Altitudinal shifts in forest birds in a Mediterranean mountain range: causes and conservation prospects

Abstract

Summary Mediterranean mountains are biodiversity hotspots where northern species occur surrounded by drier and warmer lowlands. In this context, global warming is pushing these species to higher elevations. This paper assesses whether forest birds have experienced a shift upwards over the elevation gradient in the last 35 years in the Guadarrama Mountains (600–2,400 m asl; central Spain). Alternatively, the paper tests whether the reported shifts are related to changes in forest structure resulting from rural abandonment and/or forest management. To do this, sampling carried out from 1976 to 1980 along the elevation gradient was repeated in 2014–2015. In addition, the habitat preferences of birds were used to test if the elevation shifts were related to changes in forest structure. Results show that the mean range position of birds associated with tree cover shifted downwards, a trend supported by an increase in tree-dependent birds at mid-elevations. These trends suggest that an increase in tree cover has buffered the altitudinal shifts of forest birds predicted by climate warming. Results also suggest that proper forest management may improve the resilience of forest bird communities to the pervasive effects of climate warming.

Butterfly communities track climatic variation over space but not time in the Iberian Peninsula

“…There was little evidence for geographic variation in changes to TAOc, suggesting a widespread trend. Faunal changes towards insects and birds using more closed vegetation have been observed in several parts of Mediterranean Europe (Clavero et al ., 2011; Barnagaud et al ., 2013; Herrando et al ., 2016; Dantas de Miranda et al ., 2019; Wölfling et al ., 2019; Tellería, 2019, 2020), and their consequences for functional and taxonomic diversity merit research.…”

“…Apart from promoting population recovery in woodland butterflies (Stefanescu et al ., 2011) greater vegetation cover could counteract the ecological effects of climate change by providing cooler microclimates (Barnagaud et al ., 2013; De Frenne et al ., 2019). Mountain bird communities in the Iberian Peninsula have recently become increasingly dominated by forest species, in some cases with evidence that forest species have expanded downhill to take advantage of increasing habitat availability (Tellería, 2019) and reducing Community Temperature Index despite climatic warming (Clavero et al ., 2011; Stefanescu et al ., 2011). However, in our study, there was little evidence that changes to the TAOc index for butterfly communities were correlated with changes to climatic associations, or that increasing contributions by species of closed habitats would act either antagonistically or synergistically to the community changes expected from climate change.…”

“…Over recent decades, Mediterranean butterfly communities have responded to climatic warming (Zografou et al ., 2014; Nieto‐Sánchez et al ., 2015) and drying (Herrando et al ., 2019), as well as vegetation encroachment (Ubach et al ., 2020) and changing agricultural practices (Lee et al ., 2020). Some evidence from these regional studies suggests that topographic variation or vegetation cover may counteract effects of climate change on insects (Nieto‐Sánchez et al ., 2015; Herrando et al ., 2019), as has been observed for Mediterranean bird communities (Clavero et al ., 2011; Barnagaud et al ., 2013; Tellería, 2019, 2020). However, wider geographic tests of the scope for topography or vegetation to offset the impacts of climate change are limited by availability of longer‐term or larger‐scale evidence of changes to Mediterranean insect communities (Lobo et al ., 2018).…”

Feather traits in four southern populations of the Eurasian blackcapSylvia atricapilla: do altitudinal movements explain the differences?

“…In our case, blackcap populations of the Iberian highlands and lowlands (Guadarrama and Alcornocales; Fig. 1) have been classified as migratory and sedentary, respectively (Tellería andCarbonell 1999, Pérez-Tris andTellería 2002). Although the migratory behaviour of North African blackcaps remains yet unclear (Thévenot et al 2003, Delmore et al 2020, bird count data suggest that this species reduces its abundance at high elevation areas (Atlas mountains) during winter, suggesting the existence of seasonal altitudinal movements (Supporting information).…”

“…We used wing morphology to infer the strength of seasonal movements of the Eurasian blackcap populations, since migratory populations are expected to have a more developed flight morphology (i.e. longer and more pointed wings) than sedentary ones (Tellería andCarbonell 1999, Fiedler 2005). We performed a principal component analysis (PCA) with the primary lengths to describe wing shape.…”