Wednesday January 8, 2014

Acorn woodpecker cache

Birds use trees for everything from shelter to food, but the acorn woodpecker (Melanerpes formicivorus) shows a particular knack for tree storage and a flair for display. As their name suggests, acorn woodpeckers inhabit oak woodlands throughout the western and southwestern United States, as well as Mexico, where they specialize in harvesting and hoarding acorns. A single bird can stash an average of 325 acorns a year, so the estimated 7.3 million acorn woodpeckers in California alone tuck away about 2.4 billion acorns a year (Koenig et al. 2008). While the distinctive black-and-white birds with dapper red caps eat a good deal of their crop, they also play a role in dispersing oak seeds.

Stocking the pantry is a communal effort: acorn woodpeckers live in family groups of 2 to 15 birds, and lodge the nuts in one or more storage trees, or granaries, located in their territory. Flying back and forth with one acorn at a time makes for a busy harvest. The birds stockpile acorns from a variety of oak species, including valley oak, blue oak, and coast live oak, and their harvesting activity peaks in October to December. Researchers found that the birds tend to transport seeds relatively short distances (150 m or less), compared to other birds like jays, which may carry acorns for a kilometer or more before caching them in the ground. (Koenig et al. 2008). Acorn woodpeckers use their beaks to drill a series of nooks and crannies into a tree trunk, and may even co-opt an unsuspecting fence post or telephone pole to suit their storage needs. The result looks a bit like a wine bottle rack – hopefully these nuts are a good vintage.

Link copied successfully