Irruptive migration, or movements that are irregular in timing and extent, are common in many boreal forest species that feed on conifer seeds. Potential population consequences of such movements have not been studied, largely because the population of interest is literally a moving target. Broad-scale citizen science surveys may overcome this limitation, and Red-breasted Nuthatch (Sitta canadenis) is a good choice for investigation because it is well sampled in all seasons and is less nomadic than many other irruptive species. Fall nuthatch abundance at the Long Point Bird Observatory (LPBO, southern Ontario, Canada) is shown here to be correlated with winter abundance across the entire eastern U.S. as reported by the Christmas Bird Count, Project FeederWatch, and eBird. Irruption dynamics at LPBO can therefore serve as a surrogate for events taking place at much broader regional scales. Increased size of fall irruption recorded at LPBO corresponded with reduced Breeding Bird Survey abundance throughout eastern Canada the following summer. Despite presumed benefits of irruption as an adaptive response to food shortage when population levels are high, negative population consequences can ensue.
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Vol. 136 • No. 2