Birds of three worlds: moult migration to high Arctic expands a boreal-temperate flyway to a third biome

Abstract

Background Knowledge on migration patterns and flyways is a key for understanding the dynamics of migratory populations and evolution of migratory behaviour. Bird migration is usually considered to be movements between breeding and wintering areas, while less attention has been paid to other long-distance movements such as moult migration. Methods We use high-resolution satellite-tracking data from 58 taiga bean geese Anser fabalis fabalis from the years 2019–2020, to study their moult migration during breeding season. We show the moulting sites, estimate the migratory connectivity between the breeding and the moulting sites, and estimate the utilization distributions during moult. We reveal migration routes and compare the length and timing of migration between moult migrants and successful breeders. Results All satellite-tracked non-breeding and unsuccessfully breeding taiga bean geese migrated annually to the island of Novaya Zemlya in the high Arctic for wing moult, meaning that a large part of the population gathers at the moulting sites outside the breeding range annually for approximately three months. Migratory connectivity between breeding and moulting sites was very low (rm = − 0.001, 95% CI − 0.1562–0.2897), indicating that individuals from different breeding grounds mix with each other on the moulting sites. Moult migrants began fall migration later in autumn than successful breeders, and their overall annual migration distance was over twofold compared to the successful breeders. Conclusions Regular moult migration makes the Arctic an equally relevant habitat for the taiga bean goose population as their boreal breeding and temperate wintering grounds, and links ecological communities in these biomes. Moult migration plays an important role in the movement patterns and spatio-temporal distribution of the population. Low migratory connectivity between breeding and moulting sites can potentially contribute to the gene flow within the population. Moult migration to the high Arctic exposes the population to the rapid impacts of global warming to Arctic ecosystems. Additionally, Novaya Zemlya holds radioactive contaminants from various sources, which might still pose a threat to moult migrants. Generally, these results show that moult migration may essentially contribute to the way we should consider bird migration and migratory flyways.

Genetic assessment reveals inbreeding, possible hybridization, and low levels of genetic structure in a declining goose population

“…In Finland, the taiga bean goose is listed as vulnerable (the Red List of Finnish species; Lehikoinen et al, 2019) with the breeding population size estimated to be 1700–2500 pairs (i.e., 3400–5000 breeding individuals; Valkama et al, 2011). Subadults and failed breeders perform a molt migration to Novaya Zemlya (Nilsson et al, 2010; Piironen et al, 2021) and thus are not counted. In addition to the taiga bean goose, a very small number of tundra bean geese may breed in Finland in the most northernmost Lapland adjacent to their breeding range in Norwegian Finnmark (Aarvak & Øien, 2009; Figure 2).…”

“…For geese that have bred successfully, the nest site is most probably close to the brood‐rearing/molting site because the geese travel by foot with the goslings. Failed breeders have a different molting site outside of Finland in Novaya Zemlya (Piironen et al, 2021), and their molted feathers were not collected in this study. The samples collected in the present study are hereafter referred to as the “Finnish population.” We used mostly a citizen‐science approach—in which the public is involved in scientific research—to collect feather samples.…”

When and where to count? Implications of migratory connectivity and non-breeding distribution to population censuses in a migratory bird population

“…The copyright holder for this preprint this version posted March 1, 2022. ; https://doi.org/10.1101/2022.02.26.482079 doi: bioRxiv preprint white-fronted goose Anser albifrons; Kölzsch et al, 2019), and taiga bean geese from the entire breeding range of the CF population have common moulting grounds in Novaya Zemlya (Piironen et al, 2021;Figure 1 in this article). Future research should concentrate on the comprehensive study of the genetic structure of taiga bean geese from different breeding origins, and on determining the timing of pair formation in taiga bean geese and its implications for the genetic structure of the population.…”

“…For the birds marked in Denmark (all females), we identified the nesting sites using the same method (location revisitation metrics; Picardi et al, 2020) that was previously used to identify taiga bean goose nest sites from the same tracking data (Piironen et al, 2021). However, we adjusted criteria to fit the GPS resolution (two hours) used for the birds marked in Denmark.…”

“…Regarding birds marked in Finland, this study is based on the same satellite tracking data as the previous study by Piironen et al (2021), so we used individual breeding sites and status provided in that study (see Additional file 2), determined using the same method as used in this study for the birds marked in Denmark. The two birds marked in 2018 in Finland were caught during moult at the breeding grounds from flocks containing adults and their offspring, and we thereby considered them as breeding birds at their breeding sites.…”