Publications for Dr Steffen Oppel

Population reinforcement and demographic changes needed to stabilise the population of a migratory vulture

One approach to stabilise small and declining populations is to breed individuals in captivity and release them into the wild to reinforce existing populations while working to reduce threats. Population reinforcement programmes require long-term commitments to be successful and can divert limited resources from other conservation measures. A rigorous evaluation whether reinforcement can stabilise a population is therefore essential to justify investments.

Many migratory species incur high mortality during their first migration, and releasing captive-bred birds at an older age may therefore benefit reinforcement programmes for migratory birds. We examine whether a small and declining population of a long-distance migratory raptor—the Egyptian Vulture Neophron percnopterus—can be stabilised using population reinforcement that reduces mortality during the first migration. We used an integrated population model to evaluate realistic reinforcement and survival improvement scenarios to estimate how many captive-bred birds would need to be released to stabilise the population.

Survival probability of wild juveniles during their first year (0.296; 95% CI 0.234–0.384) was too low for a stable population (population growth rate 0.949; 95% CI 0.940–0.956), but captive-bred juveniles released in their second calendar year had improved survival (0.566; 95% CI 0.265–0.862) during their first year in the wild.

Reinforcement of 15 birds per year for 30 years was insufficient to achieve a neutral or positive population growth rate. However, reinforcement reduced the probability of extinction by 2049 from 48% without reinforcement to <1% if 12 or more birds were released every year for 30 years. A 6% increase in annual survival probability would likely lead to a stable population without any reinforcement.

Synthesis and applications. Although releasing captive-bred birds can reduce high juvenile mortality during first migration and assist in postponing local extinction, further improvements of survival in the wild are required to safeguard a migratory population where threats in the wild will persist for decades despite management.

Date
25 July 2021
RSPB Authors
Dr Steffen Oppel
Authors
Saravia, Victoria Bounas, Anastasios Arkumarev, Volen Kret, Elzbieta Dobrev, Vladimir Dobrev, Dobromir Kordopatis, Panagiotis Skartsi, Theodora Velevski, Metodija
Published in
Journal of Applied Ecology 90 (5): 1228-1238
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Differential survival throughout the full annual cycle of a migratory bird presents a life‐history trade‐off

Long-distance migrations are among the most physically demanding feats animals perform. Understanding the potential costs and benefits of such behaviour is a fundamental question in ecology and evolution. A hypothetical cost of migration should be outweighed by higher productivity and/or higher annual survival, but few studies on migratory species have been able to directly quantify patterns of survival throughout the full annual cycle and across the majority of a species’ range.

Here, we use telemetry data from 220 migratory Egyptian vultures Neophron percnopterus, tracked for 3,186 bird months and across approximately 70% of the species’ global distribution, to test for differences in survival throughout the annual cycle.

We estimated monthly survival probability relative to migration and latitude using a multi-event capture–recapture model in a Bayesian framework that accounted for age, origin, subpopulation and the uncertainty of classifying fates from tracking data.

We found lower survival during migration compared to stationary periods (β = −0.816; 95% credible interval: −1.290 to −0.318) and higher survival on non-breeding grounds at southern latitudes (<25°N; β = 0.664; 0.076–1.319) compared to on breeding grounds. Survival was also higher for individuals originating from Western Europe (β = 0.664; 0.110–1.330) as compared to further east in Europe and Asia, and improved with age (β = 0.030; 0.020–0.042). Anthropogenic mortalities accounted for half of the mortalities with a known cause and occurred mainly in northern latitudes. Many juveniles drowned in the Mediterranean Sea on their first autumn migration while there were few confirmed mortalities in the Sahara Desert, indicating that migration barriers are likely species-specific.

Our study advances the understanding of important fitness trade-offs associated with long-distance migration. We conclude that there is lower survival associated with migration, but that this may be offset by higher non-breeding survival at lower latitudes. We found more human-caused mortality farther north, and suggest that increasing anthropogenic mortality could disrupt the delicate migration trade-off balance. Research to investigate further potential benefits of migration (e.g. differential productivity across latitudes) could clarify how migration evolved and how migrants may persist in a rapidly changing world.

Date
30 March 2021
RSPB Authors
Dr Steffen Oppel
Authors
Buechley, Evan R Efrat, Ron Phipps, W Louis Carbonell Alanís, Isidoro Álvarez, Ernesto Andreotti, Alessandro Arkumarev, Volen Berger‐Tal, Oded Bermejo Bermejo, Ana
Published in
Journal of Animal Ecology
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Mouse eradication is required to prevent local extinction of an endangered seabird on an oceanic island

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.

Date
15 February 2021
RSPB Authors
Dr Steffen Oppel
Authors
Jones, Christopher W Risi, Michelle M Osborne, Alexis M Ryan, Peter G
Published in
Animal Conservation
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Reduction in seabird mortality in Namibian fisheries following the introduction of bycatch regulation

Many industrial activities impose a threat on biodiversity, and it is unclear to what extent environmental regulations can reduce the threat of such activities. Bycatch in industrial fisheries is one of the greatest sources of mortality for seabirds, but a threat for which effective mitigation exists.

Here we quantify whether the introduction of a new regulation that required the use of bird-scaring lines reduced seabird mortality in two of the most hazardous fisheries in the South Atlantic. The Namibian hake demersal trawl and longline fisheries, estimated to be killing 20,000–30,000 birds/year, have been required to use bird-scaring lines since 2015.

We used data from BirdLife International's Albatross Task Force and the Namibian Fisheries Observer Agency to quantify changes in seabird mortality in these fisheries before and after the introduction of these regulations. Our estimated bycatch rates in the longline fleet were 0.468 birds/1000 hooks (95% confidence interval 0.067–1.450) before regulations and 0.004 birds/1000 hooks (0.001–0.013) following their introduction, a 98.4% reduction. Our estimate suggests that 215 (1–751) seabirds were killed across this fleet in 2018 compared to 22,222 (3187–68,786) in 2009.

In the trawl fleet, observers recorded seabird mortality resulting from interactions with trawl cables. The average rate of heavy interactions was 1.09 interactions/h (0.81–1.39) before the regulation came into effect, and 0.49 interactions/h (0.23–0.84) since then. Extrapolations based on the number of observed fatal interactions suggest 1452 (0–3865) birds were killed by this fleet in 2017 compared to 7030 (0–16,374) in 2009. The lower mortality reduction in the trawl fleet is likely due to incomplete implementation of regulations and highlights the importance of adequate enforcement for effective bycatch mitigation.

Overall, we demonstrate that regulations that mandate that well-tested safeguards are used during industrial operations can have enormous benefits for the conservation of threatened species.

Date
01 January 2021
RSPB Authors
Dr Steffen Oppel
Authors
Da Rocha, Nina Prince, Stephanie Matjila, Samantha Shaanika, Titus M Naomab, Clemens Yates, Oliver Paterson, John RB Shimooshili, Kaspar Frans, Ernest
Published in
Biological Conservation 253
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A framework for mapping the distribution of seabirds by integrating tracking, demography and phenology

1. The identification of geographic areas where the densities of animals are highest across their annual cycles is a crucial step in conservation planning. In marine environments, however, it can be particularly difficult to map the distribution of species, and the methods used are usually biased towards adults, neglecting the distribution of other life-history stages even though they can represent a substantial proportion of the total population.
2. Here we develop a methodological framework for estimating  population level density distributions of seabirds, integrating tracking data across the mainlife-history stages (adult breeders and non-breeders, juveniles and immatures).
We incorporate demographic information (adult and juvenile/immature survival, breeding frequency and success, age at first breeding) and phenological data (average timing of breeding and migration) to weight distribution maps according to the proportion of the population represented by each life-history stage.
3. We demonstrate the utility of this framework by applying it to 22 species of albatrosses and petrels that are of conservation concern due to interactions with fisheries. Because juveniles, immatures and non-breeding adults account for 47%–81% of all individuals of the populations analysed, ignoring the distributions of birds in these stages leads to biased estimates of overlap with threats, and may misdirect management and conservation efforts. Population-level distribution maps using only adult distributions underestimated exposure to longline fishing effort by 18%–42%, compared with overlap scores based on data from all lifehistory stages.
4. Synthesis and applications. Our framework synthesizes and improves on previous approaches to estimate seabird densities at sea, is applicable for data-poor situations, and provides a standard and repeatable method that can be easily updated as new tracking and demographic data become available. We provide scripts in the R language and a Shiny app to facilitate future applications of our approach.
We recommend that where sufficient tracking data are available, this framework be used to assess overlap of seabirds with at-sea threats such as overharvesting, fisheries bycatch, shipping, offshore industry and pollutants. Based on such an analysis, conservation interventions could be directed towards areas where they have the greatest impact on populations.

Date
02 March 2020
RSPB Authors
Dr Steffen Oppel
Authors
Carneiro, Ana PB Pearmain, Elizabeth J Oppel, Steffen Clay, Thomas A Phillips, Richard A Bonnet‐Lebrun, Anne‐Sophie Wanless, Ross M Abraham, Edward Richard, Yvan Rice, Joel
Published in
Journal of Applied Ecology 57 (3) 514-525
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A successful Pacific rat Rattus exulans eradication on tropical Reiono Island (Tetiaroa Atoll, French Polynesia) despite low baiting rates

We successfully eradicated rats from Reiono Island despite reducing the interval between bait applications from the recommended 10-21 days to 7 days, and reducing bait availability from the recommended >4 nights, to 2 nights. We focused on meeting the eradication principle of exposing all rats to poison bait by ensuring complete bait coverage across the island. Relative to current practice our approach saved 3,032 kg of bait and 168 persondays of labour on a 22-ha island, or US$42,626 in bait and accommodation costs. In line with other recent cases,
the Reiono eradication suggests that using moderate baiting rates and short baiting intervals can lead to
significant financial and logistical savings. Yet, baiting strategies should be tailored to the risk environment of
each project.

Date
06 January 2020
RSPB Authors
Dr Steffen Oppel
Authors
Samaniego, Araceli Griffiths, Richard Gronwald, Markus Murphy, Frank Le Rohellec, Moana Oppel, Steffen Meyer, Jean-Yves Russell, James C
Published in
Conservation Evidence 17: 12-14
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Foraging ecology of tropicbirds breeding in two contrasting marine environments in the tropical Atlantic

Studying the feeding ecology of seabirds is important not only to understand basic aspects of their ecology and threats but also for the conservation of marine ecosystems. In this regard, tropical seabirds have been relatively neglected, and in particular the trophic ecology of tropicbirds is scarcely known. We combined GPS tracking, environmental variables...

Date
02 December 2019
RSPB Authors
Dr Steffen Oppel
Authors
Diop, N., Zango, L., Beard, A., Ba, C.T., Ndiaye, P.I., Henry, L., Clingham, E., Oppel, S. & Gonzalez-Solis, J.
Published in
Marine Ecology Progress Series 607: 221-236
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Density of three skink species on a sub-tropical Pacific Island estimated with hierarchical distance sampling

 

Henderson Island, an island in the United Kingdom Overseas Territory of the Pitcairn Islands, is an uninhabited oceanic raised coral atoll with four endemic land birds, nine endemic flowering plants, and at least 18 endemic invertebrate species (Graves 1992; Benton 1995; Benton and Lehtinen 1995; Florence et al. 1995). Despite a wealth of knowledge about most native biodiversity, very little is known about the reptile species that are present on the island. Because previous reptile surveys on Henderson Island...

Date
02 December 2019
RSPB Authors
Dr Steffen Oppel
Authors
Havery, S., Oppel, S., Cole, N. & Duffield, N.
Published in
Herpetological Conservation and Biology 13 (3): 507-516
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Spatial and temporal variability in migration of a soaring raptor across three continents

Disentangling individual- and population-level variation in migratory movements is necessary for understanding migration at the species level. However, very few studies have analyzed these patterns across large portions of species' distributions. We compiled a large telemetry dataset on the globally endangered Egyptian Vulture Neophron percnopterus (94 individuals, 188 completed migratory journeys), tracked across ~70% of the species' global range, to analyze spatial and temporal variability of migratory movements within and among individuals and populations. We found high migratory connectivity at large spatial scales (i.e., different subpopulations showed little overlap in wintering areas), but very diffuse migratory connectivity within subpopulations, with wintering ranges up to 4,000 km apart for birds breeding in the same region and each subpopulation visiting up to 28 countries (44 in total). Additionally, Egyptian Vultures exhibited a high level of variability at the subpopulation level and flexibility at the individual level in basic migration parameters. Subpopulations differed significantly in travel distance and straightness of migratory movements, while differences in migration speed and duration differed as much between seasons and among individuals within subpopulations as between subpopulations. The total distances of the migrations completed by individuals from the Balkans and Caucasus were up to twice as long and less direct than those in Western Europe, and consequently were longer in duration, despite faster migration speeds. These differences appear to be largely attributable to more numerous and wider geographic barriers (water bodies) along the eastern flyway. We also found that adult spring migrations to Western Europe and the Balkans were longer and slower than fall migrations. We encourage further research to assess the underlying mechanisms for these differences and the extent to which environmental change could affect Egyptian Vulture movement ecology and population trends.

Date
10 September 2019
RSPB Authors
Dr Steffen Oppel
Authors
Phipps, W Louis López-López, Pascual Buechley, Evan Oppel, Steffen Álvarez, Ernesto Arkumarev, Volen Bekmansurov, Rinur Berger-Tal, Oded Bermejo, Ana Bounas, Anastasios
Published in
Frontiers in Ecology and Evolution 7: 323
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Important areas and conservation sites for a community of globally threatened marine predators of the Southern Indian Ocean

In the Southern Ocean, the impact of environmental changes and increasing human encroachment is causing declines in several populations of seabirds. Amsterdam island (77 degrees 33'E; 37 degrees 50'S) hosts some emblematic but globally threatened seabird species with alarming population trends. In 2017, concerns about Amsterdam Island's marine biodiversity led to the extension of a marine reserve to the boundaries of the exclusive economic zone (EEZ). Nevertheless, it is unknown whether this protected area is sufficiently large to encompass the most important foraging hotspots of the threatened seabirds, particularly during key stages of their life cycle (e.g. breeding period). We analysed movements of four threatened seabird species using a tracking dataset acquired over several breeding seasons from Amsterdam Island: Amsterdam albatross Diomedea amsterdamensis, sooty albatross Phoebetria fusca, Indian yellow-nosed albatross Thalassarche carted and northern rockhopper penguin Eudyptes moseleyi. Our objectives were threefold: (1) characterise the at-sea distribution of the above-mentioned populations and delineate the marine Important Bird and Biodiversity Areas (mIBAs) triggered by them; (2) assess the potential threat at-sea by quantifying the overlap between seabird distribution and longline fishing efforts; (3) evaluate the coverage of identified mIBAs by marine protected areas and suggest complementary conservation actions. The identified important areas fell within the boundaries of the EEZ, but vastly exceeded the former reserve. Thus, our results reinforce the justification of the recent expansion of the reserve to the boundaries of the EEZ. However, overall seabird distributions extended beyond the EEZ (5 to 50% of the locations) and we found substantial overlap with longline fishing in the high seas. Our results provide a spatio-temporal envelope of where and when bycatch mitigation and observer coverage of longline fisheries should be mandated and enforced.

Date
03 June 2019
RSPB Authors
Dr Steffen Oppel
Authors
Heerah, K. Dias, M. P. Delord, K. Oppel, S. Barbraud, C. Weimerskirch, H. Bost, C. A.
Published in
Biological Conservation
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