Fitting the lens of climate change on bird conservation in the twenty-first century

Understanding and predicting future ecological impacts of climate change, and then developing a conservation strategy to minimize the negative impacts on biodiversity, remains one of the greatest environmental challenges of the twenty-first century. We lack a robust understanding of how climate variability (e.g., temperature, precipitation) itself influences the biology of organisms and, when evidence points to a species being vulnerable to the effects of climate change, there is a lack of specific and timely recommendations for managers to reduce that vulnerability. This chapter reviews how we assess which species are most impacted by climate change and then provides a framework and examples of common strategies and tactics managers can use to incorporate climate change adaptation into bird conservation. In doing so, we present a suite of strategies designed to translate broad conservation concepts into targeted and prescriptive actions for birds.

Predator–prey interactions and climate change

Climate change is likely to impact all trophic levels, although the response of communities and ecosystems to it has only recently received considerable attention. Further, it is expected to affect the magnitude of species interactions themselves. In this chapter, we summarize why and how climate change could affect predator–prey interactions, then review the literature about its impact on predator–prey relationships in birds, and provide prospects for future studies. Expected effects on prey or predators may include changes in the following: distribution, phenology, population density, behaviour, morphology, or physiology. We review the currently available information concerning particular key topics: top-down versus bottom-up control, specialist versus generalist predators, functional versus numerical responses, trophic cascades and regime shifts, and lastly adaptation and selection. Finally, we focus our review on two well-studied bird examples: seabirds and raptors. Key future topics include long-term studies, modelling and experimental studies, evolutionary questions, and conservation issues.

Consequences of climatic change for distributions

Species’ distributions, population sizes, and community composition are affected, directly and indirectly, by climatic changes, leading to changes in location, extent, and/or quality of distributions, range fragmentation or coalescence, and temporal discontinuities in suitable conditions. Quaternary fossil records document these responses, emphasizing individualism of species’ responses and impermanence of communities. Recent observations document similar changes attributable to recent climatic changes, including rapid decreases and increases in ranges and/or populations. Both also document extinctions associated with rapid climatic changes. Modelling studies predict substantial changes in species’ distributions, population sizes, and communities in response to future climatic changes. Implicit assumptions that genetic variation enabling adaptation is ubiquitous throughout species’ ranges, or that gene flow may be sufficiently rapid to allow adaptation, may be invalid. Work is needed to investigate spatial structuring of adaptive genetic variation and rates of gene flow, and to develop new models. Without this, species extinction risks may be severely underestimated.

Projected population consequences of climate change

To anticipate the future state of avian populations in a changing climate, forecasts must rigorously account for uncertainty in future climate and population processes. This requires fusing IPCC-class climate projections with population models. In this chapter, we review the steps for developing climate-dependent population forecasts, while highlighting key biological considerations and methodological challenges. Throughout, we use examples from a long-term study of emperor penguins (Aptenodytes forsteri) to illustrate key points. We then conduct a literature review to compile a list of studies that have linked IPCC climate models with avian population models. At present, only a handful of studies have fused IPCC climate projections with avian population models, and generalities across systems thus remain elusive. Yet, the increasing availability and sophistication of climate models, coupled with new population modelling methods, hold promise for reducing forecast uncertainties and improving the relevance of population forecasts for policy.

Physiological and morphological effects of climate change

The direct impacts of higher temperatures on birds are manifested over timescales ranging from minutes and hours to years and decades. Over short timescales, acute exposure to high temperatures can lead to hyperthermia or dehydration, which among arid-zone species occasionally causes catastrophic mortality events. Over intermediate timescales of days to weeks, high temperatures can have chronic sub-lethal effects via body mass loss or reduced nestling growth rates, negatively affecting sev eral fitness components. Long-term effects of warming manifested over years to decades involve declining body mass or changes in appendage size. Key directions for future research include elucidating the role of phenotypic plasticity and epigenetic processes in avian adaptation to climate change, examining the role of stress pathways in mediating responses to heat events, and understanding the consequences of higher temperatures for species that traverse hot regions while migrating.

Changes in migration, carry-over effects, and migratory connectivity

Studies of the timing (phenology) of bird migration provided some of the first evidence for the effects of climate change on organisms. Since the rate of climate change is uneven across the globe, with northern latitudes experiencing faster warming trends than tropical areas, animals moving across latitudes are subject to diverging trends of climate change at different stages of their annual life cycle, and, consequently, they can become mistimed with the local ecological conditions, with potentially negative effects on population size. This chapter reviews the modifications induced by climate change in different migration traits, like the timing of migration events, the distribution of organisms, and the direction and the speed of movements. It also considers the effects of ecological carry-over effects and migratory connectivity on the response of birds to climate change.

Climate change in other taxa and links to bird studies

Phenological responses to climate change are the most commonly measured responses of plants and animals to climate change, and most studies show that species are advancing the timing of their seasonal activities in response to warming temperatures. Birds interact with a wide range of other species, playing roles as herbivores, predators, prey, and disease hosts. Because the species they interact with are all likely changing phenology and distribution in response to the changing climate, but often at different rates, mismatches with historical patterns are affecting ecological communities in a variety of ways. Unexpected phenomena such as increases in frost damage, and less surprising ones such as developing phenological mismatches between migratory and sedentary species, are discussed as case histories illustrating these changes.

Predicting the effects of climate change on bird population dynamics

Climate variation strongly influences fluctuations in size of avian populations. In this chapter, we show that it is difficult to predict how the abundance of birds will respond to climate change. A major reason for this is that most available time series of fluctuations in population size are in a statistical sense short, thus often resulting in large uncertainties in parameter estimates. We therefore argue that reliable population predictions must be based on models that capture how climate change will affect vital rates as well as including other processes (e.g. density-dependences) known to affect the population dynamics of the species in question. Our survey of examples of such forecast studies show that reliable predictions necessarily contain a high level of uncertainty. A major reason for this is that avian population dynamics are strongly influenced by environmental stochasticity, which is for most species, irrespective of their life history, the most important driver of fluctuations in population size. Credible population predictions must therefore assess the effects of such uncertainties as well as biases in population estimates.

Conclusions

Since the first edition of this book we have made significant advances in understanding how climate change is affecting the ecology and evolution of birds. We also have much better tools and databases for future research at a global scale. Forecasting the projected population size and distribution of species has also improved and is rapidly becoming more rigorous. Nonetheless, there are still several outstanding issues with current research on the effects of climate change on birds. One of the most important is that research is compartmentalized into specific topics (e.g. phenology or modelling) and one part of the annual cycle (e.g. breeding or migration). We believe that more collaborative teams are needed to examine the entire annual cycle of species and how it relates to population size. Luckily, there are some excellent examples of this new approach which gives us some optimism for dealing with an uncertain future.

Evolutionary consequences of climate change in birds

There is now overwhelming evidence that the recent rapid climate change has multiple consequences for birds: their abilities to adapt to climate change is thus a major issue. To understand the evolutionary consequences of climate change, an assessment of how it alters selection pressures is needed. As expected, climate change increases selection for earlier breeding but non-intuitive selection patterns are likely to arise for traits other than phenology. Evolutionary responses to these new selection pressures depend on the evolutionary potential in wild bird populations. Heritability alone is not sufficient to predict responses to selection, as many genetic factors (e.g., genetic correlations, indirect genetic effects) can affect evolutionary trajectories. Altogether, studies investigating the nature of responses to climate change in wild populations (plastic vs microevolutionary responses) are still scarce but suggest that the majority of responses would be due to plasticity.