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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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Upwelling systems in the migration ecology of Roseate Terns (Sterna dougallii) breeding in northwest Europe

For migratory seabirds, staging and wintering areas may be important targets for conservation. Declines of Roseate Tern Sterna dougallii populations have led to conservation initiatives at breeding sites on both sides of the North Atlantic. However, these could be compromised by environmental conditions in non-breeding areas. The migratory ecology of Roseate Terns is poorly known and we used light-level biologgers (geolocators) to identify the migratory routes, staging and wintering areas of Roseate Terns from two European colonies. Most birds wintered off the Ghanaian coast in the Gulf of Guinea, but some wintered further west off Sierra Leone and Liberia, or changed locations during the winter. In these areas, cold-water upwellings of the Guinea Current Large Marine Ecosystem (GCLME) may provide vital foraging resources. Geolocations in combination with temperature measurements and satellite sea-surface temperature data show that cold-water upwellings of the Canary Current Large Marine Ecosystem (CCLME) were important areas for migratory staging, particularly on the return migration which was slower than the outward journey. These results emphasize the importance of productive cold-water upwellings in the migratory ecology of Roseate Terns. The GCLME and CCLME are under threat from over-exploitation, pollution and climate change; effective conservation of these environments will be important to secure the long-term future of these and other seabirds.

Date
01 April 2021
RSPB Authors
Dr Mark Bolton
Authors
Redfern, Chris PF Kinchin‐Smith, David Newton, Stephen Morrison, Paul Bolton, Mark Piec, Daniel
Published in
Ibis 163 (2): 549-565
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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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Effect of GPS tagging on behaviour and marine distribution of breeding Arctic Terns Sterna paradisaea

Tracking tags have been used to map the distributions of a wide variety of avian species, but few studies have examined whether the use of these devices has impacts on the study animals that may bias the spatial data obtained. As Global Positioning System (GPS) tags small enough for deployment on terns (family: Laridae) have only recently become available, until now tracking of this group has been conducted by following unmanipulated individuals by boat, which offers a means of comparing distributions obtained from GPS-tracking. We compared the utilization distributions (UDs) of breeding Arctic Terns Sterna paradisaea obtained by GPS-tracking 10 individuals over 2 weeks, with UDs derived from contemporaneous visual boat tracks from 81 individuals. The 50% and 95% UDs of both methods had high similarity scores, indicating good agreement in the density distributions derived from the two methods. The footprints of the UDs of tagged birds were ~ 75–80% larger, which may reflect an effect of tagging on foraging range or the occasional inability to follow by boat individuals which roamed further from the colony. We also compared the nest attendance and chick provisioning rates of adults that were (1) fitted with a GPS tag and leg-flag, (2) handled and marked with a leg-flag but not tagged and (3) fitted with a leg-flag in a previous year but unhandled in the year of the study. There was some evidence that birds fitted with both a GPS tag and leg-flag spent slightly less time at the nest compared with unhandled birds and those fitted with a leg-flag only. Both treatments where birds were fitted with a leg-flag in the year of the study had similarly lower provisioning rates to those of unhandled control birds > 48 h after handling, suggesting that negative effects on provisioning are due to capture and handling or leg-flag attachment rather than to GPS tag attachment/loading per se. Overall brood-provisioning rate was compensated for by the increased effort by the unhandled partner. Our study suggests that despite slight effects of GPS-tagging on behaviour, the estimates of marine density distribution obtained were very similar to those of unmanipulated birds.

Date
01 January 2021
RSPB Authors
Stephen Dodd, Dr Ian Johnstone, Dr Mark Bolton
Authors
Seward, Adam Taylor, Rachel C Perrow, Martin R Berridge, Richard J Bowgen, Katharine M
Published in
Ibis 163 (1): 197-212
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Restoration of afforested peatland: immediate effects on aquatic carbon loss

•We investigated short-term aquatic carbon losses following bog restoration.

•There were no significant changes in aquatic carbon concentrations or exports.

•Seasonally increased DOC concentrations may be associated with restoration.

•Restoring small catchment portions (e.g., ≤12%), should minimise aquatic carbon losses.

Date
10 November 2020
RSPB Authors
Dr Mark Hancock
Authors
Gaffney, Paul PJ; Taggart, Mark A; Andersen, Roxane
Published in
Science of The Total Environment 742
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An investigation of the effects of GPS tagging on the behaviour of black-legged kittiwakes Rissa tridactyla

The deployment of animal-borne tracking devices has revolutionised the study of animal behaviour, providing the opportunity to understand aspects of animal movement, physiology and ecology that were previously difficult to study. Such advances have been particularly important in the study of seabirds where the introduction of GPS tagging has allowed researchers to track the movement and behaviour of individuals while they are at sea. However, it is widely recognized that the negative effects associated with tag instrumentation on animal behaviour cannot be completely avoided and needed to be considered when using tracking data. For example, tagging an individual may lead to changes in its behaviour causing it to act atypically, which casts doubt upon any biological interpretation that arises from such data. In order to design studies in which the effect of tagging on behaviour is minimized researchers have typically sought to use the lightest tags available. Researchers have often used one of two commonly encountered rules-of-thumb that 1) a tag should not exceed 5% of the body mass of the tagged animal; or 2) a tag should not exceed 3% of the body mass of the tagged animal. However, there is little evidence supporting these general rules and it has been recommended that tagging studies provide some empirical examination of the potential effects of tagging when possible.

Here, we investigate the effect of GPS-tagging on the behaviour of black-legged kittiwakes, Rissa tridactyla, that were tagged during the breeding season across multiple UK colonies in the North Sea as part of the RSPB FAME / STAR tracking project.

Date
12 October 2020
RSPB Authors
Dr Aly McCluskie, Dr Ellie Owen, Saskia Wischnewski, Linda Wilson, Dr Lucy Wright, Dr Mark Bolton
Published in
RSPB Technical Report
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The impacts of non-native gamebird release in the UK: an updated evidence review

Recreational shooting of non-native gamebirds (pheasants and red-legged partridges) in the UK is
underpinned by a suite of management practices. A major aspect is the annual large-scale release
of birds to be shot, which is steadily increasing with an estimated 57 million birds released in 2016;
this scale of non-native gamebird release exceeds any similar activity in Europe or North America.

Approximately one third of released birds are shot, while the majority of the remaining birds die
from other causes during the year of release or survive in very low numbers to join the population
of pheasants and partridges now residing in the wild in the UK.

The number of gamebirds released has increased since the 1990s, while the number shot has
remained relatively stable, and this reduction in releasing-efficiency is potentially driven by a
reduction in gamebird survival and an increase in late winter shooting, meaning that more birds
must be released during autumn to ensure enough survive to be shot in January.
There is concern that this large and increasing release of gamebirds and associated shooting practices may be having negative impacts on the UK’s native wildlife. However, there may also be positive ecological, economic and social impacts of gamebird release activities.

Date
12 October 2020
RSPB Authors
Lucy Mason, Dr Jen Smart, Dr Will Peach
Authors
Lucy R. Mason, Jake E. Bicknell, Jennifer Smart, Will J. Peach
Published in
RSPB Research Report No. 66
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From a research study to a conservation partnership: Developing approaches to restoring common scoter populations

1.     Like many sea-duck populations, the British breeding population of common scoters Melanitta nigra has declined markedly. In 2009, a study was established to measure factors affecting lake use by breeding scoters, to inform conservation measures. That study, published in Aquatic Conservation: Marine and Freshwater Ecosystems (AQC) in 2016, showed that lakes used by scoters had relatively more shallow water and large invertebrates. Furthermore, lakes with abundant large invertebrates had relatively few brown trout Salmo trutta. These results probably reflect the importance of foraging habitat (shallow water), prey abundance (large invertebrates), and competition for prey (trout abundance) in influencing scoter lake use.

2.     To develop this study, additional research, and scoter conservation measures, we formed a long-term partnership, comprising nature conservation non-governmental organizations, statutory agencies, fisheries managers and the regional hydropower company. The partnership meets regularly to coordinate and review research and develop conservation measures, building on the earlier lake-use study.

3.     At key scoter lakes managed for hydropower, the partnership negotiated a revised water level management regime, favouring shallow water availability in the breeding season. This regime was informed by additional research, showing the value of certain islands for nesting scoters, and water level requirements to maintain these as islands.

4.     In a different key scoter area — an extensive near-natural peatland where recreational angling takes place — the partnership established a trial of increased brown trout angling, with increased fish removal, to determine whether this would increase invertebrate prey abundance and benefit breeding scoters. Both conservation interventions are currently being evaluated by detailed monitoring.

5.     Overall, the earlier study published in AQC, was important in strengthening and informing our researcher–practitioner partnership, as we collaborated within an adaptive management framework to reverse scoter declines. Long-term interdisciplinary partnerships are likely to have an important role to play in general, for the successful conservation of aquatic biodiversity.

Date
18 September 2020
RSPB Authors
Dr Mark Hancock, Trevor Smith
Authors
Robson, Hannah J; Stephen, Alastair; Byrne, Paul; MacLennan, Alison; Klein, Daniela; Mitchell, Carl; Griffin, Larry R; Hilton, Geoff
Published in
Aquatic Conservation: Marine and Freshwater Ecosystems 30 (9): 1770-1774
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