Seasonal patterns of fecundity and diet of roof rats in a Hawaiian macadamia orchard

Abstract

We determined seasonal patterns of fecundity and diet of roof rats (Rattus rattus) snap-trapped in an orchard of macadamias (Macadamia integrifolia), and assessed the implications for controlling rat damage to macadamia nuts. In all, 903 males, 756 females, and 16 rats of unidentified sex were captured between June 1990 and April 1991. Sex ratios varied from 1 : 1 only during August, when males outnumbered females (P < 0.05). Subadult rats were present throughout the study and comprised 31% of captures. Adult male roof rats were in reproductive condition throughout the year, and females bore young during every month of the study. Average monthly pregnancy rates varied from 8% to 54% and were highest in April. Mean prenatal litter size ranged from 3.0 to 6.5 among months. Macadamia nut was the dominant food item throughout the study, and was present in all 199 stomachs inspected, with a mean relative frequency of 85%. Insect fragments, primarily lepidopteran larvae, occurred in 66% of the stomachs, with a mean relative frequency of 8%. Moss was found in 48% of the stomachs, with a mean relative frequency of 4%. Grass seeds, fruit seeds and non-insect animal material were present in small amounts. These results show that, in areas with prolonged macadamia flowering and subsequent extended periods of nut availability, roof rats breed throughout the year on a diet consisting mostly of macadamia nuts. In such situations, growers may need to apply control measures throughout the crop cycle to keep rat damage at acceptable levels.