Avian Predation on the Larch Sawfly, Pristiphora Erichsonii (HTG.), (Hymenoptera: Tenthredinidae)

Forty—three of the 54 species of birds collected in or near tamarack bogs were predators of the larch sawfly. Birds feeding in the tree crowns utilized sawflies to a greater degree than birds feeding in the shrub layer or those that captured their prey while in flight. Predation varied within and between taxonomic groups of birds and important predators were found in every group collected. Some species popularly regarded as vegetarian (viz. sparrows) proved to prey heavily upon sawflies. The warblers, popularly regarded as important insect predators, were clearly of less importance as predators of the larch sawfly than the fringillids. A preference was indicated by many bird species for adult sawflies, even when they were relatively rarer than larvae. Larger and then smaller larvae followed in order of preference. Some species decapitated larvae and ate the body and either rejected or swallowed the head capsule. Positive functional responses were indicated at low and high prey densities for 22 predators, negative for four, and no response for two. The remaining predators were collected only at one of the two prey densities encountered. Population censuses provided data on 34 of the predator species in two plots. Numerical responses were suggested for all except those of sporadic occurrence. Nonresident species were prominent in the plot with a high prey density. Birds are likely to influence sawfly population trends at low insect densities, and perhaps at higher densities as well. The importance of predation on adult sawflies is stressed.