Weather‐dependent survival: implications of climate change for passerine population processes

Abstract

Understanding demographic processes will be essential to construct robust models of population responses to climate change. We show that survival is related to the strength of the North Atlantic Oscillation in five out of ten British resident passerine species, and explore the importance of biologically more specific variables (duration of winter frosts and snow periods; occurrence of cold, wet days; spring temperature; and summer drought). The most important variables differed between species in relation to differences in foraging strategy. In almost all cases, first‐year survival was influenced by weather more than was the survival of adult birds. Particularly vulnerable species, such as the Wren Troglodytes troglodytes, may exhibit a 25% reduction in juvenile survival rates due to adverse weather within the range experienced in the last 30 years; variation in survival by 10% or more is commonplace in most species. Thus, climate influences on food availability may provide the mechanism by which populations will alter under changed climatic conditions, though the presence of density dependence may reduce the impact of this on long‐term population trajectories.

Effects of extreme weather on two sympatric Australian passerine bird species

“…Cold exposure can cause mortality of small passerines in winter, even in conditions that are relatively mild [17,22,44]. For example, prolonged exposure to cold wet weather with daily minima less than 58C was associated with high mortality in a range of similar-sized passerine species in Britain [23]. Although such conditions are relatively mild, they have been shown to cause thermal stress in small passerines, increasing the metabolic costs of keeping warm at a time when food is limited [22,23,29].…”

“…Here, we use a statistical definition of climate extremes, as the tails in either end of the summer and winter temperature range at the study site [24]. Specifically, for each year, we quantified the number of cold wet days on which rainfall more than 0 mm and minima less than 58C were recorded (NColdWetDays) and the number of hot dry days with no rainfall and maxima more than 308C (NHotDryDays), because cold wet conditions in winter and hot dry conditions in summer can cause thermal stress and affect fitness [14,22,23].…”

“…For example, prolonged exposure to cold wet weather with daily minima less than 58C was associated with high mortality in a range of similar-sized passerine species in Britain [23]. Although such conditions are relatively mild, they have been shown to cause thermal stress in small passerines, increasing the metabolic costs of keeping warm at a time when food is limited [22,23,29]. In the case of species at our study area, temperatures rarely dropped below zero (2 days in 37 years) so temperatures less than 58C were the most severe experienced, and can be considered to represent ECEs.…”

“…Our study populations have experienced increases in mean temperatures in winter and summer. We focus on occurrence of 'extremes' (ECEs) defined by the extreme tails of the temperature distribution at our study site, which represent conditions that affect survival in a range of bird species including small passerines [15,22,23]. In particular, we test whether survival is more clearly predicted by occurrence of extreme events than by mean temperatures.…”

Weather conditions and conspecific density influence survival of overwintering DunlinCalidris alpinain North Wales

“…Declines in many migratory bird species have increased the demand to create accurate models of their life histories, in order to identify the factors affecting their populations (Warnock et al 1997, Green 1999, Robinson et al 2005, 2007, Duriez et al 2009, Schaub & Royle 2014. Long-term and large-scale monitoring and data collection that allows the estimation of key parameters, such as population size, breeding productivity and survival rates (Clobert & Lebreton 1991, Pienkowski 1991, Lebreton et al 1992, will improve the understanding of the demography of given species and define their requirements to help target conservation efforts (Pienkowski 1991, Sandercock 2003, Stroud et al 2006.…”