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Higher PFOS Was Linked to Lower Egg Temperatures in Finnish Common Eiders

Female common eider incubating on a nest
Research: Behaviour, Physiology

PFAS are highly persistent synthetic chemicals that can contaminate aquatic food webs and may affect wildlife reproduction through hormonal and behavioural pathways. PFOS is one of the best-known compounds in this group. In a Finnish study, higher PFOS concentrations were linked to lower average egg temperatures in incubating common eiders (Somateria mollissima). The same clear relationship was not detected in common goldeneyes (Bucephala clangula), suggesting that PFAS-related incubation patterns may differ between the two species.

Researchers studied 18 female common goldeneyes and 37 female common eiders during the 2022 and 2023 breeding seasons. Blood plasma was analysed for PFAS and the thyroid hormones triiodothyronine (T3) and thyroxine (T4), which are involved in metabolism and thermoregulation. Artificial eggs containing data loggers recorded egg temperature and how often females turned their eggs.

The two species incubate under very different energetic conditions

The two ducks have contrasting breeding strategies. Goldeneyes are cavity-nesting income breeders that continue feeding during incubation, whereas eiders nest on the ground and rely much more heavily on stored body reserves while incubating. Goldeneye females maintained higher average egg temperatures than eider females in the study.

Higher PFOS was linked to cooler eggs in eiders

Among eiders, higher PFOS was clearly associated with lower average egg temperature. The equivalent relationship was not clearly detected in goldeneyes. The study could not determine whether the eider pattern reflected changes in nest-attendance behaviour, changes in the female’s own thermoregulation, or a combination of processes.

Goldeneyes showed a different possible PFAS-related pattern. Exploratory follow-up analyses suggested that females with higher total PFAS and PFOS concentrations turned their eggs more often. Because these were exploratory follow-up analyses prompted by weaker species differences, the authors treat them as suggestive rather than as a primary confirmed result.

Thyroid hormones did not explain the incubation patterns

PFAS concentrations were not clearly associated with T3 or T4 in either species, and thyroid hormone levels were not clearly related to the measured incubation behaviour. PFAS concentrations were also not clearly related to hatching success. The study therefore found species-specific links between PFAS and aspects of incubation, but no evidence in this dataset that thyroid hormones explained those patterns or that the measured PFAS levels reduced hatching success.

Sources and image credit

  1. Vakili, F. S., Shaffer, S. A., Jaspers, V. L. B., et al. (2026). Nest attendance in two Finnish waterfowl species in relation to per- and polyfluoroalkyl substances and thyroid hormones. Environmental Research, 303, 124643.Primary open-access article. The final article states 'Available online 5 May 2026'; the journal issue is dated 15 August 2026. The study examined 18 female common goldeneyes and 37 female common eiders in Finland.

Image: Female common eider (Somateria mollissima) incubating on Kigigak Island, Yukon Delta National Wildlife Refuge, Alaska, USA, 20 June 2012. Photo: Casey Setash / U.S. Fish and Wildlife Service / Wikimedia Commons. Public domain. Representative incubation image; not a bird from the Finnish study. · Public domain · Source

About this content: This story was produced with AI assistance within an editorial workflow developed by Wildlife Vagabond. Editorial responsibility remains with Wildlife Vagabond.How AI is used

Behaviour

SPECIES IN THIS STORY

Species in this story

Common Goldeneye Bucephala clangula Explore species Common Eider Somateria mollissima Explore species

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