Data from the MAPS program form the basis of much of IBP’s work assessing and predicting the effects of climate change on birds. Scientists have hypothesized that climate change, which is leading to earlier springs, may cause more phenological (timing), mismatches between birds and their food sources because plants, insects, and the birds that eat them may adjust to the earlier springs at different rates. A recent study by Dr. Casey Youngflesh of Clemson University, as well as colleagues from IBP, UCLA, and other institutions, used 18 years of MAPS data on 41 songbird species to examine phenological mismatch between breeding songbirds and spring “green-up.” They also explored the consequences of mismatch for birds’ productivity, or the number of young they produce.

This phenological mismatch has consequences. The study showed that when birds experienced larger mismatches, they produced fewer young. This loss of productivity could have significant implications for bird populations. The researchers estimated that if climate change proceeds as projected, the number of young that birds produce could decline by about 12% by the end of the century. This is concerning given the population declines many of these species have experienced over the last 50 years.

An earlier study by Youngflesh and colleagues from IBP and UCLA used MAPS data to explore how climate change is affecting the size and shape of birds. Using more than 250,000 banding records from 105 bird species, they found that within species, smaller body size was associated with warmer temperatures over space and time. Individuals breeding at lower latitudes are smaller, and as the climate warms, individuals at a given latitude are getting even smaller over time. A smaller body size increases the ratio of surface area to volume which makes it easier for an organism to shed heat.

While species do seem to be adapting their body size to a warmer climate, body size responded more slowly over time than it did over space (latitude). This suggests that birds may not be changing their morphology quickly enough to keep up with the warming climate. Youngflesh and colleagues note that populations and species of birds that already live in hot, arid environments may be especially at risk as climate warms because they are closer to their maximum tolerable temperatures.