From the Introduction:
This review aims to answer the question: what is the threat of climate change to birds? Knowledge in this field is advancing rapidly. More is known about birds than any other class of animals, and of all groups of plants and animals the scientific analysis of likely future impacts from climate change is most developed for birds. Furthermore, birds provide some of the clearest examples of impacts already underway.
However, to date relatively few studies -- with some notable exceptions -- seek to provide an overarching view of how birds as a group are responding to climate change at the regional, continental or global level. At the same time, hundreds of localised studies on individual bird species or groups of species provide insight into how the threat is playing out in a multitude of ecosystems. This research is most detailed in Europe and North America, with far fewer studies from Asia and the southern hemisphere.
This review seeks to provide a global overview of current effects of climate change on birds as well as a picture of future impacts. It provides a scientific assessment of current research data, achieved by surveying hundreds of research articles and reports on the topic.