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Reproductive Indices Fell in Green-winged Teal and Eurasian Wigeon in Long-Term UK Wing Records

Male and female Eurasian teal together at RSPB Titchwell, Norfolk
Conservation · Population & status

A long-term UK wing survey found marked demographic changes in harvested green-winged teal (Anas crecca) and Eurasian wigeon (Mareca penelope). Hunters submitted wings that allowed researchers to determine age and sex, providing a demographic sample from the harvested birds between the 1987/88 and 2024/25 hunting seasons.

The study period spans 37 years, but the series was not continuous: no wings were collected from 2002/03 through 2016/17. The authors use the harvested sample as a proxy for demographic changes in the wider populations, rather than treating the wing records as direct counts of breeding success or total population size.

The reproductive index fell in both species

For green-winged teal, the reproductive index — juveniles per adult female in the wing sample — declined and was about half its earlier level by the end of the study. The proportion of females among adult teal also declined.

Eurasian wigeon showed the same two broad demographic changes. The proportion of adult females declined, while the reproductive index fell by about one third over the study period.

The demographic signals did not mirror flyway counts

The trends in the UK harvested sample did not simply follow the overall wintering-population trajectories. The northwest European wintering population of green-winged teal has increased over the long term even while the UK reproductive index and adult-female proportion declined. Eurasian wigeon, meanwhile, experienced a substantial wintering-population decline during the past decade but had begun to increase again by the time of the study.

The authors argue that age and sex ratios can therefore reveal demographic changes that total winter counts alone may not show. They call for coordinated long-term monitoring across migratory flyways so that harvest management can take both population size and demographic structure into account.

Sources and image credit

  1. Warrender, H. E., McNicol, C. M., Brides, K., Stafford, S., & Ellis, M. B. (2026). Long-term demographic changes in harvested Eurasian teal (Anas crecca) and Eurasian Wigeon (Mareca penelope) in the UK. European Journal of Wildlife Research, 72, 16. https://doi.org/10.1007/s10344-025-02050-yPrimary research article published online 10 January 2026. A 37-year UK dataset of harvested wildfowl wings showed a significant decline in the Green-winged Teal reproductive index, which halved over the study period, alongside a decline in the proportion of adult females. Eurasian Wigeon showed a significant decline in adult-female proportion and a reproductive-index decline of about one third.

Image: gailhampshire / Wikimedia Commons / Flickr — male and female Green-winged Teal (Anas crecca) at RSPB Titchwell, Norfolk, United Kingdom, 10 March 2017; representative UK image showing both sexes; original uncropped image. · CC BY 2.0 — https://creativecommons.org/licenses/by/2.0/ · Source

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