Adult Black-headed Gull Feathers Contained More Mercury Than Juvenile Feathers
Feathers from adult black-headed gulls (Chroicocephalus ridibundus) wintering at Dianchi Lake in southwest China contained significantly more mercury than feathers from juveniles. The study, first available online on 30 January 2026, combined mercury concentrations with carbon, nitrogen and mercury isotope analyses to examine both age-related exposure and the geographical origins of that exposure.
Researchers analysed chest feathers from 70 adults and 28 juveniles. Mean total mercury was 4.4 mg/kg in adults and 3.3 mg/kg in juveniles. Mean methylmercury was also higher in adults, at 3.3 mg/kg compared with 2.3 mg/kg in juveniles.
More adult feather samples exceeded the study’s toxicological threshold
Using a literature-based feather-mercury threshold of 5.0 mg/kg, samples from 25 of 70 adults—35.7%—were above the level, compared with samples from three of 28 juveniles, or 10.7%. Crossing that threshold indicates potential toxicological concern; it does not show that every bird above it suffered clinical poisoning or a particular effect on survival or reproduction, which the study did not measure.
The authors discuss several mechanisms that may contribute to the age difference. Adults have had longer to encounter contaminated food webs and may differ from juveniles in migration history, habitat use and feeding ecology. Mercury incorporated into a growing feather is then retained after the feather becomes biologically inert, preserving a record of exposure during feather formation.
Adults fed at higher trophic levels
Stable carbon and nitrogen isotopes showed age-related differences in feeding ecology. Adult feathers indicated feeding at higher trophic levels and a wider range of dietary sources than juvenile feathers. This provides a plausible pathway to higher methylmercury exposure because methylmercury biomagnifies through food webs.
The isotope results do not identify individual prey species, and the authors do not attribute the adult–juvenile difference to a single cause. Longer cumulative exposure, differences in diet and differences in where the age groups spend time may all contribute.
Feathers integrated mercury from several parts of the migration route
Mercury isotope signatures indicated that the feather record was consistent with exposure integrated from inland breeding areas and major migration stopover sites. The mercury measured in birds sampled at Dianchi Lake should therefore not be interpreted as contamination acquired solely at the wintering lake.
This geographical signal is central to the study: feathers from migratory black-headed gulls can preserve mercury signatures accumulated across separated ecosystems during the annual cycle. The isotope data identify mixtures of source regions rather than one exact polluted locality, but they show that exposure recorded at a wintering site can reflect conditions far beyond that site.
Threats
Related news
Four African Wild Dog Dispersals Totalled 9,863 km but Produced Little Genetic or Demographic Connectivity
GPS-tracked African wild dogs from Zambia crossed protected and human-dominated landscapes, including one journey of more than 2,300…
Read story →
Western Finland’s Short-eared Owl Breeding Population Fell More Than 50% as Grassy Habitat Shrunk 46%
Over 47 years in western Finland, the local Short-eared Owl breeding population fell by more than 50% while…
Read story →
Common Tern Eggs Had More PCBs, HCB and Mercury Than Oystercatcher Eggs in 40-Year Wadden Sea Study
Monitoring from 1981–2023 found higher PCB, HCB and mercury levels in common tern eggs than in Eurasian oystercatcher…
Read story →SPECIES IN THIS STORY
Species in this story
Independent research and conservation news archive
Did you find this information useful?
Wildlife Vagabond is independently built and maintained. Voluntary support helps cover source verification, hosting and continued work on research and conservation news.
Support Wildlife VagabondThe news archive will remain freely available.