A study examines links between rising temperatures and nesting in Californian birds. Species respond to climate change by shifting their geographical ranges poleward or upward to remain in their preferred temperature zones, or by shifting the timing of life history events to mirror changes in resource availability. Jacob Socolar and colleagues examined the relationship between temperature and breeding dates for 150 bird species in California's Coast Range and 160 bird species in California's Sierra Nevada. Pairing bird data collected from 1911-1940 with 2003-2010 resurveys performed at the same sites, the authors found that breeding dates for California birds have advanced by approximately 5-12 days. The shift in nesting dates reduced average temperatures during nesting by more than 1 °C--approximately the same magnitude that average regional temperatures have warmed over the same period. Using national nest monitoring data, the authors found that in the early summer across North America, warm temperatures are associated with high nest success in the cold parts of the birds' ranges and low nest success in the warm parts of the birds' ranges. By nesting earlier, California birds are nesting at temperatures similar to those at which they nested a century ago, thus reducing the need for range shifts, according to the authors.
Article #17-05897: "Phenological shifts conserve thermal niches in North American birds and reshape expectations for climate-driven range shifts," by Jacob B. Socolar, Peter N. Epanchin, Steven R. Beissinger, and Morgan W. Tingley.