Effects of extreme weather on two sympatric Australian passerine bird species

Abstract

One contribution of 14 to a theme issue 'Behavioural, ecological and evolutionary responses to extreme climatic events'. Despite abundant evidence that natural populations are responding to climate change, there are few demonstrations of how extreme climatic events (ECEs) affect fitness. Climate warming increases adverse effects of exposure to high temperatures, but also reduces exposure to cold ECEs. Here, we investigate variation in survival associated with severity of summer and winter conditions, and whether survival is better predicted by ECEs than mean temperatures using data from two coexisting bird species monitored over 37 years in southwestern Australia, red-winged fairy-wrens, Malurus elegans and white-browed scrubwrens, Sericornis frontalis. Changes in survival were associated with temperature extremes more strongly than average temperatures. In scrubwrens, winter ECEs were associated with survival within the same season. In both species, survival was associated with body size, and there was evidence that size-dependent mortality was mediated by carry-over effects of climate in the previous season. For fairy-wrens, mean body size declined over time but this could not be explained by size-dependent mortality as the effects of body size on survival were consistently positive. Our study demonstrates how ECEs can have individual-level effects on survival that are not reflected in long-term morphological change, and the same climatic conditions can affect similar-sized, coexisting species in different ways.This article is part of the themed issue 'Behavioural, ecological and evolutionary responses to extreme climatic events'.

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

“…Here, we test for direct associations and carryover effects between weather variables and body condition, and explore whether body condition may underlie winterrelated mortality. Our study populations have experienced increases in mean temperatures in winter and summer as well as a decrease in the frequency of days with thermal minima < 5°C [32]. However, despite a slight increase in the number of days > 35°C, the summer climate remains relatively mild and no associations with survival were found [32].…”

“…Studies that have investigated climate-related changes in body condition have tended to focus on migratory populations living at high latitudes where winter conditions are harsh, or on arid zone species where temperature extremes prevail in summer under conditions of low water availability. Here we test for associations between weather and body condition in two sedentary co-existing passerine bird species from temperate south-west Western Australia, red-winged fairy-wrens, Malurus elegans and white-browed scrubwrens, Sericornis frontalis, in populations which have been monitored over 39 years [32]. In a recent study of these populations, we showed that winter-related mortality in white-browed scrubwrens was associated with higher frequencies of cold, wet days with thermal minima < 5°C [32].…”

“…Here we test for associations between weather and body condition in two sedentary co-existing passerine bird species from temperate south-west Western Australia, red-winged fairy-wrens, Malurus elegans and white-browed scrubwrens, Sericornis frontalis, in populations which have been monitored over 39 years [32]. In a recent study of these populations, we showed that winter-related mortality in white-browed scrubwrens was associated with higher frequencies of cold, wet days with thermal minima < 5°C [32]. In addition, in both species mortality was associated with carry-over effects of weather conditions in the preceding season, suggesting climate-related changes in body condition may be involved.…”

“…Our study populations have experienced increases in mean temperatures in winter and summer as well as a decrease in the frequency of days with thermal minima < 5°C [32]. However, despite a slight increase in the number of days > 35°C, the summer climate remains relatively mild and no associations with survival were found [32]. We predict that reductions in selection pressures in winter (fewer wet days with minima < 5°C) along with positive effects of increased mean temperatures in both winter and summer, will have positive effects on body condition over time.…”

How birds cope physiologically and behaviourally with extreme climatic events

“…Many animals and plants are adapted to seasonal heat especially by using micro-habitats (for reviews see [15,32,33], see also Gardner et al [34], for longer term responses). This tolerance of what to us are extreme conditions can be exacerbated by further extreme events of even higher environmental temperatures.…”