Food-Base Flavor Additive Improves Bait Acceptance by Ricefield Rats

Abstract

Philippine ricefield rats (Rattus rattus mindanensis) that were accustomed to eating rice grain showed greatly increased preference for granulated rice when it was enriched by the volatiles from ground unpolished rice. This was the best of 11 formulations involving 8 rice components that were tested with an automated brief-exposure preference tester. This formulation was also highly preferred (P 2X ) of the treated bait and showed 88 percent mortality. These results indicate that intensifying the flavor cues associated with a familiar or preferred food is a fruitful approach in the development of an effective bait enhancer. J. WILDL. MANAGE. 41(2):290-297 The familiar problem of bait acceptance in rat control programs readily applies to the Philippine ricefield rat. In their 1971 Annual Report (p. 61) scientists of the Philippine Rodent Research Center (College Laguna, Philippines) stated: suspect that bait acceptance is a major factor limiting the effectiveness of acute toxicants as now used for rodent population reduction in Philippine ricefields; methods to improve acceptance need further investigation. Because of this need, we began a program to develop highly palatable baits for rat control in ricefields. The food preference behavior of wild rats is very complex. The drive to satisfy energy requirements affects preference (Schein and Orgain 1953, Cornwell and Bull 1967, Brooks and Bowerman 1973). Novelty also can be important (Welker and King 1962, Bronson 1966, Long and T pp 1967, Valle 1970). A novel stimulus may direct an animal's exploratory behavior and lead it to the bait, but consumption of the bait may or may not follow, depending n how much wariness the same novel cue elicits. As the bait's novelty decreases, so d es its ability to direct exploratory behavior (Long and Tapp 1967). Furthermore, novel factors such as taste, odor, color, and texture may provide cues for bait aversion (shyness). However, response to a familiar food is more predictable. Previous experience is an important factor (Barnett and Spencer 1953, Jackson 1965, Cornwell and Bull 1967, Reif 1969, Bull 1972, Howard and Marsh 1974). In tests and observations of feeding behavior, we have found that rats consistently prefer familiar foods over unfamiliar ones. The durability and strength of this response seem to increase when the familiar food has been a major diet item and is satisfying the animal's nutritional needs. Tigner (1972) found that when there is enough rice grain in the paddies to sustain ricefield rats, it makes up 60-85 percent of the 1 Investigations were supported by funds provided to the U.S. Fish and Wildlife Service by the Agency for International Development under the project Control of Vertebrate Pests: Rats, Bats and Noxious Birds PASA RA(ID) 1-67. 290 J. Wildl. Manage. 41(2):1977 This content downloaded from 207.46.13.148 on Sun, 11 Sep 2016 04:33:41 UTC All use subject to http://about.jstor.org/terms FLAVOR ENHANCEMENT OF RAT BAITS * Bullard and Shumake 291 volume of food in their stomachs. Thus, the most familiar food of the rats that damage rice plants is the rice grain itself. Could a rice fraction that intensified the familiar flavor cues of rice provide the key to developing a highly palatable bait? The series of studies described below was designed to answer this question. The authors gratefully acknowledge G. Holguin, S. E. Gaddis, and K. A. Crane for their technical assistance throughout the project. We also thank C. P. Breidenstein for statistical assistance and A. H. Bean for critical review of the manuscript.