… Interestingly, winter rainfall in the same year as acorn production-the factor most commonly thought to determine crop size-does not correlate positively with mean annual crop size of any of the species we studied. … For coast and canyon live oaks, mean acorn production is positively correlated with rainfall occurring one and (for canyon live oak) two years earlier.
#ACORN WOODPECKER DRIVERS#
So what does the future hold for our clown-faced friends? Is crop failure due to drought or just cyclical variation in acorn production? University of California’s Oak Woodland Conservation Workgroup sheds some light on the drivers of crop size:įor valley and blue oaks, the most important single factor is weather in April, the peak month for pollination, with crops being heavier in years when mean April temperatures are warmer. The valley oak crop is reasonably good but, overall, acorn production is the worst it has been since 2003, and less than half the crop production of 20. Blue oaks are generally fair to poor and it’s a fairly poor year for tanoaks. Results are particularly poor for live oaks: it is either the worst or next-to-worst year ever for coast live oaks, canyon live oaks, and interior live oaks. 2014 edition of the California Acorn Report, this is a medium-to-poor acorn year. This year appears to be one of those years.
Groups that exhaust their stores often abandon their territories and wander off in search of alternative food. N areas where there are large seasonal fluctuations in insects and other foods, year-round residency is dependent on the birds’ ability to store sufficient acorn mast to provide food throughout the winter. Only about half their diet actually consists of acorns - the other half is made up of fruit, insects, and other vegetable matter - but the acorn granaries are the staple food source that gets them through lean times. They develop communal granaries that may consist of tens of thousands of holes drilled in tree trunks and limbs, each stuffed with an acorn. True to their name, Acorn Woodpeckers are acorn specialists. What’s driving it? The most likely answer is acorn crop failure. This irruption – the term for a sudden upsurge in a bird population - is particularly noteworthy because Acorn Woodpeckers are not migratory. They’ve also been sighted across the Bay in San Francisco. In Berkeley, they have been reported near McKinley and Bancroft streets, at the UC Botanical Gardens, in Claremont Canyon, and behind the Seabreeze restaurant near the Berkeley Waterfront. 1, Acorn Woodpecker reports started rolling in from multiple East Bay sites from Oakland to Richmond. Photo: Larry and Dena Hollowoodīeginning around Sept.