Birds on the move : Understanding elevational distributions and shifts of birds across European mountains

Mountain ecosystems are biodiversity hotspots characterised by steep environmental gradients and complex topography and are particularly sensitive to climate and land-use change. Climate warming is expected to drive species to higher elevations, yet, many species do not move as fast as expected, possibly because of habitat limits, microclimatic conditions, or species traits. Understanding how abiotic factors such as climatic trends, habitat characteristics, and species traits shape elevational distributions is crucial to predict biodiversity responses and inform conservation strategies under global change. This thesis investigates these factors across European mountains over the past two decades using birds as a study system, combining cross-scale community and trait-based approaches. Across all chapters, I estimated the mean elevations of bird species abundances, i.e. elevation at which a species abundance peaked, and their shifts over time to investigate the drivers of elevational dynamics in European mountain ecosystems. In Chapter I, I quantified the impact of solar radiation on mean elevational distributions and the rate of elevational shifts of 177 bird species across four European mountain regions (Alps, Pyrenees, Scandinavia, UK uplands) from 2001 to 2021. I found that birds occurred at higher elevations in areas receiving more solar radiation, usually south-facing. Across Europe, mean elevations of birds shifted uphill by 0.5 m per year, with similar rates across low, medium, and high solar radiation areas. However, I found that the rate of shifts differed between mountain regions with significant uphill shifts in Scandinavia and the Alps, but not in the UK and Pyrenees. These findings demonstrate the importance of abiotic factors in shaping elevational distributions while highlighting that microclimatic variation may not strongly constrain large-scale shifts. In Chapter II, I investigated how habitat type (open habitat and forest), changes in habitat availability, and climate trends (temperature and precipitation) influence the distributions of mean elevations and elevational shifts of 186 bird species. I found that abundances peaked at higher elevations in forested habitats, which may partly reflect the occurrence of forest at higher elevations. On average, species shifted uphill by 0.6 m per year, with faster shifts in open habitats and in areas experiencing increased habitat availability and precipitation. While rising temperatures may drive the general uphill shifts, local habitat and precipitation changes modulate shift magnitudes. These results underscore the combined effects of habitat and climate on species’ elevational dynamics. In Chapter III, I tested whether species’ life-history traits and population trend influence elevational shifts in bird abundances in the Scandinavian mountains. Across 13 years, mean abundances of 76 bird species shifted uphill by 0.9 m per year. Only seven species showed significant individual shifts, yet community-wide patterns indicated that species abundances are moving uphill. Short-lived species showed faster uphill shifts than long-lived species, suggesting that life-history traits mediate species capacity to track climate change. Overall, this thesis shows that elevational distributions and shifts in mountain birds are shaped by the interplay of abiotic factors, habitat, and species traits. While uphill shifts are widespread, their magnitude varies regionally and among species, highlighting the need to consider both environmental context and ecological characteristics when predicting biodiversity responses to global change. These findings advance understanding of mountain bird vulnerability and adaptive capacity in rapidly changing ecosystems.

Grantor dc:publisher

Helsingin yliopisto

Year dc:date.issued

2026

Author dc:creator

• Couet, Joséphine

• ecology

Statement dc:rights

• Julkaisu on tekijänoikeussäännösten alainen. Teosta voi lukea ja tulostaa henkilökohtaista käyttöä varten. Käyttö kaupallisiin tarkoituksiin on kielletty.
• This publication is copyrighted. You may download, display and print it for Your own personal use. Commercial use is prohibited.
• Publikationen är skyddad av upphovsrätten. Den får läsas och skrivas ut för personligt bruk. Användning i kommersiellt syfte är förbjuden.

Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/10138/624691

OAI record oai:identifier

https://helda.helsinki.fi/server/oai/request?verb=GetRecord&metadataPrefix=dim&identifier=oai%3Ahelda.helsinki.fi%3A10138%2F624691