DIETARY CIRCUMVENTION OF ACORN TANNINS BY BLUE JAYS - IMPLICATIONS FOR OAK DEMOGRAPHY

Blue jays consume large quantities of acorns to fuel energy-demanding caching flights in the fall. Yet blue jays possess no known physiologi cal adaptation to counter the negative effects of a high tannin diet o n protein digestion. Dietary experiments were conducted to determine i f blue jays could subsist on an acorn-only diet, and if they could not , to determine whether supplements of acorn weevil larvae (Curculio), present inside acorns, enabled them to maintain their mass. Comparativ e tannin assays also were conducted on Lepidobalanus (low tannin; whit e oak) and Erythrobalanus (high tannin; pin oak) acorns using radial d iffusion assay. Captive jays consumed considerable acorn material, yet were unable to maintain mass on ad lib. acorn-only diets or on an aco rn + 1.5 g larvae/day supplement. There were no significant difference s in mass loss between high and low tannin diets. In contrast, blue ja ys were able to stabilize mass on a diet of acorns + 5.0 g larvae supp lement/day. These results suggest that acorn weevil larvae, or perhaps other insects, counteract the effects of acorn tannins in the jay die t allowing jays to subsist largely on acorns during the fall caching s eason. Oak demographic processes may be partly regulated by a tri-trop hic relationship among plant, insect and bird. Acorn weevil larvae, co nsidered damaging to oak populations, may actually facilitate oak recr uitment and population vagility in the long-term.