Low breeding propensity in a declining Arctic-breeding swan revealed by telemetry data
By Tohar Tal, Bart A. Nolet, Tom S.L. Versluijs, Judy Z. Shamoun-Baranes, Götz Eichhorn, Sabine Urban, Hans Linssen
The Western Palearctic population of Bewick’s Swans has experienced one of the most alarming population declines among migratory waterbirds, dropping from approximately 30,000 individuals in 1995 to just 13,000 in 2020. Whereas low reproductive output has been identified as the primary driver, a fundamental question remains: which components of the reproductive cycle are responsible? We analysed GPS-tracking and accelerometer data from over 60 adult female Bewick’s Swans collected across 8 years to quantify breeding propensity (the decision to breed or not) and nesting success (completing incubation).
Bewick’s swans (Cygnus columbianus bewickii). Photo by Frederick Fleet.
We found that earlier arrival at the breeding grounds increases the odds of attempting to breed, and that nesting success responds slightly positively to earlier snowmelt, suggesting a moderate beneficial effect of the climate change-induced advancement of spring onset. However, the proportion of females attempting to breed remained consistently low throughout the entire study period. Furthermore, we compared our telemetry-derived breeding estimates with winter juvenile counts which revealed that at least a third of hatchlings die before their first winter.
Our findings suggest that low breeding propensity may be a key driver of the poor reproductive output and that factors other than climatic conditions impact this propensity of Bewick’s Swans. In our paper we contextualise these results from a conservation perspective and propose several next steps that could help further elucidate the population dynamics of Bewick’s Swans to effectively address the flyway-level decline.
The full article can be found here
