U.S. Department of Agriculture: Animal and Plant Health Inspection Service


Date of this Version



Published in Journal of Herpetology, Vol. 33, No. 2, pp. 281-291, 1999.


Brown tree snakes (Boiga irregularis, BTS), inadvertently introduced to the island of Guam shortly after World War II, have had catastrophic effects on the native fauna of this U.S. territory. We used radio-telemetry to monitor daytime refugia and nightly movements of 60 BTS (30 during each of two seasonal periods) to determine the extent of nightly, weekly, and monthly movements. Eighty-three percent of subadult daytime sightings were in trees, compared to only 49% of adult daytime sightings. Most measures of movement did not vary with seasonal period, sex, or age class. BTS moved an average of 64 m (Range: 9-259 m) between successive daily refugia. Mean total cumulative distance traveled between successive locations from one afternoon to the next was 238 m during January-March and 182 m during May- July. However, over the course of each seasonal period (60-70 d), most snakes concentrated their activity within core areas. During each of the two seasonal periods, snakes were located a mean distance of only 78 m and 93 m, respectively, from their original release points 30-50 d after release. Sixty to 70 d after release, snakes were a mean distance of 92 m and 68 m, respectively, from their original release points. Snakes frequently crossed dirt roads that separated forested areas at the study site. They also utilized grassy and brushy clearings, but less than would be predicted by the occurrence of such clearings in the study area. These results suggest that under the conditions of this study, BTS would be slow to reinvade areas where snakes have been removed by trapping or other means.