
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Antarctic Science 22(1), 39–42 (2010) & Antarctic Science Ltd 2009 doi:10.1017/S0954102009990459
Evidence of mouse attacks on albatross chicks on sub-Antarctic
Marion Island
M.G.W. JONES* and P.G. RYAN
Percy FitzPatrick Institute, DST/NRF Centre of Excellence, University of Cape Town, Rondebosch 7701, South Africa
*MGenevieveWJones@gmail.com
Abstract: Introduced house mice Mus musculus have recently been discovered to be significant predators
of chicks of Tristan albatrosses Diomedea dabbenena and several burrowing petrels at Gough Island. We
summarize evidence for mouse attacks on albatross chicks at sub-Antarctic Marion Island, where mice are
also the only introduced mammal following the eradication of feral cats Felis catus in the early 1990s.
Wounds consistent with mouse attacks have been found on wandering albatrosses Diomedea exulans since
2003 and dark-mantled sooty albatrosses Phoebetria fusca in 2009. To date, attacks on wandering albatross
chicks have been infrequent, affecting ,1% of chicks in study colonies, and only about half of the attacks
have been fatal. Small chicks may also die when mouse burrows collapse under chicks, trapping them.
Mouse attacks appear to be a recent phenomenon, supporting the contention that mice pose a significant
threat when they are the only introduced mammal species. Ongoing monitoring is needed to assess whether
the impacts of mice increase over time . Our observations add impetus to calls for the eradication of mice
from Marion Island.
Received 29 June 2009, accepted 6 August 2009
Key words: alien species, conservation, Diomedea exulans, Mus musculus, Phoebetria fusca
Introduction
Until recently, populations of house mice Mus musculus L.
introduced to oceanic islands were considered to have little
impact on breeding bird populations. However, recent
observations at Gough Island have shown significant
impacts on both seabirds and endemic landbirds (Cuthbert
& Hilton 2004, Wanless et al. 2007, 2009, Ryan &
Cuthbert 2008). Wanless et al. (2007) argued that mice are
likely to be mos t problematic at islands where they are the
only introduced mammal. In the absence of competition
and predation by other, larger introduced mammals, mice
attain high population densities that may trigger predatory
behaviour. Sub-Antarctic Marion Island is one such island.
Mice were introduced to Marion presumably by sealers
sometime before 1818, and cats Felis catus L.
were brought to the island in 1949 to control mice at
the weather station, resulting in a feral population (Cooper
2008) that decreased breeding success of burrowing petrel s
and caused local extinction of some species (De Villiers &
Cooper 2008). Cats were eventually eradicated from the
island by 1992/93 (Bester et al . 2002), leaving mice as the
only introduced mammal.
Marion Island supports significant breeding populations
of several threatened or near-threatened albatrosses: 22%
of the world’s wandering albatrosses Diomedea exulans
L. (Vulnerable), 9% of dark-mantled sooty albatrosses
Phoebetria fusca (Hilsenberg) (Endangered), 7% of grey-
headed albatrosses Thalassarche chrysostoma (Forster)
(Vulnerable) and 3% of light-mantled sooty albatrosses
P. palpebrata (Forster) (Near-Threatened; Ryan et al.
in press). These species are listed as threatened largel y
due to accidental mortality on fishing gear, especially
longlines (BirdLife Interna tional 2008 - www.birdlife.org).
Both species of giant petrels Macronectes spp. (Near-
Threatened) are also common surface-nesters at the island,
and at least nine other species of petrels breed in burrows
on the island, including white-chinned petrels Procellaria
aequinoctialis L. (Vulnerable; Ryan & Bester 2008). In this
paper we report evidence of mouse attacks on seabird
chicks on Marion Island following the eradica tion of cats
from the island.
Study area and methods
Marion Island (46854'S, 37 845'E, 290 km
2
) has a vegetated
coastal plain that rises to volcanic scoria peaks (highest
point 1243 m). The island is home to large breeding
populations of seabirds and pinnepeds, and ornithological
research has been conducted on the island since 1965
(Cooper & Brown 1990, Ryan & Bester 2008), with regular
monitoring of breeding success of three wandering
albatross (c. 195–270 nests per annum) and three northern
giant petrel (c. 70–135 nests per annum) colonies since the
1980s (Cooper et al. 2001, Nel et al. 2003), and one grey-
headed albatross (c. 90–140 nests per annum) colony since
1996 (Ryan et al. 2007). In these study colonies, breeding
attempts were monitored from egg laying to fledging. Once
the chicks were no longer brooded, they were checked
every 2–4 weeks, and any wounded chicks recorded.
39
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Ad hoc observations have also been made of albatross chicks
outside study colonies, including chicks of light-mantled and
dark-mantled sooty albatrosses, as well as small numbers
of white-chinned and great-winged petrel Pterodroma
macroptera (Smith) chicks observed in monitored burrows
of low intensity studies. Wounded chicks were photographed,
and where feasible, their fate was checked by repeated visits.
Since the mid-1980s, annual counts of the entire breeding
population of wandering albatrosses on Marion Island have
been conducted during early incubation (January), and counts
of large chicks have been made prior to fledging (October),
allowing crude estimates of breeding success around
the island.
Results
Since 2003, 12 wandering albatross chicks have been found
on Marion Island with wounds on their backs, rumps and
flanks that were identical to those exhibited by Tristan
albatross Diomedea dabbenena Matthews chicks following
attacks by mice (Fig. 1). Six were recorded among
study colony chicks, with 0–2 records per year (0–2% of
Fig. 1. a. A well-feathered wandering albatross chick on Marion
Island exhibits wound on its lower back (photo: M.G.W.
Jones) very similar to b. those inflicted by mice on a Tristan
albatross chick on Gough Island (photo: P.G. Ryan).
Table I. Numbers of wandering albatross chicks attacked and killed by
mice in relation to breeding effort and success in study colonies at
Marion Island since the first record of a mouse attack in 2003.
2003 2004 2005 2006 2007 2008 Total
Eggs laid 268 197 242 199 257 249 1420
Chicks hatched 204 153 173 132 213 223 1098
Chicks attacked 201201 6
Chicks killed 101000 2
Breeding success (%) 80 71 79 77 72 64 74
Fig. 2. The head and neck wounds exhibited by one of nine
dark-mantled sooty albatross chicks near the south-western
point of Marion Island in April 2009 (photo: P.G. Ryan).
40 M.G.W. JONES & P.G. RYAN
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chicks that hatch; Table I). The other six were observed
incidentally, mostly close to the research station, where
observer effort is greatest, but one attack occurred on the
island’s west coast, indicating that attacks occur around the
island. The fates of 11 wounded chicks were followed, of
which six (55%) died. Counts of incubating adults and large
fledglings showed no consistent regional differences in
breeding success around the island.
There has been no evidence of mouse attacks on grey-
headed albatross or northern giant petrel chicks, either
in the study colonies or from incidental observations.
However, in April 2009 localized attacks were recorded on
dark-mantled sooty albatross chicks at Marion Island.
Seven of 19 large chicks on two ledges of an inland cliff in
the south-west of the island (Old Sea Cliffs, Toffee Lava)
bore open wounds on the backs of their heads and/or necks
(Fig. 2) similar to wounds observed on some Tristan
albatross chicks on Gough Island (K. Cita, unpublished
photographs). Another dark-mantled sooty albatross chick
bearing similar wounds was observed on sea cliffs near
Bullard Beach on the eastern coast of the island during the
same period (Bo Bonnevie, personal communicatio n 2009).
There have been no incidental observations of attacks on
other seabirds. Mouse activity has been seen in many petrel
burrows, including mice running over and around chicks,
but no definite attacks have been recorded.
Mouse holes are frequently found in nests of wandering
albatrosses and, to a lesser extent, in grey-headed albatross
nests. Many such mouse holes lead into the base of the nest
cup where the mice may obtain a thermal advantage,
especially in winter (Sinclair & Chown 2006). In April 2009
two small wandering albatross chicks died under brooding
adults after they apparently were unable to extricate
themselves from large hollows (c. 10 cm in diameter) in the
nest cup. After death, their carcases required considerable
force to be pulled from these hollows. It is probable that mouse
nests had caved in under the chicks, indirectly killing them.
Discussion
Although mice have not been observed attacking albatross
chicks on Marion Island, the nature of the chicks’ wounds
strongly suggests that mice were responsible. Based on our
observations, currently , 1% of wandering albatross chicks
at Marion Island are attacked by mice. At Gough Island,
mouse attacks on Tristan albatrosses were overlooked
previously because of spatial differences in the frequency
of attacks (Cuthbert & Hilton 2004), but this does not
appear to be the case at Marion Island. It is also probable
that the attacks at Marion only commenced in the last few
years, because monitoring of wandering albatross chicks
has been conducted at the same intensity since the study
colonies were established in the early 1980s without any
records of wounded birds.
Wanless et al. (2007) hypothesized that mice have a greater
effect on native vertebrates when they are the sole introduced
mammal on an island. This is because their populations
increase when the comb ined effects of dominance,
competition and predation are removed. Our observations
lend further support to this hypothesis because the first mouse
attacks were recorded a decade after the eradication of feral
cats, the only other introduced mammal on the island. The
worrying conclusion is that mouse attacks might be expected
to increase at Marion Island, especially if mouse populations
benefit from global warming (de Villiers & Cooper 2008).
This would be cause for serious concern given the large
proportion of the global population of wandering albatrosses
that breeds on Marion Island (Ryan et al. in press). Given the
serious impacts of mice on insular populations when they are
the sole alien mammal, precautions should be taken if
competing aliens are eradicated. Every attempt should be
made to eradicate mice as well as other predatory mammals.
The apparent attacks on dark-mantled sooty albatrosses are
also cause for alarm. One sooty albatross chick has been
recorded killed by mice on Gough Island (Cuthbert et al.
unpublished), but this is the first occurrence of multiple
attacks on chicks in a single colony. Sooty albatrosses are
listed as Endangered (BirdLife International 2008), and are
the only albatross species whose population is decreasing at
Marion Island (Ryan et al. in press). It is also likely that
burrowing petrels are victims of mouse predation at Marion
Island, but that it goes undetected because they are less easily
observed and are not currently studied at this island. In the
1980s, blue petrel Halobaena caerulea (Gmelin) chicks were
apparently attacked by mice on Marion Island (Fugler
et al. 1987). South Africa is a party to the Agreement on
the Conservation of Albatrosses and Petrels (ACAP) and as
such has international obligations to ensure the conservation
of these birds. Continued monitoring of seabird chicks on
Marion Island for signs of mouse predation is required. Our
study provides further support for the need to attempt to
eradicate mice from Marion Island.
Acknowledgements
We thank Bo Bonnevie, Linda Clokie, Nico de Bruyn,
Quentin Hagens, Henk Louw, Edith Mertz, Cornelia
Niewenhuys, Samantha Petersen, Cheryl Tosh and Paul
Visser, for their observations. Research on Marion Island is
supported by the South African National Antarctic Programme
through the National Research Foundation, with logistical
support from the Directorate: Antarctica and Islands of the
former Department of Environmental Affairs and Tourism.
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... The disease, caused by the bacterium Pasteurella multocida, appears to be responsible for the death of a large proportion of albatross chicks . Introduced rodents likely also contribute to the low breeding success of the population (Micol & Jouventin 1995) as observed in other seabird populations worldwide (Cuthbert & Hilton 2004, Jones & Ryan 2010, Caravaggi et al. 2019, Holmes et al. 2019. ...
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Ego net analysis is a well-known practice in social sciences, where an ego net (EN) consists of a focal node, the ego, and its links to other nodes, called alters, and alter-alter links may also be included. An EN describes how a focal node is embedded in its interaction context. Here, I introduce EN analysis to ecology in a study of the trophic network of a sub-Antarctic land bird, Lesser Sheathbill (Chionis minor). Data originate from the sheathbill population on Marion Island in the Southern Ocean. The bird is ego and its enemies and food are alters. The EN is organized along three dimensions: habitat, interaction type, and time (from before human arrival in 1803 and until a future year 2100). Ten EN descriptors are defined, estimated, and used to track the 300 years of change in sheathbill EN structure. Since 1803, the EN has passed two major, but reversible shifts-seal exploitation in the 19th century and presence of cats from 1949 to 1991. These shifts can be read as structural changes in the sheathbill EN. In the future, a third, perhaps irreversible change is predicted, driven by climate change and a surprising, recent shift to seabird predation by House Mouse, the most detrimental of all extant invaders on Marion. In a warmer and drier future, the mouse will proliferate, and if this forces seabirds to abandon the island, their accumulation of detritus runs dry, starving a rich invertebrate detritivore fauna, which also is a key food source to sheathbills. These detritivores together with plants have also constituted the main food sources of mice. The EN descriptors quantify that story. In the future, these events may lead to a collapse of the island ecosystem, including extinction of the sheathbill-unless plans for mouse eradication are implemented.
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This paper reviews the history of the feral cat eradication programme on sub-Antarctic Marion Island based on unpublished minutes of meetings, reports, letters, theses and published scientific papers; and reflects on the outcome of the eradication campaign. The 19-year programme comprised seven phases, commencing with a description of the effect of the cats on the Marion Island ecosystem, the characteristics of the cat population and the formulation of a management policy (phase 1: 1974-1976). Methods for control were selected and preparations were made for the implementation of the primary control measure, biological control with the feline panleucopaenia virus (phase 2: 1976/77). The virus was released in 1977 (phase 3: 1977), followed by the determination of its effects (phase 4: 1977-1980). Monitoring of the effects of the virus continued, and the secondary control measure of hunting at night was tested (phase 5: 1981-1983). Full-scale implementation of hunting and continued monitoring of the effects of both the disease and hunting followed (phase 6: 1986-1989). The inclusion of intensive trapping and poisoning as tertiary control measures culminated in the final eradication of cats from Marion Island in 1991 (phase 7: 1989-1993).
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Blue Petrels breed in dense, often large, colonies at the Prince Edward Islands. They are summer-breeding burrowing petrels and are absent from the islands during June to August. Moult occurs at sea after breeding and takes 83- 13 1 days. The mean laying and hatching dates were 23 October and 9 December respectively; chicks fledged between 25 January and 14 February. Wing, culmen and tarsus length growth curves are described for 43 chicks. The mean peak mass of the nestlings was c. 210 g at about 40 days of age. The distributions of Blue Petrel colonies are given for both Marion and Prince Edward Islands; the species is more abundant at the latter island, which is free of cats. Burrowing petrels have suffered severely from cat predation at Marion Island and the future of the Blue Petrel population is discussed.
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The subantarctic Prince Edward Islands (Marion and Prince Edward) support the largest breeding population of the Vulnerable wandering albatross Diomedea exulans. The number of birds breeding at Marion Island has fluctuated over the past three decades apparently as a result of both real changes in the size of the population and changes in the proportion of the population that attempts to breed in a given year. Changes in several demographic parameters that appear to be influenced by both environmental and anthropogenic effects are described. From 1994–2001, the proportion of first-time breeders in the population was positively correlated with the maximum ENSO (Niño 3) index, whereas from 1984–2000 the annual survival rates of breeding adults were negatively correlated with Japanese pelagic longline fishing effort in the southern Indian Ocean. Adult survival rates were significantly correlated with those on neighbouring Possession Island, Crozet Islands, but differed from those at South Georgia, suggesting common factors operating at an ocean-basin scale. The average survival rate of adult females was lower than that of males. Males who lost partners took 40% longer than females to find a new mate, suggesting a male-biased population. Survival rates of juvenile males and females did not differ. The age distribution of first-time breeders shifted progressively towards younger birds during the 1990s. Higher than expected survival rates of breeding adults during the late 1990s may be linked to large amounts of supplementary food being made available by the initiation of a longline fishery for Patagonian toothfish Dissostichus eleginoides close to the islands at this time. Overall, breeding success was better than recorded at other localities, indicating that breeding conditions at Marion Island were comparatively favourable. The early implementation of both international and national conservation initiatives to reduce the impact of longline fishing on this species and improve its conservation status is encouraged.
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