Publications for Dr Steffen Oppel

Winter colony attendance by adult Southern Giant Petrels Macronectes giganteus: implications for rodent eradications

Southern Giant Petrels Macronectes giganteus are partial migrants, but the proportion of adult males and females that visit the colony on Gough Island during winter is poorly defined. A better understanding of winter colony attendance is important to predict the possible impact of non-target mortality during restoration efforts involving poison baiting to eradicate introduced mammals. We repeatedly checked the individual identity of all giant petrels attending the largest breeding colony on Gough Island for rings during April-May 2021. Although the maximum number of individually identifiable ringed adults in a single check was 202, overall, 353 ringed adults were recorded, including almost 90% of the individuals that bred in 2020. Males were more likely to be present than females, but the ratio of males to females decreased from the end of April (3.24:1) to the latter half of May (1.25:1). Many birds were paired with their previous breeding partners by the end of May, despite egg laying not starting until late August. Our observations indicate that most adult Southern Giant Petrels are present at their breeding colonies on Gough Island 3-4 months before breeding, and are thus potentially susceptible to non-target poisoning during mammal eradication operations.

Date
10 February 2022
RSPB Authors
Dr Steffen Oppel
Authors
Ryan, Peter G Oppel, Steffen
Published in
Marine Ornithology
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Better utilisation and transparency of bird data collected by powerline companies

There is in an ongoing expansion of powerlines as a result of an increasing global demand for energy. Powerlines have the potential to negatively impact wild bird populations through collisions and/or electrocution, and reducing bird powerline collision and electrocution risk is a priority for companies running high-voltage powerlines (known as Transmission System Operators (TSOs)). Most TSOs are legally required to assess any potentially significant impacts via Enivronmental Impact Assessments, and so potentially collect a significant amount of data on the presence of species, species behaviour, and observed mortality rates. The value of such data, if available, for reducing and preventing bird casualties could be enhanced by increasing availability across TSOs and other decision-makers. We review the extent to which the sharing of data is happening across Europe, and how the quality, scope and availability of bird data collected by European TSOs could be improved, through use of a questionnaire and workshop with TSOs, conservationists and academics. Sixteen European TSOs responded to the questionnaire and 30 stakeholders attended the workshop. There was wide recognition of the value of different types of data on birds at powerlines, and a positive attitude to working together to share and enhance data across stakeholders to achieve the shared goal of reducing bird mortalities. Key barriers to the sharing of data included a lack of a centralised database, the lack of standardised methods to collect bird data and concerns over the confidentiality of data and reports. In order to overcome these barriers and develop a collaborative approach to data sharing, and ultimately inform best practice to reduce significant negative impacts on bird populations, we suggest a stepwise approach that (1) develops guidance around the field methods and data to be collected for mitigation effectiveness and (2) shares meta-data/bibliography of studies of powerline impacts/mitigation effectiveness for birds. In time, a more structured approach to the sharing of data and information could be developed, to make data findable, accessible, interoperable and reusable.

Date
15 January 2022
RSPB Authors
Dr Steffen Oppel
Authors
Kettel, Esther F Thaxter, Chris Oppel, Steffen Carryer, Andrew Innis, Liam Pearce-Higgins, James W
Published in
Journal of environmental management
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track2KBA: An R package for identifying important sites for biodiversity from tracking data

Identifying important sites for biodiversity is vital for conservation and management. However, there is a lack of accessible, easily-applied tools that enable practitioners to delineate important sites for highly mobile species using established criteria. We introduce the R package ‘track2KBA’, a tool to identify important sites at the population level using tracking data from individual animals based on three key steps: (1) identifying individual core areas, (2) assessing population-level representativeness of the sample, and (3) quantifying spatial overlap among individuals and scaling up to the population. We describe package functionality and exemplify its application using tracking data from three taxa in contrasting environments: a seal, a marine turtle, and a migratory land bird. This tool facilitates the delineation of sites of ecological relevance for diverse taxa and provides output useful for assessing their importance to a population or species, as in the Key Biodiversity Area (KBA) Standard. As such, ‘track2KBA’ can contribute directly to conservation planning at global and regional levels.

Date
07 September 2021
RSPB Authors
Dr Steffen Oppel
Authors
Beal, Martin Oppel, Steffen Handley, Jonathan Pearmain, Elizabeth J Morera‐Pujol, Virginia Carneiro, Ana PB Davies, Tammy E Phillips, Richard A Taylor, Philip R Miller, Mark GR
Published in
Methods in Ecology and Evolution
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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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Direct evidence of a prey depletion “halo” surrounding a pelagic predator colony

Colonially breeding birds and mammals form some of the largest gatherings of apex predators in the natural world and have provided model systems for studying mechanisms of population regulation in animals. According to one influential hypothesis, intense competition for food among large numbers of spatially constrained foragers should result in a zone of prey depletion surrounding such colonies, ultimately limiting their size. However, while indirect and theoretical support for this phenomenon, known as “Ashmole’s halo,” has steadily accumulated, direct evidence remains exceptionally scarce. Using a combination of vessel-based surveys and Global Positioning System tracking, we show that pelagic seabirds breeding at the tropical island that first inspired Ashmole’s hypothesis do indeed deplete their primary prey species (flying fish; Exocoetidae spp.) over a considerable area, with reduced prey density detectable >150 km from the colony. The observed prey gradient was mirrored by an opposing trend in seabird foraging effort, could not be explained by confounding environmental variability, and can be approximated using a mechanistic consumption–dispersion model, incorporating realistic rates of seabird predation and random prey dispersal. Our results provide a rare view of the resource footprint of a pelagic seabird colony and reveal how aggregations of these central-place foraging, marine top predators profoundly influence the oceans that surround them.

Date
06 July 2021
RSPB Authors
Dr Mark Bolton, Dr Steffen Oppel
Authors
Weber, Sam B Richardson, Andrew J Brown, Judith Bolton, Mark Clark, Bethany L Godley, Brendan J Leat, Eliza Oppel, Steffen Shearer, Laura Soetaert, Karline ER
Published in
Proceedings of the National Academy of Sciences
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Buoys with looming eyes deter seaducks and could potentially reduce seabird bycatch in gillnets

Bycatch of seabirds in gillnet fisheries is a global conservation issue with an estimated 400 000 seabirds killed each year. To date, no underwater deterrents trialled have consistently reduced seabird bycatch across operational fisheries. Using a combination of insights from land-based strategies, seabirds' diving behaviours and their cognitive abilities, we developed a floating device exploring the effect of large eyespots and looming movement to prevent vulnerable seabirds from diving into gillnets. Here, we tested whether this novel above-water device called ‘Looming eyes buoy' (LEB) would consistently deter vulnerable seaducks from a focal area. We counted the number of birds present in areas with and without LEBs in a controlled experimental setting. We show that long-tailed duck Clangula hyemalis abundance declined by approximately 20–30% within a 50 m radius of the LEB and that the presence of LEBs was the most important variable explaining this decline. We found no evidence for a memory effect on long-tailed ducks but found some habituation to the LEB within the time frame of the project (62 days). While further research is needed, our preliminary trials indicate that above-water visual devices could potentially contribute to reduce seabird bycatch if appropriately deployed in coordination with other management measures.

Date
05 May 2021
RSPB Authors
Ian Cleasby, Dr Ellie Owen, Dr Steffen Oppel
Authors
Rouxel, Yann Crawford, Rory Cleasby, Ian R Kibel, Pete Owen, Ellie Volke, Veljo Schnell, Alexandra K Oppel, Steffen
Published in
Royal Society open science
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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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