Reproductive biology and behavior of the brown tree snake (Boiga irregularis) on Guam

While there are many more species of reptiles in the tropics than in temperate latitudes, relatively little is known about the natural history of tropical species of snakes. Even basic information, such as reproductive ecology and behavior, is lacking. Patterns of reproduction in tropical species differ from patterns in temperate species in important ways, such as the duration of gonadal activity and environmental factors that influence the frequency and timing of reproductive bouts. One tropical species, the brown tree snake (Boiga irregularis), was accidentally brought to the island of Guam and quickly became established throughout the island. Although this population has been monitored for over twenty years, many aspects of its basic biology, including its reproductive cycle, have yet to be described. The purpose of this dissertation research was to describe the reproductive biology and behavior of brown tree snakes on Guam. I used aggregation and shelter choice trials to determine whether females show aggregation behavior and to identify the cues that elicit aggregation. Reproductive state of the test snakes did not affect their response to the scent of a single male or female, but did change their response to multiple female scents. Measurements of gonad development and steroid hormones over a four-month period from captive snakes on Guam were compared to those obtained over the same time period from free-living snakes. Reproduction on Guam was found to be extended but seasonal, with females becoming vitellogenic in the latter part of the dry season and into the wet season. I also found that the corticosterone stress response did not vary with sex, size, or body condition, but the response of gonad sex hormones to acute stress was greater in larger snakes. I measured the body condition index and corticosterone levels of brown tree snakes on Guam to determine whether that population still showed the chronic stress and poor condition apparent in an earlier study. Significantly lower levels of corticosterone in all snakes in 2003 suggests that although juveniles did not have significantly improved energy stores they, along with mature males and females, were no longer under chronic levels of stress.