No abstract

Globally, high elevation habitats have been independently colonized by taxa separated by millions of years of evolution. Mountains thus represent excellent systems to study how distantly related species adapt to the same environmental challenges. Cold temperatures influence the elevational distribution of birds along montane gradients. Yet the eco-physiological adaptations that may explain this pattern, such as variation in insulative feather structure across high elevation and low elevation species has not been quantified. We used a comparative approach to understand if elevation, evolutionary history and body size drive variation in thermo-insulative feather traits across 1715 specimens of 249 Himalayan passerines. Controlling for phylogenetic relationships between species, we found that the proportion of the feather's plumulaceous (downy) section increased with elevation. Body size also had a predictable effect on thermo-insulative variables with small birds having relatively longer feathers and thus a more insulative plumage than large birds. We show that an increase in the proportion of the feather's downy section at colder temperatures is an evolutionarily widespread response across temperate and tropical taxa, and overall, smaller-bodied birds tend to have longer and more insulative feathers. Our results reveal convergent patterns in feather structure variation as a response to cold temperatures across species separated by millions of years of evolution.

Disentangling associations between species occupancy and its environmental drivers –– climate and land cover –– along tropical mountains is imperative to predict species distributional changes in the future. Previous studies have primarily focused on identifying such associations in temperate mountain systems. Using 1.29 million robustly processed citizen science observations contributed to eBird between 2013 and 2021, we examined the role of climatic and landscape variables and its association with bird species occurrence within a tropical biodiversity hotspot, the southern Western Ghats in India. Using an occupancy modeling framework, we found that temperature seasonality, precipitation seasonality, and the proportion of evergreen forests were significantly associated with species‐specific probabilities of occupancy for 78% (n=43 birds), 38% (n=21 birds), and 27% (n=15 birds) of bird species examined, respectively. Our study shows that several forest birds (n=18 species) were negatively associated with temperature seasonality, highlighting narrow thermal niches for such species. The probability of occupancy of six forest species and eight generalist species was positively associated with precipitation seasonality, indicating potential associations between rainfall and resource availability, and thereby, species occurrence. A smaller number of largely generalist species (n=9 birds) were positively associated with human‐modified land cover types –– including the proportion of agriculture/settlements and plantations. Our study shows that rigorously filtered citizen science observations can be used to identify associations between environmental drivers and species occupancy on tropical mountains. Though current distributions of tropical montane birds of the Western Ghats are strongly associated with climatic factors (mainly, temperature seasonality), naturally occurring land cover types (forests) are critical to sustaining montane avifauna across human‐modified landscapes in the long run.

Ecological restoration is crucial to mitigate climate change and conserve biodiversity, and accurately monitoring responses to restoration is imperative to guide current and future efforts. This study examines the impact of ecological restoration of a tropical dry forest in Central India. Here, the state forest department and a nongovernmental organization work with local communities to remove an invasive shrub, Lantana camara, in the forest, to assist natural regeneration, primarily for the purpose of improving access to forest resources for forest‐dependent people. We used acoustic technology to examine the bird community composition and the acoustic space used (ASU) across comparable restored, unrestored (with L. camara), and naturally low L. camara density (LLD) sites. We found no significant difference in the cumulative number of bird species detected between the site types (median in restored and LLD = 38, unrestored = 41). We found a significant difference in bird community composition across sites (r2 = 0.049, p ≤ 0.001). ASU differs between site types (r2 = 0.023, p ≤ 0.10), with restored sites positively associated with ASU compared to unrestored and LLD sites, which could represent a temporary increase in ASU as animal communities are reorganized after the complete removal of L. camara. Our results suggest that small‐scale restoration efforts that aim to help meet livelihood needs have the potential to contribute to ecological goals in this landscape. However, it is necessary to continue to monitor the regeneration trajectory in restored sites and the possible changes in the ASU.