Fluctuations of Vanessa cardui butterfly abundance with El Niño and Pacific Decadal Oscillation climatic variables


Robert Vandenbosch, tel. (206) 543-1090, fax (206) 685-8665, e-mail: v@npl.washington.edu


Annual 4th of July Butterfly Count data spanning more than 20 years are examined to explore Vanessa cardui (Painted Lady) population fluctuations with ENSO (El Niño) and Pacific Decadal Oscillation (PDO) indices. California, Colorado and Nebraska censuses exhibit a strong positive correlation with the strong El Niño events of 1982–1983 and 1997–1998 and the weaker event of 1991–1992. Regression analysis shows the population fluctuations are strongly coupled to climate variations on both short (El Niño) and longer (Pacific Decadal Oscillation) time scales. Recognizing the sensitivity to these time scales is important for predicting longer-term global climate change effects.