ISSN 2333-0694 JNAHThe Journal of North American Herpetology Volume 2017(1): 11-18 29 March 2017 jnah.cnah.org NOCTURNAL ARBOREALITY IN SNAKES IN THE SWAMPLANDS OF THE ATCHAFALAYA BASIN OF SOUTH-CENTRAL LOUISIANA AND BIG THICKET NATIONAL PRESERVE OF SOUTHEAST TEXAS BRAD M. GLORIOSO1,2 AND J. HARDIN WADDLE1 1U.S. Geological Survey, Wetland and Aquatic Research Center, 700 Cajundome Blvd., Lafayette, LA 70506, USA 2 Corresponding author: [email protected] ABSTRACT — The southeastern United States is home to a diverse assemblage of snakes, but only one species, the Rough Greensnake (Opheodrys aestivus), is considered specialized for a predominantly arboreal lifestyle. Other species, such as Ratsnakes (genus Pantherophis) and Ribbonsnakes/ Gartersnakes (genus Thamnophis), are widely known to climb into vegetation and trees. Some explanations given for snake climbing behavior are foraging, thermoregulation, predator avoidance, and response to flood. Reports of arboreality in snake species typically not associated with life in the trees (such as terrestrial, aquatic, and even fossorial species) usually come from single observations, with no knowledge of prevalence of the behavior. Here, we report on arboreality of snake species detected during 8 years of night surveys in the Atchafalaya Basin of south-central Louisiana and 5+ years of night surveys in Big Thicket National Preserve in southeast Texas. We recorded a total of 1,088 detections of 19 snake species between the two study areas, with 348 detections above ground level (32%). The Rough Greensnake and Western Ribbonsnake (Thamnophis proximus) accounted for nearly 75% of total arboreal detections among the two study areas. However, with one exception, all snake species detected more than once between both study areas had at least one arboreal detection. These observations demonstrate that snakes with widely varying natural histories may be found in the trees at night, and for some species, this behavior may be more common than previously believed. INTRODUCTION into the trees for various reasons. Snakes may climb Like many things in the natural world, arboreality in into trees to exploit seasonally available food sources. snakes exists in a continuum (Lillywhite and Henderson For instance, large colubrid snakes in the United States 1993). There are bona fide tree snakes that confine all often forage in trees each spring as they seek bird eggs of their activities to the vegetation above ground. These and chicks as prey (e.g. Cunningham 1955; Mullin et snakes are most common in the tropics, and typically al. 2000; Sajdak 2010). Copperheads (Agkistrodon exhibit large eyes, slender bodies, long prehensile tails, contortrix) are known to climb to prey upon seasonally and remarkable camouflage (Lillywhite and Henderson abundant cicadas (Gloyd and Conant 1990; Beaupre and 1993). On the other side of the spectrum, there are Roberts 2001; Sajdak 2010). Snakes may climb into decidedly terrestrial or aquatic snake species with poor trees to avoid terrestrial predators (Martins 1993; Sajdak climbing ability that are rarely found off of the ground. 2010). The North American Racer, Coluber constrictor, Then there are snake species that are intermediate in is well documented to flee into trees to avoid capture their use of arboreal situations, sometimes referred to (Conant and Collins 1998; Mitchell et al. 2000; Sajdak as semi-arboreal species, which may use both habitats 2010). In Amazonian forests, many diurnal snake efficiently for different purposes, possibly following regular species, even categorically terrestrial species, were found diel or seasonal patterns (Lillywhite and Henderson at night sleeping on low vegetation, perhaps in avoidance 1993). Still other terrestrial or aquatic snake species of terrestrial predators (Dixon and Soini 1986; Martins may ascend vegetation, sometimes at great heights, 1993). Snakes may ascend into trees for better basking either sporadically or opportunistically (Lillywhite and sites and shelter (Brown 1992; Sajdak 2010). For Henderson 1993; Sajdak 2010). Even fossorial snakes example, in Canada, hundreds of Red-sided Gartersnakes have been known to climb occasionally (e.g. Stidham (Thamnophis sirtalis parietalis) were observed ascending 2001; Olsen and Lee 2007; Langford and Janovy 2011). into low trees during the day when thermal reversals Snake species that are typically associated with aquatic, caused by rain showers caused the ground to have lower terrestrial, or fossorial habitats may be driven to ascend temperatures than what was available in the trees (Shine Journal of North American Herpetology 2017(1) 11 et al. 2005). The motivations of snake climbing behavior et al. 2012; but see Avila-Villegas 2008; Graham 2013). from other reports may be related to courtship or ecdysis Here, we report on arboreality of snake species detected (e.g. Galbraith 2001; Rudolph et al. 2004; Bartz and during 8 years of night surveys in the Atchafalaya Basin Sajdak 2004; Gray 2009). of south-central Louisiana and 5+ years of night surveys The Rough Greensnake, Opheodrys aestivus, is the in Big Thicket National Preserve in southeast Texas. We only truly arboreal species in snake assemblages in the include data on relative rates of arboreality by species, southeastern United States. In addition, the semi-arboreal perch heights, lengths of snakes found in arboreal habits of Ratsnakes (Pantherophis) and Gartersnakes/ situations, and the surfaces on which snakes were Ribbonsnakes (Thamnophis) are well known (e.g. Tinkle observed. 1957; Jackson 1976; Leonard and Leonard 1996; Mullin and Cooper 2002; Shine et al. 2005). There are reports of MATERIALS AND METHODS arboreality in other snake species from the southeastern Study Area — We conducted our study in the Atchafalaya United States, but these are usually based on one or few Basin of south-central Louisiana (2008-2015), and the Big observations at one point in time with little or no data Thicket National Preserve in southeastern Texas (2010- on how prevalent the behavior is in a population (e.g. 2015). The two study areas are of similar latitude and Mitchell et al. 2000; Beaupre and Roberts 2001; Cupp separated by about 230 km (Figure 1). The Atchafalaya Figure 1. Map of the study sites within the two study areas, showing their similar latitudes and relative distances from one another (top). Study sites are also shown over aerial imagery at both Big Thicket National Preserve in Texas (bottom left) and the Atchafalaya Basin of south-central Louisiana (bottom right) to show general habitats. © The Center for North American Herpetology 12 Basin encompasses 339,100 ha of bottomland hardwoods, headlamps, nighttime visual encounter surveys (VES), forested wetlands, bayous, and back-water lakes (Piazza which included searching under cover objects, were 2014). The original extent of the Atchafalaya Basin was the sole means by which snakes were observed during likely double that of today’s estimate, but the boundaries surveys at both study areas. There were typically two were changed after the Great Mississippi River Flood of searchers per survey, where one person would generally 1927, when the East and West Atchafalaya Protection focus on ground searching while the other would search Levees were built to eliminate catastrophic flood loss the vegetation and trees. We surveyed a subset of sites (Piazza 2014). The National Park Service manages over each night beginning 30 minutes after sunset and usually 40,000 ha of public land at Big Thicket National Preserve, ending before 1:00 a.m. Surveys were both time and which represents a small fraction of the estimated spatially constrained. In the Atchafalaya Basin, we initially 405,000–810,000 ha original extent of the Big Thicket performed 1 person-hr VES at each site, but by mid-2010 (Parks and Cory 1936; Cozine 2004). The Big Thicket of this was changed to 20-min surveys. We performed 10- southeastern Texas is known for its dense forests and min VES surveys at Big Thicket sites because there was high biodiversity, but much of the area was heavily logged less search area compared to Atchafalaya sites. Surveys in the 19th and 20th centuries (Cozine 2004). each year generally began in February and ended in Study Sites — In the Atchafalaya Basin, there were a total of 70 sites, with 40 sites accessible by truck occurring north of Interstate 10 (hereafter I-10) in the Sherburne Wildlife Management Area, Atchafalaya National Wildlife Refuge, and Indian Bayou areas, and 30 sites accessible only by boat occurring on state lands and the Attakapas Wildlife Management Area south of I-10 (Figure 1). Six of the northern Atchafalaya sites were suspended after 2008 (these sites are not depicted in Figure 1), but the remaining 34 sites were surveyed 4-6 times every year from 2008-2015. Fourteen sites were added mid-season in the southern Atchafalaya Basin in 2008, and 16 more were added before surveys began in 2009. All 30 southern Atchafalaya sites were surveyed 4-6 times from 2009- 2013, after which surveys in that area were suspended. The hydrology at sites in the northern Atchafalaya Basin is primarily influenced by local rainfall, as inner levees prevent river water from spreading out over the floodplain until it reaches near I-10. The hydrology at southern sites, however, is influenced primarily by Mississippi River water levels, and can fluctuate in backwater areas from 2–3 m within a typical season, with higher pulses during floods (USGS, unpubl. data). Northern sites contained mixed hardwoods, with cypress-tupelo near wetlands, whereas southern sites were mostly cypress-tupelo- willow, with some mixed hardwoods along higher spoils. In the Big Thicket National Preserve, there were 52 total sites, all along tributaries of the Neches River near Beaumont, Texas, with 32 southern sites occurring along Lake Bayou and 10-Mile Creek, and 20 northern sites in Cooks Lake and along Pine Island Bayou (Figure 1). The southern sites were surveyed once in 2010, and 4-6 times from 2011-2015.