Associations between changing climate and body condition over decades in two southern hemisphere passerine birds

Abstract

Background: Climate change presents considerable challenges for endotherms because they must maintain high, relatively constant body temperatures across a range of environmental conditions to ensure survival and optimise performance. Individuals exposed to changing weather must manage energy and water allocation to maintain thermal homeostasis, with consequences for body condition, and hence there is potential for selection because body condition is strongly linked to fitness. Understanding how weather drives changes in body condition is therefore fundamental to understanding how fitness is affected by climate change. Here we test for associations between weather and body condition and how this changes over time, in two co-existing species of small insectivorous passerines, the red-winged fairy-wren, Malurus elegans and white-browed scrubwren, Sericornis frontalis, that have been the subject of a ringing study for 39 years in temperate south-western Australia. The study populations have experienced increases in minimum temperatures in winter and summer as well as decreases in the frequencies of days with thermal minima < 5°C, but the summer climate remains relatively mild with few days experiencing thermal maxima > 35°C. Although, warming temperatures may reduce thermoregulatory costs, repeated exposure to hot conditions has been shown to have negative effects on body condition. Thus, we predict that the reduction over time in daily minima < 5°C, along with the influence of increased maximum and minimum temperatures in summer and winter, will have positive effects on body condition. Results: In accordance with thermoregulatory predictions, colder daily minima in the range 1-19°C prior to capture were associated with reduced body condition in winter in both species. Furthermore, in summer, in fairy-wrens but not scrubwrens, warmer daily maxima were associated with increasing body condition, and repeated exposure to temperatures > 30°C over consecutive days was negatively associated with body condition. Body condition increased over the 39 years of the study for fairy-wrens but there was no change in scrubwrens, which is consistent with observed within-season associations between body condition and weather, and the change in climate over time.

How extreme is extreme? Demographic approaches inform the occurrence and ecological relevance of extreme events

“…Previous studies have found that body condition increases winter survival Grubb 2002, Danner et al 2013) and can interact with temperature to modify an animals' sensitivity to extreme weather (Williams et al 2014, Gardner et al 2018. We found some support that body condition influenced winter survival, but not an individuals' sensitivity to extreme winter weather.…”

“…, Gardner et al. ). We found some support that body condition influenced winter survival, but not an individuals’ sensitivity to extreme winter weather.…”

“…) or condition (Gardner et al. ) may play a critical role in mediating the impact of extreme heat or cold on animal populations.…”

“…In contrast, smaller-bodied endotherms may confer thermal benefits during extreme heat because their larger surface area to volume ratios enables more efficient heat dissipation (McKechnie and Wolf 2010). Therefore, body size (Gardner et al 2017) or condition (Gardner et al 2018) may play a critical role in mediating the impact of extreme heat or cold on animal populations.…”

Compensatory Breeding in Years Following Drought in a Desert-Dwelling Cooperative Breeder

“…Variations in seasonal weather patterns and the occurrence of extreme weather events such as droughts, floods, and heatwaves are among the primary drivers of variation in individual success in vertebrates, influencing reproduction and survival both directly and indirectly, often via effects on resource availability (Harrison et al, 2011). To date, most research on the within and between season effects of weather patterns and extreme events has focused on the influence within an annual cycle (Saino et al, 2011;Laplante et al, 2019) of (a) conditions during early development on individual success as a nestling (Pérez et al, 2008;Auer and Martin, 2017;Ospina et al, 2018), fledgling (Blomberg et al, 2014;de Zwaan et al, 2019), or adult (Porcelli et al, 2016;Hsu et al, 2017;Marshall et al, 2017) and (b) seasonal weather conditions on body mass (Loison and Langvatn, 1998;van de Pol et al, 2016), behavior (Akresh et al, 2019;Rauber et al, 2019), survival (Berryman and Lima, 2006;Gardner et al, 2017Gardner et al, , 2018Woodworth et al, 2017;Chiffard et al, 2019), and reproductive investment (Clutton-Brock et al, 1991;Monteuil-Spencer, 2017).…”