Section: Ecology
Topic: Ecology, Environmental sciences, Population biology

Long term trend and short-term dynamics of a willow ptarmigan population

Willebrand, Tomas1 orcid ; Hörnell-Willebrand, Maria1 orcid; Brittas, Rolf2; Kleiven, Eivind Flittie3 orcid
1Department of Forestry and Wildlife Management, Faculty of Applied Ecology and Agricultural Sciences, Inland Norway University of Applied Sciences, Elverum, Norway
2Fjällgrycksbo 113, 79021 Bjursås, Sweden
3Norsk institutt for naturforskning, Framsenteret, 9296 Tromsø, Norway

Corresponding author(s): Willebrand, Tomas (tomas.willebrand@inn.no)

10.24072/pcjournal.590 - Peer Community Journal, Volume 5 (2025), article no. e98

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Willow ptarmigan Lagopus lagopus is abundant in Arctic and tundra regions, but rapid climate warming has raised concerns about possible declines as has been observed in several bird species. In this study, we used a hierarchical state-space model to analyze data from a 139 km line transects in mid-Sweden over 48 years. Adult numbers and breeding success were analyzed separately, and we included covariates on vole abundance, numbers of snow-free days in autumn and spring, and the last day of frost in May. We assessed long-term trends in the adult population and estimated the effects of breeding success and weather variation on short-term changes. The estimates of adult density did not show any trend for the period 1976 to 2023, and the dynamics were characterized by a strong direct negative density dependence indicating a stationary process. A number of possible mechanisms have been suggested for how a warmer climate affects willow ptarmigan population dynamics, but our results do not support the hypothesis that lack of snow in autumn and spring increases the vulnerability of willow ptarmigan to predation and leads to population decline. Breeding success is an important driver of changes in, but independent of, adult density. In addition to predation, we propose that climate conditions and emerging vegetation during egg formation and laying are important. We suggest that our results can be explained by a diverse predator assemblage that makes it difficult for the population to escape top-down control, resulting in short-term fluctuations at lower densities.

Published online:
DOI: 10.24072/pcjournal.590
Type: Research article
Keywords: Lagopus lagopus, trend, population dynamic

Willebrand, Tomas  1 ; Hörnell-Willebrand, Maria  1 ; Brittas, Rolf  2 ; Kleiven, Eivind Flittie  3

1 Department of Forestry and Wildlife Management, Faculty of Applied Ecology and Agricultural Sciences, Inland Norway University of Applied Sciences, Elverum, Norway
2 Fjällgrycksbo 113, 79021 Bjursås, Sweden
3 Norsk institutt for naturforskning, Framsenteret, 9296 Tromsø, Norway
License: CC-BY 4.0
Copyrights: The authors retain unrestricted copyrights and publishing rights
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Willebrand, T.; Hörnell-Willebrand, M.; Brittas, R.; Kleiven, E. F. Long term trend and short-term dynamics of a willow ptarmigan population. Peer Community Journal, Volume 5 (2025), article  no. e98. https://doi.org/10.24072/pcjournal.590

PCI peer reviews and recommendation, and links to data, scripts, code and supplementary information: 10.24072/pci.ecology.100540

Conflict of interest of the recommender and peer reviewers:
The recommender in charge of the evaluation of the article and the reviewers declared that they have no conflict of interest (as defined in the code of conduct of PCI) with the authors or with the content of the article.

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