DECADES OF RIPARIAN BREEDING BIRDS SHOW PERSISTENT REDUCTION AFTER EXTREME HEAT
|Dave L Riensche; email@example.com;
Historical records show that diverse Canaries in our “coal mine” environment generally have been disappearing, despite protections. Since 1994, we have been conducting periodic, consistent breeding bird censuses in a protected riparian area on San Francisco Bay’s east (downwind) shore, relatively stable in local weather and vegetation. We detected an overall decline in breeding birds there, hypothetically corresponding to steadily increasing human activity in adjacent areas. Yet bird declines were not steady at all. Reports of unusually warm, calm weather around San Francisco Bay in 2004, and unusually warm, humid weather in 2006 prompted us to compare these old and newer bird data to weather records, which also illustrated a 2000 heat event locally. To test hypothetical effects of these unusual heat events of 2000/2004/2006, we compared bird data before and after those years, yielding a clear, persistent reduction in most breeding avifauna, after those events. Annual Maximum temperatures also became repeatedly >36 degrees C, which might be a threshold for many of these birds. Such heat again in 2017 did not appear to decrease these bird populations further. Historical data from 1973 suggested >34% more territories there, but only minor subsequent heat through our 1994- data, illustrating additional limits on these birds. Trends in comparing general weather and breeding bird data might not be clear in such coastal, relatively benign climates, within birds’ adaptations. Yet occasional, extreme environmental events, particularly in a protected area avoiding much habitat degradation, appears to have additional major negative, lasting effects on these breeding populations.