Plastics threat to seabirds
A BirdLife-led research team has assessed the movements of 7,137 birds of 77 tubenose species, comparing the birds’ distributions with maps of plastic prevalence in the world’s oceans (https://bit.ly/3KyPOMf). The species looked at in the study included shearwaters, fulmars, prions and Pterodoma petrels. The team found that a number of threatened species faced a high risk of exposure to plastic.
The data have revealed that areas of the Mediterranean and Black Sea pose a particularly high risk to seabirds, together accounting for more than half of plastic exposure risk. Other high-risk areas include remote areas of the high seas and waters surrounding the USA, Japan and Britain.
Bethany Clark, Seabird Science Officer at BirdLife International and lead author of the study, said: ‘Plastics are a widespread threat to marine life, but pollution is not spread evenly around the world’s oceans. Our study shows that petrels are exposed to plastics in enclosed, busy seas, such as the Mediterranean, and remote mid-ocean gyres that concentrate plastics from distant sources. However, even species with low exposure risk have been found to eat plastic. This shows that plastic levels in the ocean are a problem for seabirds worldwide, even outside these high exposure areas.’
For almost all species tracked, the highest likelihood of exposure to plastics largely occurs outside the national waters of the countries in which they breed, while a quarter of all plastic exposure risk comes from international waters. Tubenoses are particularly vulnerable to plastics as they can’t easily regurgitate plastic and have been recorded feeding plastic to chicks during the breeding season.
The researchers also gave each study species an ‘exposure risk score’ to indicate their likelihood of encountering plastics whilst at sea. Species found to be particularly at risk include the critically endangered Balearic Shearwater Puffinus mauretanicus and Newell’s Shearwater P. newelli, and the endangered Hawaiian Petrel Pterodroma sandwichensis. Given that these birds already face an array of human pressures, their high risk of exposure to plastics is of great conservation concern.
Cuckoos unable to shift their annual migration
New research from the BTO has revealed why Common Cuckoos Cuculus canorus are unable to shift the timings of their annual migration in response to a changing climate (https://bit.ly/44VGNoa). The research has shown that Cuckoos must wait for the arrival of the spring rains in West Africa, the timing of which has remained constant, before they can cross the Sahara.
This constant timing of rains in Africa juxtaposed with the shift towards an earlier spring in Europe has resulted in the Cuckoos’ arrival on their breeding grounds being out of sync with the peak availability of prey and the breeding cycle of many of their host species.
The BTO used data from the long-running BTO Cuckoo tracking project (www.bto.org/cuckoos) to investigate why Cuckoos are unable to bring forward their arrival in Europe in response to climate change on their breeding grounds. This lack of response has been linked to severe population declines in some migratory species. For Cuckoos, the results suggest that they may be exposed to a greater risk of death as they are forced to travel in unfavourable conditions to make it to their breeding grounds on time. This increased mortality could be one mechanism through which populations are impacted.
Providing better-quality habitat at strategic locations along Cuckoo migration routes is one way in which the species could be helped to complete its migration in a more timely and less energetically costly way.
Chris Hewson, BTO Cuckoo tracking Project lead scientist, said: ‘Understanding why these [Cuckoos] are not arriving back earlier – and the possible costs that individual Cuckoos pay for trying to do so – will help us to best direct efforts of flyway restoration that may allow them to make their migrations in a more timely and successful fashion.’
Capercaillie lek count report 2023
Counts of male Capercaillies Tetrao urogallus attending lek sites, undertaken by licensed surveyors, have been used as a tool to consistently monitor numbers in Scotland since 2002. The surveys are coordinated by the Capercaillie Advisory Officer and funded by the Cairngorms Capercaillie Project, NatureScot and the RSPB.
The 2023 counts detected an increase in lekking males, from 149 in 2022 from 168 (https://cairngormscapercaillie.scot/capercaillie-lek-count-report-2023). This increase was seen mainly in the Strathspey and Easter Ross populations, while numbers in Deeside remained the same as in 2022 and numbers in Perthshire and Moray & Nairn were both one down on last year. There was also an increase in the number of leks occupied, with six more compared to 2022. Again, the increase came from Strathspey and Easter Ross.
The 2023 survey represents the first year since 2015 that there has been an increase in the total number of lekking males recorded in Scotland. The 2021/2022 survey estimated there to be just 542 Capercaillies in Scotland, the lowest number since the start of the survey. Strathspey remains the stronghold for Capercaillies in Scotland, while the periphery populations remain in a perilous position.
‘Divorce’ rates in birds
Socially monogamous birds may occasionally ‘divorce’ – but the driving factors of these separations have so far remained contentious. A new study recently published in Proceedings of the Royal Society B set out to investigate the broad-scale drivers and the influence of sexual roles in avian divorce (https://bit.ly/3pYvzAp).
The study looked at data from 186 species of bird across 61 families, allowing correlations between divorce rate and a group of factors including promiscuity of both sexes, migration distance and adult mortality to be tested. The results showed that only male – and not female – promiscuity had a positive relationship with separation rates, in that partnerships were more likely to split up if the male had more than one female partner. In addition, migration distance was also positively correlated with divorce rate, where birds that migrated further experienced higher instances of pair separation, perhaps owing to longer migrations leading to a higher chance of ‘accidental loss’ of a partner. However, adult mortality rate showed no direct relationship with divorce rate.
The findings from the paper indicate that divorce in monogamous birds might not be a simple adaptive (by sexual selection) or non-adaptive (by accidental loss of a partner) strategy in birds but rather could be a mixed response to sexual conflict and stress from the ambient environment.
British Golden Pheasant population no longer self-sustaining
A new study has concluded that the British population of Golden Pheasants Chrysolophus pictus is now functionally extinct, with no evidence to suggest that the species persists as a self-sustaining population (https://bit.ly/3Y3f9TK).
Large populations of Golden Pheasants established in Britain during the nineteenth century, derived from birds deliberately released into the wild. However, despite apparently initially thriving, populations of Golden Pheasants in Britain have now declined to the point where there are no viable wild populations remaining. Illegal releases continue, meaning that some birds – mostly males – are still seen at some sites, but the continued ‘wild’ status of the species in Britain is dubious.
The paper concludes there are between 37 and 40 wild Golden Pheasants left in Britain, all located within two regions. This represents a significant decline, with the population estimated at between 1,000 and 2,000 individuals in 1993. Both of the remaining populations are dependent on human management via food provision, predator control and supplementary releases; consequently, the species can no longer be considered to be truly naturalised.
The authors suggest that the species should be moved from Category C1 of the British List to Category C6 – a formerly naturalised species which is now either extinct or no longer self-sustaining.
Black-winged Stilt chicks hatch in Lincolnshire
A pair of Black-winged Stilts Himantopus himantopus has successfully bred at RSPB Frampton Marsh, Lincolnshire, hatching four chicks. It is the first time the species has nested in the county.
The Frampton Marsh breeding attempt comes amid an exceptional spring for Black-winged Stilts in Britain, with no fewer than 50 different sites recording the species during May.
Avocet chicks hatch in Devon for the first time
In another long-legged breeding success, a pair of Avocets Recurvirostra avosetta hatched two chicks at Seaton Wetlands, Devon, in June – the first time the species has successfully bred in the county.
Bronze Age pin made from Golden Eagle bone discovered in Oxfordshire
A pin made from the phalanx (toe bone) of a Golden Eagle Aquila chrysaetos has been discovered by archaeologists during work to build a park and ride in Oxfordshire (https://bit.ly/3rObL2Y).
Cotswold Archaeology found an Iron Age settlement and the Early Bronze Age cremation burial of a young child at the A40 excavation site in Eynsham, and the worked eagle bone was one of the artefacts uncovered. This is currently the only example found in a funerary context in England. One other similar example has been identified in Scotland, also associated with the burial of a child.
Jo Barker, Post-Excavation Manager for the project, said: ‘The choice of eagle bone is likely to have been significant and it is possible such an object could have been considered talismanic, or was linked perhaps with afterlife beliefs, raising further questions about its use as a pyre good for a child.’
Urban Great Tits less stressed than those in woodland
New research by scientists at Lund University, Sweden, has found that urban Great Tits Parus major have lower levels of stress hormones than those found in woodland habitats (https://bit.ly/3O3wIhX).
Anders Brodin, biologist at Lund University and lead author of the paper published in Conservation Physiology, said: ‘The Great Tit’s high cognitive capacity means it is highly adaptable, and urban Great Tits seem to have adapted so well to the new environment that they are not stressed by high population density. Another possible explanation is that it was the most intelligent and most flexible individuals who succeeded in colonising urban environments in the first place.’
The most common stress hormone in birds is corticosterone, and the researchers took samples of the birds’ tail feathers as a non-intrusive way of measuring hormone levels.
BTO 90th Anniversary
Members and supporters of the BTO came together with BTO staff recently to celebrate 90 years of working in partnership for birds, science and people. The BB eye in the January issue recorded the more recent history of those 90 years (Brit. Birds 116: 2–7).
The event brought together all generations of birdwatchers, from long-standing BTO member Rose Newsom, who also celebrated her 90th birthday this year and helped to cut the BTO’s anniversary cake, to members of the BTO Youth Advisory Panel, who spoke about their work to engage more young people with birds and conservation (https://bit.ly/3KafMFs).
Staff from the organisation presented updates on its vital conservation work. A talk on the history of ringing was led by BTO’s Mark Grantham, and visitors were able to see a ringing demonstration in progress during the event, alongside moth-trapping and various guided walks around the Nunnery Lakes Reserve. Guests were also invited to explore the Chris Mead Library and BTO archives, which hold material from many notable ornithological figures, from pioneering photographer Emma Louise Turner to George Bristow, accused fraudster of the Hastings Rarities affair.
Malta publishes its first bird report
BirdLife Malta, in association with the Malta Rarities and Records Committee, has published the first national bird report, covering all species recorded in 2021 – from common breeders to rare vagrants.
Cambridgeshire’s largest traditional orchard under threat
Coton Orchard, the largest traditional orchard in Cambridgeshire, located just two miles from Cambridge city centre, is under threat from the Greater Cambridge Partnership (GCP). It lies along the proposed route for a Cambourne to Cambridge Busway (C2C). Traditional orchards are UKBAP priority habitats but in addition three hedgerows within the orchard, which are habitats of principal importance, will also be largely destroyed.
Traditional, pesticide-free orchards – such as Coton Orchard – are important habitats for a large number of Birds of Conservation Concern-listed species.
Surveys commissioned by the GCP identified 14 species of nationally scarce invertebrates in Coton Orchard; eight of these species were found in the veteran apple trees (more than 100 years old), and these trees are likely to be removed during development of the proposed busway.
Bird surveys were untaken in the orchard on behalf of the GCP in winter, but no breeding-season surveys were undertaken on the rather questionable basis that ’the majority of the habitats would be retained’. Local birdwatchers have recorded a number of Amber- and Red-listed species breeding at the site, including Turtle Dove Streptopelia turtur, Lesser Spotted Woodpecker Dryobates minor and Spotted Flycatcher Muscicapa striata.
The fragments of the orchard remaining after the busway and its adjacent access road are constructed are unlikely to support this diversity of species, and mitigation in the form of new plantings cannot replace 100-year-old orchard trees. A petition has been set up to save the orchard – https://www.change.org/p/save-the-green-corridor-cambourne-to-cambridge-bus-lane-not-busway
