Richard T. Kazmaier

Microhabitat selection by Texas horned lizards in southern Texas

The Texas horned lizard (Phrynosoma cornutum) has declined throughout its range. Understanding habitat selection by the Texas horned lizard is an important factor in its conservation. We examined daily and seasonal habitat requirements of Texas horned lizards and determined whether habitat selection differed among land management treatments in southern Texas. We used 5 study sites, each with a different burning and grazing treatment. Adult lizards caught in the study sites were fitted with backpacks carrying radiotransmitters and relocated daily. Habitat characteristics at radio locations and random points 10 m from the lizard were assessed using 50- × 20-cm quadrats. Relocations were made during 3 time intervals (morning, afternoon, evening) and 2 seasons (active, inactive). Horned lizards used bare ground and herbaceous vegetation similar to their availability in the morning and evening for thermoregulation and foraging purposes, but avoided bare ground in the afternoon. In the afternoons, lizards selected woody vegetation and litter as thermal refuges and cover from predators. Lizards also appeared less dependent on herbaceous vegetation and more dependent on woody vegetation and litter in the inactive season compared to the active season as a result of increased temperatures. We did not detect differences in habitat selection among land management treatments. Habitat management for Texas horned lizards should focus on creating a mosaic of bare ground, herbaceous vegetation, and woody vegetation in close proximity.

Habitat selection by the Texas tortoise in a managed thornscrub ecosystem

Brush encroachment on semiarid shrublands resulting from livestock grazing has created global concern. Southern Texas is dominated by Prosopis-Acacia mixed brush communities typical of the Tamaulipan Biotic Province, and the geographic range of the state-threatened Texas tortoise (Gopherus berlandieri) is nearly identical to the boundaries of this biotic province in Texas. In light of the perceived threat to Texas tortoises because of habitat change caused by brush encroachment, we monitored 36 Texas tortoises by radiotelemetry during 1994-1996 to assess habitat selection on a site containing grazed and ungrazed pastures. Tortoises did not exhibit habitat selection at the level of locations within home ranges. Differential habitat selection at the level of home ranges within study areas was not apparent for sex, but was evident for treatment (grazed or ungrazed). Analysis of pooled data indicated that tortoises exhibited broad-scale selection for home ranges within study areas. Selection was expressed as preferential avoidance of old-field and riparian habitats, which represented vegetational extremes of canopy cover. However, tortoises tolerated the broad continuum of other brush communities on the study site. Apparent treatment differences may be an artifact of our inability to adequately pair study areas given the scale of tortoise movement. Our data indicate that increases in the extent of woody canopy cover resulting from grazing-induced brush encroachment will not be detrimental to Texas tortoises. Furthermore, large-scale range improvement practices, such as root-plowing, create unsuitable habitats for this species.

Mark-Recapture Analysis of Population Parameters in a Texas Tortoise (Gopherus berlandieri) Population in Southern Texas

Techniques to assess population changes in reptiles across large landscapes are a conservation and management need. We studied a population of Texas tortoises (Gopherus berlandieri) on a large study area (6150 ha) of contiguous thornscrub vegetation in southern Texas from 1990 to 1999. We examined cohort and temporal variation in capture probabilities; and estimated survival, population size, and A (finite pop- ulation growth rate) for a population of Texas tortoises. We captured 2128 tortoises a total of 3132 times during the study period. The distribution of the frequency of captures by sex varied during the active season and across years, but annual capture probabilities were similar between sexes. The ratio of juvenile to adults varied by a month-by-year interaction. Tortoises exhibited a temporary response to marking that was modeled in survival analysis. Capture probabilities of adult tortoises on an annual basis ranged from 0.12-0.38, and annual survival rate of adults was estimated to be 0.79 ? 0.05. We estimated the density of the adult population to be 0.26 tortoises/ha, a level of magnitude lower than previous work conducted on habitat islands. Lambda (population growth rate) was estimated to be 0.981 (95% confidence limits: 0.945- 1.019) from a Jolly-Seber model. Road-cruising was an effective large-scale method for population moni- toring of the Texas tortoise in our study area and may prove useful in thornscrub habitats that compose the majority of its geographic range.

The Effects of Winter Burning and Grazing on Resources and Survival of Texas Horned Lizards in a Thornscrub Ecosystem

Abstract The ecological effects of land-use practices on reptiles, especially endangered or threatened species, are of conservation and scientific interest. We describe the effects of rotational livestock grazing and prescribed winter burning on resources and survival of the Texas horned lizard (Phrynosoma cornutum) during the summers of 1998 to 2001 in southern Texas, USA. We evaluated survival rates of Texas horned lizards (n  =  111) on 6 study sites encompassing 5 different burning and grazing treatments. We also measured indices of cover (i.e., vegetation) and food abundance (i.e., harvester ants [Pogonomyrmex rugosus]). We telemetered and relocated adult lizards daily. We divided the study into 2 seasons, spring (15 Apr–30 Jun) and summer (1 Jul–15 Aug), corresponding to the relative activity of horned lizards. Winter burning provided an increase in food resources and led to increased survival of Texas horned lizards in the second growing season after fire, but grazing-induced changes in vegetation cover reduced survival, likely by increasing lizard vulnerability. Fire and grazing reduced litter and increased bare ground and forb cover but did not affect woody vegetation. Ant activity was greater in burned sites and varied with grazing level, season, and year. Summer survival functions of horned lizards varied by burning treatment, with higher survival observed on burned sites in the second year after burning. Survival rates were ordered from highest in ungrazed sites to lowest in heavily grazed sites. We recognize the limitations of our work resulting from a lack of spatial replication of treatments. However, our mensurative study provides fertile ground for future hypothesis testing regarding the effects of land management on shrubland and grassland reptiles. We propose that future studies focus on the population consequences of variation in burn frequency, burn timing, and grazing intensity.

SHORT-TERM RESPONSE OF HERPETOFAUNA TO VARIOUS BURNING REGIMES IN THE SOUTH TEXAS PLAINS

Abstract Data on effects of fire on herpetofauna generally are lacking. With increased use of prescribed fire to manage rangelands in South Texas for wildlife and livestock, a better understanding of effects of fire on the herpetofauna is needed. We investigated effects of combinations of winter and summer prescribed fire on rangeland sites on the Chaparral Wildlife Management Area in southern Texas. Dormant-season fires had little effect on diversity and abundance of the herpetofauna. Inclusion of growing-season fire into the burning regime tended to increase diversity and abundance of grassland species, such as the six-lined racerunner (Cnemidophorus sexlineatus). Although our experimental design limits interpretation of results to the study site, our data suggest that prescribed fire may be used to manage rangelands in South Texas without negative affects on the herpetofauna. A varied burning regime is recommended to increase herpetofaunal diversity.

Temporal Differences in Activity Patterns of Male and Female Texas Horned Lizards (Phrynosoma cornutum) in Southern Texas

Abstract The Texas Horned Lizard (Phrynosoma cornutum) is a species of special conservation concern in Texas and the southwestern United States.This study was designed to compare capture rates of adult female and male Texas Horned Lizards by time and month. Horned lizards were captured by road cruising at Chaparral Wildlife Management Area in southern Texas. We found a female bias in morning capture rates compared with evening capture rates. These sex-specific differences in timing of activity may indicate an important difference in physiological constraints on the sexes. Sex-biased movement patterns must be accounted for in population sampling and plans to conserve this imperiled species.