Lauretta M. Bushar

Foraging behavior of the timber rattlesnake, Crotalus horridus

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Foraging Ecology of Timber Rattlesnakes, Crotalus horridus

Abstract The geographic range of the Timber Rattlesnake (Crotalus horridus) encompasses most of the eastern half of the United States. Although the overall diet composition of C. horridus has been well documented and has been reported to be very broad, local population variation has not been studied. We examined the diet and foraging behavior of C. horridus from four separate populations in Pennsylvania and New Jersey. A total of 253 prey items from scat samples, stomach samples, and field observation were identified to species or family level. Although voles (Myodes gapperi) and mice (Peromyscus spp.) comprised the bulk of the diet in all populations, relative prey species frequency differed significantly among the four populations. These data indicate that the food habits of C. horridus varied widely even within relatively small geographic distances. Comparisons with small mammal trapping data further suggest that the diet composition of this ambush predator may not simply reflect the availability of prey species. Radiotelemetric observations of C. horridus further indicate differing frequencies of log-oriented foraging behavior among the study sites. Analysis of body posture revealed an alternative ambush foraging posture (non-log-oriented posture) which also exhibited variation in frequency among study sites. However, selected foraging habitats at all study sites were typified by a locally high density of fallen logs and other woody debris (6% of forest-floor cover/m2). These findings indicate geographic variation in the foraging ecology of C. horridus and suggest behavioral plasticity in foraging response to available prey.

Response of Timber Rattlesnakes to Commercial Logging Operations

ABSTRACT Forest management practices in the eastern United States directly impact large parcels of land that serve as habitat for timber rattlesnakes (Crotalus horridus). We assessed the behavioral response of timber rattlesnakes to commercial logging activities and the impact of such activities on a timber rattlesnake population in northcentral Pennsylvania. We radiotelemetrically monitored 67 individual snakes over periods of up to 4 years, marked and recaptured 306 snakes, and conducted search and survey efforts before, during, and after commercial logging operations on 3 timber sale parcels (totaling 154.2 ha). Location and timing of timber sales created the maximum opportunity for interaction of snakes with logging operations and with altered habitat. Observed logging-related mortality of snakes was low (<2% of the population/yr), but potential mortality could have reached 7%. Logging activity and resulting habitat changes did not alter behavior or movement patterns of telemetrically monitored snakes. Snakes with established activity ranges in timber sale areas continued to use these areas both during and after logging operations. Similarly, snakes with activity patterns that did not include timber sale areas did not alter their movement patterns to include such sites in the short-term. Timbering increased structural diversity of the habitat and, concurrently, diversity of habitat used by timber rattlesnakes increased. Our results suggest that the opportunity exists to develop forest management practices that provide timber products while limiting impacts on behavior and habitat use of timber rattlesnakes. To further reduce impacts to timber rattlesnake populations we recommend that management agencies require commercial logging contractors, sub-contractors, and field employees to adhere strictly to a policy that prohibits the intentional killing of rattlesnakes encountered during logging activities.

Genetic Structure of Timber Rattlesnake (Crotalus horridus) Populations: Physiographic Influences and Conservation Implications

The distribution and genetic structure of wildlife populations may be impacted by landscape features and anthropogenic factors. The role of these factors in the genetic relationships among Timber Rattlesnakes (Crotalus horridus) from 21 locations in Pennsylvania, New Jersey, and Virginia was investigated using microsatellite genetic markers. Evidence for null alleles was found in 8 of the 21 populations studied, with frequencies ranging from 0.018 to 0.185. However, the presence of null alleles appeared to have no effect on the interpretation of the patterns of genetic relationships among the populations studied. The analyses showed that the overall extent of genetic differentiation was consistent with isolation by distance; however, a substantial amount of among-groups variation could not be accounted for by geographic distance alone. Bayesian analysis (STRUCTURE), genetic distance analysis, and factorial correspondence analysis (FCA) all indicated that the sampled populations represented three genetic groups, which corresponded closely with physiographic regions. These three groups consisted of an Atlantic Coastal Plain group, an Appalachian Plateau group, and an Appalachian Ridge and Valley group. We recommend that these be considered as separate conservation management units (MUs) for C. horridus in Pennsylvania and New Jersey. Several potential barriers to gene flow were identified, including the Appalachian Mountains, several large rivers, and major roadways. The lowest levels of genetic variation were found in the highly isolated populations from the Atlantic Coastal Plain.

Population Isolation and Genetic Subdivision of Timber Rattlesnakes (Crotalus horridus) in the New Jersey Pine Barrens

Abstract:  Timber Rattlesnakes, Crotalus horridus, are an endangered species in New Jersey, where high human population density places extraordinary pressures on natural populations. Disjunct populations are found in both the northern part of the state and a few scattered locations in the southern Pine Barrens. The Pine Barrens populations were previously shown to have reduced levels of genetic diversity compared to other populations in the Mid-Atlantic region. In this study, we used microsatellite DNA to examine the remaining six known C. horridus populations in the Pine Barrens and two in the northern part of the state. Bayesian analysis, genetic distance analysis, and factorial component analysis were performed, and the results indicated that the sampled populations represented four genetic subgroups, the two northern populations comprised one subgroup and the remaining six Pine Barrens populations comprised the other subgroups. Although there was evidence for isolation by distance among the Pine Barrens populations, geographic distance alone did not account for a substantial amount of among-group variation. The combined analyses implicated paved roads as primary isolating barriers between populations. Given their geographic isolation and reduced levels of genetic diversity, intensive efforts may be required to ensure the persistence of the behaviorally and genetically unique C. horridus populations of the New Jersey Pine Barrens.

Multiyear Sampling Reveals an Increased Population Density of an Endemic Lizard after the Establishment of an Invasive Snake on Aruba

Abstract The island of Aruba is home to several endemic species, and has been colonized recently by the invasive boa, Boa constrictor. We present data for a multiple-year sampling effort on one of Arubas endemic species, the Aruban Whiptail Lizard (Cnemidophorus arubensis). Our sampling began before the invasion of B. constrictor and ended after their firm establishment, thus affording us the unique opportunity to document the potential effects of this invasive snake on the endemic lizard. Additionally, we compare our data with earlier studies with an average lizard density of 235.1/ha (SE = 73.42, n = 11). After the invasion of the B. constrictor we calculated densities of C. arubensis as high as 2,185/ha. Although B. constrictor regularly preys upon C. arubensis, the relationship between B. constrictor and C. arubensis likely represents ecological facilitation of the lizard species. Herein, we further develop a hypothesis that may explain how the invasive B. constrictor has caused an increase in the population of this endemic lizard. Additionally, we suggest and discuss a few alternative hypotheses that may also account for this observed pattern of increased density. This study identifies a need for continued monitoring of Arubas native fauna, as well as the need for further experimental approaches to understand the mechanism by which invasive predators ecologically interact with native prey.

Genetic Characterization of an Invasive Boa constrictor Population on the Caribbean Island of Aruba

Abstract Boa constrictor was first documented on the Caribbean island of Aruba in 1999. Despite intensive efforts to eradicate the snake from the island, B. constrictor has established a stable, reproductively successful population on Aruba. We generated mitochondrial sequence and multilocus microsatellite data for individuals from this population to characterize the origins and means of introduction to the island. Phylogenetic analyses and measures of genetic diversity for this population were compared with those for invasive B. constrictor imperator from Cozumel and B. constrictor constrictor from Puerto Rico. Cozumel populations of B. c. imperator had significantly higher numbers of alleles and significantly higher values for FIS than the Puerto Rico and Aruba populations. Observed, expected, and Neis unbiased heterozygosities, as well as effective number of alleles, were not significantly different. The effective population sizes from Aruba and Puerto Rico were generally lower than those for either of the Cozumel populations; however, there were broad confidence intervals associated with published estimates. We conclude that the present B. constrictor population on Aruba most likely resulted from the release or escape of a small number of unrelated captive snakes originating from South America (B. c. constrictor) and are phylogenetically distinct from introduced boas on Puerto Rico and Cozumel. This study adds to the growing body of evidence suggesting the ease with which a small number of relatively slow-maturing B. constrictor can quickly invade, become established, and avoid eradication efforts in a new location with suitable habitat.