Measuring avian specialization

Abstract

Measuring the extent to which a species is specialized is a major challenge in ecology, with important repercussions for fundamental research as well as for applied ecology and conservation. Here, we develop a multidimensional index of specialization based on five sets of ecological characteristics of breeding bird species. We used two recent databases of species traits of European birds based on foraging ecology, habitat, and breeding characteristics. The indices of specialization were calculated by applying the Gini coefficient, an index of inequality. The Gini coefficient is a measure of statistical dispersion on a scale between 0 and 1, reflecting a gradient from low to high specialization, respectively. Finally, we tested the strength of the phylogenetic signal of each specialization index to understand how the variance of such indices is shared throughout the phylogeny. The methods for constructing and evaluating a multidimensional index of bird specialization could also be applied to other taxa and regions, offering a simple but useful tool, particularly suited for global or biogeographic studies, as a contribution to comparative estimates of the degree of specialization of species.

Avian trait specialization is negatively associated with urban tolerance

“…Such studies can highlight important urban planning processes (e.g. that insectivores are at particular risk from urbanization; Chace and Walsh ) but they often fail to account for the complicated measures of niche specialization (Morelli et al ). Indeed, future work should continue to elucidate specific life history traits which predict a species’ risk to urban ecosystems (Kark et al , Fuller et al , Evans et al a, Guetté et al , Palacio ).…”

“…At the same time, large global databases on traits are becoming increasingly available and standardized (Moretti et al , Schneider et al ). Our methodological framework, reliant on a publicly‐available global remote‐sensing layer (Elvidge et al ) and a generalized method to measure trait specialization (Morelli et al ), ensures that our approach is likely applicable to many different taxa in different parts of the world, dependent on available data. We rely on VIIRS night‐time lights, which have been previously been shown to be a good predictor of urban environments and urban sprawl (Pandey et al , Zhang and Seto ), but we aggregate these data to relatively large spatial scales (1 km reduction) to match the broad continental scale of our analysis and account for noise in the eBird sampling.…”

“…The data on ecological traits were obtained from published literature and all variables are from European breeding birds, developed for European bird species based on two databases of species traits (Pearman et al , Storchová and Hořák ). The diet is focused on diet all year, but this is strongly correlated to the diet of species during the breeding period (Morelli et al ). We also used an overall specialization index, which is the mean value considering the five individual indices (Morelli et al ).…”

“…We integrated two novel approaches to understand the relationship between species’ specialization and urban tolerance: 1) one which measures species specialization based on a suite of traits (Morelli et al ), providing a continuous measure of overall specialization for specific life‐history characteristics; and 2) a method which leverages citizen science data to assign species‐specific urban tolerance scores to bird species at macro‐ecological scales (Callaghan et al ). We begin by investigating the relationship between overall specialization and urban tolerance, but importantly, we move past this approach and provide a novel analysis which focuses this question along five unique axes of specialization: diet, foraging substrate, habitat, nesting site and foraging behaviour.…”

Diet specialization and brood parasitism in cuckoo species

“…Such data can be used to assess the potential capacities of cuckoos to respond when facing eventual environmental challenges or effects of climate change. Indications suggest that this information could be included in the assessment criteria currently used during the redaction of the IUCN Red List of threatened species (Morelli et al, 2019; Webb, 2008). An additional understanding of the main characteristics which make a species more susceptible to extinction is important, especially in conservation ecology.…”