APPLICATION OF AN AVIAN BIOENERGETICS SIMULATION MODEL TO RED-WINGED BLACKBIRD - CROP RELATIONS

The impact of bird populations upon the properties or processes of ecosystems is mediated through patterns and magnitudes of energy flow. This impact may be either direct, by processing of large quantities of energy or nutrients, or indirect, through feedback control of other ecosystem rate processes or components. In either case, however, the impact is a result of the population dynamics and the pattern and magnitude of food consumption of the birds. Recent research by several groups points to a relatively small direct impact on birds on most natural ecosystems (Wiens 1973). Impact through feedback control, a more difficult relationship to study, is just beginning to receive close attention in a total systems framework. In managed ecosystems, however, where our interest is in either the bird population or its prey as an aesthetic or economic resource, the direct impacts are of considerable importance. These direct impacts are a reflection of prey consumption, which in turn is a result of the interactions of prey selection and energy demand. There is little field information available on either of these components for most bird populations, however, and we have therefore employed simulation modelling, coupled with existing information on dietary composition, to generate estimates of prey consumption rates and thus of potential impact. Our modelling tactic has been to stress generality and biological realism at the expense of precision (Levins 1966), since we are interested in models which are both robust and broadly applicable. Also, we recognize that the data base of the model is frequently imprecise, and it seems intuitively illogical to build extremely precise models for imprecise data inputs, even though this if often done

PLANT-ANIMAL INTERACTIONS: THE EFFECTS OF REDWINGED BLACKBIRDS ON CORN GROWTH

Red-winged Blackbirds (Agelaius phoeniceus) in agricultural crops likely create the worst possible images in the minds of various segments of our society today. To some there is only repulsion, which results in desire for total annihilation of Red-wings (by many agriculturists); while to others there is only attraction, which results in desire to leave the situation absolutely alone (by conservancy minded purists). The great middle ground includes those who vascillate back and forth, between these extremes, those who are not cognizant of the problems, and those that do not care. This picture apparently is a common problem for our wildlife resources in America today when they come into conflict with man’s interests. The problem often erupts in several different ways, but often pits the two most extreme sides against one another and squeezes governmental agencies given the responsibility of solving the problem into a nearly helpless position. However, these agencies are also partially responsible for the overall situation by not having obtained sufficient amounts of the right kind of information. The end result is a constant spiral of activities in time without solutions of the problem. In modern jargon, the entire situation is an endless “DØ LØØP” This is the best simile that I can provide at this time