DOI: 10.5061/dryad.vx0k6djwh
title: Heat tolerance limits of Mediterranean songbirds and their current and future vulnerabilities to temperature extremes

description: Songbirds are one of the groups most vulnerable to extreme heat events.
 Although several recent studies have assessed their physiological
 responses to heat, most of them have focused on arid-zone species solely.
 We investigated thermoregulatory responses to heat in eight small-sized
 songbirds occurring in the Mediterranean Basin, where heatwaves are
 becoming more frequent and intense. Specifically, we determined their heat
 tolerance limits (HTL) and evaporative cooling efficiency and evaluated
 their current and future vulnerabilities to heat in southwestern Iberia, a
 Mediterranean climate warming hotspot. To do this, we exposed birds to an
 increasing profile of air temperatures (Ta) and measured resting metabolic
 rate (RMR), evaporative water loss (EWL), evaporative cooling efficiency
 (the ratio between evaporative heat loss and metabolic heat production)
 and body temperature (Tb). HTL ranged between 40 and 46°C across species,
 and all species showed rapid increases in RMR, EWL and Tb in response to
 increasing Ta. However, only the crested lark Galerida cristata achieved
 an evaporative cooling efficiency greater than 1. The studied songbirds
 currently experience summer Ta maxima that surpass their upper critical
 temperatures of their thermoneutral zone and even their HTL. Our estimates
 indicated that five of the eight species will experience moderate risk of
 lethal dehydration by the end of the century. We argue that the limited
 heat tolerance and evaporative cooling efficiency of small-sized
 Mediterranean songbirds make them particularly vulnerable to heatwaves,
 which will be exacerbated under future climate change scenarios.
description: We captured birds and measured physiological key traits (RMR,
 EWL, EHL/MHP, Tb) in response to heat by using open-flow-trough
 respirometry. As specify in Material and Methods we only considered for
 the analyses those data from calm animals (activity levels from
 0-3).  We extracted phsyiological data in response to
 heat from previews studies to compare those results with that from our
 species. To to that, we limit the comparisons to songbirds species from
 previous studies among a body mass range between 5-60 grames. 
 Besides, we modelled their current and future vulnerability to
 heat by employing daily maximum temperature data provining from 16
 regional predictive models from AdapteCca platform, which use data from
 EUROCORDEX. Then we determined the number of days in which maximum
 temperature surpass the upper critical temperature (risk of sublethal
 effects) or their heat tolerance limits (risk of lethal hyperthermia)
 thorugh Extremadura (which was divided in grids, referred to them in the
 database as point-x).  Finally, we employed evaporative
 water loss slopes to estimate lethal risk of dehydration following the
 methodology employed by Albright et al. (2017) (see Material and Methods
 for deeper description). Hourly temperature data were obtained by
 averaging the hourly profiles from the 10 hottest days in the last 20
 years in the study site. To this profile we added 1.7 a 2.8 ºC to estimate
 future risk of dehydration under a mitigated climate change scenario and
 an unmitigated scenario, respectively. See Material and Methods for
 complete description of the methodology. 
description: We employed R studio from R Core team to perform all the
 analyses, and all the graphs were made with ggplot2 package.