BY NICK PEARCE
The photograph of a wing-tagged Marsh Harrier (below) grounded at Brighton Marina has renewed scrutiny of marking practices used on protected raptors. The bird bears yellow tags coded SN and MS—markers consistent with the North West Norfolk Ringing Group’s long-running wing tagging project, which has tagged over 1,000 Marsh Harriers since 2011. The practice is licensed and promoted as a conservation research tool, but the scientific literature on tagging impacts presents a more complex picture than project proponents typically acknowledge.
The North West Norfolk Ringing Group reports a recovery or resighting rate of 41.64% for wing-tagged Marsh Harriers, compared to a metal-ring-only recovery rate so low that between 1990 and 2010, only 7 of 213 ringed nestlings were ever recovered—all dead. The project has generated novel distribution data, including confirmed sightings of British-ringed Marsh Harriers in Senegal, the Canary Isles, Belgium, Portugal, Germany, the Netherlands, Spain and Norway. Project coordinators describe the tagging procedure as analogous to ear-piercing, with tags applied to nestlings before fledging.
The broader literature on avian marking does not support the position that tagging is uniformly benign. A meta-analysis published in Methods in Ecology and Evolution found negative associations between tagging and both survival and reproduction, with effects more pronounced in species using flapping flight. The authors noted that most tagging studies fail to report essential information necessary to assess impacts, and that only about one-third of studies provide the complete data needed to evaluate device effects.
How would you like to walk around with a massive tag digging into you? Maybe you should be, savages.
A separate review by the British Trust for Ornithology, examining over 3,400 publications, found that the proportion of studies reporting effects of tracking devices on birds has declined, while the proportion providing no information on effects has increased. The review identified that invasive attachment methods are associated with a high incidence of effects, and that adverse effects were more likely with heavier devices relative to a bird’s mass. Notably, 55% of studies contained no information on potential effects, and documentation in many others was inadequate.
Research on raptors specifically has documented attachment-related harm. A study on Black Kites found that harness attachments—used for longer deployment—can cause injuries, with severe injuries occasionally documented in congeneric species. The authors emphasised that fewer than 10% of studies based on marking devices incorporate any assessment of their potential impact on subjects, a frequency that has not increased over time. They further noted that maximum admissible mass-loads for birds vary from 1% to 5% with no clear agreement, leaving researchers lax about thresholds.
A specific concern for harriers is the potential for wing tags to attract predators. Research has questioned whether patagial wing tags, which are conspicuous to humans, may also attract the attention of potential predators for harriers (Circus spp.). This represents a welfare consideration distinct from the energetic or survival costs documented in other tagging studies.
Tagging of Marsh Harriers in the UK operates under licence from bodies including NatureScot and the BTO, with training delivered through a buddy system rather than formal accreditation such as LANTRA courses. The Scottish Gamekeepers Association has petitioned the Scottish Parliament on this issue and has raised concerns about the lack of independent monitoring and transparency in raptor tagging projects. Similar photographic evidence has been submitted to MSPs questioning the actions of ringers and taggers operating under licence and the welfare implications for birds at nest sites.
The scientific record does not support an unequivocal position that wing tagging is without consequence for the birds involved. Meta-analyses show measurable negative associations with survival and reproduction, reporting of effects has declined even as tagging has expanded, and species-specific risks—including potential predator attraction for harriers—remain insufficiently studied. The high resighting rate achieved by the Marsh Harrier project demonstrates the utility of individual marking for distribution research, but utility is not the same as harmlessness. Until tagging programmes routinely publish comprehensive welfare assessments alongside their distributional findings, claims that these practices are without cost to the birds remain assertions rather than evidence-based conclusions; a bit like the propaganda on Raptor Persecution; as factual or scientific as a Chris Packham or Mr Tumble.