Contents lists available at ScienceDirect Journal of Arid Environments journal homepage: www.elsevier.com/locate/jaridenv Thermally-driven thresholds in terrestrial avifauna waterhole visitation indicate vulnerability to a warming climate Simon E. Votto a,b,* , Fiona J. Dyer b , Valerie Caron b,c , Jenny A. Davis a a Research Institute for the Environment and Livelihoods, Charles Darwin University, Casuarina, Northern Territory, 0810, Australia b Centre for Applied Water Science, University of Canberra, Bruce, Australian Capital Territory, 2617, Australia c Commonwealth Scientific and Industrial Research Organisation, Black Mountain, Australian Capital Territory, 2601, Australia ARTICLE INFO Keywords: Avian functional groups Arid zone Groundwater-dominated waterholes Thermal thresholds Climatic warming ABSTRACT Warming global climates represent major threats to avian populations, particularly those reliant on surface water within arid biomes. We investigated terrestrial avian use of groundwater-dominated arid zone waterholes in central Australia to identify species vulnerable to climate change. Camera traps set in Watarrka National Park recorded avian species over 14 months at three waterholes during 2014 and 2015. Recorded species were as- signed to functional groups, which included nectarivores, granivores, carnivores and omnivores. Generalised Additive Mixed Models (GAMMs) were used to model daily trapping rates (DTRs) for each functional group at waterholes in relation to daily maximum temperature and days since last rainfall. Granivores exhibited high DTRs across the entire daily maximum temperature range (15 °C–43 °C). Increasing threshold responses beyond specific daily maximum temperatures were exhibited by nectarivores (35 °C), carnivores (30 °C) and omnivores (30 °C). The DTRs for all functional groups increased with days since last rainfall. These data indicate species within all functional groups are vulnerable to a warming climate, even those that are considered to be surface water independent, as increasing waterhole visitations in torrid conditions reduces foraging time and could lead to reduced fitness in particular individuals. 1. Introduction The mean global air temperature has increased by 0.74 °C in the past 100 years (Stocker, 2014) and may rise by as much as 4.8 °C by the year 2100 (Hughes, 2003). Warmer temperatures experienced over the last 100 years have begun to affect the function and composition of avian communities throughout the world (Crick, 2004; Iknayan and Beissinger, 2018; Jetz et al., 2007). These effects include shifts in their phenology (Menzel et al., 2006; Møller et al., 2008), range/distribution (Hitch and Leberg, 2007; Thomas and Lennon, 1999), composition (Lemoine et al., 2007) and population dynamics (Both et al., 2006; Lindström et al., 2013; Sæther et al., 2000). In Australia, a continent largely characterised by arid and semi-arid environments, the rate of warming associated with climate change has been greater, on average, than that experienced globally in the same time period (0.9 °C vs 0.74 °C) (Head et al., 2014; Zhou et al., 2015). Increased rates of warming will likely have ecological implications for arid zone waterholes (Davis et al., 2013) and their associated avifauna, which may be exacerbated by extended droughts in some years. This is particularly the case for terrestrial birds (bush birds, birds of prey and parrots) that rely on surface water in arid landscapes and have dis- tributions that are constrained by its availability within them (Abdu et al., 2018b; Fisher et al., 1972). Some species considered to not be dependent on surface water may even be drawn to waterholes to drink under these increasingly hot and dry conditions (Albright et al., 2017; Reside et al., 2013). The dependency a particular avian species displays towards surface water is generally related to their diet and how much water they can derive from it (MacMillen and Baudinette, 1993; Merrick, 2006). For this reason, consideration of functional groups based on dietary re- quirements is likely to provide useful insights into water use patterns across the avian community (Tischler et al., 2013). The relatively high moisture content of nectarivore, carnivore and omnivore diets suggests that they are less dependent on waterholes to meet their water re- quirements (Dawson and Bartholomew, 1968; Fleming et al., 2004; Smyth and Coulombe, 1971) in comparison with granivores, which have a dry seed diet (Cade and Dybas, 1962; Zann and Bamford, 1996). However, in arid environments, air temperature is a significant en- vironmental driver that affects water consumption of avian species (Tieleman et al., 2003). Under hot and dry conditions, changes in https://doi.org/10.1016/j.jaridenv.2020.104217 Received 6 July 2018; Received in revised form 8 November 2019; Accepted 13 May 2020 * Corresponding author. Research Institute for the Environment and Livelihoods, Charles Darwin University, Casuarina, Northern Territory, 0810, Australia. E-mail address: simon.votto@cdu.edu.au (S.E. Votto). Journal of Arid Environments 181 (2020) 104217 0140-1963/ © 2020 Elsevier Ltd. All rights reserved. T