The study reviews the observed impacts of climate change on birds and mammals and aims to identify the relationships between their response to climate change and a set of selected intrinsic traits and spatial factors, based on a total of 70 studies covering 120 mammal species and 66 studies relating to 569 bird species whose populations had (or sought evidence for) a response to climate change in recent decades.

The authors found evidence of observed responses to recent changes in climate for almost 700 species, but only 7% of mammals and 4% of birds that showed a negative response are coded on the IUCN Red List of Threatened Species as threatened by ‘climate change and severe weather’ under the ‘threats classification scheme’.
Mammals most at risk from climate change are not fossorial, and have low precipitation seasonality within their distributions. For birds, negative responses in both breeding and non-breeding areas were generally observed in species that live at high altitudes, and have low temperature seasonality within their distributions. In addition, large changes in temperature in the last decades negatively affected both mammals and birds.

According to predictions, it is likely that for 47% of threatened mammals and 23% of threatened birds at least one population has already responded negatively to climate change. “This implies that, in the presence of adverse environmental conditions, populations of these species have a high probability of being negatively impacted also by future climatic changes”, says lead author Dr. Michela Pacifici at Sapienza University of Rome. The lab is partner of the IUCN Red List with the Global Mammal Assessment Program.

The list of charismatic species likely to have been negatively impacted include the snow leopard, the cheetah, the Bornean orangutan, both species of elephants, the western and eastern gorillas, the Javan, Sumatran and black rhinos among mammals, and the Fiordland crested penguin, the Spanish eagle and the Steller's eider among birds.
By making predictions on the species for which the levels of climatic hazard experienced are known, the authors provide the first quantification of the number of taxa that may have already been impacted, and also validate trait-based vulnerability assessments.

The results of this work, published in the journal Nature Climate Change, suggest that the impact of climate change on mammals and birds in the recent past is currently greatly underappreciated, and this may have important implications for both the scientific community and intergovernmental policy fora.
“Solid evidence is accumulating that climate change has already affected some species, but not others. Based on this evidence, we identify the traits that can help species cope with change, or doom them to decline and endangerment” says lead Dr. Carlo Rondinini, coordinator of the Global Mammal Assessment Program at Sapienza University of Rome. “Our conclusion is that many more species not yet affected may be threatened by climate change in the near future”.