Identification of sex in Boiga irregularis: Implications for population dynamics in Guam
No abstract available.
Journal of Herpetology↗
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Bottomland vegetation distribution along Passage Creek, Virginia, in relation to fluvial landforms
Persistent distribution patterns of woody vegetation within the bottomland forest of Passage Creek, Virginia, were related to fluvial landforms, channel geometry, streamflow characteristics, and sediment—size characteristics. Vegetation patterns were determined from species presence as observed in transects and traverses on landforms developed along the stream. Distinct species distributional patterns were found on four common fluvial geomorphic landforms: depositional bar, active—channel shelf, floodplain, and terrace. Independent hydrologic characteristics (flow duration and flood frequency) were determined for each of the landforms. Vegetation data were analyzed by binary discriminant analysis, principal components analysis, and detrended correspondence analysis. Results and related field observations suggest that certain species are significantly associated with specific fluvial landforms. Vegetation patterns appear to develop more as a result of hydrologic processes associated with each fluvial landform rather than from sediment—size characteristics. Flood disturbance may be an important factor in maintaining the vegetation patterns, which may therefore be used as indicators for particular hydrogeomorphic site conditions.
Ecology↗
Mathematical models for non-parametric inferences from line transect data
A general mathematical theory of line transects is developed which supplies a framework for nonparametric density estimation based on either right angle or sighting distances. The probability of observing a point given its right angle distance (y) from the line is generalized to an arbitrary function g(y). Given only that g(0) = 1, it is shown there are nonparametric approaches to density estimation using the observed right angle distances. The model is then generalized to include sighting distances (r). Let f(y I r) be the conditional distribution of right angle distance given sighting distance. It is shown that nonparametric estimation based only on sighting distances requires we know the transformation of r given by f(0 I r).
Biometrics↗
Stem demography and post-fire recruitment of a resprouting serotinous conifer
The contribution of resprouts and seedling recruitment to post-fire regeneration of the South African fynbos conifer Widdringtonia nodiflora was compared eight months after wildfires in 1990. Stems on all trees were killed by fire but resprouting success was > 90 % at all but one site. A demographic study of burned skeletons revealed that prior to these fires, nearly all plants were multi-stemmed (4–9 stems/plant) and multi-aged, indicating continuous sprout production between fires. All stems were killed by these 1990 fires and at most sites > 90 % of the stems were burned to ground level. All diameter stems were susceptible to such incineration as, at most sites, there was no difference in average diameter of stems burned to ground level and those left standing. Individual genets usually had all ramets incinerated to ground level or all ramets charred, but intact, suggesting certain micro-sites burned hotter, whereas other sites were somewhat protected. Although not true of the 1990 fires, there was evidence that occasionally Widdring-tonia stems may survive fire. At one site, four of the 16 plants sampled had a burned stem twice as old as the oldest burned stem on the other 12 plants at the site, suggesting some stems had survived the previous fire (ca. 1970) and this conclusion was supported by fire-scars on these four stems that dated to ca. 1970. Based on the highly significant correlation between stem diameter and cone density left standing after the 1990 fires, we calculated that for most sites > 80 % of the initial cone crop was incinerated by fire. This is important because we observed a strong relationship between size of the canopy cone crop surviving fire and post-fire seedling recruitment. Under these conditions we hypothesize that sprouting confers a selective advantage to genets when fires cause heavy losses of seed. The infrequent occurrence of sprouting in the Cupressaceae suggests the hypothesis that resprouting is an apomorphic or derived trait in Widdringtonia. Data from this study suggests resprouting provides a selective advantage under severe fynbos fires, which are not only 'stand-replacing fires,’but also are intense enough to incinerate cone-bearing stems.
Journal of Vegetation Science↗
Fall and winter foods of northern pintails in the Sacramento Valley, California
Food habits of northern pintails ( Anas acuta ) were investigated on 3 national wildlife refuges in the western portion of the Sacramento Valley, California, from August to March 1979-82. Pintails consumed >97% (aggregate % dry wt) plant food during diurnal foraging on national wildlife refuge rice, summer- irrigated, and summer-dry habitats from August through January. Invertebrate use increased to 28.9-65.6% of the diet in these habitats during February and March. Rice, swamp timothy ( Heleochloa schoenoides ), flatsedges ( Cyperus spp.), common barnyardgrass ( Echinochloa crusgalli ), southern naiad ( Najas guadalupensis ), and smartweed ( Polygonum spp.) seeds, miscellaneous vegetation, snails (Gastropoda), and midge (Diptera) and water beetle (Coleoptera) larvae were most important. These foods usually were taken proportional to or greater than availability. Rice was the most important food of pintails feeding nocturnally off the refuges in harvested rice fields from October through January (99.7%) and February and March (63%; barnyardgrass formed 31% of the diet). In August and October, some pintails consumed invertebrates or bulrush ( Scirpus spp.) seedlings in marshes soon after feeding in refuge rice (Aug) or harvested commercial rice fields (Oct), thereby increasing dietary protein. In late winter, females and males obtained similar (P > 0.05) percentages of invertebrates from refuge habitats. Important dietary seeds and invertebrates contained high protein or metabolizable energy content. Management should maintain adequate seed production in fall and mid-winter and invertebrate biomass in late winter.
California↗
Estimating carcass fat and protein in northern pintails during the nonbreeding season
I used northern pintails ( Anas acuta ) collected from August through March 1979-82 in the Sacramento Valley, California to derive equations to predict ether-extracted carcass fat, carcass protein, and skeletal lean dry weight. Ether-extracted carcass fat was best predicted by total fat depot weight (wet skin, abdominal fat, and intestinal fat) (r 2 = 0.94) and estimates based on carcass water content (r 2 = 0.93-0.98). Measured carcass protein was best predicted by a multiple regression including total protein depot weight (breast muscles, leg muscles, and gizzard) and tarsus length (R 2 = 0.79). I predicted skeletal lean dry weight by a multiple regression incorporating culmen, tarsus, and wing length (R 2 = 0.77). Predicted carcass fat agreed well with measured carcass fat in an independent data set of 30 pintails using total fat depot (r 2 = 0.92-0.96) and carcass water (r 2 = 0.97-0.99), but predicted carcass protein agreed less well with measured protein.
California↗
Survival of female northern pintails wintering in southwestern Louisiana
The North American breeding population of northern pintails ( Anas acuta ) has reached previously unprecedented low numbers 4 times since 1983. Because pintails show high fidelity to wintering areas, regional survival estimates and identification of factors influencing survival are needed to guide management of wintering pintails. We used radiotelemetry to estimate survival rates of female pintails wintering in southwestern Louisiana. We tested for variation in survival and hunting mortality rates in relation to age (immature or adult), winter (1990-91, 1991-92, 1992-93), time period (prehunting season, first hunting season, time between split hunting seasons, second hunting season, posthunting season), body condition (body mass when released, adjusted for body size), and region (southwestern Louisiana or elsewhere on the Texas-Louisiana Gulf Coast or Mississippi Alluvial Valley). Within southwestern Louisiana, the 147-day (5 Oct-28 Feb) survival rate of adults (0.714 ± 0.045; x̅ ± SE) was greater ( P = 0.02) than that of immatures (0.550 ± 0.068), primarily because immatures had higher hunting mortality. Female survival was lower ( P s < 0.01) during hunting than during nonhunting seasons but did not differ between first and second hunting seasons ( P = 0.58) or among non-hunting seasons ( P s >0.25). Survival did not differ in relation to winter or condition ( P s > 0.12). Hunting mortality did not differ ( P s > 0.13) in relation to winter, condition, or region, but hunting mortality of immatures (0.287 ± 0.046) was greater ( P < 0.001) than that of adults (0.130 ± 0.025). Despite conservative hunting regulations (30-day seasons and 1 pintail daily), hunting mortality rates of pintails in southwestern Louisiana were high. Pintails in southwestern Louisiana rely on a small number of key refuges for protection but feed almost exclusively in privately owned agricultural fields. If increased winter survival of female pintails in southwestern Louisiana is desired, we recommend that managers increase food available.
Louisiana↗
Effect of restrictive harvest regulations on survival and recovery rates of American black ducks
Population management of waterfowl requires an understanding of the effects of changes in hunting regulations on harvest and survival rates. Mean survival and recovery rates of American black ducks (Anas rubripes) were estimated during 3 periods of increasingly restrictive harvest regulations: 1950-66, 1967-82, and 1983-93. From the first to the second period, direct recovery rates declined for at least 1 age class in 4 of 6 reference areas, with a mean decline of 14% for adult and 7% for immature black ducks. From the second to the third period, direct recovery rates declined in all areas, declines averaging 37% for adults and 27% for immatures. Estimated mean survival rates increased from the first to the second period, consistent with a model of additivity of hunting mortality. Limited evidence existed for increases in survival rates from the second to the third period for immature males. For adults, however, survival increased less between these periods than would be expected if hunting mortality were additive and changes in recovery rates were proportional to changes in hunting mortality. Changes in survival and recovery rates of black ducks banded postseason were similar to those of adults banded preseason. Comparisons among estimates by degree blocks of latitude and longitude indicate that, at least between 1967 and 1983, estimated survival rates of immature and adult black ducks were lower in areas with high direct recovery rates. Smaller samples of banded birds and changes in banding locations in recent years may be limiting ability to evaluate consequences of recent changes in harvest rates. These correlation-based studies are limited in their ability to explain causes of observed changes in survival rates, suggesting the need for alternative approaches such as adaptive harvest management to increase understanding of the effects of hunting on black duck populations.
Journal of Wildlife Management↗
Survival of radiomarked canvasback ducklings in northwestern Minnesota
Duckling survival, an important factor affecting annual recruitment, has not been determined adequately for canvasbacks ( Aythya valisineria ). We investigated the magnitude, timing, and causes of mortality of canvasback ducklings from hatch to fledging at the Agassiz National Wildlife Refuge (NWR) in northwestern Minnesota during 1987-90. During the 4 years, 217 day-old ducklings were radiomarked and released in 52 broods. Another 141 ducklings were radiomarked at ≥ to 4 weeks of age. Survival was estimated with the Kaplan-Meier nonparametric estimator and the Weibull parametric model. Most mortalities occurred within 10 days after hatch. Total brood loss occurred in 18 (85%) of 52 broods released. The primary sources of mortality were predation principally by mink ( Mustela vison ), and exposure to precipitation and cold temperature. For combined years, females had lower survival than males ( P =0.03). If the disparate survival between sexes of canvasbacks observed in this study is representative of canvasbacks in their breeding range, this phenomenon contributes to reduced reproductive potential and the male-biased sex ratio of the species.
Minnesota↗
Estimating age of sea otters with cementum layers in the first premolar
We assessed sources of variation in the use of tooth cementum layers to determine age by comparing counts in premolar tooth sections to known ages of 20 sea otters ( Enhydra lutris ). Three readers examined each sample 3 times, and the 3 readings of each sample were averaged by reader to provide the mean estimated age. The mean (SE) of known age sample was 5.2 years (1.0) and the 3 mean estimated ages were 7.0 (1.0), 5.9 (1.1) and, 4.4 (0.8). The proportion of estimates accurate to within ± 1 year were 0.25, 0.55, and 0.65 and to within ± 2 years 0.65, 0.80, and 0.70, by reader. The proportions of samples estimated with >3 years error were 0.20, 0.10, and 0.05. Errors as large as 7, 6, and 5 years were made among readers. In few instances did all readers uniformly provide either accurate (error <1 yr) or inaccurate (error >1 yr) counts. In most cases (0.85), 1 or 2 of the readers provided accurate counts. Coefficients of determination (R2) between known ages and mean estimated ages were 0.81, 0.87, and 0.87, by reader. The results of this study suggest that cementum layers within sea otter premolar teeth likely are deposited annually and can be used for age estimation. However, criteria used in interpreting layers apparently varied by reader, occasionally resulting in large errors, which were not consistent among readers. While large errors were evident for some individual otters, there were no differences between the known and estimated age-class distribution generated by each reader. Until accuracy can be improved, application of this ageing technique should be limited to sample sizes of at least 6-7 individuals within age classes of ≥ 1 year.
Alaska, California↗
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↗
Wood duck brood movements and habitat use on prairie rivers in South Dakota
Wood duck (Aix sponsa) populations have been increasing in the Central Flyway, but little is known about wood duck brood rearing in prairie ecosystems. We compared movements and habitat use of radiomarked female wood ducks with broods in South Dakota on 2 rivers with contrasting prairie landscapes. The perennial Big Sioux River had a broad floodplain and riparian forest, whereas the intermittent Maple River had emergent vegetation along the river channel. Movements between nest sites and brood-rearing areas were longer on the Maple River than on the Big Sioux River (P = 0.02) and were among the longest reported for wood duck broods. Movements on the Big Sioux River were longer in 1992 (P = 0.01), when the floodplain was dry, than in 1993 or 1994. Before flooding occurred on the Big Sioux River, broods used semipermanent wetlands and tributaries outside the floodplain; thereafter, females selected forested wetlands along the river. Broods on the Maple River used emergent vegetation along the river channel throughout the study. Because median length of travel to brood-rearing areas was 2-3 km we recommend maintenance of brood-rearing habitat every 3-5 km along prairie rivers. Wildlife managers should encourage landowners to retain riparian vegetation along perennial rivers and emergent vegetation along intermittent streams to provide brood-rearing habitat during wet and dry cycles.
Journal of Wildlife Management↗
Incidence of embedded shot in canvasbacks
No abstract available.
Illinois, Maryland, North Dakota, Wisconsin↗
Indices used to assess status of sea otter populations: A reply
The California sea otter ( Enhydra lutris ) population, after increasing for more than half a century, stabilized and probably declined from the mid-1970's to the mid-1980's. Estes et al. (1986) suggested that the stabilization and decline were not due to food limitation. Garshelis et al. (1990) challenged this suggestion, although in doing so they misrepresented arguments made by Estes et al. (1986), provided no evidence for alternative hypotheses, and offered no constructive recommendations for a better means of population assessment. While acknowledging some of the points made by Garshelis et al. (1990), I believe the collective evidence presented by Estes et al. (1986) provided a reasonable basis for rejecting the food-limitation hypothesis, and point out that recent increases in the California sea otter population following a legislated reduction in net entanglement mortality is strong evidence against the food-limitation hypothesis.
California↗
Band reporting rates for mallards with reward bands of different dollar values
Adult male mallards ( Anas platyrhynchos ) were banded in summer 1987 with reward bands of different dollar values (0-$400) to determine the lowest dollar value that would yield a reporting rate approaching 1.0. During the 1987-88 and 1988-89 hunting seasons, rewards of between 50 and $100 were required to yield a reporting rate near 1.0. We estimated reporting rate of standard bands to be 0.32. Reward bands with 5 and $10 values produced reporting rates that were 1.5-2.0 times as large as those of standard bands. We developed a linear-logistic model to predict reporting rate as a function of the dollar value of reward bands.
Manitoba, Saskatchewan↗
Evaluating habitat selection with radio-telemetry triangulation error
Radio-telemetry triangulation errors result in the mislocation of animals and misclassification of habitat use. We present analytical methods that provide improved estimates of habitat use when misclassification probabilities can be determined. When misclassification probabilities cannot be determined, we use random subsamples from the error distribution of an estimated animal location to improve habitat use estimates. We conducted Monte Carlo simulations to evaluate the effects of this subsampling method, triangulation error, number of animal locations, habitat availability, and habitat complexity on bias and variation in habitat use estimates. Results for the subsampling method are illustrated using habitat selection by redhead ducks ( Aythya americana ). We recommend the subsampling method with a minimum of 50 random points to reduce problems associated with habitat misclassification.
Wisconsin↗
Evidence for maternal style among adult female dolphins when sharing pectoral fin contacts with their calves
Adult bottlenose dolphins share pectoral fin contacts (PFC) to manage their social relationships but less is known about how mothers share PFC with their calves. Using a dataset collected over 16 years, we analyzed how 10 matrilines, including three second generation female dolphins in a maternal role, used PFC with their pre-weaned calves. Mothers had different rates of initiation with their calves forming a continuum from those initiating few contacts (15%) to those initiating more (44%). For mothers with all-aged calves, the lateral side was contacted the most to start interactions with mothers contacting body parts at a similar rate. All mothers assumed the same posture regardless of their role as initiator or receiver, with horizontal the most prevalent posture. Two maternal styles were found for PFC: high and low use of PFC. Within the high PFC group, there was individual variation that was related to calf sex. Even though evidence of maternal style was confirmed in PFC exchanges between adult female dolphins and their calves, the number of PFC shared between these kin was only ~9% of all documented PFC contacts (N = 4,345) over 16 years, suggesting that other forms of tactile contact may be more important within the confines of the mother-offspring relationship in delphinids.
Bailey’s Key, Roatan↗
Remote sensing of soil moisture using airborne hyperspectral data
Landscape assessment of soil moisture is critical to understanding the hydrological cycle at the regional scale and in broad-scale studies of biophysical processes affected by global climate changes in temperature and precipitation. Traditional efforts to measure soil moisture have been principally restricted to in situ measurements, so remote sensing techniques are often employed. Hyperspectral sensors with finer spatial resolution and narrow band widths may offer an alternative to traditional multispectral analysis of soil moisture, particularly in landscapes with high spatial heterogeneity. This preliminary research evaluates the ability of remotely sensed hyperspectral data to quantify soil moisture for the Little River Experimental Watershed (LREW), Georgia. An airborne hyperspectral instrument with a short-wavelength infrared (SWIR) sensor was flown in 2005 and 2007 and the results were correlated to in situ soil moisture values. A significant statistical correlation ( R 2 value above 0.7 for both sampling dates) for the hyperspectral instrument data and the soil moisture probe data at 5.08 cm (2 inches) was determined. While models for the 20.32 cm (8 inches) and 30.48 cm (12 inches) depths were tested, they were not able to estimate soil moisture to the same degree.
GIScience and Remote Sensing↗
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