Kelly, John P., T. E. Condeso.
Twelve models addressing the current and delayed effects of seasonal rainfall and rainfall volatility (a measure of storm intensity) were used to evaluate changes in nest abundances of herons and egrets in the San Francisco Bay area, from 1991 to 2010. Wetter- or drier-than-average conditions, two winters before nesting, were associated with reduced growth rates of Great Egret (Ardea alba) nest abundance. Similarly, growth rates of Great Blue Heron (Ardea herodias) nest abundance were maximized near average levels of rainfall volatility two winters prior nesting. Annual growth rates of Snowy Egret (Egretta thula) and Black-crowned Night-Heron (Nycticorax nycticorax) abundances declined with heavier-than-usual winter rainfall volatility immediately prior to nesting and with increases in spring rainfall volatility 2 years prior to nesting. The dynamics of heron and egret nest abundances were not associated with annual production of fledglings within the region, The results suggest the possibility of regional declines in the growth or resilience of heron and egret abundances with increasingly rainy or stormy seasonal conditions in northwestern California.
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Kelly, J.P. and T. E. Condeso. 2014. Rainfall Effects on Heron and Egret Nest Abundance in the San Francisco Bay Area. Wetlands (2014) 34: 893. doi:10.1007/s13157-014-0551-0