Predictive modeling of climate change impacts assumes the existence of a climatic niche that ultimately defines the limits of each species’ range. Climatic variables that strongly correlate with occurrences in one time period are expected to drive patterns of occurrence in future time periods. It remains largely unknown, however, just how valid these assumptions are. We used historical bird survey and resurvey data from 82 sites, sampled a century apart throughout the Sierra Nevada of California, to test for a relationship between a species’ climatic niche and patterns of movement in climate space over time. We used the entire North American breeding range (as defined by museum specimens) for each of our 53 focal species to define the optimal average temperature and precipitation conditions in which each species breeds. These estimates were compared against each species’ corresponding historic and modern estimates of breeding season temperature and precipitation in the Sierra Nevada. Observed responses to climate change were evident by species moving towards their optimal range-wide estimates of temperature or precipitation (“niche tracking”). Independent predictions of these movements were based on climatic niche models and compared against the observed movements in the Sierra Nevada in order to determine whether documented movements conformed to model expectations.

Results/Conclusions

Changes in geographic range and climate resulted in bird species shifting their average climatological range over time. Comparing the directions of these shifts relative to the position of species’ climatic niches, we found that 48 of 53 avian species were tracking their climatic niche by shifting their climatic range toward the climatic optimum on either temperature or precipitation axes. Additionally, the independent predictions of climatic sensitivity derived from niche models on range-wide distributions significantly predicted particular environmental gradients tracked by species. Finally, we used occupancy models to examine support for different hypotheses relating colonization and extinction at sites to climatic niche dynamics. In 50 out of 53 species, models including the climatic position of each site relative to the niche centroid explained occupancy change dynamics better than a null model with constant probabilities. Our results indicate that not only have birds in the montane regions of California moved in response to climate change over the last century, but that they have moved in a predictable fashion. Consequently, our results imply that predictive climatic models derived from niche theory might be used successfully to plan for future movements.