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Mallard Population Growth Was Lower in Years With Longer Growing Seasons at Higher Latitudes

Wild mallards in Potter Marsh, Alaska
Research · Ecology

Across 38 years of breeding-duck surveys in the western boreal forest of North America, annual mallard (Anas platyrhynchos) population growth was lower in years with longer growing seasons at higher latitudes. At the lower latitudes in the study area, the relationship was close to neutral. This was the opposite of the researchers’ prediction that a longer season would generally benefit breeding ducks.

The study used breeding-population estimates from 1982 to 2019 for eight duck species or species groups. Satellite vegetation data described four aspects of each year’s growing season: when spring growth began, when vegetation peaked, how long the growing season lasted and how much vegetation was produced.

Duck species responded differently to longer and more productive seasons

For mallards, neither the timing of spring nor peak vegetation showed a clear relationship with annual population growth, and cumulative vegetation productivity also had no detectable effect. Growing-season length was different: the relationship became increasingly negative toward higher latitudes.

The combined goldeneye group — common goldeneye (Bucephala clangula) and Barrow’s goldeneye (B. islandica) — showed the opposite response to growing-season length, with higher population growth in years with longer seasons at lower latitudes and a weaker effect farther north. Higher vegetation productivity was also linked to higher population growth in goldeneyes and, at lower latitudes, in buffleheads (B. albeola) and green-winged teal (Anas crecca).

Regression coefficients for growing-season effects on population growth in boreal-breeding ducks
Standardized effects of growing-season variables and their latitude interactions on annual population growth across the studied duck species and groups. Figure 3 from Messmer et al. (2026), Oecologia, CC BY 4.0.

Why longer seasons may not help mallards

The researchers had expected longer seasons to provide more time for renesting and raising young. They discuss several reasons why that extra time might not translate into faster population growth. A later nesting attempt may still leave too little time for ducklings to fledge and begin migration in good condition, while repeated nesting can expose females to additional nesting mortality and reduce body condition before autumn migration.

These mechanisms were not tested directly in the study. The authors conclude more broadly that simple measures such as growing-season length or total vegetation productivity do not affect all boreal ducks in the same way; more complex biotic and abiotic interactions can modify or outweigh the expected benefits of a longer growing season.

Sources and image credit

  1. Messmer, D. J., Slattery, S., Drever, M. C., Derksen, C., & Clark, R. G. (2026). Divergent demographic responses of boreal-breeding ducks to growing season variability. Oecologia, 208(2), Article 28. https://doi.org/10.1007/s00442-026-05865-xPrimary peer-reviewed open-access article, published and version of record 4 February 2026. In mallards, the effect of growing-season length on annual population growth was near neutral at lower latitudes but became increasingly negative toward higher latitudes; the result remained statistically supported after multiple-testing adjustment. CC BY 4.0.

Image: Diego Delso / Wikimedia Commons — wild mallards (Anas platyrhynchos) at Potter Marsh, Alaska, USA, photographed 22 August 2017. Illustrative photograph from the northern part of the species’ boreal breeding range, not birds from the population survey. · CC BY-SA 4.0 — https://creativecommons.org/licenses/by-sa/4.0/ · 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

Ecology

SPECIES IN THIS STORY

Species in this story

Mallard Anas platyrhynchos Explore species Common Goldeneye Bucephala clangula Explore species Green-winged Teal Anas crecca Explore species

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