Johnson W Carter, Thomas Libby, Adkisson Curtis S
Department of Horticulture, Forestry, Landscape and Parks, South Dakota State University, 57007, Brookings, SD, USA.
Oecologia. 1993 May;94(2):159-164. doi: 10.1007/BF00341312.
Blue jays consume large quantities of acorns to fuel energy-demanding caching flights in the fall. Yet blue jays possess no known physiological adaptation to counter the negative effects of a high tannin diet on protein digestion. Dietary experiments were conducted to determine if 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. Comparative tannin assays also were conducted on Lepidobalanus (low tannin; white oak) and Erythrobalanus (high tannin; pin oak) acorns using radial diffusion assay. Captive jays consumed considerable acorn material, yet were unable to maintain mass on ad lib. acorn-only diets or on an acorn +1.5 g larvae/day supplement. There were no significant differences in mass loss between high and low tannin diets. In contrast, blue jays were able to stabilize mass on a diet of acorns +5.0 g larvae supplement/day. These results suggest that acorn weevil larvae, or perhaps other insects, counteract the effects of acorn tannins in the jay diet allowing jays to subsist largely on acorns during the fall caching season. Oak demographic processes may be partly regulated by a tri-trophic relationship among plant, insect and bird. Acorn weevil larvae, considered damaging to oak populations, may actually facilitate oak recruitment and population vagility in the long-term.
冠蓝鸦在秋季会消耗大量橡子，为能量需求大的贮藏飞行提供能量。然而，冠蓝鸦没有已知的生理适应性来对抗高单宁饮食对蛋白质消化的负面影响。进行了饮食实验，以确定冠蓝鸦能否仅以橡子为食，如果不能，则确定橡子内部的橡实象鼻虫幼虫（Curculio）补充剂是否能使它们维持体重。还使用径向扩散法对白栎属（低单宁；白栎）和红栎属（高单宁；针栎）的橡子进行了单宁含量比较测定。圈养的冠蓝鸦消耗了大量的橡子，但仅以橡子为食或每天补充1.5克幼虫时无法维持体重。高单宁饮食和低单宁饮食之间的体重减轻没有显著差异。相比之下，冠蓝鸦在每天补充5.0克幼虫的橡子饮食中能够稳定体重。这些结果表明，橡实象鼻虫幼虫，或者可能是其他昆虫，抵消了橡子单宁对冠蓝鸦饮食的影响，使冠蓝鸦在秋季贮藏季节能够主要以橡子为食。橡树的种群动态过程可能部分受植物、昆虫和鸟类之间的三级营养关系调节。橡实象鼻虫幼虫虽然被认为对橡树种群有危害，但从长远来看，实际上可能有助于橡树的更新和种群迁移。
