Article

Mouse predation affects breeding success of burrow-nesting petrels at sub-Antarctic Marion Island

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Abstract

We report the breeding success of four species of burrow-nesting petrels at sub-Antarctic Marion Island where house mice Mus musculus are the sole introduced mammal. Feral cats Felis catus were present on Marion for four decades from 1949, killing millions of seabirds and greatly reducing petrel populations. Cats were eradicated by 1991, but petrel populations have shown only marginal recoveries. We hypothesize that mice are suppressing their recovery through depredation of petrel eggs and chicks. Breeding success for winter breeders (grey petrels Procellaria cinerea (34±21%) and great-winged petrels Pterodroma macroptera (52±7%)) were lower than for summer breeders (blue petrels Halobaena caerulea (61±6%) and white-chinned petrels Procellaria aequinoctialis (59±6%)) and among winter breeders most chick fatalities were of small chicks up to 14 days old. We assessed the extent of mouse predation by monitoring the inside of 55 burrow chambers with video surveillance cameras (4024 film days from 2012–16) and recorded fatal attacks on grey (3/18 nests filmed, 17%) and great-winged petrel chicks (1/19, 5%). Our results show that burrow-nesting petrels are at risk from mouse predation, providing further motivation for the eradication of mice from Marion Island.

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... Most recently, M. musculus has been observed feeding on the live chicks of surface-nesting (Dilley et al. 2016) and on burrowing (Dilley et al. 2018) seabirds on Marion Island (Fig. 8.1b). The first such occurrence on Marion Island was only observed in 2003, where attacks on surface-nesting seabirds started, seemingly independently, at different sites simultaneously across the island (Dilley et al. 2016). ...
... The first such occurrence on Marion Island was only observed in 2003, where attacks on surface-nesting seabirds started, seemingly independently, at different sites simultaneously across the island (Dilley et al. 2016). The incidence of M. musculus attacks on affected populations of four seabird species was recorded to be high, with up to 9% chick mortality (once an attack has taken place) in surface-nesting species, and up to 100% mortality in burrowing species (Dilley et al. 2016(Dilley et al. , 2018 because chicks do not defend themselves against M. musculus attacks (Wanless et al. 2007). However, the occurrence of feathers in the gut content of M. musculus was recorded as early as the early 1990s and was initially put down to scavenging (Smith et al. 2002); it may well have been an earlier indication of active predation of seabirds by M. musculus (Smith 2008)-perhaps of the burrowing petrels. ...
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The sub-Antarctic Prince Edward Islands (PEIs) constitute South Africa’s most remote territory. Despite this, they have not been spared from biological invasions. Here, we review what is known about invasions to the PEIs for terrestrial taxa (vertebrates, invertebrates, plants and microbes), freshwater taxa and marine taxa. Currently, Marion Island is home to 46 alien species, of which 29 are known to be invasive (i.e. they are alien species that have established and spread on the island). Prince Edward Island, which has no permanent human settlement and is visited only infrequently, has significantly fewer alien species: only eight alien species are known from Prince Edward Island, of which seven are known to be invasive. The House Mouse (Mus musculus), which occurs on Marion Island, can be considered the most detrimental invader to the islands; it impacts on plants, insects and seabirds, which result in changes to ecosystem functioning. The impacts of other terrestrial invaders are less well understood. At present, no invasive freshwater or marine taxa are known from the PEIs. We conclude by discussing how invasion threats to the PEIs are changing and how the amelioration of the climate of the islands may increase invasion threats to both terrestrial and marine habitats.
... Inspection hatches (a removable plug of earth secured with a large stone) were dug through the roof of the burrow passage to gain access to the nest chamber for regular nest checks with a burrowscope (custom-made burrowscope with a high resolution conical pinhole camera, LED torch and an 18×21 cm colour monitor). In addition to the study burrows, infra-red motion-activated video cameras were used to record activity inside the nest chambers of White-chinned Petrel burrows (16 burrows over the five year study period) in summer and Grey (18) and Petrel burrows in winter (details in Dilley et al. 2018). The video files recorded a date and time stamp, which enabled us to record a detailed sequence of activity for each filmed nest. ...
... The observations presented here are anecdotal and we did not accurately quantify how frequently such instances occur, but we give an indication based on our observations. Further information on the footage reviewed and breeding phenology can be found in Dilley et al. (2018). Breeding years refer to austral seasons (i.e. ...
Article
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Competition for nest sites is relatively common amongst burrow-nesting Procellariiformes, especially on some sub-Antarctic islands where there is limited availability of good burrow-nesting habitat. Where space is limited, petrels may even successfully share a common burrow entrance or nest chamber and burrow densities can reach >7000 burrows/ha. Interspecies burrow competition and chick evictions generally occur as a result of an overlap in breeding seasons, yet there are few documented records of this behaviour and even within study colonies many evictions are unconfirmed or probably go undetected. Here we report on interactions among three burrow-nesting petrels (White-chinned Petrels Procellaria aequinoctialis, Grey Petrels P. cinerea and Great-winged Petrels Pterodroma macroptera) at Marion Island which we observed through regular nest checks with a burrowscope and using infra-red video cameras inside burrow chambers. Despite relatively low petrel densities, White-chinned Petrels were responsible for 17% (8/46) of the Great-winged Petrel chick mortalities over the five breeding seasons (3% of the breeding attempts), but two were also recorded feeding Great-winged Petrel chicks. A pair of White-chinned Petrels evicted a Grey Petrel chick, but then had their own chick killed by Grey Petrels the following season, who went on to breed successfully in the same burrow. Feral Cats Felis catus were eradicated in 1991 and the greatly reduced petrel populations are slowly recovering, which could exacerbate competition for burrows on Marion.
... In its feral habitat the laboratory mouse (Mus musculus) is subject to predation by many other animal species but the mouse is also a predator [1][2][3]4,5]. For the mouse and a large number of other rodent species insect hunting and eating have been documented both in their natural habitat and in laboratory investigations, [6,[7][8][9]10]; Levenrets et al., 2019; [11][12][13][14]. ...
... Predation is a widely expressed animal behavior ( [24], Elewa 2007, Eisenburg 1972) and plays a central role in diet (Pineda-Munoz 2014, Eubank 2004). Predation is also featured in omnivorous rodents that are themselves subject to predation [1][2][3]; [4,5]). The prevalence of predation in animals has led to the suggestion by early investigators that the motivation, if not the movements for the behavior, are instinctive (for a review see [25]). ...
Article
Although the mouse (Mus musculus) is preyed upon by many other species of animals, it is also a predator and will hunt and consume crickets. There has been no previous description of how mice learn to hunt and no report on the extent to which they use their hands and mouth to assist prey capture and these were the objectives of the present study. Mice given one cricket each day displayed decreasing hunt times over 25-days for three phases of a hunt: investigate, in which a mouse explored and periodically encounter a cricket and often bit at it; pursue, in which a mouse’s approach remained focused on the cricket until it was captured; and consume, in which the cricket was handled, decapitated, its core eaten, with its shell discarded. Although visual and auditory cues may contribute to locating a cricket, the vibrissae appeared to provide guidance in pursuit and capture when the cricket and mouse were proximate. Cricket capture involved extensive collaborative use of the mouth and the hands and mice could initiate capture with either the mouth or hands. Handling to eat involved manipulating the cricket into a head-up, ventrum-in position for decapitation and selective eating of the core of the cricket. The results are discussed in relation to mouse learning of a complex natural behavior, the use of tactile cues in the species-specific behavior of predation, and the contributions of the hands and mouth to predation.
... Post-cat eradication, the recovery of burrow-nesting petrel numbers on Marion Island has been much slower than anticipated, and continuing predation by mice is the most probable explanation for the limited recovery of the island's petrel populations (Dilley et al. 2017a). Currently, mice are suppressing the recovery of burrow-nesting petrel populations, especially among petrel species that breed in winter, through depredation of eggs and chicks (Dilley et al. 2017b). ...
... Grey petrel (Procellaria cinerea (Gmelin)) burrows were not surveyed, but are mentioned here as they are the only other petrel species on Marion Island that also breeds in large burrows (Schramm 1986). On Marion Island, grey petrels breed in caves and burrows (Schramm 1986, Dilley et al. 2017b), but nests are extremely scarce; burrows are renovated in late February with peak laying from late March to mid-April (Fig. 5), so at the time of the survey, grey petrels were incubating. ...
Article
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We compared systematic and random survey techniques to estimate breeding population sizes of burrow-nesting petrel species on Marion Island. White-chinned ( Procellaria aequinoctialis ) and blue ( Halobaena caerulea ) petrel population sizes were estimated in systematic surveys (which attempt to count every colony) in 2009 and 2012, respectively. In 2015, we counted burrows of white-chinned, blue and great-winged ( Pterodroma macroptera ) petrels within 52 randomized strip transects (25 m wide, total 144 km). Burrow densities were extrapolated by Geographic Information System-derived habitat attributes (geology, vegetation, slope, elevation, aspect) to generate island-wide burrow estimates. Great-winged petrel burrows were found singly or in small groups at low densities (2 burrows ha ⁻¹ ); white-chinned petrel burrows were in loose clusters at moderate densities (3 burrows ha ⁻¹ ); and blue petrel burrows were in tight clusters at high densities (13 burrows ha ⁻¹ ). The random survey estimated 58% more white-chinned petrels but 42% fewer blue petrels than the systematic surveys. The results suggest that random transects are best suited for species that are widely distributed at low densities, but become increasingly poor for estimating population sizes of species with clustered distributions. Repeated fixed transects provide a robust way to monitor changes in colony density and area, but might fail to detect the formation/disappearance of new colonies.
... There were no reports of house mice Mus musculus attacking seabird chicks on Antipodes Island, in contrast to the severe injuries and high mortality to multiple species caused by mice on Gough Island in the South Atlantic and Marion Island in the southern Indian Ocean (Cuthbert & Hilton 2004;Wanless et al. 2009;Jones & Ryan 2010;Cuthbert et al. 2013a,b;Davies et al. 2015;Dilley et al. 2016Dilley et al. , 2018Caravaggi et al. 2018). The endemic Atlantic petrel Pterodroma incerta is among the seabird species on Gough Island that suffers high chick mortality due to mouse attacks (Wanless et al. 2012;Dilley et al. 2015). ...
... The endemic Atlantic petrel Pterodroma incerta is among the seabird species on Gough Island that suffers high chick mortality due to mouse attacks (Wanless et al. 2012;Dilley et al. 2015). Mice have also been filmed killing two soft-plumaged petrel chicks on Gough Island and a great-winged petrel Pt. macroptera chick on Marion Island (Dilley et al. , 2018. All seven Atlantic petrel chicks in filmed study burrows on Gough Island were killed within a day of hatching, despite the presence of an adult petrel in the burrow, and there was an overall chick failure rate of 87% among 83 hatchlings . ...
Article
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New Zealand is a global centre of diversity for gadfly petrels (family Procellariidae, genus Pterodroma). The 11 extant breeding species include six endemic species (grey-faced petrel Pt. gouldi, Chatham Island täiko/Magenta petrel Pt. magentae, mottled petrel Pt. inexpectata, Chatham petrel Pt. axillaris, Cook's petrel Pt. cookii and Pycroft's petrel Pt. pycrofti) and two further species of which more than 90% of the world population breeds in New Zealand (white-naped petrel Pt. cervicalis and black-winged petrel Pt. nigripennis). Within New Zealand, hotspots for Pterodroma species diversity include the Kermadec Islands (three species, none of which is endemic), islands off the northeast coast of the North Island (four species, three of which are endemic to New Zealand, with one endemic to the northeast North Island) and the Chatham Islands (three species, two of which are endemic to both New Zealand and the Chatham Islands). With the exception of the recently colonised soft-plumaged petrel Pt. mollis, all living New Zealand gadfly petrel species have suffered population declines and/or range contractions as a result of predation by introduced mammals (especially feral cats Felis catus and rats Rattus spp.), with nine of these 10 species recently responding positively to pest mammal eradications or species recovery programmes. Population sizes for each species range from about 35 known pairs for Chatham Island täiko to more than 2.8 million pairs for black-winged petrel. Population trends are poorly known for most species, although eight species are considered to be stable or increasing.
... Rattus spp. (Crozet Islands, Jouventin et al. 1984; Tristan da Cunha, Richardson 1984) and House Mice Mus musculus (Marion Island and almost certainly Gough Island, Dilley et al. 2018). The current global population estimate of some 1.5 million birds (BirdLife International 2018; The IUCN Red List of Threatened Species 2018) is based on Brooke's (2004) estimate, although that is for both Great-winged and Grey-faced Petrels. ...
Article
Although burrow-nesting petrels are the most abundant group of seabirds in the Southern Ocean, their global populations are poorly known, because most species breed on remote islands. For example, there are no accurate estimates for Great-winged Petrel Pterodroma macroptera populations at any of its major breeding sites. Moreover, current global population estimates for Great-winged Petrels of approximately 1.5 million birds include counts of the closely related Grey-faced Petrel P. gouldi, which is now recognised as a different species. On sub-Antarctic Marion Island, Great-winged Petrel burrows found within random strip transects were counted and then burrow densities were extrapolated by GIS-derived habitat attributes to generate an island-wide burrow estimate (33 000 burrows). Burrow occupancy rates at the start of incubation averaged 48 ± 29% (range 10–94%) during one-off surveys at ten sites around the island, and repeat surveys found at least 42% of burrows were occupied by breeders. This suggests there were approximately 14 000 occupied burrows (95% CI 9 500–18 500) on Marion Island in 2015. Collating data from other breeding sites suggests that the global breeding population is perhaps 100 000–150 000 pairs (400 000–600 000 birds).
... Such strong preference for certain prey items suggests that mice are systematically consuming their way through the terrestrial ecosystem by exhausting preferred prey and then moving on to the next preferred prey source. The end point of this may be similar to that observed on other subantarctic islands where diet shifting from lower trophic levels to large seabirds eventually occurs (Cuthbert et al. 2013Dilley et al. 2018;McClelland et al. 2018). This is potentially an outcome of mice, having been present for much longer on those islands, exhausting all other available food resources. ...
Article
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House mice (Mus musculus) are a widespread invasive species on islands. Where they are the sole introduced mammal they can have particularly strong negative impacts on recipient ecosystems. House mice impacts have been documented on almost every component of the terrestrial ecosystem on Southern Ocean islands, including plants, invertebrates, birds and ecosystem function. We undertook a comprehensive study to determine the impacts of house mice on Antipodes Island, New Zealand. This study was done prior to mouse eradication to inform monitoring and restoration. We used invertebrate pitfall trapping on the main Antipodes Island and neighbouring mouse-free offshore islands together with mouse stomach contents and stable isotope analyses of mouse livers to examine dietary preferences. We identified directly impacted and consumed invertebrate Orders relative to their abundance and provided a comprehensive picture of resource flow and overlap in the invaded terrestrial ecosystem. The remote terrestrial ecosystem of Antipodes Island was tightly circumscribed with strong resource overlap. Mouse diet varied seasonally with resource availability, dominated by invertebrates and land birds in summer, and plants and seabirds in winter. Invertebrates that were preferentially preyed upon were Amphipoda, Lepidoptera and some species of Coleoptera. These patterns suggest the ecosystem is annually driven by a seasonal bottom-up resource pulse over summer, where mice are a selective predator, differentially preying on invertebrates relative to invertebrate abundance. Mice appear to be exhausting preferred prey as they systematically consume their way through the terrestrial ecosystem. Land bird diet also varied seasonally and some of these birds likely competed with mice for invertebrate prey. Eradication of mice from Antipodes Island should reduce the predation on invertebrates and reduce the effects of competition and predation on land birds. This should have flow-on effects to the abundance of invertebrates and endemic land bird sub-species of pipit and snipe.
... Invasive species have devastating impacts on global biodiversity, particularly on islands (Mack et al. 2000;McCreless et al. 2016). These impacts may occur directly through predation (Courchamp et al. 2003;Angel et al. 2009;Wanless et al. 2012;Dilley et al. 2018;Lebouvier et al. 2020), or indirectly, for example via habitat transformation (Croll et al. 2005; Abstract Spanning the Southern Ocean high latitudes, Sub-Antarctic islands are protected areas with high conservation values. Despite the remoteness of these islands, non-native species threaten native species and ecosystem function. ...
Article
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Spanning the Southern Ocean high latitudes, Sub-Antarctic islands are protected areas with high conservation values. Despite the remoteness of these islands, non-native species threaten native species and ecosystem function. The most ubiquitous and speciose group of non-native species in the region are invertebrates. Due to their cryptic habits and ambiguous establishment history, the impacts of non-native invertebrates on native species and ecosystems in the region remains largely unknown. Understanding how non-native invertebrate species are transported, disperse, establish and colonise new habitats is key to understanding their existing and future impacts. This research is fundamental to improving biosecurity practise and informing future management of Southern Ocean islands. We undertook invertebrate surveys on Macquarie Island to determine the current status of four non-native macro-invertebrates—Kontikia andersoni and Arthurdendyus vegrandis (Platyhelminthes: Geoplanidae), Styloniscus otakensis (Isopoda: Styloniscidae) and Puhuruhuru patersoni (Amphipoda: Talitridae). Arthurdendyus vergrandis was not intercepted in our surveys, while we found S. otakensis and P. patersoni had not expanded their range. In contrast, K. andersoni has more than doubled its previously mapped area and expanded at a rate of ~ 500 m-yr since 2004. We discuss the possible underlying mechanisms for the dramatic range expansion of K. andersoni and consider the implications for the future management of Macquarie Island.
... and feral cats Felis catus to their breeding islands (Brooke et al., 2018). However, house mice Mus musculus can have significant impacts on seabirds at islands where they are the only introduced predator, such as Gough Island in the central South Atlantic Ocean or Marion Island in the South-Western Indian Ocean (Cuthbert & Hilton, 2004;Wanless et al., 2007;Wanless et al., 2009;Cuthbert et al., 2013;Davies et al., 2015;Dilley et al., 2015;Dilley et al., 2016;Caravaggi et al., 2018;Dilley et al., 2018;Jones et al., 2019). While rats and cats are typical predators that start depredating seabird eggs and chicks soon after the invasion of an island, this behaviour appears to evolve gradually in invasive mouse populations only at a later stage of invasion when other primarily exploited food sources have been depleted (McClelland et al., 2018;Russell et al., 2020). ...
Article
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 MacGilliv-ray' 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.
... Estimates of petrel populations are commonly made to inform trend and threat assessments, but 384 they currently perform rather poorly in this role. Therefore it might be appropriate to focus research 385 on parameters better able to inform management such as productivity and survival (Caravaggi et al., 386 2019;Dilley et al., 2018) and population trends derived from repeat sampling (Buxton et al., 2016). 387 ...
Preprint
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Population estimates are commonly generated and used in conservation science. All estimates carry inherent uncertainty, but little attention has been given to when and how this uncertainty limits their use. This requires an understanding of the specific purposes for which population estimates are intended, an assessment of the level of uncertainty each purpose can tolerate, and information on current uncertainty. We conducted a review and meta-analysis for a widespread group of seabirds, the petrels, to better understand how and why population estimates are being used. Globally petrels are highly threatened, and aspects of their ecology make them difficult to survey, introducing high levels of uncertainty into population estimates. We found that by far the most common intended use of population estimates was to inform status and trend assessments, while less common uses were trialling methods to improve estimates, and assessing threat impacts and conservation outcomes. The mean coefficient of variation for published estimates was 0.17 (SD = 0.14), with no evidence that uncertainty has been reduced through time. As a consequence of this high uncertainty, when we simulated declines equivalent to thresholds commonly used to trigger management, only 5% of studies could detect significant differences between population estimates collected 10 years apart for populations declining at a rate of 30% over three generations. Reporting of uncertainty was variable with no dispersion statistics reported with 38% of population estimates and most not reporting key underlying parameters: nest numbers/density and nest occupancy. We also found no correlation between population estimates and either island size, body size or species threat status—potential predictors of uncertainty. Synthesis and applications —Key recommendations for managers are to be mindful of uncertainty in past population estimates if aiming to collect contemporary estimates for comparison, to report uncertainty clearly for new estimates, and to give careful consideration to whether a proposed estimate is likely to achieve the requisite level of certainty for the investment in its generation to be warranted. We recommend a practitioner-based Value of Information assessment to confirm where there is value in reducing uncertainty.
... In particular, invasive house mice continue to be (temporarily) managed with lowgrade rodenticide; as house mice are discouraged from consuming seabirds, house mice foraging activities and food preferences may also change. Although house mice on MANWR have been observed to attack and depredate nesting albatross during the breeding season (Duhr-Schultz et al. 2018), house mice may shift to alternative food sources, such as arthropods, which may result in increased arthropod consumption and possibly population-level and or community-level "knock-on" effects (see Wanless et al. 2009Wanless et al. , 2012Dilley et al. 2018). ...
Thesis
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Invertebrates are key to island ecosystems, but impacts from invasive mammalian predators are not well documented or understood. Given this knowledge gap, we studied terrestrial arthropod communities in the presence of a common invasive rodent (house mice, Mus musculus) on a subtropical atoll—Midway Atoll National Wildlife Refuge (MANWR). Here, invasive mice recently began to attack and depredate nesting seabirds, prompting a mouse eradication. Although eradication planning efforts are underway, uncertainty remains regarding the ecosystem’s response to mouse removal. As part of a pre-eradication investigation, we conducted a baseline survey of MANWR’s arthropod community structure and diversity, comparing islands with and without mice. From April 2018 to February 2020, we used pitfall traps to monitor ground-dwelling arthropods on MANWR’s Sand Island (mice present) and Eastern Island (mice absent). During our study, we captured over 450,000 specimens from 24 taxonomic units. Arthropods on MANWR form six community clusters and differ between islands and habitats. Richness is relatively similar among clusters and islands, but diversity of common and dominant taxa is significantly higher on Sand Island, as well as in anthropogenically built habitats. Arthropod communities and diversity vary marginally throughout the year; temperature and rainfall are minor environmental drivers. Additionally, anthropomorphic landscape-level alteration of MANWR may still influence arthropod communities today. Continued monitoring and research will provide better insight into how arthropod communities recover following invasive mouse eradications. Our study contributes to the body of knowledge of arthropods in the Northwestern Hawaiian Islands, arthropod community ecology, and potential mouse impacts on islands.
... Estimates of petrel populations are commonly made to inform trend and threat assessments, but they currently perform rather poorly in this role. Therefore, it might be appropriate to focus research on parameters better able to inform management such as productivity and survival (Caravaggi et al., 2019;Dilley et al., 2018) and population trends derived from repeat sampling (Buxton et al., 2016). While population estimates are used in various ways (Table 1) only really when small populations are compared against criteria thresholds for status assessments and when informing 1% thresholds is the actual estimate important. ...
Article
Full-text available
Population estimates are commonly generated and used in conservation science. All estimates carry inherent uncertainty, but little attention has been given to when and how this uncertainty limits their use. This requires an understanding of the specific purposes for which population estimates are intended, an assessment of the level of uncertainty each purpose can tolerate, and information on current uncertainty. We conducted a review and meta‐analysis for a widespread group of seabirds, the petrels, to better understand how and why population estimates are being used. Globally petrels are highly threatened, and aspects of their ecology make them difficult to survey, introducing high levels of uncertainty into population estimates. We found that by far the most common intended use of population estimates was to inform status and trend assessments, while less common uses were trialling methods to improve estimates and assessing threat impacts and conservation outcomes. The mean coefficient of variation for published estimates was 0.17 (SD = 0.14), with no evidence that uncertainty has been reduced through time. As a consequence of this high uncertainty, when we simulated declines equivalent to thresholds commonly used to trigger management, only 5% of studies could detect significant differences between population estimates collected 10 years apart for populations declining at a rate of 30% over three generations. Reporting of uncertainty was variable with no dispersion statistics reported with 38% of population estimates and most not reporting key underlying parameters: nest numbers/density and nest occupancy. We also found no correlation between uncertainty in petrel population estimates and either island size, body size or species threat status – potential predictors of uncertainty. Key recommendations for managers are to be mindful of uncertainty in past population estimates if aiming to collect contemporary estimates for comparison, to report uncertainty clearly for new estimates, and to give careful consideration to whether a proposed estimate is likely to achieve the requisite level of certainty for the investment in its generation to be warranted. We recommend a practitioner‐based value of information assessment to confirm where there is value in reducing uncertainty. Population estimates are commonly generated and used in conservation science. All estimates carry inherent uncertainty, but little attention has been given to when and how this uncertainty limits their use. This requires an understanding of the specific purposes for which population estimates are intended, an assessment of the level of uncertainty each purpose can tolerate, and information on current uncertainty. We conducted a review and meta‐analysis for a widespread group of seabirds, the petrels, to better understand how and why population estimates are being used. Globally petrels are highly threatened, and aspects of their ecology make them difficult to survey, introducing high levels of uncertainty into population estimates. We found that by far the most common intended use of population estimates was to inform status and trend assessments, while less common uses were trialling methods to improve estimates and assessing threat impacts and conservation outcomes. The mean coefficient of variation for published estimates was 0.17 (SD = 0.14), with no evidence that uncertainty has been reduced through time. As a consequence of this high uncertainty, when we simulated declines equivalent to thresholds commonly used to trigger management, only 5% of studies could detect significant differences between population estimates collected 10 years apart for populations declining at a rate of 30% over three generations. Reporting of uncertainty was variable with no dispersion statistics reported with 38% of population estimates and most not reporting key underlying parameters: nest numbers/density and nest occupancy. We also found no correlation between uncertainty in petrel population estimates and either island size, body size or species threat status – potential predictors of uncertainty. Key recommendations for managers are to be mindful of uncertainty in past population estimates if aiming to collect contemporary estimates for comparison, to report uncertainty clearly for new estimates, and to give careful consideration to whether a proposed estimate is likely to achieve the requisite level of certainty for the investment in its generation to be warranted. We recommend a practitioner‐based value of information assessment to confirm where there is value in reducing uncertainty. Uncertainty when estimating population sizes may limit the utility of the estimates. We reviewed published population estimates for a threatened seabird family, the Procellariidae, to identify the motives behind them and the level of uncertainty reported. Estimates were most commonly intended to detect trends, but uncertainty suggests they are unlikely to be able to do this reliably in most cases.
Preprint
Full-text available
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.
Technical Report
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Seabirds are amongst the most threatened birds in the world (Dias et al. 2019). Albatrosses and petrels are particularly vulnerable as they are long-lived, have a delayed sexual maturity, and low annual reproductive output. They have a wide at-sea distribution, occurring across all oceans and adjacent coastlines and islands. These extensive ranges overlap with multiple threats in national and international waters. Incidental bycatch in fisheries is one of the primary causes of population declines for many seabird species. Although attention focused initially on industrial longlining, there is a growing number of studies highlighting the negative impact on seabirds of other fisheries, such as trawl and artisanal fisheries. The impact of bycatch can affect elements of seabird populations in different ways. For instance, sex-and age-biases are common features of seabird bycatch that appear to be associated largely with differences in at-sea distributions. Accounting for different life-history stages is therefore essential in threat assessment in order to direct management and conservation efforts towards areas where they have the greatest impact on populations. The purpose of this paper is to identify areas and periods of greatest density for albatrosses and petrels within the South Indian Ocean Fisheries Agreement (SIOFA) area. We overlapped the SIOFA boundary to the maps presented by Carneiro et al., (2019, 2020), which includes information from across different life-history stages, to give an overview of the importance of SIOFA area for albatrosses and petrels year-round and by year-quarter. We aimed to fill in gaps in the knowledge of at-sea distributions for these species.
Technical Report
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The National Biodiversity Assessment (NBA) 2018 is a collaborative effort to synthesise the best available science on South Africa’s biodiversity. For the first time, South Africa’s southernmost territory, the sub-Antarctic Prince Edward Islands (PEIs), have been included in the NBA. A map of 34 ecosystem types was developed, supporting a greater understanding of biodiversity patterns and providing a foundation for a systematic assessment of all marine and terrestrial ecosystem types. The Threat Status of ecosystems and some species is discussed and Ecosystem Protection Levels reported for the first time.
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The Southern Ocean represents a continuous stretch of circumpolar marine habitat, but the potential physical and ecological drivers of evolutionary genetic differentiation across this vast ecosystem remain unclear. We tested for genetic structure across the full circumpolar range of the white‐chinned petrel (Procellaria aequinoctialis) to unravel the potential drivers of population differentiation and test alternative population differentiation hypotheses. Following range‐wide comprehensive sampling, we applied genomic (genotyping‐by‐sequencing or GBS; 60,709 loci) and standard mitochondrial‐marker approaches (cytochrome b and 1st domain of control region) to quantify genetic diversity within and among island populations, test for isolation by distance, and quantify the number of genetic clusters using neutral and outlier (non‐neutral) loci. Our results supported the multi‐region hypothesis, with a range of analyses showing clear three‐region genetic population structure, split by ocean basin, within two evolutionary units. The most significant differentiation between these regions confirmed previous work distinguishing New Zealand and nominate subspecies. Although there was little evidence of structure within the island groups of the Indian or Atlantic oceans, a small set of highly‐discriminatory outlier loci could assign petrels to ocean basin and potentially to island group, though the latter needs further verification. Genomic data hold the key to revealing substantial regional genetic structure within wide‐ranging circumpolar species previously assumed to be panmictic.
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The current estimate of the number of breeding pairs of Great-winged Petrels Pterodroma macroptera on Tristan Island is 1 000 or less. In the last few hours of daylight on 11 April 2018 we observed large numbers of Great-winged Petrels off the southeast coast of Tristan Island and estimated from this a breeding population of 3 000–4 000 pairs. This article details the initial observation and the method used to derive the estimate of the number of breeding pairs.
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The current estimate of the number of breeding pairs of Great-winged Petrels Pterodroma macroptera on Tristan Island is 1 000 or less. In the last few hours of daylight on 11 April 2018 we observed large numbers of Great-winged Petrels off the southeast coast of Tristan Island and estimated from this a breeding population of 3 000–4 000 pairs. This article details the initial observation and the method used to derive the estimate of the number of breeding pairs.
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Blue Petrels (Halobaena caerulea) are known to breed at seven locations in the Southern Ocean. Population estimates have been made recently for the two major breeding sites, but accurate estimates are lacking for the remaining locations. We used a systematic survey technique to estimate the size of the population breeding at Marion Island (290 km2 ), the larger of the two Prince Edward Islands. A combination of colony area and density estimates suggested there were 214 700 Blue Petrel burrows on Marion Island in 2012. Burrow occupancy rates at the mid-incubation stage averaged 82% (range 36–98%), suggesting a total breeding population of 145 000 pairs (95% confidence interval 110 000–180 000). There appeared to be some range expansion since the population was mapped in the mid-1980s. Predation of chicks and eggs by introduced house mice (Mus musculus) could be affecting the recovery of Blue Petrels since feral cats (Felis catus) were eradicated in 1991. Based on our count from Marion Island alone, the Prince Edward Islands support the third largest population of Blue Petrels globally, after Diego Ramirez Islands and the Kerguelen Islands.
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Introduced predators are one of the main threats facing seabirds breeding on oceanic islands. Cats (Felis catus) were introduced to subantarctic Marion Island (290 km2) in 1949, and by the 1970s some 2000 cats were killing about 450,000 seabirds per year, greatly reducing burrowing petrel populations. Cats were eradicated by 1991, but house mice (Mus musculus) remain. The densities of utilised petrel burrows were estimated in 2013 by systematically searching for their burrows in 741 10 × 10 m sample quadrats in the north-eastern sector of Marion Island, repeating the sampling design and methods used by Schramm in 1979. The mean burrow densities and 95 % CIs were compared between surveys by species for the different habitat and vegetation types, with non-overlapping CIs considered indicative of an increase in burrow density. With cats eradicated and the potential for immigration from nearby Prince Edward Island (free of introduced mammals), we could expect a multi-fold increase in petrel numbers over the last two decades; however, burrow densities at Marion have increased by only 56 % since 1979. White-chinned petrels (Procellaria aequinoctialis) showed the greatest increase, despite being listed as vulnerable due to incidental mortality on fishing gear at sea. The recovery of other summer-breeding species decreased with decreasing body size, and winter-breeding species showed even smaller recoveries, similar to patterns of breeding success at Gough Island, where mice are major predators of petrel chicks and eggs. Predation by mice is the most likely explanation for the limited recovery of Marion’s petrel populations.
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Great-winged petrels Pterodroma macroptera and blue petrels Halobaena caerulea bred more successfully after the eradication in 1991 of feral domestic cats Felis catus at Marion Island. The larger white-chinned petrel Procellaria aequinoctialis did not show such improvement, although percentage burrow occupancy in the late breeding season increased significantly between 1982/83 and 1988/89 for that species, suggesting decreased cat predation during this period of cat control. -from Authors
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Breeding success of Pterodroma macroptera, Procellaria aequinoctialis and Pachyptila vittata salvini in three cat-free and three control areas were used to evaluate the effects of cat Felis catus predation on the avifauna of Marion Island. Breeding success of all three species was significantly higher in the combined cat-free areas than in the combined control areas. However, breeding success in one cat-free area failed to show a significant difference from its particular control area, probably as a result of higher skua (Catharacta antarctica) predation inside the cat-free area. Chicks of P. macroptera and P. aequinoctialis were especially vulnerable to cat predation, since cats can enter their nesting burrows. P. macroptera was seriously affected by cat predation because it is the most abundant of only two winter-breeding petrels. Significant changes in the number of nest visits by these petrels during their breeding season followed hatching dates, which in turn were concomitant with, or were followed by significant differences in the combined breeding success between the cat-free and control areas. The cat-free areas show that an elimination of cat predation would still favour the recovery of the petrel population.Broeisukses van Pterodroma macroptera, Procellaria aequinoctialis en Pachyptila vittata salvini in drie katvrye- en drie kontrole-gebiede is gebruik om die effekvan katpredasie (Felis catus) op die avifauna van Marioneiland te evalueer. Broeisukses van die drie spesies was in die gekombineerde katvrye-gebiede betekenisvol hoër as in die gekombineerde kontrole-gebiede. Broeisukses in een van die katvrye-gebiede het egter nie ’n betekenisvolle verskil met sy spesifieke kontrole-gebied getoon nie, waarskynlik weens ’n hoër roofmeeu- (Catharacta antarctica) predasie binne die katvrye-gebied. Kuikens van P. macroptera en P. aequinoctialis was veral vir katpredasie kwesbaar, omdat katte hulle nestonnels kon betree. P. macroptera is ernstig deur katpredasie beïnvloed omdat dit die volopste van slegs twee winterbroeiende stormvoëls is. Betekenisvolle veranderinge in die aantal nesbesoeke deur die stormvoëls gedurende hulle broeiseisoene het gevolg op uitbroeidatums wat op hulle beurt deur betekenisvolle veranderings in broeisukses tussen die katvrye- en kontrole-gebiede gevolg is. Die katvrye-gebiede het getoon dat ’n uitskakeling van katpredasie die herstel van die stormvoëlbevolking sal bevoordeel.
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House mice ( Mus musculus L.) were introduced to sub-Antarctic Marion Island more than two centuries ago, and have been the only introduced mammal on the island since 1991 when feral cats were eradicated. The first mouse-injured wandering albatross ( Diomedea exulans L.) chick was found in 2003 and since then attacks have continued at a low level affecting <1% of the population. In 2009, the first ‘scalpings’ were detected; sooty albatross ( Phoebetria fusca Hilsenberg) fledglings were found with raw wounds on the nape. In 2015, mice attacked large chicks of all three albatross species that fledge in autumn: grey-headed ( Thalassarche chrysostoma Forster) (at least 102 wounded chicks; 4.6% of fledglings), sooty ( n =45, 4.3%) and light-mantled albatross ( P. palpebrata Forster) ( n =1, 4%). Filming at night confirmed that mice were responsible for wounds. Attacks started independently in small pockets all around the island’s 70 km coastline, separated by distances hundreds of times greater than mouse home ranges. The widespread nature of mouse attacks in 2015 on large, well-feathered chicks is alarming and highlights not only Marion Island as a priority island for mouse eradication but also that mice alone may significantly affect threatened seabird species.
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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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Since 2004 there has been mounting evidence of the severe impact of introduced house mice (Mus musculus L.) killing chicks of burrow-nesting petrels at Gough Island. We monitored seven species of burrow-nesting petrels in 2014 using a combination of infra-red video cameras augmented by burrowscope nest inspections. All seven camera-monitored Atlantic petrel (Pterodroma incerta Schlegel) chicks were killed by mice within hours of hatching (average 7.2 ± 4.0 hours) with an 87% chick failure rate (n = 83 hatchlings). Several grey petrel (Procellaria cinerea Gmelin) chicks were found with mouse wounds and 60% of chicks failed (n = 35 hatchlings). Video surveillance revealed one (of seven nests filmed) fatal attack on a great shearwater (Puffinus gravis O'Reilly) chick and two (of nine) on soft-plumaged petrel (Pterodroma mollis Gould) chicks. Mice killed the chicks of the recently discovered summer-breeding MacGillivray's prion (Pachyptila macgillivrayi Mathews), with a chick mortality rate of 82% in 2013/14 and 100% in 2014/15. The closely-related broad-billed prion (P. vittata Forster) breeds in late winter and also had a chick mortality rate of 100% in 2014. The results provide further evidence of the dire situation for seabirds nesting on Gough Island and the urgent need for mouse eradication.
Article
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The White-faced Storm-petrel (Pelagodroma marina) breeds on several tropical, sub-tropical and temperate islands in both hemispheres, but some aspects of its breeding biology are still poorly known. The European subspecies hypoleuca is almost confined to a small archipelago, the Salvage Islands, about 300 km south of Madeira Island, North-east Atlantic. Because of its very localized distribution, this subspecies is relatively vulnerable to extinction and its population dynamics need to be understood and monitored. We studied the breeding biology of the White-faced Storm-petrel at Selvagem Grande Island in 1996. Birds first arrived at the colony in mid-December, eggs were laid from mid-March to early June, and the last chicks fledged in mid-August. Mean incubation period was 53.7 days, but was highly variable due to frequent egg-neglect that affected at least two thirds of the clutches. Mean nestling period was 60.3 days. Chick growth (body mass and wing length) is described. Hatching success was 60.7% (N = 89) and fledging success was 88.9% (N = 54). Breeding success (53.9%) was not low, in spite of frequent predation by house mice (Mus musculus), the main cause of nesting failures. Rabbits (Oryctolagus cunniculus) and Yellow-legged Gulls (Larus cachinnans), two species thought to pose threats to other seabirds of the region, had no measurable negative effect on breeding performance at our study nests. However, we had some evidence that gulls prey upon chicks and adult birds. Breeding success did not correlate with egg size. There was a highly significant seasonal decline in both hatching and fledging success. Using data on burrow density and occupancy obtained in the main colony, we estimated the breeding population on Selvagem Grande at around 36,000 pairs.
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Whilst there is good evidence for negative impacts of introduced rat species on island ecosystems, the effects of house mice (Mus musculus) are generally less well documented. In some situations, introduced house mice can exert severe impacts, particularly where this is the only introduced mammal. Here, we examine the distribution, relative abundance and breeding success of small burrowing seabirds on Steeple Jason Island, Falklands, in relation to habitat types and the distribution of house mice which is the sole introduced mammal species, and we make comparisons with seabird distribution and densities on the neighbouring island of Grand Jason where mice are absent. Grey-backed storm-petrel (Garrodia nereis) and Wilson's storm-petrel (Oceanites oceanicus), which due to their extremely small size are likely to be the most vulnerable to mouse predation, were considerably more abundant on mouse-free Grand Jason than on Steeple Jason. Grey-backed storm-petrel, which are typically associated with tussac grass, avoided this habitat on Steeple Jason where it is associated with high levels of house mouse activity (assessed from the proportion of wax baits gnawed overnight), whereas on mouse-free Grand Jason, there was no such avoidance. Wilson's storm-petrel nesting on Steeple Jason suffered high rates of egg and chick loss. Whilst we found evidence for detrimental impacts of house mice on the two small storm-petrel species, there was no relationship between relative mouse activity levels and the distribution or abundance of the larger thin-billed Prion (Pachyptila belcheri).
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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 waters around South Africa provide rich foraging opportunities for pelagic seabirds. They also support a pelagic longline fleet targeting tunas Thunnus spp. and swordfish Xiphias gladius, which set a total of 41.5 million (average 5.2 million per year) and 10.2 million hooks (average 1.3 million per year) respectively during the period 1998-2005. Fisheries observers collected seabird bycatch data from 2 256 sets (4.4 million hooks) and recorded a total of 1 954 birds killed during that period. In all, 11 species of seabird are confirmed incidentally caught by the fishery, eight of which are considered threatened. Birds were caught at an average rate of 0.44 per 1 000 hooks, resulting in an average of 2 900 seabirds killed per year, decreasing from approximately 5 900 in 1998 to 1 800 in 2005. Three techniques for extrapolating total seabird mortality were investigated and little difference between the estimates found. Generalised linear models were used to explain bycatch patterns and revealed that individual vessel is the most important explanatory variable, followed by vessel flag, moon phase, season, sea state, the use of a tori line, time of set, area and bathymetry. Estimates of the numbers of seabirds killed per year were lower than other studies, an improvement most likely linked to the termination of foreign bilateral agreements, as well as to improved awareness among fishers as a result of ongoing education campaigns. Some of the apparent decreases in catch rate could reflect reduced numbers of seabirds at sea, the result of ongoing population decreases in several key species.
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On Marion Island, house mice ( Mus musculus) establish burrow systems that range from unbranched corridors 0.5 m long with a single chamber (in some instances without a chamber) to complexly branched systems extending over an area of up to 4 m2 and containing up to four chambers. Total underground area occupied by burrow systems (chambers plus corridors) was from 5 to 23 m2 ha-1, corresponding to burrow-system volumes of 250-1,300 dm3 ha-1. In autumn, about three-quarters of chambers contained small food caches. Most (87%) entrances to burrow systems faced away from prevailing winds, especially winds that bring snow, hail or rain. Seasonal and diurnal temperature variations in burrows are considerably dampened (daily minimum in burrows seldom drops below 2°C), compared with the air just above the vegetation canopy. Over the whole year, total night-time warmth in a burrow (heat sum, 24,883 degree hours) was 53% greater than at the top of the canopy (16,317 degree hours). Burrows' entrances are generally connected above ground by runways (paths and tunnels through the vegetation). Runways also represent a warmer environment than the air above the canopy during the breeding season at night (13,466 degree hours at the runway surface compared with 11,900 degree hours at the top of the canopy). House mice, which are living close to their physiological limits, temperature-wise, on Marion Island thus evade the worst extremes of the island's climate by constructing burrows and above-ground runways and this is an important factor in their survival.
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The diet of breeding white-chinned petrels was studied during the summers of 1996 and 1998 at South Georgia. Krill abundance/availability was high throughout 1996 but apparently low at the beginning of the 1998 breeding season. The diet of white-chinned petrels was similar between years and consistent with previous studies. Krill Euphausia superba (41–42% by weight) was the single most important prey item followed by fish (39–29%) and squid (19–25%). Meal mass was consistent (110 g in 1996, 119 g in 1998) between years but a significant decrease (46%) in feeding frequency in 1998 (0.54 meals day−1 compared to 0.75 meals day−1 in 1996) resulted in 19% less food delivered to chicks in 1998 than in 1996. Breeding success, however, was consistent between years at 44% and similar to that recorded previously at Bird Island. This is in contrast to black-browed and grey-headed albatrosses, both of which experienced almost total breeding failure in 1998. It is suggested that their varied and versatile feeding methods, together with their greater diving ability, capacity to feed at night and extensive foraging range, help white-chinned petrels minimise the effects of krill shortage.
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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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The white-chinned petrel is a subantarctic seabird that requires urgent implementation of conservation measures for the species. At sea, adults suffer heavy mortality due to fisheries' practices. On land, introduced rats prey on chicks at several localities, and we test here if and how rats can be efficiently controlled. Since 1994, we have conducted an intensive rat-control program during each breeding season in a white-chinned petrel colony on Ile de la Possession (150km2; Crozet archipelago, southern Indian Ocean), which had been monitored since 1986. On the same island, a control white-chinned petrel colony, where no poisoning occurred, was also monitored, and we assessed the seasonal variations of rat abundance. We compared three situations: high rat-poisoning, low rat-poisoning and control conditions without poisoning. Low-poisoning trials performed in our experimental colony between 1988 and 1991 did not lead to higher chick production than for the previous two control years. However, petrel-breeding success was significantly higher when intensive poisoning occurred (50%) than for the previous years (16%). The duration of our study (8years before intensive poisoning, plus 8years afterwards), combined with a comparison of petrel annual breeding success between our experimental and control colonies, allowed us to assess more effectively the impact of rats. Forty-one per cent of breeding failures occurring in non-poisoned areas were attributed to rats. We conclude that threatened insular bird populations can be conserved and restored in localities even where total rat eradication is not possible. However, only intensive and repeated (long-term) poisoning will control rats sufficiently.
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Recent changes in the climate of the sub-Antarctic may influence the number of house mouse (Mus musculus sensu lato) living on islands in the region. An increase in mouse numbers, as conditions became milder, could amplify the effects of climate change on native prey species. However, we have no direct evidence of the influence of climate on mouse numbers in the sub-Antarctic. We, therefore, assessed demographic trends in the mouse population on Marion Island between 1991 and 2001. Both the climate and mouse numbers were relatively stable during our study. Mice, however, increased their reproductive output in years when ambient temperatures were relatively high. Moreover, reduced reproductive output followed high densities at the onset of a breeding season, implying density-dependent limitation. We conclude that both temperature and density limited the increase in numbers during the summer breeding season. Major die-offs during winter probably limit population size and explain the relative stability in numbers across the 10years of our study.
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MARK provides parameter estimates from marked animals when they are re-encountered at a later time as dead recoveries, or live recaptures or re-sightings. The time intervals between re-encounters do not have to be equal. More than one attribute group of animals can be modelled. The basic input to MARK is the encounter history for each animal. MARK can also estimate the size of closed populations. Parameters can be constrained to be the same across re-encounter occasions, or by age, or group, using the parameter index matrix. A set of common models for initial screening of data are provided. Time effects, group effects, time x group effects and a null model of none of the above, are provided for each parameter. Besides the logit function to link the design matrix to the parameters of the model, other link functions include the log—log, complimentary log—log, sine, log, and identity. The estimates of model parameters are computed via numerical maximum likelihood techniques. The number of parameters that are estimable in the model are determined numerically and used to compute the quasi-likelihood AIC value for the model. Both the input data, and outputs for various models that the user has built, are stored in the Results database which contains a complete description of the model building process. It is viewed and manipulated in a Results Browser window. Summaries available from this window include viewing and printing model output, deviance residuals from the model, likelihood ratio and analysis of deviance between models, and adjustments for over dispersion. Models can also be retrieved and modified to create additional models. These capabilities are implemented in a Microsoft Windows 95 interface. The online help system has been developed to provide all necessary program documentation.
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The arrival of humans on oceanic islands has precipitated a wave of extinctions among the islands' native birds. Nevertheless, the magnitude of this extinction event varies markedly between avifaunas. We show that the probability that a bird species has been extirpated from each of 220 oceanic islands is positively correlated with the number of exotic predatory mammal species established on those islands after European colonization and that the effect of these predators is greater on island endemic species. In contrast, the proportions of currently threatened species are independent of the numbers of exotic mammalian predator species, suggesting that the principal threat to island birds has changed through time as species susceptible to exotic predators have been driven extinct.
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Invasive rats are some of the largest contributors to seabird extinction and endangerment worldwide. We conducted a meta-analysis of studies on seabird-rat interactions to examine which seabird phylogenetic, morphological, behavioral, and life history characteristics affect their susceptibility to invasive rats and to identify which rat species have had the largest impact on seabird mortality. We examined 94 manuscripts that demonstrated rat effects on seabirds. All studies combined resulted in 115 independent rat-seabird interactions on 61 islands or island chains with 75 species of seabirds in 10 families affected. Seabirds in the family Hydrobatidae and other small, burrow-nesting seabirds were most affected by invasive rats. Laridae and other large, ground-nesting seabirds were the least vulnerable to rats. Of the 3 species of invasive rats, Rattus rattus had the largest mean impact on seabirds followed by R. norvegicus and R. exulans; nevertheless, these differences were not statistically significant. Our findings should help managers and conservation practitioners prioritize selection of islands for rat eradication based on seabird life history traits, develop testable hypotheses for seabird response to rat eradication, provide justification for rat eradication campaigns, and identify suitable levels of response and prevention measures to rat invasion. Assessment of the effects of rats on seabirds can be improved by data derived from additional experimental studies, with emphasis on understudied seabird families such as Sulidae, Phalacrocoracidae, Spheniscidae, Fregatidae, Pelecanoididae, Phaethontidae, and Diomedeidae and evaluation of rat impacts in tropical regions.
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The considerable threats of invasive rodents to island biodiversity are likely to be compounded by climate change. Forecasts for such interactions have been most pronounced for the Southern Ocean islands where ameliorating conditions are expected to decrease thermal and resource restrictions on rodents. Firm evidence for changing rodent populations in response to climate change, and demonstrations of associated impacts on the terrestrial environment, are nonetheless entirely absent for the region. Using data collected over three decades on sub-Antarctic Marion Island, we tested empirically whether mouse populations have changed through time and whether these changes can be associated significantly with changing abiotic conditions. Changes in invertebrate populations, which have previously been attributed to mouse predation, but with little explicit demographic analysis, were also examined to determine whether they can be associated with changing mouse populations. The total number of mice on the island at annual peak density increased by 530.0% between 1979-80 and 2008-11. This increase was due to an advanced breeding season, which was robustly related to the number of precipitation-free days during the non-breeding season. Mice directly reduced invertebrate densities, with biomass losses of up to two orders of magnitude in some habitats. Such invertebrate declines are expected to have significant consequences for ecosystem processes over the long term. Our results demonstrate that as climate change continues to create ameliorating conditions for invasive rodents on sub-Antarctic islands, the severity of their impacts will increase. They also emphasize the importance of rodent eradication for the restoration of invaded islands. This article is protected by copyright. All rights reserved.
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A significant change has occurred in the diet of feral House Cats, Felts catus, at Marion Island, concomitant with an artificial reduction in the Cat population. Prior to population-reduction operations, burrowing petrels (Procellariidae) and the House Mouse, Mus musculus, constituted the main prey of the Cats. After control operations, the diet of the decreasing Cat population contained an increased proportion of House Mice, and the Kerguelen Petrel, Pterodroma brevirostris, no longer featured as a food item. The causes and effects of this change are discussed in terms of the flow of energy through the Cat population.
Article
In comparison to the mainland, populations of rodents on islands are often characterized by a suite of life history characteristics termed the “island syndrome.” Populations of rodents introduced to islands are also well known for their impacts on native species that have evolved in the absence of mammalian predators. We studied the ecology and behavior of introduced house mice Mus musculus on Gough Island where they are the only terrestrial mammal and where their predatory behavior is having a devastating impact on the island’s burrowing petrel (order Procellariiformes) population and the Critically Endangered Tristan albatross Diomedea dabbenena. Mice on Gough exhibit extreme features of the island syndrome, including: a body mass 50–60% greater than any other island mouse population, peak densities among the highest recorded for island populations, and low seasonal variation in numbers compared to other studied islands. Seasonal patterns of breeding and survival were linked to body condition and mass, and mice in areas with high chick predation rates were able to maintain higher mass and condition during the winter when mouse mortality rates peak. Within-site patterns of chick predation indicate that proximity to neighboring predated nests and nesting densities are important factors in determining the likelihood of predation. We conclude that selection for extreme body mass and predatory behavior of mice result from enhanced overwinter survival. Small mammal populations at temperate and high latitudes are normally limited by high mortality during the winter, but on Gough Island mice avoid that by exploiting the island’s abundant seabird chicks.
Article
Moutohora (Whale Island) holds the largest surveyed breeding colony of grey-faced petrels (Pterodroma macroptera gouldi). For our estimate of the breeding population, we divided the island into 16 sections within which burrow densities were approximately uniform; the surface areas of these sections were found by planimetry. Apparently completed burrows were counted in 1998-2000 within each section by plots of 2 m radius along linear transects, or by 10 × 10 m contiguous plots. The total estimate (± SE) for the island was 109,000 ± 10,000 burrows, which equates to about 95,000 pairs breeding annually, given an occupancy rate of about 87%. The population has apparently more than doubled since Norway rats (Rattus norvegicus) and rabbits (Oryctolagus cuniculus) were eradicated in 1985/87.
Article
In the 1980s, penguins dominated the prey remains of sub-Antarctic skuas Stercorarius antarcticus breeding on Marion Island, whereas on neighbouring Prince Edward Island burrowing petrels made up >95% of prey remains in nest middens. This difference resulted at least in part from the impact of introduced cats Felis catus on Marion Island’s burrowing petrel populations. Cats were introduced to Marion Island in 1949, and prior to their eradication in 1991, they killed an estimated 450 000 petrels each year, greatly reducing the densities of petrels breeding on the island. A repeat survey of skua prey remains showed that penguins still dominated the prey of breeding sub-Antarctic skuas on Marion Island in the summer of 2010–11, two decades after cats were eradicated from the island. The proportion of penguin remains decreased slightly compared to 1987–88, but this might be expected given the decreases in penguin numbers on Marion Island over this period. Regurgitated pellets confirmed the dominance of penguin prey on Marion Island. Taken together with the decrease in skua numbers on Marion Island over the last two decades, our results suggest that there has been little recovery in the population of at least summer-breeding burrowing petrels since cats were eradicated.
Article
We investigated relationships between body condition (body mass scaled by body size) early in the breeding season and reproductive performance of three seabird species showing various life history traits. The study was conducted at Kerguelen Island from 1987 to 1994 on the Blue Petrel (Halobaena caerulea, an oceanic feeder), the Thinbilled Prion (Pachyptila belcheri, a neritic feeder), and the Common Diving Petrel (Pelacanoides urinatrix, a coastal feeder). Breeding success was highly variable among years in the three species, but the proportion of nonbreeding experienced breeders varied significantly only in the Blue Petrel. In the three species, body condition showed considerable year-to-year variation, suggesting substantial fluctuation in the availability of prey early in the breeding season. Relationships between early body condition and reproductive performance differed among the species. Reproductive success was significantly influenced by early condition in the Blue Petrel but not in the Thin-billed Prion and the Common Diving Petrel. In the long-lived Blue Petrel, depletion of body condition early in the breeding season resulted in a high proportion of nonbreeders and massive egg desertion. On the other hand, the shorter lived Thin-billed Prion and Common Diving Petrel seemed to respond by maintaining their reproductive output during poor years, probably investing more in the reproductive episode. Such contrasted patterns are analyzed in the light of reproductive effort and optimal clutch size theory.
Article
The impacts of predation by invasive mammals on island fauna are a major driver of insular biodiversity loss. Devastating, hitherto unsuspected impacts of predatory house mice on breeding seabirds have been described recently. We studied the fate of 178 Atlantic Petrel Pterodroma incerta nests at Gough Island, over four seasons, from October 2003 to January 2008. Introduced house mice Mus musculus were found in all study burrows checked for mouse visits. From October 2003 to September 2004, we video-recorded attacks by mice on six (of 13) live, healthy Atlantic Petrel chicks and on one (of three) great shearwater Puffinus gravis chicks. In all years, chicks died from mouse attacks. Stage-specific daily nest survival rates were modelled, from which estimates of breeding success were derived that accounted for the variable exposure periods studied among years. Average daily survival rate of eggs was 0.998, and hatching success through the entire incubation period (55.5 days) was 0.924 [95% confidence interval (CI) 0.903–0.940]. Daily chick survival rates were 0.990, which gave a modelled fledging success of 0.247 (CI 0.165–0.338) over the 138-day chick period, and average annual breeding success (chicks fledged per breeding attempt) of 0.228 (CI 0.150–0.318), which is low compared with congeners. Productivity estimates were used as a parameter in a population simulation model, which predicted a population multiplication rate (λ) of 0.993 (CI = 0.966–1.021). However, in the one season studied from laying to fledging (2007), from 58 nests, only one chick fledged (1.7%). This suggests the wide errors on the model results may obscure a more severe reality. More than 60% of model simulations resulted in an International Union for Conservation of Nature classification of Endangered. Our results add support to calls to eradicate mice from Gough Island. More generally, mice cannot be ignored as a potential threat to island fauna, and island restoration and management plans should routinely include eradication of introduced mice.
Article
The Great-winged Petrel Pterodroma macroptera, Kerguelen Petrel P. brevirostris and Soft-plumaged Petrel P. mollis breed in different habitats at different times of the year at Marion Island. P. macroptera breeds in inland slopes during winter, brevirostris breeds in flat marshy areas during early summer and mollis breeds during late summer in coastal slopes. Nesting-burrows of macroptera and rnollis have a similar simple design but burrows of brevirostris have a drainage system to cope with their waterlogged breeding habitat. Incubation periods are similar (56, 49 and 50 days in macroptera, brevirostris and mollis respectively), but fledging periods are very different (61 days in brevirostris and 91 days in mollis). The species rear chicks at different times, presumably to help reduce interspecific competition for food. In all species, the chicks are fed mostly squid, but meals of brevirostris chicks contain most crustaceans and fish. Differences in quality of meals in part explain the faster growth of brevirostris compared to macroptera or mollis. The timing of breeding influences the vulnerability of each species to predators, which is reflected in differences in breeding success (53%, 7% and 0% in brevirostris, mollis and macroptera respectively).
Article
A population of feral domestic cats Felis catus has existed at subantarctic Marion Island since 1951. From 1977 to 1990 an ongoing programme has utilized an introduced disease, shooting and gin-trapping in an endeavour to control cat numbers, with the eventual aim of their eradication. Burrowing petrels (Procellariidae) form the majority of the cats' diet. The breeding success of the winter-breeding Great-winged Petrel Pterodroma macroptera has varied between nil and 20.5% in the period from 1979 to 1984, due primarily to cat predation of chicks causing up to 100% mortality. In 1990, by which time cat numbers had been greatly reduced from their 1970s' peak, Great-winged Petrels had a breeding success of 59.6%, with chick mortality being zero. No signs of cat predation were observed. This finding provides good reason to continue the control programme until cats are finally eradicated from Marion Island.
Article
The ecological consequences of climate change are determined by many climate parameters, not just by the commonly investigated changes in mean temperature and rainfall. More comprehensive studies, including analyses of climate variability, extremes and aggregate changes in the climate system, can improve the understanding of the nature, and therefore possible consequences, of recent changes in climate. Here climate trends on the sub-Antarctic Marion Island are documented (between 1949 and 2003) in more detail than previously. Significant trends in biologically-relevant, and previously unexplored, parameters were observed, and the potential ecological consequences of these changes discussed. For example, the decline in precipitation experienced on the island comprises a trend for longer dry spells punctuated by fewer and smaller precipitation events. This more detailed understanding of the island’s drying trends enables more accurate predictions about its impacts, including, for example, particularly severe effects on plant species growing in soils with poor water-holding capacity. Therefore, in addition to changes in average conditions, more inclusive climate analyses should also examine trends in climatic variability and extremes, for individual climate parameters as well as for the climate system as a whole.
Article
Reports of nesting success that do not take into account the time span of observation for each nest usually understate losses, and sometimes the error can be very large. More than a decade ago I pointed out this problem and proposed a way of dealing with it (Mayfield 1960:192-204; 1961). Since that time many field students have used the method, and it has proved es- pecially helpful in combining fragments of data from many sources, as in the North American Nest-record Program at Cornell University. However, not every published report shows awareness of the problem, and letters of in- quiry have shown that some people are deterred from dealing with it because of difficulty with details. Therefore, I offer these further suggestions to sim- plify the procedure as much as possible. THE PROBLEM All nests are not found at the very start. Indeed, most nests of small open- nesting birds are not found until incubation is well under way or until the young have hatched. The observed success in such a sample will be greater than the true nesting success of the species. The shorter the time span of observations, the less the observed losses; that is, nest mortality-loss by destruction or desertion-is a function of time. Since nearly all field studies contain a mixture of nests found early and late, as customarily reported they show nesting success higher than real- ity; but the amount of error is indeterminable because the time each nest entered the sample is not reported. For precise analysis of mortality and sur- vival, it is not enough merely to count nests, eggs, and young. The elapsed time of the observations must also be considered. To illustrate the main difficulty, suppose you found a series of nests when incubation was far advanced. Hatching success would be nearly 100%; and in nests containing large young when found, fledging success would be nearly 100%. Yet you would hesitate to present these figures because it is plain that not enough time elapsed for many accidents to befall. In this extreme case the pitfall is obvious, but in a mixed bag of data, this kind of error may slip through unnoticed. What you are trying to determine is the nesting success of a population. Ideally you would like to find all the nests started by the birds in that pop- ulation, watch all these nests from their beginnings, and observe everything that happened up to the fledging of young. Usually this is impossible and you have to settle for a good deal less, namely, a sample that is anything but 456
Article
Aspects of the breeding biology of the whitc-chinned petrel Procellaria aequinoctialis were studied at South Georgia. Laying, hatching and fledging dates, together with egg and adult measurements, rate of weight loss of eggs and incubating adults and data on the duration of incubation shifts were recorded. Chick growth in weight, tarsus length, culmen length and wing length from hatching to fledging was followed in detail and breeding success and causes of mortality documented. Comparisons are made with other populations of the species, other members of the genus Procellaria and other Procellariiformes. Despite being the largest burrow-nesting petrel in the world, P. aequinoctialis conforms well to the overall relationships between body weight and breeding parameters for Procellariiformes in general.
Article
The Grey-faced Petrel is a non-migratory winter breeder whose reproductive season occupies 9–10 months. Males spend more time in the burrows than females during the courtship period. Some females keep company with strange males, and may be fertilized by them, but subsequently share incubation with their mate of the previous year. The duration of the pre-laying absence of females is about two months, and of the pre-incubation absence of males about seven weeks. Since copulation is presumed to occur before this absence, these petrels seem to have evolved prolonged viability of the spermatozoa, though ovulation may take place some time before laying. Eggs are laid in late June or July but chicks are rarely reared from eggs laid after 14 July; effective laying thus lasts three weeks. The single egg is about 15·5% of the female's weight; she may be able to exert slight control over timing of oviposition. She may be required to incubate, if capable, for up to 14 days from laying but the male takes over, on average, after four days. There are three main incubation spells of 17 days' average duration, two by the male. These are of a duration such that there is usually a change-over near hatching. Incubation lasts about 55 days. There is competition for burrows, resulting in two-egg nests. Norway Rats take unattended eggs and young chicks and scavenge, but their predation (less than 10–35% of chicks per year) is not considered to be endangering the population. After initially more frequent feeds, chicks are fed approximately once a week by each parent. They do not become much heavier than adults and the growth rate is slow: about 120 days to departure.
Article
At the Prince Edward Islands, temperatures have increased by approximately 1C over the past 40 years, accompanied by a decline in precipitation. This has led to a reduction in the peat moisture content of mires and higher growing season warmth. The temperature-and moisture-sensitive sedge, Uncinia compacta R. Br. (Cyperaceae), has consequently increased its aerial cover on Prince Edward Island, but harvesting of seeds by feral house mice (up to 100% removed) has prevented this from happening on Marion Island. Such extensive use of resources suggests that prey switching may be taking place at Marion Island. Scat analyses revealed that mice arenot only eating ectemnorhinine weevils to a greater extent than found in previous studies of populations at Marion Island, but that they also prefer larger weevils (6 mm). A decrease in body size of preferred weevil prey species [Bothrometopus randi Jeannel and Ectemnorhinus similis C.O. Waterhouse (Coleoptera: Curculionidae)] has taken place on Marion Island (1986–1992), but not on Prince Edward Island. This appears to be a result of increased predation on weevils. In addition, adults of the prey species, E. similis are relatively more abundant on Prince Edward Island than adults of the smaller congener E. marioni Jeannel, and could not be found on Marion Island in the late austral summer of 1991. These results not only provide support for previous hypotheses of the effect of global warming on mouse-plant-invertebrate interactions on the Prince Edward Islands, but also provide limited evidence for the first recorded case of predator-mediated speciation. They also show that the interaction of human-induced changes operating at different scales may have profound consequences for local systems.
Article
The nest-site preferences of six burrowing petrel species, Salvin's prion Pachyptila vittata salvini, blue petrel Halobaena caerulea, great-winged petrel Pterodroma macroptera, Kerguelen petrel Pterodroma brevirostris, soft-plumaged petrel Pterodroma mollis and white-chinned petrel Procellaria aequinoctialis, in the northeastern part of Marion Island (Prince Edward Island group, southern Indian Ocean) were analyzed by step-wise multiple regression. The nest-site characteristics measured were slope angle, soil depth and moisture content, percentage cover by stones or boulders and percentage cover by each of seven major plant species. The major nest-site preferences were: exposed areas with shallow soil (Salvin's prion); steep coastal slopes (blue petrel); sheltered well-drained slopes with deep soil (great-winged petrels); wet areas along drainage lines (Kerguelen petrel); steep slopes (soft-plumaged petrel); and areas with deep soil (white-chinned petrel). Similar species showed no significant avoidance of nest sites where there were burrows of potential competitors but did tend to nest spread out over different habitats. Burrow densities were determined in six habitat and seven vegetation types. Salvin's prion was the most abundant species (81% of burrows, with a maximum density of 279 burrows ha-1) and used both burrows and natural cavities for nesting. For all species combined, burrow densities at Marion Island were lower than in comparable habitats and vegetation types at neighbouring Prince Edward Island. Depredation by feral house cats Felis catus, absent from Prince Edward Island, is assumed to be largely responsible for this difference.
Article
The triggering of transitory egg desertion in fasting and incubating blue petrels (Halobaena caerulea, nocturnal burrowing seabirds living in the subantarctic region) was investigated by continuously monitoring both body temperature (T sto) and egg temperature (T egg) with a telemetry system, and by measuring body mass (BM) loss. The birds were kept captive in their burrow and incubated day and night without any interruption; there was no day-night cycle in T sto and T egg, which averaged 39.9 °C and 32.0 °C, respectively. There was no evidence of hypothermia as a way to save energy in this fasting situation. Egg desertion occurred at night and was an abrupt and definitive phenomenon reflected by a simultaneous fall in T egg and a peak in T sto. After egg desertion, a distinct day-night cycle of body temperature was observed, T sto being 0.6 °C higher during night-time (P < 0.05), probably reflecting increased nocturnal activity. BM at egg desertion averaged 166.7 ± 3.8 g in telemetered birds and 164.4 ± 1.6 g in␣a group of free-living birds. Throughout fasting, the␣specific daily BM loss remained at 46 ± 1 g · kg−1 · day−1, but increased sharply below a critical BM of 160.0 ± 2.5 g. Thus, fasting incubating blue petrels spontaneously desert their egg when reaching a BM threshold. This BM is very close to a critical value in fasting birds and mammals that corresponds to a critical depletion of fat stores and to a shift from lipid to protein utilization. This strongly suggests that such a metabolic shift triggers behavioural changes leading to egg desertion and refeeding, which is of great relevance to the understanding of the long-term control of food intake and BM.
Article
The arrival of humans on oceanic islands has precipitated a wave of extinctions among the islands' native birds. Nevertheless, the magnitude of this extinction event varies markedly between avifaunas. We show that the probability that a bird species has been extirpated from each of 220 oceanic islands is positively correlated with the number of exotic predatory mammal species established on those islands after European colonization and that the effect of these predators is greater on island endemic species. In contrast, the proportions of currently threatened species are independent of the numbers of exotic mammalian predator species, suggesting that the principal threat to island birds has changed through time as species susceptible to exotic predators have been driven extinct.
The Prince Edward Islands: land-sea interactions in a changing ecosystem
  • N J M Gremmen
  • V R Smith
GREMMEN, N.J.M. & SMITH, V.R. 2008. Terrestrial vegetation and dynamics. In CHOWN, S.L. & FRONEMAN, P.W., eds. The Prince Edward Islands: land-sea interactions in a changing ecosystem. Stellenbosch: SUN Press, 215-244.
Notes on the winter-breeding great-winged petrel Pterodroma macroptera and grey petrel Procellaria cinerea at Marion Island
  • Newton
NEWTON, I.P. & FUGLER, S.R. 1989. Notes on the winter-breeding greatwinged petrel Pterodroma macroptera and grey petrel Procellaria cinerea at Marion Island. Cormorant, 17, 27-34.
Program MARK: a gentle introduction
  • J J Rotella
ROTELLA, J.J. 2009. Nest survival models. In COOCH, E. & WHITE, G., eds. Program MARK: a gentle introduction. Available at: http://www. phidot.org/software/mark/docs/book/.