Wildlife Damage Management, Internet Center for


Date of this Version

November 1976


Within the past decade interactions among plants and animals have received increasing attention, mostly pertaining to selection of plants that produce toxic secondary compounds as a direct result of herbivory (Gilbert and Raven, 1975; Feeny, 1975; and Rhoades and Cates, 1976) and in turn selection of animals that detoxify these plant compounds (Freeland and Janzen,1974). Indeed, the plant-herbivore association has been regarded in the context of predator-prey relationships, especially for seed eaters (Scott, 1970, 1976; Janzen, 1971; Smith, 1975; and Pulliam and Brand, 1975). However, there are other important plant-animal associations. Regulation of plant nutrients (Mattson and Addy, 1975; Chew, 1974; Owen and Wiegert, 1976) and productivity by both vertebrate and invertebrate and host plant associations (Harris, 1974; Dyer, 1973, 1975; Dyer and Bokhari, 1976) also have been described. Thus it appears there are many associations which affect populations of plants and animals in evolutionary time (Janzen, 1976) and others which have short-term effects in "physiological time," i.e., periods ranging from minutes to a single growing season. It is this latter phenomenon that I am examining in this paper. A question has been raised about the overall effects of Redwinged Blackbirds (Agelaius phoeniceus) feeding on ripening ears of field corn in the east and middle west of North America (Dyer, 1973, 1975). In several instances, fields in which Redwings fed produced more corn than fields in which feeding levels were lower; this is true for plots within fields as well (ms. in preparation). On a regional basis the question is complex. Can birds recognize more productive corn fields, or even more productive patches within fields, or is there an interaction between the animal and the corn plant that triggers higher levels of production? Of the two alternatives, I have suggested that the more likely event is that avian herbivory stimulates grain production (Dyer, 1973, 1975). Thus it is of heuristic value to examine growing field corn ears in fields of the midwest in order to determine whether there is the possibility that one or more "herbivorous events" may trigger processes which lead to compensatory growth. The approach to identifying the possibility of compensatory growth has been through simulating bird damage on maturing corn ears by mechanical manipulation. The study was conducted during 1971 in hybrid field corn raised for seed.