EFFECTS OF TRAPPING ON RAT-POPULATIONS AND SUBSEQUENT DAMAGE AND YIELDS OF MACADAMIA NUTS

During the 1990-1991 and 1991-1992 crop cycles, the effects of snap trapping on rat populations in a macadamia orchard and subsequent damage and yields of nuts were evaluated. During 1990-1991, 1681 roof rats (Rattus rattus), 22 Polynesian rats (R. exulans), and one Norway rat (R. norvegicus) were captured; 360 rats of undetermined species were captured during 1991-1992. Cumulative rat damage for the entire season varied from 0.36 to 1.34% of total annual production in the trapped sections, and from 1.71 to 3.62% of total annual production in the reference sections. However, trapping had no effect on yields: the number of nuts, mass per nut and the total mass of undamaged nuts did not differ between the trapped and reference sections. The results suggest the need to examine crop yield more closely in assessing methods for managing rodent infestations in macadamia orchards. The commonly used indices based on rodent activity and proportion of nuts damaged may overestimate the impact of rodent depredations and exaggerate the effectiveness of control measures in macadamia orchards. A large incidental take of birds points to the need for more selective techniques before trapping is utilized as a damage control measure in Hawaiian macadamia orchards.