Behavioral differences following ingestion of large meals and consequences for management of a harmful invasive snake: A field experiment

Abstract

Many snakes are uniquely adapted to ingest large prey at infrequent intervals. Digestion of large prey is metabolically and aerobically costly, and large prey boluses can impair snake locomotion, increasing vulnerability to predation. Cessation of foraging and use of refugia with microclimates facilitating digestion are expected to be strategies employed by free‐ranging snakes to cope with the demands of digestion while minimizing risk of predation. However, empirical observations of such submergent behavior from field experiments are limited. The brown treesnake (Serpentes: Colubridae: Boiga irregularis) is a nocturnal, arboreal, colubrid snake that was accidentally introduced to the island of Guam, with ecologically and economically costly consequences. Because tools for brown treesnake damage prevention generally rely on snakes being visible or responding to lures or baits while foraging, cessation of foraging activities after feeding would complicate management. We sought to characterize differences in brown treesnake activity, movement, habitat use, and detectability following feeding of large meals (rodents 33% of the snake's unfed body mass) via radio telemetry, trapping, and visual surveys. Compared to unfed snakes, snakes in the feeding treatment group showed drastic decreases in hourly and nightly activity rates, differences in refuge height and microhabitat type, and a marked decrease in detectability by trapping and visual surveys. Depression of activity lasted approximately 5–7 days, a period that corresponds to previous studies of brown treesnake digestion and cycles of detectability. Our results indicate that management strategies for invasive brown treesnakes need to account for cycles of unavailability and underscore the importance of preventing spread of brown treesnakes to new environments where large prey are abundant and periods of cryptic behavior are likely to be frequent. Characterization of postfeeding behavior changes provides a richer understanding of snake ecology and foraging models for species that consume large prey.

Use of visual surveys and radiotelemetry reveals sources of detection bias for a cryptic snake at low densities

“…For instance, recently fed BTS dramatically reduce their activity and tend to perch higher in the canopy for up to a week following consumption of large prey (Siers et al. ). Therefore, snakes located high in the canopy may have sought refuge within microhabitats conducive to digestion or periods of reduced activity (Peterson et al.…”

“…Reptiles and amphibians can be particularly challenging in this regard due to their small body sizes, habitat preferences, and secretive nature (Turner , Pough , Siers et al. ). Further, our ability to detect some of these species may be lowest in high‐quality rather than low‐quality habitat (Bailey et al.…”

“…In contrast, reptiles and amphibians have low energetic demands (Pough ), exhibit unpredictable activity patterns (Turner , Dunham ), and frequently forgo activity to avoid predation, referred to as submergent behavior (Maiorana , Siers et al. ). Therefore, to account for detection bias in cryptic species we must validate visual surveys using independent methods (e.g., total removal plots: Rodda et al.…”

Inferring the absence of an incipient population during a rapid response for an invasive species

“…While we lack information to precisely predict how detection would manifest itself on a new island where snakes might get established, we can safely assume that conditions in a new population will be less favorable for detection than those documented on Guam ([ 10 ]; p = 0.07). We therefore assumed a 50 percent reduction in snake detection because well-fed snakes are more frequently satiated and inactive [ 20 ] and then produced predictions for Rota by simply multiplying the expected snake counts in Table 1 with a specified detection ratio p Rota / p Guam (e.g., 0.035/0.07 = 0.5). Thus, the first expected value at 24 snakes/ha for 1 DEU would now yield 4.095 snakes (8.19 × 0.5) in Table 1 .…”

No room to roam: King Cobras reduce movement in agriculture

“…Shelter sites are important for species requiring extended periods of low mobility to digest meals [53] or undergo ecdysis [54]. Using an intensive radio tracking regime allowed us to identify individual shelter sites, time spent within shelters, and frequency of reuse.…”