Landbird Productivity in Central Coastal California: The Relationship to Annual Rainfall, and a Reproductive Failure in 1986

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Abstract
The avian productivity of 51 locally breeding species in coastal grassland, coastral scrub, and mixed evergreen forest habitats was estimated from 11 years of standardized mist-netting data collected between 10 May and 17 August at Point Reyes Bird Observatory''s Palomarin Field Station. A relationship between the number of young birds banded per 100 net hr and the amount of annual (winter) rainfall during the previous season was apparent for the 10 years 1976 to 1985: productivity was low (19 to 32% below the 10-year mean) in years of extremely low rainfall, increased to a maximum (21 to 39% above the 10-year mean) in years of average or slightly above average rainfall, and decreased substantially (20% below the 10-year mean) in years of very heavy rainfall. The number of young birds banded per 100 net hr in 1986, however, was 62.3% below the previous 10-year mean and fell well outside the above relationship. This high level of reproductive failure occurred in most of the 51 locally breeding species and was independent of migratory behavior, habitat choice, and nest location. It was not independent of foraging behavior, however, as swallows and woodpeckers, species that feed their young on insects produced in decomposer- or detritus-based food chains rather than in primary production-based food chains, showed no significant reduction in productivity. Timing of the derease in young birds suggests that the onset of reproductive failure occurred in mid-May, well after the nesting season began. Such a large-scale reproductive failure of virtually an entire landbird community has not been reported before and no obvious weather factors appear to explain it. Preliminary data indicate that the reproductive failure was not confined to the vicinity of Palomarin or to central coastal California but rather extended over much of northern California even to the west slope of the Sierra Nevada. It is interesting, but perhaps only coincidental, that several circumstances of this phenomenon, including its timing, appear to coincide remarkably well with the passage of a radioactive "cloud" from the Chernobyl [USSR] nuclear power plant accident and associated rainfall.