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Most research on effects of edges to vertebrate wildlife comes from eastern-deciduous, boreal, and tropical forests where most edges are abrupt and have resulted from anthropogenic forest fragmentation. California oak (Quercus) woodland, by contrast, is naturally patchy and contains abundant edges, constituting a naturally fragmented vegetative complex. No published research has characterized the vegetative structure of these natural edges in California oak woodlands. To begin to fill this information gap, we measured 10 vegetative characteristics and the number of dusky-footed woodrat (Neotoma fuscipes) dwellings on 8 edges at 4 oak-grassland sites in San Luis Obispo County, California. Stem density and shrub cover were less at edges. Canopy cover and tree diameter were greater at edges, but other vegetative characteristics were similar between the edges of the woodland stands and their interiors. Woodrat dwellings were equally abundant between edges and interiors. Concepts of nest predation, nest parasitism, and other deleterious effects of induced edges previously identified in contiguous-canopy forests might not be applicable to California oak woodlands. Further research is needed to assess wildlife response to oak woodland edges and to further quantify vegetation characteristics of natural and induced oak woodland edges at stand and landscape scales.
Timing of gametogensis and thus spawning can be inferred through changes in plasma concentrations of gonadal hormones. In preparation for ovulation and spawning, mean concentrations of 17ß-estradiol in a population of Rio Grande chub (Gila pandora) occupying the Rio Bonito, New Mexico, peaked at 37.6 ng/mL on 16 June and declined to 1.50 ng/mL by 11 August. Similarly, the gonadal somatic index (GSI) increased from 9.02 on 21 May (n = 9) to 11.85 on 16 June (n = 2) and declined to 6.10 on 11 August (n = 2). Peak concentrations of 17ß-estradiol and elevated GSI in June coincided with peak daylength for the year (14 h and 12 min) and average water temperature of 15.1°C. Concentrations of 17ß-estradiol remained low through 3 October indicating no additional spawning events in the Rio Grande chub population. We demonstrated 17ß-estradiol is a nondestructive and thus useful tool in estimating timing of spawning in a wild fish population.
We present data on diet of 2 syntopic populations of frogs, Rana vaillanti and R. brownorum collected near the Los Tuxtlas biological field station, Veracruz, México. Rana vaillanti strictly inhabits ponds, whereas R. brownorum occurs in several microhabitat types. The stomach contents of 26 specimens of R. vaillanti and 22 of R. brownorum were analyzed. Arthropods consumed by R. vaillanti and R. brownorum included 10 and 12 taxa, respectively. The main prey items for R. vaillanti were Diptera (42.3%), decapod crustaceans (16.3%), Mollusca (Stylomatophora, 8.1%), and Orthoptera (8.2%), whereas R. brownorum consumed Orthoptera (22.0%), Coleoptera (20.8%), and Hymenoptera (15.6%). A regression analysis between prey sizes and snout-vent length was significant in R. brownorum, but not in R. vaillanti. Diversity of prey items was higher in R. brownorum than in R. vaillanti.
Studies of natural history are important for determining baseline information, particularly for species that might be threatened or endangered. We collected 254 (141M:94F:19UNK) massasauga, Sistrurus catenatus edwardsii, from May 1995 through October 1996. The average snoutvent length (SVL ± SD) for adult males (355 ± 45 mm) was not significantly different than the SVL of adult females (364 ± 24 mm). Habitat descriptions indicate that the massasauga in Colorado is a semiarid grassland species that utilizes areas of relatively open shortgrass prairie. Massasaugas were active between 14 and 30°C, with an average ambient temperature during activity of 22.1 ± 2.5°C. The time of observed activity shifted through the season, with primarily diurnal activity during the cooler months (April and late September to October) and primarily early evening activity during the hotter months (May through August). Massasaugas in Colorado gave birth to litters of 5 to 7 young between late August and late September, and reproduction appeared to be biennial. Populations of S. c. edwardsii in Colorado are scattered but population size appeared to be relatively large based on number of captures and low recapture rates, particularly in Lincoln County. However, due to habitat loss and fragmentation resulting from agricultural expansion, these populations might become increasingly threatened in the future.
A new species of Diploglossus is described from the Sierra de Los Tuxtlas in southern Veracruz, Mexico. Individuals of this species are among the largest in the genus in Mexico (up to 105 mm snoutvent length). Similar to D. enneagrammus and D. legnotus, this new species has the suboculars and postoculars arranged in a single continuous series, in contrast to suboculars and postoculars in juxtaposed series. The new species differs from D. enneagrammus in having more scales around the midbody and a redorange throat and anterior flanks marked with broad dark bars; it differs from D. legnotus in possessing more scales around the midbody and more scales along the dorsal midline.
Lesser prairie-chickens (Tympanuchus pallidicinctus) occur in shinnery oak (Quercus havardii) and sand sagebrush (Artemisia filifolia) grassland habitats in New Mexico, Texas, Oklahoma, Kansas, and Colorado. Range-wide population reductions since the 1800s have been attributed to habitat loss, especially of nesting habitat. Using radio-telemetry and a vegetation map of the study area, we investigated habitat use by lesser prairie-chicken hens during the nesting season in herbicide-treated and untreated pastures (each about 1,000 ha in size). Herbicide treatment was effective in reducing shinnery oak cover. The most common vegetation types in hen home ranges were those dominated by shinnery oak. Hens were detected more often than randomly in or near untreated pastures. Although hens were detected in both treated and untreated habitats, 13 of 14 nests were located in untreated pastures, and all nests were located in areas dominated by shinnery oak. Areas immediately surrounding nests had higher shrub composition than the surrounding pastures. This study suggests that herbicide treatment to control shinnery oak might adversely impact nesting lesser prairie-chickens.
Artificial roosts known as bat houses have been developed to replace natural roosts that are destroyed and to create new roosts where they are lacking. I investigated the effects of variables related to bat house characteristics and ecological conditions on patterns of roost occupancy in 95 bat houses. Bat houses seem to have been used exclusively as day roosts, with an overall occupancy rate of 11.6%. The presence of bats roosting in the immediate area prior to the placement of the house was an important predictor of occupancy. When bats were already present at a site, the occupancy rate increased to 63.6%. Likelihood of occupancy also was increased by providing houses with larger landing areas, by mounting them on buildings instead of trees, and by placing houses in areas with low canopy cover and low levels of human disturbance. Bat houses are probably best used when a roost is going to be destroyed, or a colony excluded, and when the houses can be placed in the immediate area of the old roost.
We tested the hypotheses that intrasexual aggression among female thirteen-lined ground squirrels (Spermophilus tridecemlineatus) varies with female density and that females defend home burrows and surrounding areas. Independent of density, females used and maintained 1 home burrow preferentially. The frequencies of aggressive encounters and displays initiated by females in high-density populations were 6 and 4 times higher, respectively, than that initiated by females living at low density. In high-density populations, the average overlap of female home ranges was only 13% of home range area, suggesting female defense of these areas (territoriality). Furthermore, most aggressive encounters were initiated when females were within their territory borders. Females displaced opponents in 80.6% of these encounters, whereas they prevailed in only 26.3% of aggressive encounters initiated outside of territory borders. In experiments involving the temporary removal of individual females, 1 or more neighboring females began using the territory of the removed female, and the frequency of both encounters and displays increased during removals. Upon their return, removed females reestablished their original territories by displacing the responding neighbors. Our results indicate that female S. tridecemlineatus defend territories surrounding a home burrow site, and that intrasexual aggression relegates some females to less preferred areas.
Climatic elements can influence reproduction of mammals. In temperate zones, reproduction often is related to favorable environmental factors, such as spring and rainy seasons, which correspond to availability of food. The goal of this study was to describe the reproductive cycle of the black-tailed jackrabbit, Lepus californicus, with regards to temperature, rainfall, evaporation, and photoperiod in the Mapimí Biosphere Reserve in the central Chihuahuan Desert, Durango, Mexico. If the onset of breeding correlates with these environmental factors, we predicted that mating should be related to total rainfall. To test this prediction, we collected 39 females and 36 males between July 1996 and November 1997 and measured and recorded reproductive condition. Weights of ovaries in females were correlated with increases in photoperiod, evaporation, rainfall, and mean monthly temperature. Increases in male testicular weight were correlated with increasing photoperiod only. We concluded that differences in responses of males and females were related to differing reproductive strategies. Females experience higher reproductive costs and probably respond to a more complex set of environmental cues to increase their reproductive success.
Seasonal scarcity of forbs in southern Texas often requires white-tailed deer (Odocoileus virginianus) to subsist on browse. Deer might seek minerals during periods of high browse consumption as buffers or as precursors to conjugate-based detoxification of plant secondary compounds (PSCs) contained in many browse species. To determine importance of plant secondary compounds on mineral consumption, we fed diets of 0, 25, 50, and 75% guajillo (Acacia berlandieri), a browse species high in PSCs, to 4 male white-tailed deer in a Latin square design experiment, and we compared mineral metabolism and determined how well guajillo met mineral requirements for maintenance and productive processes as described in the literature. Concentrations of calcium, phosphorus, and sodium in the diet decreased with increases in guajillo, whereas magnesium concentration did not change. Losses of calcium, phosphorus, and magnesium occurred largely via fecal excretion, whereas sodium losses occurred via urinary excretion. Calcium, magnesium, and sodium intake rates from diets up to 100% guajillo exceeded requirements. Adult males met summer and fall phosphorus requirements with diets of 100% guajillo and their spring and annual requirements were met with diets of <75 and 97% guajillo, respectively. Phosphorus supplementation during periods of low rainfall and high guajillo consumption might reduce the phosphorus deficit in reproducing females.
Plague is an introduced bacterial disease whose primary vectors are fleas (Siphonaptera). Utah prairie dogs (Cynomys parvidens) are highly susceptible to plague, and entire colonies usually disappear shortly after plague arrives. Infusion of burrows with Pyraperm (an insecticide-dust) kills fleas and immediately halts the spread of plague within colonies. Thus, insecticide-dusts might play an important role in the conservation of prairie dogs.
Large animals occurring on Los Alamos National Laboratory (LANL) and adjoining property pose a number of concerns to area residents and government agencies. Some of these concerns are animal-related accidents that can result in human injuries and fatalities, property damage, and a loss of an economically viable resource (game). We analyzed animal-vehicle accident data with respect to time, season, location, and species for accidents occurring on LANL property and analyzed site characteristics of accident hotspots. We observed a significantly greater number of vehicleelk (Cervus elaphus) accidents during winter compared to summer and spring and a greater number of elk and mule deer (Odocoileus hemionus) vehicle accidents during late afternoon and evening hours compared to morning and afternoon hours. We estimated a cost of $136,500 per year associated with animal–vehicle accidents occurring on LANL property (excluding medical costs). Slope and vegetation height were the best predictors of the status of an area as a hotspot or a control site. These data will be used in public education efforts and to develop mitigation measures to reduce the potential for accidents.
In an algal survey of Pipe Spring National Monument, Cedar Breaks National Monument, and Zion National Park in southern Utah and northern Arizona, 186 species were identified. Overall, diatoms were the dominant group represented by 103 species (55.4% of the reported species). Cyanobacteria and green algae included 41 species each (22.0%), and red algae had only 1 species. Only at Weeping Rock in Zion National Park were cyanobacteria and green filamentous algae dominant.
A Eurasian scentless plant bug, Rhopalus tigrinus, first recorded in North America from New Jersey in 1977, has since been reported from 4 additional eastern states and 6 western states. On the basis of fieldwork and examination of museum collections, I report this crucifer-feeding insect new to New Mexico, Texas, and Utah. Despite its wide Nearctic distribution and occasional use of native Brassicaceae as hosts, the ecological, historical, and taxonomic evidence suggests that R. tigrinus is a nonindigenous species that has been introduced accidentally into the United States.
The reproductive cycles of Leptodeira maculata and L. punctata were examined from museum specimens collected in Mexico. Males followed a testicular cycle in which sperm were produced in spring, summer, and autumn. Egg production in L. maculata occured in spring and summer. The mean of 6 egg clutches was 8.7 ± 1.5 SD, range = 7 to 11. The egg clutches of 10 and 11 are the maximum known from L. maculata. Leptodeira punctata produced eggs in spring, summer, and autumn. Mean clutch size of 9 egg clutches was 7.8 ± 1.7 SD, range = 6 to 11. Apparently, only part of each female population produced eggs each year. The smallest reproductively active male L. maculata was 280 mm snout-vent length (SVL); the smallest reproductively active female was 480 mm SVL. The smallest reproductively active male L. punctata was 276 mm SVL; the smallest reproductively active female was 360 mm SVL.
On 26 August 2000, a Grand Canyon rattlesnake (Crotalus viridis abyssus) was observed and photographed while it swallowed a juvenile spotted sandpiper (Actitis macularia) on a Colorado River beach at Unkar Ruins, Grand Canyon National Park, Coconino County, Arizona. Birds have occasionally been documented as prey of Crotalus viridis, but this is the first report for C. v. abyssus and the first record of a rattlesnake preying on a shorebird (Charadriiformes).
Avian mortality at communication towers in the Rio Grande Valley of southern New Mexico was studied during the fall of 2001 to quantify mortality at radio towers and to identify avian species following this migratory corridor. Six radio towers of heights ranging from 265 to 805 m and distances of 150 to 18,000 m from the Rio Grande were selected. Each tower was visited twice per week for a total of 24 visits per tower. Only 6 mortalities were found: 1 migrant raptor and 5 migrant passerines. Other parts of the western United States that experience adverse weather, such as low, overcast conditions, might be more vulnerable to large numbers of avian mortalities at communication towers than we found in southern New Mexico.