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An estimate of population sizes of burrowing seabirds at the Diego Ramirez Archipelago, Chile, using distance sampling and burrow-scoping

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The Diego Ramirez Islands lie 60 nautical miles southwest of Cape Horn and are the breeding site for three species of burrowing seabirds: blue petrels (Halobaena caerulea), common diving petrels (Pelecanoides urinatrix) and sooty shearwater (Puffinus griseus). Burrowing seabirds are highly vulnerable to predation by introduced vertebrate pests, and Diego Ramirez is an important breeding site because it is one of a few remaining subantarctic island groups with no introduced predators. Diego Ramirez is the only known breeding site for blue petrels in the southeast Pacific region, holding about 80% of the global population of that species, and with a population ten times larger than any other population in the world. We estimated the population size in 2002, using a novel application of the distance sampling technique to determine burrow density, and a burrow-scope with excavations to determine occupying species. We found that density was correlated with slope angle and soil wetness. Burrow densities in flatter terrain with drier soils were 2.03 burrows/m2 (95% confidence intervals: 1.82–2.27) and 1.11 burrows/m2 (0.84–1.48) in steeper terrain with wetter soils. The occupation rate of burrows were significantly different between habitat types (t=2.74, d.f. 11, P<0.05); in flatter drier habitats the proportion of burrows that led to a nest was 0.85 (0.74–0.96), in steeper wetter habitats this decreased to 0.64 (0.50–0.78). We used a digital elevation model to calculate true area rather than planar area for the two habitat types on the main island of Bartolome, and charts to calculate planar area for the remainder of the archipelago. There were 1.35 (1.15–1.54) million pairs of blue petrels and 99,000 (65,000–134,000) pairs of common diving petrels on the archipelago. These are similar figures to those from the only previous estimate, made in 1980. We found breeding sooty shearwaters for the first time, and estimated a population of several thousand pairs. We emphasise the facility of distance sampling as an unbiased technique with practical advantages over commonly used area search methods for monitoring populations of burrowing seabirds. These advantages include increased survey efficiency allowing a larger sample size for a given effort and a correspondingly tighter estimation of density.
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... El archipiélago Diego Ramírez es uno de los sitios más importantes de reproducción de aves marinas de Chile (Schlatter & Riveros, 1987;Lawton et al. 2006;Kirkwood et al. 2007;Robertson et al. 2007). Aquí anidan durante la estación reproductiva (octubre-abril) grandes colonias de albatros de ceja negra (Thalassarche melanophris Temminck, 1828) y albatros de cabeza gris (T. ...
... chrysostoma Forster, 1785), petrel azulado (Halobaena caerulea Gmelin, 1789), yunco de los canales (Pelecanoides urinatrix coppingeri Mathews, 1912), pingüino de penacho amarillo (Eudyptes chrysocome Forster, 1781) y pingüino macaroni (Eudyptes chrysolophus Brandt, 1837). Varias poblaciones de estas especies han sido estudiadas y cuantificadas en los últimos años (Arata & Xavier 2003, 2004Lawton et al. 2006;Kirkwood et al. 2007;Robertson et al. 2014Robertson et al. , 2017. Además, algunas de estas especies están amenazadas y sus poblaciones encuentran un refugio reproductivo en este archipiélago austral. ...
... Dos especies de pingüino, macaroni y de penacho amarillo, están clasificadas como vulnerables, y la otra especie, pingüino de Magallanes, como casi amenazada. También se registró la presencia de colonias reproductivas de petrel azulado junto al yunco de los canales (Lawton et al. 2006). Estos registros muestran que las islas Diego Ramírez son ambientes fundamentales para la reproducción de un gran número de especies marinas oceánicas. ...
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Biocultural conservation increasingly requires transdisciplinary collaborations, which includes different disciplines, institutions and actors. The collaboration between scientists and the Chilean Navy has been an effective way to address this requirement. This inter-institutional collaboration between the Navy and the Sub-Antarctic Biocultural Conservation Program (University of Magallanes, Institute of Ecology and Biodiversity and Omora Foundation in Chile, and the University of North Texas in the US) enabled us to initiate in 2016 long term ornithological studies in the Diego Ramírez Archipelago, which includes the southernmost islands of the American continent. Until now, its avifauna has been studied exclusively during summer seasons, despite the fact that birds are one of the most sensitive and fastest responding groups of animals to climate change; modifying their periods of migration, residence and nesting, their population sizes, and their latitudinal distribution areas. In addition, subpolar regions are especially sensitive to climate change and studies in the Cape Horn Biosphere Reserve, adjacent to the Diego Ramírez Archipelago, suggest that some species could be expanding their latitudinal distribution spheres and changing their migration dates. The objective of this work is to initiate a systematic monitoring of the species composition and the nesting, migration and/or residence dates of the Diego Ramírez Archipelago birdlife at the southern tip of the Magallanes sub-Antarctic ecoregion. In this study we present an update of the avifauna records for the Gonzalo Island, Diego Ramírez Archipelago, including the first fall and winter records, and sightings at other times of year. In three expeditions, during the austral reproductive season (summer, November 29-December 1, 2016), winter (July 20-22, 2017) and fall (March 28-April 1, 2018), birds were monitored using mist-nets and creating species lists from field observations. For the observations of birds throughout the year, we used the photographic records made by José Mella (coauthor) and José Mejía (Navy petty officers at Gonzalo Island Lighthouse, years 2014-2018), and new photographic records were initiated with trained personnel of the Navy of Chile in the lighthouse of Gonzalo Island. In total, we detected 33 species belonging to 16 families. Ten of these species represent new records for the archipelago: Neotropic cormorant (Phalacrocorax brasilianus Gmelin, 1789), Western cattle egret (Bubulcus ibis (Linnaeus, 1758)), Peregrine falcon (Falco peregrinus Tunstall, 1771), Austral negrito (Lessonia rufa Gmelin, 1789), Austral thrush (Turdus falcklandii Quoy & Gaimard, 1824), Rufous-collared sparrow (Zonotrichia capensis Müller, 1776), Black-chinned siskin (Spinus barbatus Molina, 1782), Blue-and-White Swallow (Pygochelidon cyanoleuca patagonica d’Orbigny & Lafresnaye, 1837), Black-bellied storm petrel (Fregetta tropica Gould, 1844), and y Cape petrel (Daption capense capense Linnaeus, 1758). Some of these new records could be associated with global warming and a recent expansion of the latitudinal distribution areas and/or the residence periods of these birds. Among the 33 species, 26 were recorded in spring-summer, 22 in fall, and 14 in winter. However, nine were sighted only occasionally and it will be necessary in the future to determine whether they are resident or migratory species that are seldom observed, or occasional visitors. Regarding conservation status, according to the IUCN Red List of Threatened Species, the avifauna of the Diego Ramírez Archipelago includes an endangered species (Grey-headed albatross, Thalassarche chrysostoma Forster, 1785), three vulnerable species and four almost threatened. Monitoring on these islands provides a baseline to evaluate the status of bird populations under the threats of global change, among which the threat of invasive species is highlighted. It is critical to prevent the arrival of exotic invasive species that are present in other subantarctic islands, such as rats (Rattus spp.), mice (Mus musculus Linnaeus, 1758), cats (Felis catus Linnaeus, 1758), and American mink (Neovison vison Schreber, 1777), which are present in the Cape Horn Biosphere Reserve, located less than 100 km North of the Diego Ramírez Archipelago. The collaborative work with the Chilean Navy has been crucial to start these long-term ornithological studies, associated with the new Long-Term Ecological Studies Site Gonzalo Island-LTER that forms part of the Chilean Long-Term Socio-Ecological Studies Network (LTSER-Chile), and the International Long-Term Ecological Studies Network (ILTER). A main goal will be to combine avifauna monitoring with detection of potential invasive species.
... Conventionally, the number of burrows in seabird colonies are estimated by surveying burrow density using a randomised sampling design, and then multiplying mean burrow density by the extent of the area thought to be occupied (Lawton et al. 2006;Parker and Rexer-Huber 2016). This 'design-based' approach is simple but failure to adhere to the randomised design, for example due to logistical constraints, may lead to biazed estimates. ...
... We recorded the species of any birds or fresh feathers present in the burrow, as well as other signs of occupancy (egg, fresh eggshell or fresh faeces). In addition, for each plot we recorded: the slope, measured ± 5° using a clinometer; the aspect, measured ± 5° using a compass; the percentage ground cover, assessed visually ± 5%; the mean vegetation height, measured ± 5 cm using a graduated pole; and the soil moisture, assessed subjectively on a four point scale from dry to wet following Lawton et al. (2006). Hereafter, we refer to these as locally measured covariates. ...
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Small petrels are the most abundant seabirds in the Southern Ocean. However, because they breed in burrows on remote and often densely vegetated islands, their colony sizes and conservation status remain poorly known. To estimate the abundance of these species on Bird Island in the Falkland archipelago, we systematically surveyed their breeding burrow density and occupancy across this near-pristine tussac (Poa flabellata)-covered island. By modelling burrow density as functions of topography and Sentinel 2 satellite-derived Normalised Difference Vegetation Index data, we inferred habitat associations and predicted burrow abundance of the commonest species—Thin-billed Prions (Pachyptila belcheri) and Wilson’s Storm-petrels (Oceanites oceanicus). We estimate that there are 631,000 Thin-billed Prion burrows on the island (95% CI 496,000–904,000 burrows). Assuming that burrow occupancy lies between 12 and 97%, this equates to around 76,000–612,000 breeding pairs, making Bird Island the second or third largest P. belcheri colony in the world, holding approximately 3–27% of the species’ breeding population. We estimate that 8200–9800 (95% CI 5,200–18,300 pairs) pairs of Wilson’s Storm-petrels also breed on the island. Notably, the latter burrowed predominantly under and within tussac pedestals, whereas they are usually assumed to breed in rock cavities. Thin-billed Prions are declining in the Kerguelen archipelago, but their population trends in the Falklands are unknown. Given the wide confidence intervals around our own and other population estimates for these cryptic species, we recommend that their populations should be monitored regularly, at multiple sites.
... Bottom picture: a breeding red-footed booby with a chick on a Guapira discolor tree, the preferred nesting substrate in Mona, in November of 2019. used point-count surveys with distance sampling to estimate the population size of red-footed boobies in Mona Island, which have been used to obtain robust estimates of other seabird populations (Lawton et al. 2006, Barbraud et al. 2018. Second, we used drone photography to estimate numbers of both active nests and birds in the colony as a comparison to estimates from the point-count surveys. ...
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The red‐footed booby (Sula sula) is one of the most common pantropical seabird species, but its populations have been declining in the Caribbean region and elsewhere. We used distance sampling from point‐counts to estimate population size of red‐footed boobies in Mona Island, Puerto Rico, USA, before and during the breeding season in 2019. We compared results from early morning and early night surveys to determine the best survey time given that many individuals are foraging at sea during the daylight hours but not at night. We also examined the suitability of drone photography to survey active nests (a measure of breeding pairs) and compared it to point count and transect survey data. Point count surveys show that an estimated 6,130 birds occupied the colony, which is more than double previous estimates for Mona Island. Our results also showed that to avoid underestimates, red‐footed booby colonies are best surveyed at night as they yield higher bird densities than daytime surveys. For the same reason, daytime photographic surveys with a drone underestimated population size compared to nighttime point‐count surveys. However, drones were more effective than ground surveys in detecting active nests, and thus breeding pairs, which provides a better estimate of the resident population of a colony. We recommend that nighttime surveys are tailored to site‐specific conditions to improve estimates of red‐footed boobies, while drones can save significant effort and time in monitoring numbers of active nests in the remote and rugged islands where red‐footed boobies typically nest. Our purpose for this research was to demonstrate the effectiveness to estimate population size of seabirds by combining counting techniques (points, transects, drone, night vs. day) with estimation methods (distance sampling). We found that the red‐footed booby colony in Mona Island was one of the largest colonies in the Caribbean region.
... are a similar size (∼200 g). The largest breeding populations of Blue Petrels are at Diego Ramírez Islands, Chile in the southeast Pacific Ocean (>2 million individuals or ∼1.35 million pairs; Schlatter and Riveros, 1997;Lawton et al., 2006), Kerguelen Islands in the southern Indian Ocean (100,000-200,000 pairs; Weimerskirch et al., 1989) and Marion Island in the Indian Ocean (110,000-180,000 pairs; Dilley et al., 2017). Muscle tissue sampled from Blue Petrels breeding at Kerguelen Islands contains far higher Hg concentrations than expected, given the relatively low Hg levels in epipelagic fish and crustaceans in the same region . ...
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Even in areas as remote as the Southern Ocean, marine organisms are exposed to contaminants that arrive through long-range atmospheric transport, such as mercury (Hg), a highly toxic metal. In previous studies in the Southern Ocean, inter-specific differences in Hg contamination in seabirds was generally related to their distribution and trophic position. However, the Blue Petrel (Halobaena caerulea) was a notable exception among small seabirds, with higher Hg levels than expected. In this study, we compared the Hg contamination of Blue Petrels and Thin-billed Prions (Pachyptila belcheri), which both spend the non-breeding season in polar waters, with that of Antarctic Prions (Pachyptila desolata), which spend the winter in subtropical waters. We collected body feathers and blood samples, representing exposure during different time-frames. Hg concentrations in feathers, which reflect contamination throughout the annual cycle, were related to δ13C values, and varied with ocean basin and species. Blue Petrels from breeding colonies in the southeast Pacific Ocean had much higher feather Hg concentrations than expected after accounting for latitude and their low trophic positions. Both Hg concentrations and δ15N in blood samples of Blue Petrels were much lower at the end than at the start of the breeding period, indicating a marked decline in Hg contamination and trophic positions, and the carry-over of Hg burdens between the wintering and breeding periods. Elevated Hg levels may reflect greater reliance on myctophids or foraging in sea-ice environments. Our study underlines that carry-over of Hg concentrations in prey consumed in winter may determine body Hg burdens well into the breeding season.
... However, flight restrictions for UAVs may render their use impracticable in several urban settings (ENAC 2020). The distance sampling method has been successfully used in natural context to census breeding seabirds (Lawton et al. 2006;Kirkwood et al. 2007;Robertson et al. 2008) and its performance in estimating the total number of nests of a natural colony of large gulls has been compared with the strip transect counts method by Barbraud et al. (2014). Such study strongly advocates the use of distance sampling since estimates obtained by the strip transect count method were significantly lower (from 9 to 31%). ...
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The yellow-legged gull Larus michahellis has undergone widespread colonization of the urban environment in the recent past. The first urban breeding gulls were recorded in the historical centre of Venice, Italy, in 2000, and by 2005 there were already 24 roof-nesting pairs, with this number increasing significantly over the last decade. In 2016, a new door-to-door garbage collection system was introduced in Venice to prevent the accumulation of rubbish in the streets and limit the trophic resources available for the species. This study provides an up-to-date estimate of the Venice yellow-legged gull urban population using distance sampling method. We also studied the effect of the new waste collection system on the species by comparing the population estimate before (2017) and after (2018) the full implementation of this change and by analysing the trend of individuals collected in the old town by the wildlife recovery service during 2010-2018. Results estimated ca. 430 breeding pairs in June 2018 showing a 36% decrease with respect to 2017. We also found a decrease in the number of 1-year-old birds and pulli collected by the wildlife recovery service starting from 2016, when the policy implementation began. Our data did not show a significant decrease in the overall number of individuals, suggesting that the new policy has a stronger effect on the breeding success of the species than on adult survival. This study emphasizes the importance of preventing rubbish accumulation in the streets as factor for reducing the abundance of urban yellow-legged gulls. Supplementary information: The online version contains supplementary material available at 10.1007/s11252-021-01175-7.
... In addition, photogrammetry of mound modifications over time would be useful for estimating burrow-related sediment fluxes at the surfaces from loose soil patches. UAV remote sensing techniques could serve to more rapidly estimate burrow density in areas without vegetation cover (Lawton et al., 2006). Lidar data measuring vegetation structure could facilitate the identification of the occurrence and abundance of vertebrate (Müller et al., 2010) and invertebrate assemblages (Müller et al., 2018;Vierling et al., 2011). ...
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Although the burrowing activity of some species (e.g., gophers) is well studied, a comprehensive inventory of burrowing animals in adjacent biomes is not yet known, despite the potential importance of burrowing activity on the physical and chemical evolution of Earth's surface. In this study, we review the available information with a focus on the following: (a) an inventory of burrowing vertebrates and invertebrates along the climate and ecological gradient in Chile; (b) the dimensions and characteristics of burrows; and (c) calculation of excavation rates by local species compositions. Methods used include a literature compilation (> 1000 studies) of Chilean burrowing animal species integrated with global, species-specific excavation rates. A field study augments literature findings with quantification of the zoogeomorphic effects on hillslope mass transport at the animal community level and along the arid to humid–temperate climate gradient within the Chilean Coastal Cordillera (27–38∘ S latitude). The literature review indicates a minimum of 45 vertebrate and 345 invertebrate burrowing species distributed across Chile in different biomes. Burrowing depths for Chilean mammals range between 3 m (e.g., for skunks, Conepatus) and 0.25 m (for rock rats, Aconaemys). For invertebrates, burrowing depths in Chile range between 1 m for scorpions to 0.3 m for spiders. In comparison, globally documented maximum burrow depths reach up to more than 6 m for vertebrates (gopher tortoises and aardvarks) and 4 m for invertebrates (ants). Minimum excavation rates of local animal communities observed from field sites in Chile are 0.34 m3 ha−1 yr−1 for the arid site, 0.56 m3 ha−1 yr−1 for the semiarid site, 0.93 m3 ha−1 yr−1 for the mediterranean site and 0.09 m3 ha−1 yr−1 for the humid–temperate site, with the latter likely an underestimation. The calculated minimum Chilean excavation rates are within the large range of globally observed single species rates ranging between 0.01 and 56.20 m3 ha−1 yr−1 for vertebrates and from 0.01 to 37.31 m3 ha−1 yr−1 for invertebrates. Taken together, results not only highlight the diverse and latitudinally varying number of burrowing vertebrates and invertebrates present in different biomes, but also foster the understanding of how burrowing activity changes over a gradient and is influenced by mean annual temperature, mean annual precipitation, slope aspect and latitudinal-related incoming solar energy.
... Buxton et al., 2016), distance sampling (e.g. Lawton et al., 2006) or direct searching of a whole area (e.g. Wood & Otley, 2013) Occupancy method Burrowscope (e.g. ...
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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 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.
... Buxton et al., 2016); distance sampling (e.g. Lawton et al., 2006); or direct searching of a whole area (e.g. Wood and Otley, 2013) Occupancy method Burrowscope (e.g. ...
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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.
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Maximising survey efficiency can help reduce the tradeoff between spending limited conservation resources on identifying population changes and responding to those changes through management. Burrow‐nesting seabirds are particularly challenging to survey because nests cannot be counted directly. We evaluated a stratified random survey design for generating unbiased population estimates simultaneously for four petrel species nesting on Macquarie Island, Australia, where the survey cue, burrow entrances, is similar for all species. We also compared the use of design‐based and model‐based analyses for minimising uncertainty in estimates. We recorded 2845 Antarctic prion burrows, 306 white‐headed petrel burrows and two blue petrel burrows while distance‐sampling along 154 km of transects. For blue petrels and grey petrels, we completed nocturnal searches along a further 71 km and searched 249 km of tracks during follow‐up ground searches. We failed to generate unbiased population estimates for two rare and localised species, blue and grey petrels, from our stratified random survey. Only for the most widespread and abundant species, Antarctic prion, did the estimate have reasonable power to detect a rapid population change. Model‐based analyses of the stratified random survey data did not improve upon traditional design‐based analyses in terms of uncertainty in population estimates, but they did provide useful spatial representation of current populations. Models that used the targeted survey data did not reflect current population sizes and distributions of the two rare and localised species. We found that when species ecologies, distributions and abundances vary, a multi‐method approach to surveys is needed. Species with low abundance that occur patchily across large islands are likely to be best estimated using targeted surveys, whereas widespread and abundant species can be accurately and precisely estimated from randomised surveys using informative model‐based analyses.
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Although the burrowing activity of some species (e.g. gophers) is well studied, a comprehensive inventory of burrowing animals in adjacent biomes is not yet known, despite the potential importance of burrowing activity on the physical and chemical evolution of Earth’s surface. In this study, we review the available information with a focus on: a) an inventory of burrowing vertebrates and invertebrates along the climate and ecological gradient in Chile; b) the dimensions and characteristics of burrows; and c) calculation of excavation rates by local species compositions. Methods used include a literature compilation (> 1000 studies) of Chilean burrowing animal species integrated with global, species-specific excavation rates. A field study augments literature findings with quantification of the zoogeomorphic effects on hillslope mass transport at the animal community level and along the arid to humid-temperate climate gradient within the Chilean Coastal Cordillera (27–38° S latitude). The literature review indicates 45 vertebrate and 345 invertebrate burrowing species distributed across Chile in different biomes. Burrowing depths for Chilean mammals range between 3 m (e.g. for skunks, Conepatus) to 0.25 m (for rock rats, Aconaemys). For invertebrates, burrowing depths in Chile range between 1 m for scorpions to 0.3 m for spiders. In comparison, globally documented maximum burrow depths reach up to more than 6 m for vertebrates (gopher tortoises and aardvarks) and 4 m for invertebrates (ants). Minimum excavation rates of local animal communities observed from field sites in Chile are 0.34 m3 ha−1 yr−1 for the arid site, 0.56 m3 ha−1 yr−1 for the semi-arid site, 0.93 m3 ha−1 yr−1 for the mediterranean site and 0.09 m3 ha−1 yr−1 for the humid-temperate site, with the latter likely an underestimation. The calculated minimum Chilean excavation rates are within the large range of globally observed single species rates ranging between 0.01 and 146.20 m3 ha−1 yr−1 for vertebrates and from 0.01 to 53.33 m3 ha−1 yr−1 for invertebrates. Taken together, results highlight not only the diverse and latitudinally varying number of burrowing vertebrates and invertebrates present in different biomes, but also fosters the understanding of how burrowing activity changes over a gradient and is influenced by mean annual temperature, mean annual precipitation, slope aspect and latitudinal related incoming solar energy.
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The white-chinned petrel (Procellaria aequinoctialis) is an abundant, widespread petrel breeding in tussock grassland at sub-Antarctic islands. Over the last decade it has been killed in large numbers in temperate and sub-tropical longline fisheries. However no data are available on the global population status. We assessed the status of white-chinned petrels at Bird Island, South Georgia by comparing the distribution and density of occupied burrows in 1981 and 1998. In both surveys white-chinned petrel burrows occurred in one-quarter of the 460-477 36-m(2) quadrats surveyed. The total number of burrows in each quadrat was consistent between each survey but we estimate an overall decrease of 28% in those occupied (with considerable variation between sites). Concurrent data on breeding frequency and success showed that white-chinned petrels are essentially annual breeders at Bird Island; breeding success was consistent at around 44%. Significant factors determining densities of occupied burrows were crown height and percent tussock cover (accounting for 77% of variance). The former has decreased significantly, the latter increased significantly between 1981 and 1998 but there was no relationship between white-chinned petrel occupancy rate and habitat modification due to the presence of fur seals (Arctocephalus gazella). This suggests that any population decline is due to factors operating away from the breeding colony, such as those attributed to fishing.
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An infra-red camera 'burrowscope' has been designed for inspecting burrows and cavities typically used by breeding seabirds. The Kia Mau Te Titi Mo Ake Tonu Atu (Keep the Titi Forever) Research Programme in New Zealand aims to investigate the sustainable harvesting of Sooty Shearwater Puffinus griseus chicks as well as monitoring mainland breeding colonies which are threatened by predation from introduced mammals. The burrowscope is being used to determine Sooty Shearwater breeding success and to assess population trends. However, there have been preliminary indications that the burrowscope fails to detect some nests down burrows. During incubation, and after completing three repeated, consecutive burrowscope checks of nests, a plot containing 100 burrow entrances on The Snares Islands was excavated to confirm burrow contents. Using the burrowscope, researchers not only missed up to 34% of nests, but the three consecutive burrowscope checks gave divergent results. This pilot study illustrated the potential complex geometry of burrow systems and indicated that the current burrowscoping methodology may be inaccurate and imprecise in detecting Sooty Shearwater eggs, young chicks and pre-fledging chicks.
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Significant declines in many of the world's albatross and petrel populations, linked to the high mortality of birds as bycatch in fishing operations, have elevated their plight to the top of the international marine conservation agenda. We review available information on Australia's Procellariiformes, with respect to their conservation biology and management in the region. Procellariiformes face a range of threats in the marine environment and on land. At sea, threatening factors include direct interactions with fishing operations; ingestion of, and entanglement in, marine debris; contamination from pollutants; and over–fishing of prey species. At breeding colonies, increased mortality and decreased breeding success due to predation by feral pests; degradation of nesting habitat by introduced herbivores; interspecific competition for nest space; and transmission of parasites and disease occurs. Of these threats, increased mortality resulting from interactions with fishing operations and predation by feral pests are particularly important. The first mainly affects larger species (body mass >600 g), whereas the second predominantly affects smaller species (body mass <600 g). This results because the larger species are able to swallow baited hooks and habitually follow ships, whereas smaller species have difficulty swallowing baited hooks but are vulnerable to predation by virtue of their size. Ensuring the long–term survival of Australia's albatross and petrel populations depends on domestic research and conservation management programs, combined with international action that will secure the protection of these seabirds when they are foraging in waters of other jurisdictions or on the high seas.
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Second volume of exhaustive seven-volume summary of all that is known of the birds of the Australian, New Zealand and Antarctic region. [984 pages, 68 colour plates]
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