Maria A. Eifler

Differential Effectiveness of Standard and Long Sherman Livetraps in Capturing Small Mammals

Most studies of small-mammal populations rely on livetrapping, yet relatively few studies compare different types of traps. We placed one standard-length (22.9 cm) and one long (30.5 cm) Sherman livetrap at each station of a trapping grid in oldfield habitat in eastern Kansas and compared rates of capture of small mammals over a 5-year period (1985–1990). Nine of 10 species were captured more often in long traps. Of the five most commonly trapped species, only Sigmodon hispidus and Microtus ochrogaster varied seasonally in proportion of captures in long traps. Species having lower adult body mass were captured proportionately more often in long traps, suggesting that long traps might have more sensitive trigger mechanisms. However, long traps closed without capturing an animal significantly less often; furthermore, proportions of captures in the two types of trap did not differ among mass classes of S. hispidus or M. ochrogaster , so size differences alone cannot account for differential capture success. Not only were capture rates higher in long traps, but also mortality due to predators and winter exposure was lower.

The influence of prey distribution on the foraging strategy of the lizard Oligosoma grande (Reptilia: Scincidae)

Abstract The grand skink, Oligosoma grande, is a diurnal rock-dwelling lizard from the tussock grasslands of Central Otago, New Zealand, whose diet includes a variety of arthropods and fruit. We conducted a field experiment to examine the influence of prey distribution on foraging behavior and spacing patterns. On sites where prey distribution was unaltered (control sites), males and females differed in diet and foraging behavior. Most male feeding attempts were directed at large strong-flying insects, and males used a saltatory search pattern that involved relatively infrequent moves of long duration. Females spent more effort catching small weak-flying insects and visiting fruiting plants. Their search behavior involved frequent moves of short duration. The placement of meat-bait on experimental sites led to a redistribution of large flies without influencing other prey types. Experimental females switched foraging strategy by adopting a search pattern of relatively infrequent moves of long duration, increasing the frequency of attempts to capture large prey, and reducing the importance of fruit in their diet. The experimental manipulation appeared to influence space use. On control sites, both sexes had comparably sized home ranges. On experimental sites, male home ranges were significantly larger than female home ranges.

Foraging Behavior and Spacing Patterns of the Lizard Oligosoma grande

The grand skink, Oligosoma grande, is a diurnal rock-dwelling lizard from the tussock grass- lands of Central Otago, New Zealand. Foraging behavior, diet, and spacing patterns were examined for two populations of individually marked adults. Adults of both sexes search for arthropod prey using pause- move (=saltatory) searching. Males and females spent the same amount of time moving across outcrops but differed in the characteristics of their searching behavior. Females made more frequent but shorter moves than males. The two sexes also differed in diet Males directed most of their pursuit effort towards large flying insects, but occasionally consumed smaller, easy to capture prey and visited fruiting plants. By con- trast, females fed primarily on the small prey types and plant material. Males and females had home ranges (HR) and core areas (CA) of comparable size and with comparable levels of total neighbor overlap However, the patterns of HR overlap differed between the sexes. Both males and females tended to have greater average HR overlap with male neighbors. Core area overlap was less extensive than HR overlap and some animals concentrated their activity in CAs that were exclusive from those of other lizards. Females appeared to be dominant to males; the most common conspecific interaction was adult females chasing adult males.

Foraging under the risk of predation in desert grassland whiptail lizards (Aspidoscelis uniparens)

The whiptail lizard Aspidoscelis uniparens searches for fossorial prey using a series of moves and pauses punctuated by bouts of digging. We examined the effect of predation risk on foraging A. uniparens in outdoor enclosures, observing their behavior in the presence and absence of the predatory lizard Gambelia wislizenii. Predator presence led to changes in activity patterns and foraging behavior. When predators were present, A. uniparens reduced both the proportion of time active and time moving, shifted activity periods, reduced their movement rate, and changed the duration of moves. There were no apparent changes in digging effort, but the likelihood of successfully digging for food decreased when a predator was present.

Habitat use and movement patterns in the graceful crag lizard, Pseudocordylus capensis

ABSTRACT We characterized the habitat use and movement patterns of adult male, adult female and juvenile Pseudocordylus capensis, a diurnal, rock-dwelling, insectivorous lizard. Rock use was vertically stratified: males spent most of their time at local high points, females at mid-level on the rocks, and juveniles were typically in the lower regions. Movement patterns varied with demographic class as well: juveniles moved more frequently and spent a greater proportion of their time in motion than did adults, and the number of moves of different durations varied among the classes. Finally, juveniles scanned their surroundings and appeared to feed more frequently than adults.

Effect of weather on individual growth rates in cotton rats, Sigmodon hispidus

Weather can influence many aspects of mammalian life histories through its impact on growth rates. We examined the seasonal effect of rain, mean temperature, snowfall, and snow cover on changes in body mass among individual young (≤60 g) and adult (>60 g) cotton rats (Sigmodon hispidus) in northeastern Kansas from March 1978 to December 1993. Weather significantly affected growth rates among all sex-season-size groupings except for young cotton rats in summer. In seasons other than summer, weather accounted for 53-68% of the variation in growth rates of young rats. Weather generally accounted for less of the variation in growth rates of adult cotton rats. When significant, snow cover was associated negatively and rainfall was associated positively with growth rates of all cotton rats. High temperatures in summer adversely affected growth rates of adult cotton rats but were associated with higher growth rates among all size-sex combinations in autumn. Growth rates of adult females in spring and adult males in autumn were highest at intermediate temperatures and lower at extremes. In autumn, response of growth rates of adult males to mean temperature varied with body mass. Intrapopulational variation in responses to weather may reflect different environmental and reproductive constraints at various points in the life cycle.

Habitat Selection by Foraging Texas Horned Lizards, Phrynosoma cornutum

Abstract The Texas horned lizard, Phrynosoma cornutum, feeds primarily on harvester ants (Pogonomyrmex) across much of its range. We quantified behavior of P. cornutum foraging on Pogonomyrmex relative to habitat and time. For the duration of their morning activity, 14 lizards were observed; we determined their use of habitat and location of ants that were captured. Lizards spent most of their time under vegetation; the type of vegetation used varied throughout the morning. Most feeding took place in the open and involved ants dispersed away from colonies. When feeding under vegetation, most feeding took place under mesquites (Prosopis), and location of mesquites under which lizards fed was nonrandom with respect to distance from entrances to colonies of ants. Feeding at entrances to colonies was restricted to a shorter period of the morning than feeding on dispersed ants. Males and females differed in use of habitat and in foraging behavior, with males more likely to feed in the open and to feed at entrances of colonies than females.

Escape tactics in the lizard Meroles cuneirostris

Successful escape from predators may involve the use of multiple tactics. The wedge-snouted desert lizard (Meroles cuneirostris) flees from predators through a series of discrete moves with each move representing a specific manoeuvre type. By simulating the approach of a predator, we examined the role of sex and age (adult vs. juvenile) on the manoeuvre types used during escape, as well as the relationship between the number of moves needed to escape and the number of manoeuvre types employed. The eight defined manoeuvre types were used by all demographic groups, though there were differences among groups in the tendency to use certain manoeuvre types. In general, there was a strong difference in how adults and juveniles fled from predators. The number of manoeuvre types used by a lizard tended to increase with the number of moves required to escape and adults more readily added new manoeuvre types to an escape sequence. Demographic differences in escape behaviour might result from differing predation pressures incurred by juveniles and adults, and might also be related to the ontogeny of escape behaviour.

Use of Habitat by the Semiaquatic Lizard, Norops aquaticus

Abstract We assessed use of habitat by the semiaquatic lizard Norops aquaticus along the Río Java at the Las Cruces Biological Station, Costa Rica. We surveyed the river for lizards and determined characteristics of their perches relative to edge of the water. Individuals preferentially positioned themselves near eddies. Demographic classes differed in height of perches above the river, with adult males using the highest perches. Males were most likely to perch directly above water. In addition, males and juveniles tended to be in exposed areas, whereas females selected cover. Behavior of N. aquaticus on land is dependent on characteristics of rivers.

Characteristics and Use of the Tail in Signaling by the Zebra-Tailed Lizard (Callisaurus draconoides)

Abstract The zebra-tailed lizard (Callisaurus draconoides) is a diurnal territorial insectivore from arid areas of North America. The underside of its tail has a series of black bands on a white background; individuals raise the tail to expose the underside as a social signal and to deter pursuit by predators. We characterized variation in banding of the tail within a population of C. draconoides from Sonora, Mexico, and examined the relationship between characteristics and use of the tail. Number of bands on intact tails was 4–10; individuals who have experienced some natural reduction in their tail can lack bands all together. The proportion of the underside of the tail that was black was 0–0.46. For males, snout–vent length and mass were positively correlated with number of bands and mean length of bars on the tail; snout–vent length, mass, and width of head were positively correlated with the proportion of black on tails. Females in better condition (based on residuals from regression of snout–vent length to mass) tended to have more bars on the tail and a wider head; snout–vent length, mass, and width of head were positively correlated with mean length of band. We simulated predator-prey interactions using humans as predators. Males used tail displays more than females. Individuals encountered in the open were more likely to use tail displays. Neither size of body nor natural reduction in tail was related to use of tail displays. During focal observations for females with reduced tails, rates of tail displays were positively correlated with length of tail. Males with intact tails moved more frequently and fed more often than males with reduced tails.