Geology topics

Wesley E. Newton

Publications and source records attributed to Wesley E. Newton.

23 records · Page 2Linked to original sources

USGS1998

Effects of the herbicide atrazine on Ambystoma tigrinum metamorphosis: duration, larval growth, and hormonal response

We exposed larval tiger salamanders (Ambystoma tigrinum) reared in the laboratory from eggs collected from a prairie wetland in North Dakota to three concentrations of atrazine (0, 75, and 250 i??g/L) in a static renewal test to determine the pesticide's effect on (1) plasma corticosterone and thyroxine concentrations, (2) larval size, and (3) days-to-stage at stages 2 and 4 of metamorphic climax. We found significant effects of atrazine on each of these response variables. Plasma thyroxine was elevated in both atrazine-exposed groups compared to the control group; plasma corticosterone was depressed in the 75 i??g/L treatment compared with both the control and 250 i??g/L treatment. Larvae exposed to 75 i??g/L atrazine reached stage 4 later, but at a size and weight comparable to the control group. By contrast, larvae in the 250 i??g/L treatment progressed to stage 4 at the same time but at a smaller size and lower weight than larvae in the control group. These results indicate that the herbicide has the potential to influence tiger salamander life history. We present a model consistent with our results, whereby corticosterone and thyroxine interact to regulate metamorphosis of tiger salamanders based on nutrient assimilation and adult fitness

Physiological Zoology↗

USGS1998

Checklist and "Pollard Walk" butterfly survey methods on public lands

Checklist and “Pollard Walk” butterfly survey methods were contemporaneously applied to seven public sites in North Dakota during the summer of 1995. Results were compared for effect of method and site on total number of butterflies and total number of species detected per hour. Checklist searching produced significantly more butterfly detections per hour than Pollard Walks at all sites. Number of species detected per hour did not differ significantly either among sites or between methods. Many species were detected by only one method, and at most sites generalist and invader species were more likely to be observed during checklist searches than during Pollard Walks. Results indicate that checklist surveys are a more efficient means for initial determination of a species list for a site, whereas for long-term monitoring the Pollard Walk is more practical and statistically manageable. Pollard Walk transects are thus recommended once a prairie butterfly fauna has been defined for a site by checklist surveys.

American Midland Naturalist↗

USGS1997

Population and movement characteristics of radio-collared striped skunks in North Dakota during an epizootic of rabies

We observed a total of 102 striped skunks ( Mephitis mephitis ) from March to July of both 1991 and 1992 in Stutsman County, North Dakota (USA) during an experiment with food supplementation. Twenty-three apparently healthy skunks in 1991 and 56 in 1992 were equipped with radio-collars. In 1991, one of the 23 was tested and found to be rabid. In 1992, 50 of 56 were tested; 35 (70%) were rabid. Of skunks with ages estimated, 19 (66%) of 29 were first year animals in 1991 compared with nine (22%) of 41 first year animals in 1992. All 18 females captured in 1991 were pregnant or parous compared with 21 (60%) of 35 in 1992. The estimated survival rate of skunks was 0.85 during April to June 1991, but only 0.17 during April to July 1992. In 1992, the survival rate of first year skunks was 0.08, compared with 0.35 for older animals. Eleven (31%) of 36 skunks found dead of rabies or in late clinical stage were located below ground. We detected no differences in 1992 between healthy and rabid skunks in estimated mean (±SE) rate of travel (232 ± 14 m/hr), distance traveled (2,047 ± 141 m/night), or home range size (1.6 ± 0.4 km 2 ) during half-month periods from April through June. Among rabid skunks, mean rate of travel tended to decrease from 298 ± 48 m/hr during the 14 days preceding the clinical period of rabies (pre-clinical) to 174 ± 48 m/hr during the clinical period of rabies (14 days immediately before death). Similar decrease occurred in distance traveled in a night (2,318 ± 281 m, pre-clinical; 1,497 ± 281 m, clinical). Mean home range size of males (2.8 ± 0.4) was greater than of females (1.2 ± 0.4) during the pre-clinical period, but during the clinical period home range sizes of males (1.8 ± 0.4) and females (1.8 ± 0.4) were similar. Mean home range size of females did not differ between pre-clinical (1.2 ± 0.4) and clinical (1.8 ± 0.4) periods ( P = 0.22). Deaths of skunks from rabies in 1992 tended to be more spatially clumped than expected had they been random, mostly due to deaths detected before 8 May. We detected no correlation between locations of animals found dead of rabies and dates of death.

Journal of Wildlife Diseases↗

USGS1995

Survival of adult female northern pintails in the Sacramento Valley, California

North American populations of northern pintails (Anas acuta) declined between 1979 and the early 1990s. To determine if low survival during winter contributed to declines, we estimated winter (last week of Aug-Feb 1987-90) survival for 190 adult (after hatching yr [AHY]) female radio-tagged pintails in late summer in Sacramento Valley (SACV), California. Survival rates did not vary by winter ( P = 0.808), among preseason, hunting season, or postseason intervals ( P = 0.579), or by body mass at time of capture ( P = 0.127). Premolt (wing) pintails ( n = 10) tended to survive at a lower rate (0.622, SE = 0.178) than pintails that had already replaced flight feathers (0.887, SE = 0.030) ( P = 0.091). The pooled survival (all years) estimate for the 180-day winter was 0.874 (SE = 0.031). Hunting mortality rate (0.041-0.087) and nonhunting mortality rate (0.013-0.076) did not differ among years ( P = 0.332) or within years (all P > 0.149). Legal hunting ( n = 7), predation ( n = 4), cholera ( n = 2), illegal shooting ( n = 2), botulism ( n = 1), and unknown cause ( n = 1) accounted for all mortality. Nonwintering survival (annu. survival/winter survival = 0.748) was lower than winter survival; thus, if gains in annual survival are desired for this population, managers should first examine the breeding-migration period for opportunities to achieve increases.

California↗

USGS1995

Duck nest success in the prairie potholes

Since the early 1970's, the numbers of some waterfowl species such as mallard ( Anas platyrhynchos ), blue-winged teal ( A. discors ), and northern pintail ( A. acuta ) have reached or nearly reached the lowest ever recorded. Low nest success (the proportion of nests in which one or more eggs hatch) in key breeding areas, including the U.S. Prairie Pothole region, is partly responsible for declines in duck numbers (Klett et al. 1988; Johnson et al. 1992).

Prairie Pothole Region↗