Climate change will kill off many bird populations, but in some cases it’s not the heat that will do them in. Instead, less precipitation is likely to have the heaviest impact, according to a study published online ahead of print in Global Change Biology. To come to these findings, researchers analyzed the distribution and abundance of 132 bird species over a 32-year period in a region stretching from California to northern British Columbia. Precipitation was shown to be the most accurate predictor of bird population trends, acting as a factor in almost 60% of the species studied and playing the largest role in the wettest month, December. This is likely because winter snowfall has critical carry-over effects in spring and summer, as runoff from snowmelt can impact stream flow, plant growth, and the availability of insects. Because the Western region of North America is expected to experience fewer but more intense precipitation events, this will likely have further negative effects on species that require a consistently wetter environment in order to thrive. One species that is particularly vulnerable to drier conditions in the Pacific Northwest is the rufous hummingbird (Selasphorus rufus, pictured), which is declining at a rate of 3% annually.