Thermal, food and vegetation effects on winter bird species richness of Mediterranean oakwoods

Abstract

A better understanding of species–energy relationships needs to be developed using fine‐grained approaches that involve the use of small geographical scales of known characteristics, such as habitat heterogeneity, food availability, direct measures of temperature, and functional groups of species. We carried out a 2‐year study to analyze the effects of the thermal environment and food availability, while controlling for the influence of habitat structure, on winter species richness of birds living in oakwoods of a mountanious region of Central Spain of Mediterranean continental climate. The guild of ground‐foraging birds was selected as model organisms considering its susceptibility to winter conditions associated with unpredictable snowfalls. The spatial variation in species richness of this guild was determined by food availability, but only for those stable and predictable resources not affected by frequent snowfall (shrubs producing fruits; a complete lack of association was found with arthropod abundance on the ground). Thermal effects associated directly with air temperature, and mediated indirectly by vegetation structure providing a mosaic of sun‐shade patches, were also very influential. These patterns were highly repeatable across years. Daytime temperature had no influence on determining spatial variation in species richness, but night (minimum) temperature was a very important predictor (explained considering the lower temperatures at night, the longer duration of night, and the inability of diurnal birds to develop active behavioral thermoregulation during nighttime). This result highlights the need to consider physiological processes mediating species–environment relationships when analyzing the relationship between climatic variables and biodiversity phenomena.

Biogeography of species richness gradients: linking adaptive traits, demography and diversification

“…productivity, habitat availability, temperature, habitat disturbance) or in several spatially correlated environmental variables. Secondly, this environmental gradient causes in turn a geographical gradient in the number of individuals that localities hold (Currie et al , 2004; Scheiner & Willig, 2005; Mönkkönen et al , 2006; Carnicer et al , 2007, 2008 b ; Carnicer & Díaz‐Delgado, 2008; Carrascal, Villén‐Pérez & Seoanne, 2011; Table 2). In line with these two conditions, a number of empirical studies state that local environmental conditions frequently co‐vary with deterministic parameters of populations (e.g.…”

“…productivity, habitat availability, temperature, habitat disturbance) or in several spatially correlated environmental variables. Secondly, this environmental gradient causes in turn a geographical gradient in the number of individuals that localities hold (Currie et al, 2004;Scheiner & Willig, 2005;Mönkkönen et al, 2006;Carnicer et al, 2007Carnicer et al, , 2008bCarnicer & Díaz-Delgado, 2008;Carrascal, Villén-Pérez & Hodges & Derieg (2009) Functional/adaptive trait continuum: a significant axis of co-variation between a set of traits observed at the inter-specific level for a taxonomic group, which can be used as a quantitative synthetic measure of life-history variation. Wright et al (2004); Jeschke & Kokko (2009);Chave et al (2009) Fitness: a quantitative measure that describes the ability to both survive and reproduce, and is equal to the average contribution to the gene pool of the next generation that is made by an average individual of the specified genotype or phenotype.…”

Direct and Cascading Effects of Landscape Structure on Tropical Forest and Non‐forest Frugivorous Birds

“…Foraging efficiency of visually oriented animals, such as birds, can actually be increased at forest edges (Galetti et al 2003, Terreaube et al 2016, as these habitats are exposed to higher light incidence, which might affect the "communication" between birds and fruits (Galetti et al 2003). Hence, the edge exposure to a higher sunlight may directly affect the conspicuousness of the fruits, and consequently reduce the amount of time required for birds to find food resources (Galetti et al 2003, Carrascal et al 2012).…”

Vegetation associations of birds wintering in a California oak woodland

“…Due to the nature of PCA, we cannot isolate the influence of shrubs from the influence of live oaks on winter bird density and are not aware of any study conducted in California where investigators attempted to do so. However, studies in other woodland systems suggest that shrubs are an important component of habitat during the non‐breeding season for many avian species, providing food and cover during a time of the year when resources are generally scarce (e.g., Borgmann et al , Carrascal et al ). In broadleaf woodlots in Ohio, Doherty and Grubb () found that Carolina Chickadee ( Poecile carolinensis ) occurrence and densities of Downy Woodpeckers ( Picoides pubescens ) and Blue Jays ( Cyanocitta cristata ) were positively associated with shrub cover, and hypothesized that shrubs provided birds with both thermal cover and a refuge from predators.…”