Chronic, sublethal effects of high temperatures will cause severe declines in southern African arid-zone birds during the 21st century

Abstract

Birds inhabiting hot, arid regions are among the terrestrial organisms most vulnerable to climate change. The potential for increasingly frequent and intense heat waves to cause lethal dehydration and hyperthermia is well documented, but the consequences of sublethal fitness costs associated with chronic exposure to sustained hot weather remain unclear. Using data for species occurring in southern Africa’s Kalahari Desert, we mapped exposure to acute lethal risks and chronic sublethal fitness costs under past, present, and future climates. For inactive birds in shaded microsites, the risks of lethal dehydration and hyperthermia will remain low during the 21st century. In contrast, exposure to conditions associated with chronic, sublethal costs related to progressive body mass loss, reduced nestling growth rates, or increased breeding failure will expand dramatically. For example, by the 2080s the region will experience 10–20 consecutive days per year on which Southern Pied Babblers (Turdoides bicolor) will lose ∼4% of body mass per day, conditions under which this species’ persistence will be extremely unlikely. Similarly, exposure to air temperature maxima associated with delayed fledging, reduced fledgling size, and breeding failure will increase several-fold in Southern Yellow-billed Hornbills (Tockus leucomelas) and Southern Fiscals (Lanius collaris). Our analysis reveals that sublethal costs of chronic heat exposure are likely to drive large declines in avian diversity in the southern African arid zone by the end of the century.

Heat dissipation behaviour of birds in seasonally hot arid‐zones: are there global patterns?

“…We identified all observations made at T air between 35 and 40°C and then calculated the proportion of observations in which birds were active within this T air range for each species. The range was chosen to be consistent with Smit et al (), and because it is a biologically relevant range wherein arid‐zone species begin to show deleterious effects of high temperatures on foraging efficiency and reproductive success (Conradie et al ). We then logit‐transformed these proportion data for analyses.…”

“…Species living in arid, seasonally hot environments are among those most vulnerable to climate change impacts, given that temperature extremes will become more pronounced in coming decades (Blendinger , Bolger et al , Cunningham et al , Conradie et al ). Birds are ideal models for investigating the effects of increasing temperatures in these environments, as their physiological and behavioural responses to high temperatures have quantifiable consequences for correlates of fitness (Smit et al , McKechnie et al ).…”

“…While useful, this approach often disregards the functional relationships that species share with their environment (Hampe , Kearney and Porter , Gasner et al ) and with each other (Araújo and Luoto ). An increasingly popular alternative approach involves predicting the maximum spatial distribution of a given taxon by integrating its physiology, physical environment and resource availability into a mechanistic distribution model (Hijmans and Graham , Kearney and Porter , Albright et al , Conradie et al ). A major impediment to using this approach is that the physiological and behavioural data required for these complex models are lacking for most species (Heikkinen et al , Hijmans and Graham , Milne et al ).…”

Endocrinology of thermoregulation in birds in a changing climate

“…Thus, the first aim of this review is to provide an overview on thermoregulation in birds and its endocrine and molecular mechanisms, pinpointing gaps in current knowledge and recent developments. We focus on birds, because they are researched widely across the globe, and because recent work has identified their substantial vulnerability to climate change (Conradie et al, 2019;Riddell et al, 2019). However, many of the future challenges in light of climate change are not taxonspecific.…”

Thermal Imaging of Beach-Nesting Bird Habitat with Unmanned Aerial Vehicles: Considerations for Reducing Disturbance and Enhanced Image Accuracy

“…A rapidly expanding area of research in avian biology seeks to understand how high temperatures affect survival and reproductive success in order to predict population persistence. Recent heatwaves have caused widespread mortality in birds [40], and heat-related mortality is predicted to locally extinguish bird populations in the southwestern United States [41] and southern Africa [42] in response to continued climate change. Nearly all of North America's bird species are expected to experience increased extreme heat events in the future, which contributes to predictions that two-thirds of North American birds are at increased risk of extinction as a result of climate change [43].…”