With the launch this year of the latest reports by the Intergovernmental Panel on Climate Change (IPCC) and the growing public awareness of the very real impacts that climate change is already having on the natural world, Birds and Climate Change is a timely, useful, readable book.
The IPCC says that global warming is “unequivocal,” and that it is “very likely”—that is, there is a 90 percent likelihood—that humans are the major drivers of this climate change. Birds are perhaps the best-studied taxa in ecology because they are diurnal, use many of the same senses as humans, are ubiquitous, and are relatively easy to observe. As a result, there are many long-term data sets on a wide range of different aspects of bird ecology that are waiting to be explored with respect to climate change.
This book brings together many of the key practitioners in this field to provide a good overview of the current understanding of birds and climate change. Also, like all good books, Birds and Climate Change highlights much of what is not known, thus constituting a useful source for people looking for important questions to answer.
The book is a collection of 11 chapters on a variety of topics, including phenology (the study of the timing of natural events), breeding performance, evolutionary processes, population dynamics, and community structure. Although Birds and Climate Change was based on a workshop held in 2003, it is still a key reference today. The authors undertook meta-analyses and reviews that have not been published before, and extensive reference lists lead the reader to the original texts. (Unfortunately, however, the publisher provides only the authors and journal references, not the titles of the pertinent articles.)
The first chapter is a particularly good review of studies of the arrival and departures of migrant birds on their breeding grounds. Lehikoinen, Sparks, and Zalakevicius synthesize the results from more than a thousand time series to show that species are arriving on their breeding grounds earlier than before, and that many are departing later. It appears that long-distance migrants are not advancing their arrivals as much as species that fly shorter distances to migrate, and a later chapter, by Visser, Both, and Lambrechts, describes how this could affect breeding performance and population status. For example, long-distance migrants such as pied flycatchers (Ficedula hypoleuca), which time their migration from Africa on the basis of photoperiodic or other endogenous cues unrelated to temperature, are becoming out of synchrony with conditions at the breeding grounds. Thus, they return to their breeding grounds too late, when the caterpillars they feed to their young are no longer abundant. Populations that are unable to advance their arrival date are experiencing population declines. The authors then discuss how birds may cope with climate change through modifications of individual bird behavior, or by genetic adaptation and evolution.
Two interesting chapters follow, one by Coppack and Pulido on the photo-periodic response and adaptability of life cycles, and the other by Pulido and Berthold on microevolutionary responses to climate change. In bird life cycles, photoperiods (i.e., light–dark regimes) are often very important in determining when birds come into breeding condition, when they moult, and when they migrate. These responses can vary according to latitude, because, for example, the lengthening of days in spring happens at a faster rate at higher latitudes. Populations appear to be adapted to these differences. If species shift their breeding range northward in response to climate warming, however, the photoperiodic responses of the species, in determining when they become physiologically ready for breeding, might be inappropriate at the higher latitudes, leading to mistiming. Studies of adaptation and evolution are still rare, but a small number do show that species can exhibit individual plasticity through nongenetic adaptation, and that rapid evolutionary change through natural selection is possible. Further research is urgently needed in this area, as it is essential for understanding whether and how wildlife can adapt to climate change.
Another series of chapters in Birds and Climate Change looks at population processes. Dunn reviews an extensive body of work on egg-laying dates and breeding performance. Unsurprisingly, many studies show that birds are tending to lay earlier in response to climate warming, but the impacts on breeding performance are mixed. Some birds apparently benefit through larger clutch sizes and fledging success, but others experience detrimental effects resulting from changes in rainfall patterns or from mistimed reproduction.
Dunn also discusses why some 40 percent of species show no apparent response to changing temperatures; for example, larger-bodied species appear to be less affected, possibly because their thermoregulatory costs are lower than those of smaller-bodied species in temperate climates. Also, generalist species, that is, those with a broader range of diet, may be less constrained by the impacts of ambient temperature on one component of their food supply than specialist feeders that rely on a small range of prey types. Clearly, there are avenues for further research that are waiting to be explored.
Global warming has produced some interesting geographical patterns of climate change that are not uniform around the world, and these are reflected in the distributional patterns of birds, as discussed by Böhning-Gaese and Lemoine. They cite a number of studies from around the world showing that species distributions are shifting northward and into higher altitudes, but they also note that research in this area is scant compared with research on taxa such as plants and butterflies. There is even less information on bird communities and ecosystems. As species move at different rates, whole new communities will form, potentially leading to instability. Even within species, certain complexities have to be considered. For example, Saether, Sutherland, and Engen discuss how the population dynamics of a species might be affected. Several key questions emerge: Will the climate response be density dependent or density independent? Will climate changes operate primarily through productivity or through survival? Will climate change affect not only average values but also variability? Almost no population modeling has been done in this area yet.
A particularly useful feature of Birds and Climate Change is that most chapters include discussions of methodological issues and the sorts of problems that need to be considered and avoided. The availability of large historical data sets—gathered over large geographical areas and for many years by volunteer bird-watchers—has been essential in many studies of birds. Such data sets are equally valuable in the climate-change world, as Fiedler, Bairlein, and Köppen demonstrate in their analysis of data from European bird banding (affixing lightweight, coded, easily identifiable bands to birds' legs) to explore how migratory distances might be changing in response to global warming—a fascinating taste of what might be possible. In North America, data sets put together by organizations such as the Cornell Lab of Ornithology, Bird Studies Canada, and the California-based Institute of Bird Populations are likely to be the basis of many bird studies in that part of the world. I hope that this book inspires such studies on every continent, and especially from areas in the lower latitudes, because conditions and impacts are likely to be quite different in the tropics than they are in northern latitudes.
