Modelling the responses of Australian subtropical rainforest birds to changes in environmental conditions along elevational gradients

Abstract

Montane birds face significant threats from a warming climate, so determining the environmental factors that most strongly influence the composition of such assemblages is of critical conservation importance. Changes in temperature and other environmental conditions along elevational gradients are known to influence the species richness and abundance of bird assemblages occupying mountains. However, the role of speciesspecific traits in mediating the responses of bird species to changing conditions remains poorly understood. We aimed to determine whether different bird species responded differently to changing environmental conditions in a relatively understudied biodiversity hotspot in subtropical rainforest on the east coast of Australia. We examined patterns in avian species richness and abundance along two rainforest elevational gradients using monthly point counts between September 2015 and October 2016. Environmental data on temperature, wetness, canopy cover and canopy height were collected simultaneously, and trait information on body size and feeding guild membership for each bird species was obtained from the Handbook of Australian, New Zealand and Antarctic Birds. We used a generalized linear mixed modelling (GLMM) framework to determine the drivers of species richness and abundance and to quantify species' trait-environment interactions. GLMMs indicated that temperature alone was significantly positively correlated with species richness and abundance. Species richness declined with increasing elevation. When modelling abundance, we found that feeding guild membership did not significantly affect species' responses to environmental conditions. In contrast, the predicted abundance of a species was found to depend on its body size, due to significant positive interactions between this trait, temperature and canopy cover. Our findings indicate that large-bodied birds are likely to increase in abundance more rapidly than small-bodied birds with continued climatic warming. These results underline the importance of temperature as a driving factor of avian community assembly along environmental gradients.

Mixed-species bird flocks re-assemble interspecific associations across an elevational gradient

“…Previous studies have found a pattern of decline in diversity with increasing elevation in the overall avifauna [32,33].…”

“…Previous studies have found a pattern of decline in diversity with increasing elevation in the overall avifauna [32,33]. Whether the diversity and stability (species' persistence) of flocking assemblages can be maintained with increasing elevation, is still an open question, because it has been reported that flocking behaviour can buffer environmental stress [39,40].…”

“…We suggest that the range of elevation might be responsible for these differences in results among studies. The substantially higher elevation (1350–3500 m) of the study of Montaño-Centellas [16] might produce a more stressful environment by imposing extreme energetic constraints [76], which could restrict the survival of many bird species by physiological constraints [32]. This might explain why both flocking assemblages and interspecific associations responded to elevational change simultaneously in the study of Montaño-Centellas [16].…”

“…temperature, water) and vegetation (i.e. influence food, habitat) driven by elevational change [31][32][33], generate varied environments. High elevations may also represent stressful environments.…”

“…Several factors may produce environmental stress for birds at high elevations, and these factors likely work simultaneously [31]. Low temperature and limited water availability at high elevations might directly restrict bird survival through physiological constraints [32]. Indirect effects may work through changing vegetation, such as a reduction of vegetative diversity, productivity and canopy height, which could influence food availability and shelter [31,34,35].…”