Effects of local climate and habitat heterogeneity on breeding-bird assemblages of semi-natural grasslands

Abstract

The intensification of agricultural land-use, abandonment and afforestation have caused severe loss and degradation of nutrient-poor, semi-natural grasslands across Europe. Calcareous grasslands have an outstanding value for nature conservation due to their highly diverse flora and fauna, including birds. However, knowledge of environmental factors driving the composition of bird communities in calcareous grasslands is still scarce. The aim of our study was to compare the breeding-bird assemblages of calcareous grasslands and the second most common semi-natural grassland type in the study area (Diemel Valley, Central Germany), mesic grasslands, along an elevation (climate) gradient. For each grassland type, we randomly selected 27 square-shaped plots with a size of 5 ha each and a cover of the focal grassland type of at least 50% within the plot. Our study revealed that both the number and density of threatened species of breeding birds were higher in plots of calcareous grasslands than in those of mesic grasslands. Based on multivariable generalised linear mixed-effects models, the most important predictors of overall species richness and density of breeding birds in plots of calcareous grasslands were the area of juniper-rich calcareous grassland and Shannon habitat diversity. By contrast, the number and density of threatened species were in both grassland types mainly driven by breeding-season temperature. Heterogeneous, juniper-rich calcareous grasslands seem to be a key habitat for bird assemblages with high species richness and density. These grasslands usually consisted of small-scale habitat mosaics providing suitable nesting sites and foraging grounds in close proximity. By contrast, mesic grasslands had rather homogeneous swards and shrubs or trees were normally restricted to the edges of the grassland patches. Based on our study, increasing habitat heterogeneity at the landscape scale and within grasslands is the key to enhancing species richness and density of breeding birds.

Vegetation management shapes arthropod and bird communities in an African savanna

“…Heterogeneity within habitats is also an important driver of diversity and abundance of bird communities. In other systems, both bird diversity and abundance generally increase in habitats that have more complex vertical and horizontal architectures because a greater variety of resources are available and there is greater potential for segregation at the microhabitat/niche level (Brüggeshemke et al, 2022; MacArthur & MacArthur, 1961; Martin & Possingham, 2005; Parker, 2019). This relationship may explain the observed patterns of high bird abundance and richness in our control plots than the other treatment plots.…”

“…By contrast, the plots that had the highest tree density supported greater bird richness and abundance. Habitat structure and herbaceous cover are established drivers of animal communities (Aranda & Graciolli, 2015; Brüggeshemke et al, 2022; Prather & Kaspari, 2019; Schmitt et al, 2022), as such, any habitat management practice that affects vegetation structure and cover will also impact the animals relying on the vegetation. However, we show that these impacts are variable depending on the taxonomic group being assessed.…”

“…Vegetation structure is a key factor that drives both bird species assemblages (MacArthur & MacArthur, 1961; Sirami et al, 2009) and arthropod abundance (Dennis et al, 2007). For example, bird community composition differs between different management approaches (Brüggeshemke et al, 2022; Herremans, 1998; Kaphengst & Ward, 2008; Krook et al, 2007). Thus, through their effects on woody plant cover and the herbaceous layer, vegetation management, such as tree clearing with subsequent mowing, is likely to impact both bird and arthropod communities.…”

The importance of landscape heterogeneity and vegetation structure for the conservation of the Ortolan BuntingEmberiza hortulana

“…Furthermore, the variable “woody boundary” was classified into “avenue”, “copse”, “hedgerow”, “tree row”, and “single tree”. Moreover, the habitat data were used to calculate landscape heterogeneity ( H’ ) within territories (BP and UM) and CONTROL samples using the Shannon Index (Morelli et al 2013, Fartmann et al 2018, Schwarz et al 2018, Brüggeshemke et al 2022): where N is the overall area of the territory or home range and n i is the area of each habitat type within the two spatial levels. To avoid overfitting, habitat types covering an area of less than 1% either within territories or home ranges were excluded from all following analyses.…”

“…Furthermore, the variable "woody boundary" was classified into "avenue", "copse", "hedgerow", "tree row", and "single tree". Moreover, the habitat data were used to calculate landscape heterogeneity (H') within territories (BP and UM) and CONTROL samples using the Shannon Index (Morelli et al 2013, Schwarz et al 2018, Brüggeshemke et al 2022):…”