Characteristics of Bird-resistance in Agricultural Crops

The use of biochemical or morphological genetic traits in a crop to protect ripening seeds or grain from bird damage remains a promising tool under certain situations. Research on bird-resistance in crops has focused on grain sorghum, corn, sunflower and rice. This crop protection method involves feeding behavior of granivorous birds and its effectiveness depends on the availability of preferred alternate foods. That is, bird-resistant traits provide protection to the crop when other food choices are readily available; however, when alternate food is scarce or high bird populations create serious feeding competition, they are less effective. Several practical factors (i.e., efficacy expectations, agronomic considerations, and costeffectiveness) were discussed that should be considered in adopting this bird damage control strategy. Proc. Vertebr. Pest Conf. (A.C. Crabb and R.E. Marsh, Eds.), Printed at Univ. of Calif., Davis. 13:305-309, 1988 INTRODUCTION To the novice in vertebrate pest control the term "birdresistant" seems a panacea; conversely, many workers in the field consider it to be an impractical concept that has not and will not work for the farmer. Neither party is totally correct because the concept is misunderstood. Harris (1969) attempted to establish a common understanding by defining "bird-resistant" as "that mechanism or characteristic of a variety that when given a choice of feeding material, birds will not normally depredate." "Less-susceptible," or "birdtolerant" are other terms used for clarification. "Birdresistant" will be used here with the understanding that the concept works best when alternate feeding choices are available. Bird-resistance can be a useful tool in crop-protection if applied in a well-planned strategy. Typically, the plant breeder segregates genetic traits (chemical and/or morphological) which lower feeding preference for seeds, grains, or fruits at a time when bird damage likely occurs. This makes that cultivar a less desirable feeding choice for birds than other food sources in the vicinity. Doggett (1957), a pioneer of this concept, observed that "varieties may be bred which are unattractive to birds, and which are attacked only as a last resort." Chemical traits generally involve an unpleasant taste, while morphological traits are usually those that impair feeding efficiency. Depending on the crop, morphological or biochemical factors can predominate; in combination they can be synergistic (Harris 1969). If one were to select a susceptibility attribute most common to ripening crops damaged by birds, it would be the tendency of that crop to accommodate perch-feeding by the depredating species. Grain sorghum, corn, sunflower, and rice, ripening crops heavily involved in bird damage situations around the world, are good examples. Crop-damaging bird species of all sizes can perch on the stalks of grain sorghum, corn and sunflower and in most cases, on lodged rice. Most bird-resistance research has involved these crops, and thus the genetic traits involved (chemical and morphological) are discussed below with this point in mind.