Disentangling direct and indirect effects of local temperature on abundance of mountain birds and implications for understanding global change impacts

Abstract

Unravelling the environmental factors driving species distribution and abundance is crucial in ecology and conservation. Both climatic and land cover factors are often used to describe species distribution/abundance, but their interrelations have been scarcely investigated. Climatic factors may indeed affect species both directly and indirectly, e.g., by influencing vegetation structure and composition. We aimed to disentangle the direct and indirect effects (via vegetation) of local temperature on bird abundance across a wide elevational gradient in the European Alps, ranging from montane forests to high-elevation open areas. In 2018, we surveyed birds by using point counts and collected fine-scale land cover and temperature data from 109 sampling points. We used structural equation modelling to estimate direct and indirect effects of local climate on bird abundance. We obtained a sufficient sample for 15 species, characterized by a broad variety of ecological requirements. For all species we found a significant indirect effect of local temperatures via vegetation on bird abundance. Direct effects of temperature were less common and were observed in seven woodland/shrubland species, including only mountain generalists; in these cases, local temperatures showed a positive effect, suggesting that on average our study area is likely colder than the thermal optimum of those species. The generalized occurrence of indirect temperature effects within our species set demonstrates the importance of considering both climate and land cover changes to obtain more reliable predictions of future species distribution/abundance. In fact, many species may be largely tracking suitable habitat rather than thermal niches, especially among homeotherm organisms like birds.

Landscape characteristics influence regional dispersal in a high‐elevation specialist migratory bird, the water pipit Anthus spinoletta

“…The same measures would also be beneficial across the entire Alpine range, in order to maintain the current population size also in the innermost Alpine areas. In these colder sectors, alpine grasslands are still apparently entirely within the water pipit temperature optimum (Ceresa et al, 2021) and the occurrence of the species is predicted to persist in the next few decades despite a changing climate (Brambilla et al, 2022). Avoiding habitat loss and degradation in these areas is therefore crucial to maintain the core water pipit populations in the long term.…”

“…As a consequence of temperature increase, mountain bird populations are expected to change their distributions to track their thermal niches and/or to cope with habitat change (e.g., the uphill shift of wooded vegetation, Myers‐Smith et al, 2011). While species adapted to warm conditions may gain new suitable areas at higher elevations (e.g., Ceresa et al, 2021; Scridel et al, 2017), high‐elevation specialist species will, by contrast, lose suitable habitat with uphill distribution shifts, because ground area decreases with increasing elevation in mountain systems showing a pyramidal structure (Elsen & Tingley, 2015).…”

Identifying climate refugia for high‐elevation Alpine birds under current climate warming predictions

“…Grasslands are becoming increasingly encroached by shrubs and trees, and often cannot shift upward due to abiotic constraints (Cannone et al, 2007). Their contraction is exacerbated by processes of land abandonment occurring in many mountain systems, implying that extensive grassland and pastures are abandoned and the remaining ones are subject to agricultural intensification (Assandri et al, 2019), synergistically impacting on these habitats with potentially strong negative effects on several bird species (Brambilla, Gustin, et al, 2020; Scridel et al, 2018), including those less likely to be dramatically impacted by direct effects of temperature change per se (e.g., water pipit; Ceresa et al, 2021; Jähnig et al, 2020).…”

Sensitivity of tropical montane birds to anthropogenic disturbance and management strategies for their conservation in agricultural landscapes

“…Our results for Andean birds support the idea that species adapted to a broader range of environmental conditions (e.g., large global range sizes and broad elevational ranges) are better adapted to anthropogenic disturbance (Ausprey et al., 2022; Karp et al., 2019). In particular, species declining in high‐intensity agricultural landscapes had smaller elevation ranges than expected given their global range size, meaning that adaptations specifically associated with elevation (e.g., rapid changes in temperature) may pose additional constraints to species persistence (Ceresa et al., 2021; Duclos et al., 2019). Our results also point to the sensitivity of species with insectivorous diets, as has been reported at regional scales in the Andes, including in our work in Peru (Jones et al., 2021; Kattan et al., 1994; Renjifo, 1999).…”