Geology topics

M. H. Sherfy

Publications and source records attributed to M. H. Sherfy.

6 recordsLinked to original sources

USGS2011

Selection of nest-site habitat by interior least terns in relation to sandbar construction

Federally endangered interior least terns ( Sternula antillarum ) nest on bare or sparsely vegetated sandbars on midcontinent river systems. Loss of nesting habitat has been implicated as a cause of population declines, and managing these habitats is a major initiative in population recovery. One such initiative involves construction of mid-channel sandbars on the Missouri River, where natural sandbar habitat has declined in quantity and quality since the late 1990s. We evaluated nest-site habitat selection by least terns on constructed and natural sandbars by comparing vegetation, substrate, and debris variables at nest sites ( n = 798) and random points ( n = 1,113) in bare or sparsely vegetated habitats. Our logistic regression models revealed that a broader suite of habitat features was important in nest-site selection on constructed than on natural sandbars. Odds ratios for habitat variables indicated that avoidance of habitat features was the dominant nest-site selection process on both sandbar types, with nesting terns being attracted to nest-site habitat features (gravel and debris) and avoiding vegetation only on constructed sandbars, and avoiding silt and leaf litter on both sandbar types. Despite the seemingly uniform nature of these habitats, our results suggest that a complex suite of habitat features influences nest-site choice by least terns. However, nest-site selection in this social, colonially nesting species may be influenced by other factors, including spatial arrangement of bare sand habitat, proximity to other least terns, and prior habitat occupancy by piping plovers ( Charadrius melodus ). We found that nest-site selection was sensitive to subtle variation in habitat features, suggesting that rigor in maintaining habitat condition will be necessary in managing sandbars for the benefit of least terns. Further, management strategies that reduce habitat features that are avoided by least terns may be the most beneficial to nesting least terns.

Missouri River↗

USGS2011

Emergent sandbar construction for least terns on the Missouri River: Effects on forage fishes in shallow-water habitats

Emergent sandbars on the Missouri River are actively managed for two listed bird species, piping plovers and interior least terns. As a plunge-diving piscivore, endangered least terns rely on ready access to appropriately sized slender-bodied fish: <52 mm total length for adults and <34 mm total length for young chicks. As part of a multi-agency recovery programme, aimed at enhancing nesting habitat for plovers and terns, the U.S. Army Corps of Engineers mechanically created several emergent sandbars on the Missouri River. However, it was unknown whether sandbar construction is a benefit or a detriment to forage abundance for least terns. Therefore, we studied the shallow-water (<1.5 m) fish community near river and mechanically created emergent sandbars during three nesting seasons (2006–2008). We sampled every 2 weeks each year from late May to July within 15–16 areas to document the relative abundance, species richness and size classes of fish. Fish relative abundance was negatively related to depth. Catches were dominated by schooling species, including emerald shiner, sand shiner, spotfin shiner and bigmouth buffalo. Significant inter-annual differences in relative abundance were observed, with generally increasing trends in intra-seasonal relative abundance of shiners and the smallest size classes of fish (<34 mm). Significant differences in the fish communities between the sandbar types were not detected in this study. Results suggest that mechanical sandbar habitats host comparable fish communities at similar levels of relative abundance. Further analyses are required to evaluate if the levels of fish relative abundance are adequate to support least tern foraging and reproduction.

Nebraska, South Dakota↗

USGS2010

Diurnal variation in invertebrate catch rates by sticky traps: Potential for biased indices of piping plover forage

Measuring abundance of invertebrate forage for piping plovers (Charadrius melodus; hereafter plovers), a federally listed species in the USA, is an important component of research and monitoring targeted toward species recovery. Sticky traps are commonly used to passively sample invertebrates, but catch rates may vary diurnally or in response to weather. We examined diurnal variation in catch rates of invertebrates using an experiment on reservoir shoreline and riverine sandbar habitats of the Upper Missouri River in 2006 and 2008. Highest catch rates of large invertebrates (>3 mm) on dry sand habitats occurred during 08:00-11:00 Central Daylight Time (CDT) on the reservoir and 08:00-14:00 CDT on the river. On wet sand habitats, catch rates were lowest during 17:00-20:00 on both the reservoir and the river. Catch rates decreased 24% for every 10 kph increase in wind. Sticky traps deployed continuously for 12 h or more had lower catch rates than four consecutive-composited 3-hour deployments, suggesting that trap effectiveness declined for >3-hour deployments. Thus, if sticky traps are used to index plover forage abundance without controlling for time of day and wind speed, data may be highly variable or estimates could be biased.

Wetlands↗

USGS2006

A reexamination of age-related variation in body weight and morphometry of Maryland nutria

Age-related variation in morphometry has been documented for many species. Knowledge of growth patterns can be useful for modeling energetics, detecting physiological influences on populations, and predicting age. These benefits have shown value in understanding population dynamics of invasive species, particularly in developing efficient control and eradication programs. However, development and evaluation of descriptive and predictive models is a critical initial step in this process. Accordingly, we used data from necropsies of 1,544 nutria (Myocastor coypus) collected in Maryland, USA, to evaluate the accuracy of previously published models for prediction of nutria age from body weight. Published models underestimated body weights of our animals, especially for ages <3. We used cross-validation procedures to develop and evaluate models for describing nutria growth patterns and for predicting nutria age. We derived models from a randomly selected model-building data set (n = 192-193 M, 217-222 F) and evaluated them with the remaining animals (n = 487-488 M, 642-647 F). We used nonlinear regression to develop Gompertz growth-curve models relating morphometric variables to age. Predicted values of morphometric variables fell within the 95% confidence limits of their true values for most age classes. We also developed predictive models for estimating nutria age from morphometry, using linear regression of log-transformed age on morphometric variables. The evaluation data set corresponded with 95% prediction intervals from the new models. Predictive models for body weight and length provided greater accuracy and less bias than models for foot length and axillary girth. Our growth models accurately described age-related variation in nutria morphometry, and our predictive models provided accurate estimates of ages from morphometry that will be useful for live-captured individuals. Our models offer better accuracy and precision than previously published models, providing a capacity for modeling energetics and growth patterns of Maryland nutria as well as an empirical basis for determining population age structure from live-captured animals.

Journal of Wildlife Management↗

USGS2005

Does choice of estimators influence conclusions from true metabolizable energy feeding trials?

True metabolizable energy (TME) is a measure of avian dietary quality that accounts for metabolic fecal and endogenous urinary energy losses (EL) of non-dietary origin. The TME is calculated using a bird fed the test diet and an estimate of EL derived from another bird (Paired Bird Correction), the same bird (Self Correction), or several other birds (Group Mean Correction). We evaluated precision of these estimators by using each to calculate TME of three seed diets in blue-winged teal ( Anas discors ). The TME varied by <2% among estimators for all three diets, and Self Correction produced the least variable TMEs for each. The TME did not differ between estimators in nine paired comparisons within diets, but variation between estimators within individual birds was sufficient to be of practical consequence. Although differences in precision among methods were slight, Self Correction required the lowest sample size to achieve a given precision. Feeding trial methods that minimize variation among individuals have several desirable properties, including higher precision of TME estimates and more rigorous experimental control. Consequently, we believe that Self Correction is most likely to accurately represent nutritional value of food items and should be considered the standard method for TME feeding trials.

Journal of Ornithology↗

USGS2003

Invertebrate response to snow goose herbivory on moist-soil vegetation

Foraging activity by snow geese (Chen caerulescens) often creates large areas devoid of vegetation ("eat-outs") in moist-soil impoundments and coastal wetlands. Open-water habitats that result from eat-outs may be valuable foraging areas for other wetland-dependent birds (i.e., waterfowl and shorebirds). However, few studies have examined the effects of goose-induced habitat changes on invertebrates, an important food source for both waterfowl and shorebirds. We quantified changes in abundance and composition of benthic invertebrates in response to snow goose herbivory in moist-soil impoundments at Prime Hook National Wildlife Refuge, Delaware, USA. We found invertebrate taxon richness and diversity and abundance of Chironomidae, Coleoptera, and Total Invertebrates to be higher in goose-excluded sites than in adjacent eat-outs. These effects were most pronounced during January, February, and early April. We also measured invertebrate abundance in shorebird exclosures in eat-outs but found few detectable effects of shorebird predation on invertebrates. Our study demonstrated that abundant snow geese may negatively influence availability of invertebrates for other nonbreeding waterbirds, suggesting that management actions to reduce local goose populations or deter feeding in impoundments may be warranted.

Wetlands↗