Herpetological Conservation and Biology 8(2):435−446. Submitted: 24 July 2012; Accepted: 17 April 2013; Published: 15 September 2013. Herpetological Conservation and Biology

Breeding Site Fidelity and terreStrial MoveMent oF an

endangered aMphiBian, the houSton toad (Bufo houstonensis)

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Michael W. VandeWege , todd M. sWannack , kensley l. greuter , donald J. BroWn ,

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and Michael r.J. forstner

¹Department of Biochemistry, Molecular Biology, Entomology, and Plant Pathology, Mississippi State University, Mississippi
State, Mississippi 39762, USA, email: [email protected]
²United States Army Engineer Research and Development Cente r , E nvironmental Laboratory, Vicksburg, Mississippi 39180, USA
³SWCA Environmental Consultants, 4407 Monterey Oaks Boulevard, Building 1, Suite 110, Austin, Texas 78749, USA
⁴Department of Biology, Texas State University-San Marcos, Texas 78666, USA

abstract.―the houston toad (Bufo [anaxyrus] houstonensis) is a federally endangered species endemic to east-central texas,

uSa. understanding movement patterns of this species during different life stages is critical for development and implementation of landscape-scale recovery initiatives. We used breeding survey, terrestrial movement, telemetry, and juvenile dispersal data to characterize B. houstonensis movement patterns. B. houstonensis were found to exhibit a high level of breeding site fidelity within and among years, with the majority of recaptured adult toads remaining within 75 m of the pond of initial capture. however, long-distance dispersal (up to 777 m) was observed for adults, which suggests that connectivity among local subpopulations could be maintained through occasional dispersal of individuals. additionally, our movement data and the rarity of captures outside of woodlands support the assumption that B. houstonensis prefer forested habitat. to maximize the potential for long-term persistence of toad populations, we recommend that land managers focus on maintaining and restoring a matrix of ponds in forested communities that support and provide connectivity among critical habitats.

Key W o rds.—Bufo houstonensis; connectivity; dispersal; Houston Toad; juvenile; adult; site fidelity; Texas.

introduction

volume, geographical location, and distance among water bodies. The success of dispersing individuals, spatial distribution of ponds, and connectivity of breeding sites all contribute to the eventual structure of amphibian populations (Gustafson and Gardner 1996; Semlitsch and Bodie 1998; Marsh and Trenham 2001; Moilanen and Nieminen 2002). There are two basic components to connectivity, structural and functional. Structural connectivity is the spatial connection of habitat types; whereas, functional connectivity describes the utility of the habitat for dispersal across the landscape (Taylor et al. 2006). Managers typically improve structural connectivity (e.g., establishing connections among forest patches) assuming equivalence to functional connectivity (Ribeiro et al. 2011). However, even when habitat preferences are well known, it is important to understand movement patterns of all life stages to improve the functional connectivity for the most actively dispersing life stages.
Spatial distribution and habitat connectivity are important topics of study in amphibians as global

• extinctions become more apparent.
• The

tendency of amphibians to travel among subpopulations depends on habitat quality and accessibility (Martin et al. 2008; Dancose et al. 2011). Temperate pond-breeding amphibians require both aquatic and upland terrestrial habitats for breeding and foraging activities, respectively (Semlitsch 2000). However, habitat loss and fragmentation of these habitats are major contributing factors to amphibian declines (Davidson et al. 2002; Beebee and Griffiths 2005; Gallant et al. 2007; Collins and Crump 2009). Previous research has found that the wildland-urban interface, where habitat fragmentation often occurs, accounts for 9 % of land area in the United States (Radeloff et al. 2005). This human encroachment has left suitable amphibian habitat fragmented throughout the landscape (Lehtinen et al. 1999). Across mixed landscapes of ephemeral and permanent ponds, the distribution of amphibian populations is dynamic and depends on the
Several amphibian species in the family Bufonidae exhibit similar spatial habitat use patterns. While most adult individuals remain near a breeding site throughout the year,

Copyright © 2013. Michael Vandewege. All Rights Reserved.

435

Vandewege et al.—Breeding site fidelity and movements of the Houston Toad. juveniles are thought to be the primary units of houstonensis spatial dynamics, an essential dispersal among potential breeding sites (Smith component of successful recovery and and Green 2005; Semlitsch 2008). High management of this imperiled species.

• breeding site fidelity and low dispersal have
• Here, we describe B. houstonensis movement

been reported in populations separated by tens patterns and spatial habitat use among life stages of kilometers (km) connected by occasional within the Lost Pines ecoregion. We used audio migrants (Smith and Green 2005, 2006). surveys, pitfall trapping, juvenile emergent However, because amphibians exhibit a wide observations, and radio telemetry to determine range of dispersal abilities and habitat use breeding site fidelity, terrestrial movement, and patterns (Carpenter 1954; Stebbins and Cohen dispersal of adult and juvenile B. houstonensis 1995; Dodd and Cade 1998; Wells 2007), it is within and among years. In addition, we important to investigate spatial dynamics on a collected data to gauge the use of grasslands as species and life stage specific basis.

travel corridors by B. houstonensis.
The Houston Toad (Bufo [Anaxyrus]

houstonensis) is a federally endangered species endemic to east-central Texas (Gottschalk 1970). Since the 1970s, B. houstonensis has been

MaterialS and MethodS

study site.―We studied B. houstonensis

extirpated from at least three of the 12 counties populations on the Griffith League Ranch within its historic range (U.S. Fish and Wildlife (GLR), a 1,948-ha property in Bastrop County, Service 1984), with populations persisting in Texas owned by the Boy Scouts of America isolation (> 40 km from the nearest population) (BSA). This large tract of land is located within across all but one of the remaining counties designated critical habitat for B. houstonensis (Michael Forstner, unpubl. data). Prior to the (U.S. Fish and Wildlife Service 1984), and is Bastrop County Complex Fire of September considered essential for long-term persistence of 2011, the only population not threatened with the species (Hatfield et al. 2004; Duarte et al. immediate extinction occurred in the Lost Pines 2011). The GLR is primarily a forested ranch, ecoregion in Bastrop County (Brown 1971, with a canopy dominated by Loblolly Pine

1975; Duarte et al. 2011). B. houstonensis is a (Pinus taeda), Post Oak (Quercus stellata),

habitat specialist that prefers deep sandy soils Blackjack Oak (Q. marilandica), and Eastern and forest cover (U.S. Fish and Wildlife Service Red Cedar (Juniperus virginiana), and an 1984), and its precipitous decline has been understory dominated by Yaupon Holly (Ilex driven largely by habitat loss and degradation vomitoria), American Beautyberry (Callicarpa (Brown 1971; Brown and Mesrobian 2005; americana), and Farkleberry (V a ccinium

• Michael Forstner, unpubl. data).
• arboreum). The GLR supports 17 ponds, with

Few life history data have been collected for hydroperiods ranging from highly ephemeral (n this species over the last 60 years, despite its = 2) to permanent (n = 3). We have observed B. endangered status. Hybridization with Bufo houstonensis  at 15 of these ponds since we began

[Anaxyrus] woodhousii and Bufo [Incilius] monitoring reproduction on the property in 2000,

nebulifer was studied by Brown (1971). Hillis and 11 are known breeding ponds. et al. (1984) and Jacobson (1989) addressed population-level behavior and activity;

Breeding site surveys.―We conducted call

specifically breeding activity with comments on surveys between 2001 and 2010 following the sexual selection and juvenile dispersal. Finally, protocol detailed in Jackson et al. (2006) to study fluorescent powder has been tested as a tool to the use of breeding habitat by adult male and quantify juvenile dispersal (Swannack et al. female B. houstonensis during annual courtship. 2006). However, no data have been collected The annual number of call surveys ranged from describing the spatial distribution and movement 19 to 27, depending on B. houstonensis activity dynamics of either juvenile or adult B. levels during their breeding season, between houstonensis. This study represents the first January and June (Table 1). Between 2001 and major contribution to our understanding of B. 2005, and between 2009 and 2010, we measured

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Herpetological Conservation and Biology

taBle 1. Number of anuran call surveys conducted on the Griffith League Ranch, Bastrop County, Texas, USA, in seven survey years, and number of unique individual Houston toads (Bufo [Anaxyrus] houstonensis) detected at breeding ponds on the property each survey year.

year

2001 2002 2003 2004 2005 2009 2010

• number of surveys^a
• number of unique individuals^b

20 20 20 19 19 27 27
8
53 32 20 80 45 90

^aIncludes number of days each breeding season where all ponds were surveyed on the study site. ^bIncludes recaptures from previous years and individuals originally captured in traps.

and individually marked B. houstonensis during arrays with double-opening funnel traps (used visual surveys at potential breeding ponds, for a separate study conducted during the same unless individuals were in amplexus. We period) centered on each side of the flashing, marked adult B. houstonensis using Passive adjacent and parallel to known breeding ponds. Integrated Transponder (PIT) tags or toe clips We equipped all traps with predator exclusion (Donnelly et al. 1994). Between 2001 and 2005, devices (Ferguson and Forstner 2006), flotation we conducted surveys nightly during the devices to mitigate mortality during bucket breeding season except on nights when weather flooding, and sponges to provide a moist conditions were hazardous. In 2009 and 2010, environment for amphibians upon capture. The we surveyed only on nights when toads were trap locations and breeding sites used during the most likely to be active (Kennedy 1962; Hillis et terrestrial activity monitoring periods are shown

• al. 1984; James Dixon, unpubl. data).
• in Fig. 1.

We checked traps daily from 12 March 2001

adult terrestrial movement (drift fence to 30 June 2004, with the exception of seven

sampling).―We monitored terrestrial movement days in July 2002 and 13 days in August 2003. in open grassland areas, forested habitat, and Between 2008 and 2011, we conducted most of along drainages from 2001 to 2004 and 2008 to our terrestrial monitoring during the spring, 2011 using linear and Y-shaped drift fences with when B. houstonensis are most active. In 2008, pitfall traps and double-opening funnel traps we trapped from 1 March to 1 May, with the (See Dodd et al. 2007 and Swannack et al. 2007 exception of five days in April, from 1 February for design information). In 2001, we installed to 1 May in 2009, from 31 January to 1 May in five linear drift fences (two 121 m and three 153 2010, and from 13 February to 23 May in 2011, m) in grasslands parallel to the forest edge, three excluding seven days in May. were 25 m from the forest edge, one was directly adjacent to the forest, and the remaining drift

• adult
• terrestrial
• movement
• (radio

fence was 100 m from the nearest forest edge. telemetry).―Between 2003 and 2005, we fitted We installed additional drift fences to monitor 21 (16 M : 5 F) B. houstonensis with external movement within forested habitat, including radio transmitters (model # BD-2, mass: 1.8g, three additional Y-shaped arrays in 2001, ten Y- Holohil Systems, Carp, Ontario, Canada). We shaped arrays in 2002, and nine Y-shaped arrays collected toads for telemetry during the first in 2008. Due to low Houston Toad capture rates chorusing event in March and tracked toads up in double-opening funnel traps, they were not to six weeks. We selected toads based on weight used with Y-shaped arrays between 2008 and and body condition. We used toads weighing 2011. In 2009, we added seven 15 m linear over 20 g to remain within the recommended

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Vandewege et al.—Breeding site fidelity and movements of the Houston Toad.

Figure. 1. Pond and drift fence locations on the Griffith League Ranch, Bastrop County, Texas, USA, used for investigating movement activity patterns of the endangered Houston Toad (Bufo [Anaxyrus] houstonensis). Counties with known choruses of Houston Toad as of 2011 are shaded gray and listed as extant. We used 18 arrays during the first sampling period (2001 to 2004 Drift Fences), and 26 arrays during the second sampling period (2008 to 2010 Drift Fences), 10 of which were shared between sampling periods (Shared Drift Fences). When drift fences were less than 10 m from ponds, fence symbols were moved and connected by lines to their specific locality.

ratio of transmitter mass to body mass (White being less than 3 cm snout-vent length (SVL). and Garrott 1990). We tested three external- We initially captured toadlets using three fitting techniques for the transmitters, a spandex semicircle pitfall trap arrays constructed to jacket, stainless steel bead chain, and nylon surround B. houstonensis egg strands laid in a ribbon (see Swannack 2007 for details). We breeding pond. The trap arrays were made of released all captured and fitted toads at the edge flashing and placed 2 m, 5 m, and 8 m from the of the pond closest to their initial capture point pond’s edge, with each array extending 1 m into and located toads again at least once every three the pond on each side to measure the rate of days during the life of the transmitter. To dispersal from the pond’s edge after determine whether toads were moving during metamorphosis and emergence. We positioned daylight hours, we initially located toads during covered 2.4 L pitfall traps along each array at 3 the day and then located each toad again that m intervals and filled each one with leaf litter night. We tracked each toad until the transmitter and water. We toe-clipped all juveniles captured

• fell off or the batteries died.
• in the array (Donnelly et al. 1994) and

subsequently released them on the opposite side