Byall, C., H. M. Smith, and D. Chiszar. 1993. Response of Brown Tree Snakes (Boiga irregularis) to synthetic monkey pheromone. Journal Colorado-Wyoming Academy Science 25:28. Abstract: Responses of B. irregularis to numerous chemical compounds has been measured in our laboratory in an attempt to discover attractants that might lure these snakes to traps. Synthetic monkey pheromone is the most recent substance to be tested, courtesy of Denver Wildlife Research Center. The presentation will review the history of this research program, and our results to date. The attractiveness of synthetic monkey pheromone will be compared to attractiveness of about 20 other substances. Chiszar, D., T. M. Dunn, P. Stark, and H. M. Smith. Submitted. Response of Brown Treesnakes (Boiga irregularis) to mammalian blood: whole blood, serum, and cellular residue. Journal of Chemical Ecology. Abstract: Brown treesnakes (Boiga irregularis) responded with more tongue flicks to blood (from rabbits, rats, and mice) than to water. When rat blood was centrifuged at 3500 rpm for 5 min, separating serum from cellular residue, snakes responded strongly to serum but not to blood residue. Chiszar, D., K. Kandler, and H. M. Smith. 1988. Stimulus Control of Predatory Attack in the Brown Tree Snake (Boiga irregularis). The Snake 20. 151-155pp. Abstract: Brown tree snakes (Boiga irregularis) failed to respond to prey-derived chemical cues with increased tongue flicking or with predatory attacks. The snakes did, however, respond strongly to visual cues arising from prey, even under very dim illumination. Although it is tempting to assert that these animals are primarily sight hunters, this conclusion would be premature until more naturalistic foraging tests are conducted. Chiszar, D., K. Kandler, and H. M. Smith. 1988a. Stimulus control of predatory attack in the Brown Tree Snake (Boiga irregularis). 2. Use of chemical cues during foraging. Amphibia-Reptilia 9:77-88. Abstract: Brown Tree Snake (Boiga irregularis) failed to respond to prey-derived chemical cues with increased tongue-flicking or with predatory attacks. The snakes did, however, respond strongly to visual cues arising from prey, even under very dim illumination. Although it is tempting to assert that these animals are primarily sight hunters, this conclusion would be premature until more naturalistic foraging tests are conducted.
Chiszar, D. 1992. Chemical control of predatory behavior in the Brown Tree Snake (Boiga irregularis). The Snake 24:108. Abstract: This presentation will review the history of research on chemical cues that guide foraging and predatory attack by Brown Tree Snakes. The snakes use prey-derived chemicals of integumentary origin as well as chemicals associated with prey excrement. Trails made with these materials were detected and followed by snakes. Cotton-tipped applicators dipped into these chemicals triggered tongue flicking and predatory attacks. Recently we have demonstrated that Brown Tree Snakes are attracted to (and will attack) applicators and other objects bearing mammalian, including human, blood. A large sample of commercially available chemical attractants is being tested for effectiveness with B. irregularis. Some of these compounds are used to attract fur-bearing mammals, others are used to attract fish. We have found some of them to be potent predatory stimulants for B. irregularis while others have little or no effect. All of this work will be summarized and related to the goal of generating an attractant to enhance trapping success on Guam. Chiszar, D. and T. M. Dunn. 1993. Grooming in the brown tree snake (Boiga irregularis). Bulletin of the Psychonomic Society 31:299-300 pp. Abstract: Brown tree snakes, Boiga irregularis, exhibited an elevated frequency of haw rubbing when a small quantity of petroleum jelly was placed on their lips. Jaw rubbing has the effect or removing foreign material from the lips, and it represents a behavior that cleans and maintains a particular part of the body surface. Although few such behaviors have been reported in reptiles, we suspect that many exist and simply have gong unnoticed because herpetologists have attached no theoretical significance to them. Chiszar, D., W. Lukas, and H. M. Smith. 1997, Response to rodent saliva by two species of rodentiophagous snakes. Journal of Chemical Ecology 23:829-836. Abstract: Brown tree snakes (Boiga irregularis) and prairie rattlesnakes (Crotalus viridis) responded with higher rates of tongue flicking to rodent saliva than to water. Both materials were presented on cotton-tipped applicators touched gently to the snake s lips. Rattlesnakes also struck more frequently at applicators bearing saliva than at control applicators. Since rodents frequently lick themselves during bouts of grooming behavior, saliva is certainly a component of the chemical patina of rodent integument. It is concluded that this association has given rise in rodentiophagous predators, ontogenetically or phylogenetically, to sensitivity to saliva, causing the present snakes to respond to saliva with behaviors characteristic of predatory patterns
Chiszar, D., G. H. Rodda, and H. M. Smith. 1997. Experiments on chemical control of behavior in Brown Tree Snakes. Pages 121-127 in J. R. Mason, editor. Repellents in wildlife management. National Wildlife Research Center, Fort Collins, CO. Abstract: The brown tree snake (Boiga irregularis), accidentally introduced on Guam shortly after World War II, is the target of extensive efforts aimed at reducing populations and preventing their spread to other Pacific islands. Chemical attractants and repellants have been investigated, and this paper presents an overview of this knowledge. In particular, chemical cues that have strong effects in laboratory tests have had only modest (though significant) effects in field tests on Guam. Reasons for the different outcomes of the laboratory and field studies are discussed along with recommendations for the redesign of laboratory experiments. Clark, L. 1997. Responsiveness of Brown Tree Snakes to odors. Pages 129-137 in J. R. Mason, editor. Repellents in wildlife management. National Wildlife Research Center, Fort Collins, Colorado, USA. Abstract: The brown tree snake (Boiga irregularis) is native to the islands of Papua New Guinea and Northern Australia. An introduced population on Guam has been implicated in the decline of that island s avifauna, and the snakes regularly cause power outages on the island. Concern exists for accidental introduction on the Hawaiian Islands. Traps baited with live mice have been used in control efforts, but the logistics of maintaining live mice in the field is difficult and expensive. This study has two objectives. First, using efficacy reports of small mammals and bird feces as attractants, we set out to identify active fractions of these potential prey odor sources. If active fractions are identified, there is a possibility of encapsulating reagent grade attractant without having to process feces or urine. Second, any successful snake lure should result in the snake s entry into the trap. Four snakes, 2-4 m in length, were obtained from the Philadelphia Zoo. These snakes were attracted to warm water-extracted vole and starling feces, but tended to avoid aqueous acid bird free extracts. Snakes were indifferent to aqueous-base bird feces extracts. Snakes avoided Big Game Repellent, cadaverie, butanethiol, and ethanethiol. In summary, potential prey odors lost their attractiveness quickly upon fractionation, suggesting the overall odor profile is important for attractiveness. We are focusing efforts to encapsulate chemicals so that field operatives will not need to process raw feces. In general, sulfur- and amine-bearing volatiles seem to repel brown tree snakes, but these same compounds are attractive to mammalian carnivores. If proven true, commercially available predator odors may be used to treat potential hiding places around air cargo areas and electric power plants.
Fox, K., D. E. Miller, A. Topple, H. M. Smith, and D. Chiszar. 1990. Abstract: Stimulus control of predatory behavior in Brown Tree Snakes (Boiga irregularis). Journal of Colorado-Wyoming Academy of Science. 22:5. Abstract: Five experiments studied the predatory responses of brown tree snakes (Boiga irregularis) to various stimulus properties of prey. Although visual cues usually have the strongest effect on predatory attack, chemical cues also have effect under certain conditions. Hence the snakes are both sight hunters and scent hunters. Integumentary cues drive from prey where among the chemical cues that influenced chemosensory searching by the snakes. Chemical cues associated with mammalian reproduction (i.e., birth products and milk) may also be significant attractors of these snakes. Gee, D. E., II. 2002. Appraisal of visual stimuli in the contexts of directional movement and courtship in the Brown Tree Snake (Boiga irregularis). Department of Biology, Independent Study Thesis, College of Wooster, Wooster Ohio, USA. Abstract: Brown tree snakes (Boiga irregularis) are a pest species on the island of Guam. They have caused millions of dollars worth of physical damage to electrical equipment, and have extirpated most bird species on the island through predation. Plans to eradicate the population have unsuccessful to date, as have measures taken to stop the species from reaching another area as stowaways in cargo or on aircraft. I believe that trapping has been unsuccessful due to the locations and designs of traps they are often placed in well-lit areas, and may be avoided by the nocturnal snakes. To investigate this problem, 18 snakes (nine male, nine female) were given 21 trials each in a T-Maze with lights of different intensities on either side. Snakes were allowed five minutes inside of the maze to choose a direction in which to move. In 234 of 346 trials (P < 0.001), snakes chose to move toward the dark side of the maze. When they did move toward the bright side, the distance they traveled was significantly less than the distance they moved when approaching the dark side (n = 346, P < 0.001). These results are expected for a nocturnal species such as B. irregularis, and may have implications for the removal of the snakes from Guam. New or improved trapping methods can be developed using the snakes aversion to bright light. Efforts to prevent their spread may also benefit if bright light is used to prevent from entering cargo storage areas.
Gee, D.E., II., M. Kern, and M. Ehlert. 2002. Appraisal of visual stimuli in the contexts of directional movement and courtship in the brown tree snake (Boiga irregularis). M.S. Thesis. College of Wooster, Wooster, Ohio, USA. Abstract: To evaluate the importance of vision, four males were given a choice between a filter paper treated with non-volatile attractive female sex pheromone and either a live female or a rope on the floor. It was hypothesized that males would approach the female or the rope rather than court the filter paper. The filter paper was placed so that it was the first stimulus that they encountered. In 21 of 29 trials, the males' response was to court the visual stimuli. Lankford, J. D. 1989. Stimulus control of foraging Brown Tree Snakes (Boiga irregularis). Journal of Colorado-Wyoming Academy of Science 21:12. Abstract: Predation by the brown tree snake (Boiga irregularis) has been implicated in the demise of the avifauna on Guam where the snake was accidentally introduced during the or shortly after World War II. Previous studies in our lab give rise to the hypothesis that the snakes are primarily sight hunters, but that they will switch to chemical cues when visible ones are insufficient to confirm the presence or absence of the prey. These present experiments were designed to test this hypothesis. Snakes were presented with rodent and control odors in clear and in black Plexiglas containers (perforated on all sides). Little response to rodent odors was observed when clear Plexiglas containers were used. There was, however, a substantial response to such odors in black Plexiglas containers. We infer that snakes could see that prey were absent from clear Plexiglas containers, and this visual information precluded further examination by the snakes. With black Plexiglas containers, visual inspection could not confirm the presence or absence of prey, and chemical cues were then examined. Consequently, we conclude that the snakes indeed switch to chemical modalities when visual cues are unavailable, and the present methodology might be useful in developing a bait for a trapping program designed to control B. irregularis on Guam.
Mason, R.T. 1992. The isolation and chemical characterization of skin lipid pheromones in the brown tree snake, Boiga irregularis. Page 110. The Snake 1992. 24:110. Abstract: The brown tree snake, Boiga irregularis, is a serious introduced pest on the island of Guam and other islands in the Pacific. The brown tree snake is native to Australia and New Guinea where it is unremarkable in terms of its effects on the ecology of endemic species of vertebrates. Sometimes during or after World War II, the snake was introduced onto Guam. During the 1970 s, biologists first became aware of the problem when endemic populations of birds started to go extinct. Populations of snakes on Guam have reached levels estimated to be as high as 10,000 per square kilometer. Currently, biologists are attempting to utilize a variety of techniques to control the populations of brown treed snakes. One of these methods is the use of pheromones to both attract and repel snakes. Snakes rely more on their chemical senses than any other vertebrate to gather information from the environment. Chemical communication by means of semiochemicals of pheromones is widespread in reptiles but few pheromones have been isolated and described. However, behaviors elicited in response to pheromonal cues are known in many snakes. For example, pheromones produced by female snakes are detected by tongueflicking males, which elicits courtship behavior. Pheromone cues can also be used by males to trail females. Thus, pheromone cues might be utilized to lure males into traps. In addition, other pheromones such as cloacal gland secretions may serve as alarm pheromones. These may be exploited to exclude snakes from any areas such as bird nesting sites. Results of our ongoing efforts to isolate and chemically characterize the attractant and repellent pheromones of the brown tree snake will be discussed. Rodda, G. H., and D. Chiszar. 1993. Are cotton swab presentations a sufficient model for ophidian prey recognition? Page 222 in Second World Congress of Herpetology, Adelaide, Australia. Abstract: A large number of studies of prey recognition in snakes has involved the presentation of prey extracts or other chemical cues of cotton swabs. When given the opportunity, snakes often attack and attempt to ingest the swab, confirming realism of the laboratory model. Work by Chiszar and others has shown a consistent strong response of Brown Tree Snakes, Boiga irregularis, to a variety of chemical cues, especially those of vertebrate blood. The relative efficacies of chemical cues for attracting Brown Tree Snakes was tested in the field by setting 100 snake traps on Guam for 41 days. Each of the randomized traps had one of the five bait types: live mice, blood, another inanimate bait that elicited a strong laboratory response (a catfish bait), a commercial snake lure (which failed to elicit a strong response in the laboratory), and a control. The total capture using these baits were: 507 (mice), 29 (blood), 25 (catfish bait), 19 (snake lure), and 10 (control). Under field conditions, the chemical cues had about 1/20 of the effectiveness of a natural prey item, and the relative differences in efficacies of the inanimate attractants were not demonstrable. We will evaluate evidence for causes of this lack of correspondence between laboratory and field tests.
Shivik, J. A. and L. Clark. 1997. Carrion-seeking in Brown Tree Snakes: importance of olfactory and visual cues. Journal of Experimental Zoology 270:549-553. Abstract: We performed field experiment to examine brown tree snake (Boiga irregularis) attraction to carrion. These snakes were attracted to carrion and entered traps baited with dead mice as readily as traps baited with live mice. Using the cues arising from both dead and live prey, we examined the relative importance of visual and chemical cues to brown tree snakes. With carrion lures, chemical cues alone were sufficient for attracting and capturing snakes, but with live prey lures, visual cues were required to attract and capture brown tree snakes. Our study presents the first experimental field evidence showing carrion to be attractive to an ophidian predator and suggests that the relative importance of chemical and visual sensory stimuli to brown tree snakes is context-specific. Shivik, J. A. 1998. Brown Tree Snake response to visual and olfactory cues. Journal of Wildlife Management 62:105-111. Abstract: The brown tree snake (Boiga irregularis), an exotic on Guam, is primarily an arboreal colubrid thought responsible for the decline and extinction of many species. Brown tree snakes on Guam currently are trapped, with live mice as lures, to minimize the likelihood of the snakes being transported elsewhere. It is desirable to end the use of live mice in traps, but the successful development of inanimate lures requires initial knowledge about snake foraging behavior. I tested whether visual or chemical cues most stimulate appetitive behavior in brown tree snakes, and I examined the effectiveness of artificial lures for capturing snakes. Using trials in both a laboratory and field setting, I determined that both visual and olfactory cues were important for trapping brown tree snakes. The effectiveness of live mice as a lure greatly diminished with the loss of either sensory cue, apparently because of synergy between combined cues. Development of simple artificial lures based on cues provided by live mice is likely to be difficult. Lures based on cues associated with live mice may require complex odor and visual stimuli; however, odors from other sources may lure snakes without a visual stimulus.
Shivik, J. A. 1999. Carrion, context, and lure development: the relative importance of sensory modalities to foraging Brown Treesnakes (Boiga irregularis). Ph.D. dissertation, Colorado State Univ., Fort Collins, CO. Abstract: Since the brown treesnake was introduced on Guam, it has caused the decline and extinction of avifauna and herpetofauna, numerous power outages, loss of domestic animals, and it is a threat to other land masses. Trapping, using live mouse lures, is an effective method for removing brown treesnakes from an area, but using live mice in traps presents animal care and maintenance problems. These problems can be allieviated if an effective artificial lure for brown treesnakes can be developed, but effective lure development necessities further study of the sensory biology and foraging ecology of brown treesnakes. By performing experiments in the laboratory at Ft. Collins and in field conditions on Guam, I have determined that both visual and odor cues are important for attracting brown treesnakes when live mice are used as lures. When using mouse carrion, however, the importance of visual cues is reduced. I identified and tested major components of dead mouse odor, as well as a variety of natural components for attracting brown treesnakes, but did not find a single chemical that would lure snakes into traps. The attractiveness of dead mouse odor varies widely between seasons, and future lures for brown treesnakes should incorporate the concept a super normal stimulus suite using multiple sensory cues from an odorized mechanical model. In light of these results, I discuss evolutionary trends in scavenging among taxa. Shivik, J. A., J. Bourassa, and S. N. Donnigan. 2000. Elicitation of Brown Treesnake predatory behavior using polymodal stimuli. Journal of Wildlife Management 64:969-975. Abstract: The brown treesnake (Boiga irregularis) is a species of special management concern, requiring improvement of capture methods through the development of effective artificial lures. Toward this end, we used night-vision cameras and mechanical models to study the interplay of sensory modalities for stimulating predatory behavior in brown treesnakes. Snakes oriented toward live mouse (Mus musculus) lures in complete darkness as much as they did to live mouse lures under visible-light illumination; however, brown treesnakes in an unlighted environment responded qualitatively differently by probing and biting at the lure holder rather than striking at the mouse within (as did snakes in lighted trials). We altered the odors and vibratory cues of mechanical models to partition attractive stimuli and to measure snake response to vibratory cues. Fur-covered odorized (by rubbing with freshly defrosted dead neonatal mouse) models were more attractive than fur-covered non-odorized models, odor alone, and empty lure holders. Brown treesnakes response to live mice did not differ from their response to smooth, odorized models, and moving versions of the smooth, odorized models stimulated more predatory behavior than unmoving models. Response from brown treesnakes appears to increase as odor and mechanical vibration stimuli are increased quantitatively and-or qualitatively. Conceptually, we hypothesize that polymodal stimuli synergize to promote predatory behavior in foraging snakes and that for trapping purposes, a multi-sensory attractant, optimized at each modality will be required to achieve capture success similar to or better than that obtained using live mice lures.
Stark, C. P., D. Chiszar, K. Stiles, and H. M. Smith. 2002. A laboratory stimulation for studying the effects of chemical and visual cues on prey trailing in Brown Treesnakes (Boiga irregularis). Journal of Herpetology 36:57-62. Abstract: Because of the deleterious effects of predation by nonnative brown treesnakes (Boiga irregularis) on of native vertebrates on the island of Guam, efforts have been focused on developing effective means of controlling B. irregularis and and preventing its spread to neighboring islands. Past laboratory attempts to evaluate potential baits for trapping B. irregularis have often not agreed with field results. Here we present a new laboratory situation for studying effects of various baits on prey findings ability of B. irregularis that uses trailing latencies as a measure of bait efficacy. Our results show that B. irregularis will follow trails made by rodent blood, whole rodent carcasses, and synthetic bait compounds. However, snakes followed trails made be rodent carcasses and blood at a significantly faster rate than those made by synthetic bait compounds. Further, the presence of visual distracter cue significantly increases trailing latencies. Implications of these results for trapping efforts are discussed.