Temperature and Long-Term Breeding Trends in California Birds: Utilizing an Undervalued Historic Database

Publication Number:    CEC-500-2010-002

Abstract:

Long-term data recorded before regional temperatures were greatly affected by human emissions of greenhouse gases provide a historical baseline with which to compare modern and future trends. Long-term ecological data needed to investigate the influence of temperature on the time of songbird breeding are rare. Significant amounts of data exist in collector descriptions of bird eggs taken in the wild from mid-1800s to mid-1900s. The researchers draw on these data from three museums and find that seven of 21 species examined had significant trends in laying date, with some species laying eggs earlier and others later. The largest changes were in the oak titmouse with an average shift of 20 days later per decade and phainopepla with the largest earlier shift of 8 days earlier per decade. The associations between the average California temperatures a month or two before laying and times of breeding were strong for six out of the nine resident California songbirds. For migrating species, only two of nine had a strong association between laying date and mean California temperature. These findings provide a baseline to which modern and future phenological shifts may be compared and calibrated. The researcher team offers suggestions for future studies and recommendations for California. 

Keywords: Global warming, avian, non-traditional data, spring phenology, museum egg collection, historic data, breeding date, directional trend, temperature anomaly, oology, laying date

Author(s):  Judsen Bruzgul, Terry Root

Commission Division:    Technology Systems Division - R&D, PIER (500)

Office/Program:    PIER: Public Interest Energy Research

PIER Program Area:    Climate Change

Date Report Completed:    February 2010

Date On Line:    02/26/2010

Acrobat PDF File Size: 47 pages, 1,600 kilobytes**