Clinging on to alpine life: Investigating factors driving the uphill range contraction and population decline of a mountain breeding bird

Abstract

Climate change and anthropogenic nitrogen deposition are widely regarded as important drivers of environmental change in alpine habitats. However, due to the difficulties working in high‐elevation mountain systems, the impacts of these drivers on alpine breeding species have rarely been investigated. The Eurasian dotterel (Charadrius morinellus) is a migratory wader, which has been the subject of uniquely long‐term and spatially widespread monitoring effort in Scotland, where it breeds in alpine areas in dwindling numbers. Here we analyse data sets spanning three decades, to investigate whether key potential drivers of environmental change in Scottish mountains (snow lie, elevated summer temperatures and nitrogen deposition) have contributed to the population decline of dotterel. We also consider the role of rainfall on the species' wintering grounds in North Africa. We found that dotterel declines—in both density and site occupancy of breeding males—primarily occurred on low and intermediate elevation sites. High‐elevation sites mostly continued to be occupied, but males occurred at lower densities in years following snow‐rich winters, suggesting that high‐elevation snow cover displaced dotterel to lower sites. Wintering ground rainfall was positively associated with densities of breeding males two springs later. Dotterel densities were reduced at low and intermediate sites where nitrogen deposition was greatest, but not at high‐elevation sites. While climatic factors explained variation in breeding density between years, they did not seem to explain the species' uphill retreat and decline. We cannot rule out the possibility that dotterel have increasingly settled on higher sites previously unavailable due to extensive snow cover, while changes associated with nitrogen deposition may also have rendered lower lying sites less suitable for breeding. Causes of population and range changes in mountain‐breeding species are thus liable to be complex, involving multiple anthropogenic drivers of environmental change acting widely across annual and migratory life cycles.

Functional traits and environment jointly determine the spatial scaling of population stability in North American birds

“…In comparison, precipitation had a weak effect on bird populations, consistent with a previous analysis showing a weaker synchronizing effect of precipitation on bird population dynamics than that of temperature (Koenig & Liebhold, 2016). This finding is also in line with previous studies showing that bird species vary in their responses to precipitation changes depending on local context (Brawn et al, 2017;Mares et al, 2017), with the strongest responses typically detected in "climate-sensitive" conditions (e.g., high altitude, high latitude or high aridity) (Anctil et al, 2014;Ewing et al, 2020;Mares et al, 2017). Our results suggest that an increasing spatial synchrony in temperature and/or leaf area index leads to increased spatial population synchrony and thus lower IAR slopes in birds, a factor associated with reduced population persistence (i.e., through extinction events arising from simultaneous population declines).…”

Drivers of change in mountain and upland bird populations in Europe

“…However, the impacts on demographic parameters of bird populations might be complex and mediated over longer timescales (Ewing et al . 2020), for example through altered species interactions (Ockendon et al . 2014), and may be more challenging to detect in comparison with other direct impacts (e.g.…”

“…Climate change in particular is one of the most studied drivers for bird populations (Pearce-Higgins et al 2014) and warming is particularly marked in mountain regions (Gobiet et al 2014). However, the impacts on demographic parameters of bird populations might be complex and mediated over longer timescales (Ewing et al 2020), for example through altered species interactions (Ockendon et al 2014), and may be more challenging to detect in comparison with other direct impacts (e.g. hunting).…”

Climate and land‐use change drive habitat loss in a mountain bird species

“…Like other mountain species, it is potentially highly vulnerable to climate warming, which might have caused the observed range retraction through uphill shifts at the lower distribution boundary (e.g. Stuhldreher & Fartmann 2018, Ewing et al 2020. The mechanisms driving such range shifts and retractions can differ strongly across different taxa.…”

“…In the study area, other endangered cold-adapted species such as the Moorland Clouded Yellow Colias palaeno or the Citril Finch Carduelis citronella may also depend on long periods of snow cover. Further examples of possible snow cover-areal relationships include the Eurasian Dotterel Charadrius morinellus (Ewing et al 2020) and the Woodland Ringlet Erebia medusa (Stuhldreher et al 2014, Stuhldreher & Fartmann 2018. Future research should thus focus more on the impact of advanced thawing.…”