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L.A. Powell

Publications and source records attributed to L.A. Powell.

11 recordsLinked to original sources
USGS2015

Reservoir rehabilitations: Seeking the Fountain of Youth

Aging of reservoirs alters the functions, and associated services, of these systems through time. The goal of habitat rehabilitation is often to alter the trajectory of the aging process such that the duration of the desired state is prolonged. There are two important characteristics in alteration of the trajectory—the amplitude relative to current state and the subsequent rate of change, or aging—that ultimately determine the duration of extension for the desired state. Rehabilitation processes largely fall into three main categories: fish community manipulation, water quality manipulation, and physical habitat manipulation. We can slow aging of reservoirs through carefully implemented management actions, perhaps even turning back the hands of time, but we cannot stop aging. We call for new, innovative perspectives that incorporate an understanding of aging processes in all steps of rehabilitation of reservoirs, especially in planning and assessing.

Fisheries↗
USGS2011

Multimodel inference and adaptive management

Ecology is an inherently complex science coping with correlated variables, nonlinear interactions and multiple scales of pattern and process, making it difficult for experiments to result in clear, strong inference. Natural resource managers, policy makers, and stakeholders rely on science to provide timely and accurate management recommendations. However, the time necessary to untangle the complexities of interactions within ecosystems is often far greater than the time available to make management decisions. One method of coping with this problem is multimodel inference. Multimodel inference assesses uncertainty by calculating likelihoods among multiple competing hypotheses, but multimodel inference results are often equivocal. Despite this, there may be pressure for ecologists to provide management recommendations regardless of the strength of their study’s inference. We reviewed papers in the Journal of Wildlife Management (JWM) and the journal Conservation Biology (CB) to quantify the prevalence of multimodel inference approaches, the resulting inference (weak versus strong), and how authors dealt with the uncertainty. Thirty-eight percent and 14%, respectively, of articles in the JWM and CB used multimodel inference approaches. Strong inference was rarely observed, with only 7% of JWM and 20% of CB articles resulting in strong inference. We found the majority of weak inference papers in both journals (59%) gave specific management recommendations. Model selection uncertainty was ignored in most recommendations for management. We suggest that adaptive management is an ideal method to resolve uncertainty when research results in weak inference.

Journal of Environmental Management↗
USGS2008

Effects of habitat disturbance on survival rates of softshell turtles (Apalone spinifera) in an urban stream

We monitored Spiny Softshell Turtles (Apalone spinifera) using mark-recapture during 1994-2005 in Gin Creek, Searcy, Arkansas. In 1997-2000 the creek bed and riparian zone were bulldozed in an effort to remove debris and improve water flow. This disturbance appeared to reduce the quantity and quality of turtle habitat. We tested for the potential effect of this habitat disturbance on the survival rates of marked turtles. We estimated annual survival rates for the population using models that allowed for variation in survival by state of maturation, year, and effects of the disturbance; we evaluated two different models of the disturbance impact. The first disturbance model incorporated a single change in survival rates, following the disturbance, whereas the second disturbance model incorporated three survival rates: pre- and postdisturbance, as well as a short-term decline during the disturbance. We used a state-transition model for our mark-recapture analysis, as softshells transition from juveniles to adults in a variable period of time. Our analysis indicated that survival varied by maturation state and was independent of a time trend or the disturbance. Annual survival rates were lower for juveniles (S?? = 0.717, SE = 0.039) than for adults (S?? = 0.836, SE = 0.025). Despite the dramatic habitat disturbance, we found no negative effects on survival rates. Our results demonstrate that, like a few other freshwater turtle species known to thrive in urban environments, populations of A. spinifera are resilient and can persist in urban environments despite periodic habitat disturbances. Copyright 2008 Society for the Study of Amphibians and Reptiles.

Journal of Herpetology↗
USGS2006

A productivity model for parasitized, multibrooded songbirds

We present an enhancement of a simulation model to predict annual productivity for Wood Thrushes (Hylocichla mustelina) and American Redstarts (Setophaga ruticilla); the model includes effects of Brown-headed Cowbird (Molothrus ater) parasitism. We used species-specific data from the Driftless Area Ecoregion of Wisconsin, Minnesota, and Iowa to parameterize the model as a case study. The simulation model predicted annual productivity of 2.03 ?? 1.60 SD for Wood Thrushes and 1.56 ?? 1.31 SD for American Redstarts. Our sensitivity analysis showed that high parasitism lowered Wood Thrush annual productivity more than American Redstart productivity, even though parasitism affected individual nests of redstarts more severely. Annual productivity predictions are valuable for habitat managers, but productivity is not easily obtained from field studies. Our model provides a useful means of integrating complex life history parameters to predict productivity for songbirds that experience nest parasitism. ?? The Cooper Ornithological Society 2006.

Condor↗
USGS2006

An assessment of bird habitat quality using population growth rates

Survival and reproduction directly affect population growth rate (lambda) making lambda a fundamental parameter for assessing habitat quality. We used field data, literature review, and a computer simulation to predict annual productivity and lambda for several species of landbirds breeding in floodplain and upland forests in the Midwestern United States. We monitored 1735 nests of 27 species; 760 nests were in the uplands and 975 were in the floodplain. Each type of forest habitat (upland and floodplain) was a source habitat for some species. Despite a relatively low proportion of regional forest cover, the majority of species had stable or increasing populations in all or some habitats, including six species of conservation concern. In our search for a simple analog for lambda, we found that only adult apparent survival, juvenile survival, and annual productivity were correlated with lambda; daily nest survival and relative abundance estimated from point counts were not. Survival and annual productivity are among the most costly demographic parameters to measure and there does not seem to be a low-cost alternative. In addition, our literature search revealed that the demographic parameters needed to model annual productivity and lambda were unavailable for several species. More collective effort across North America is needed to fill the gaps in our knowledge of demographic parameters necessary to model both annual productivity and lambda. Managers can use habitat-specific predictions of annual productivity to compare habitat quality among species and habitats for purposes of evaluating management plans.

Minnesota, Iowa, Wisconsin, Illinois↗
USGS2002

Wood Thrush movements and habitat use: Effects of forest management for Red-cockaded Woodpeckers

We monitored adult and juvenile breeding-season movements and habitat use of radio-tagged Wood Thrushes ( Hylocichla mustelina ) at the Piedmont National Wildlife Refuge, central Georgia, USA. We investigated the effects that management for Red-cockaded Woodpeckers ( Picoides borealis ), thinning and burning >30 year old loblolly pine ( Pinus taeda ) habitat, had on Wood Thrushes, a ground-foraging and midstory-nesting species. Adult Wood Thrush pairs regularly moved long distances between nesting attempts (range 1 to 17,388 m). The only experimental effect we found on adult movements was a decrease in weekly emigration rates (Ψ) from thinned and burned compartments after silvicultural management. Adult males preferred riparian hardwoods with sparse to moderate cover and those preferences increased following management. Juveniles remained near their nest site ( x̄ = 177 m, SE = 113) for an average 24 days (SE = 6.3), and then dispersed a mean 2,189 m (SE = 342). Before dispersal, juveniles preferred upland hardwood–pine mixed habitat ( P < 0.05) with moderate overstory cover ( P < 0.05). We found no management effects on dispersal distances or predispersal habitat use. However, juveniles from thinned and burned compartments dispersed to hardwood habitats with dense cover, whereas birds from control compartments dispersed to pine-dominated habitats with sparse cover. All juveniles dispersed to areas with habitat similar to what they used before dispersal. Small-scale thinning and burning for Red-cockaded Woodpeckers may have had little effect on Wood Thrush habitat use and movements because typical movements were often larger than the scale (stand or compartment) targeted for management.

The Auk↗
USGS2000

Effects of forest management on density, survival, and population growth of wood thrushes

Loss and alteration of breeding habitat have been proposed as causes of declines in several Neotropical migrant bird populations. We conducted a 4-year study to determine the effects of winter prescribed burning and forest thinning on breeding wood thrush ( Hylocichla mustelina ) populations at the Piedmont National Wildlife Refuge (PNWR) in Georgia. We estimated density, adult and juvenile survival rates, and apparent annual survival using transect surveys, radiotelemetry, and mist netting. Burning and thinning did not cause lower densities ( P = 0.25); wood thrush density ranged from 0.15 to 1.30 pairs/10 ha. No radiomarked male wood thrushes ( n = 68) died during the 4 years, but female ( n = 63) weekly survival was 0.981 ± 0.014 (SE) for females ( n = 63) and 0.976 ± 0.010 for juveniles ( n = 38). Apparent annual adult survival was 0.579 (SE = 0.173). Thinning and prescribed burning did not reduce adult or juvenile survival during the breeding season or apparent annual adult survival. Annual population growth (lambda) at PNWR was 1.00 (95% confidence interval = 0.32-1.63), and the considerable uncertainty in this prediction underscores the need for long term monitoring to effectively manage Neotropical migrants. Population growth increased on experimental compartments after the burn and thin (95% CI before = 0.91-0.97, after = 0.98-1.05), while control compartment declined (before = 0.98-1.05, after = 0.87-0.92). We found no evidence that the current management regime at PNWR, designed to improve red-cockaded woodpecker ( Picoides borealis ) habitat, negatively affected wood thrushes.

Georgia↗
USGS2000

Simultaneous use of mark-recapture and radiotelemetry to estimate survival, movement, and capture rates

Biologists often estimate separate survival and movement rates from radio-telemetry and mark-recapture data from the same study population. We describe a method for combining these data types in a single model to obtain joint, potentially less biased estimates of survival and movement that use all available data. We furnish an example using wood thrushes ( Hylocichla mustelina ) captured at the Piedmont National Wildlife Refuge in central Georgia in 1996. The model structure allows estimation of survival and capture probabilities, as well as estimation of movements away from and into the study area. In addition, the model structure provides many possibilities for hypothesis testing. Using the combined model structure, we estimated that wood thrush weekly survival was 0.989 ± 0.007 ( ± SE). Survival rates of banded and radio-marked individuals were not different ( α [ S radioed , S banded ] =log[ S radioed / S banded ]=0.0239 ± 0.0435). Fidelity rates (weekly probability of remaining in a stratum) did not differ between geographic strata ( Ψ = 0.911 ± 0.020; α [ Ψ 11 , Ψ 22 ]=0.0161 ± 0.047), and recapture rates ( p = 0.097 ± 0.016) banded and radio-marked individuals were not different ( α [ P radioed , P banded ]=0.145 ± 0.655). Combining these data types in a common model resulted in more precise estimates of movement and recapture rates than separate estimation, but ability to detect stratum or mark-specific differences in parameters was week. We conducted simulation trials to investigate the effects of varying study designs on parameter accuracy and statistical power to detect important differences. Parameter accuracy was high (relative bias [RBIAS] <2 %) and confidence interval coverage close to nominal, except for survival estimates of banded birds for the 'off study area' stratum, which were negatively biased (RBIAS -7 to -15%) when sample sizes were small (5-10 banded or radioed animals 'released' per time interval). To provide adequate data for useful inference from this model, study designs should seek a minimum of 25 animals of each marking type observed (marked or observed via telemetry) in each time period and geographic stratum.

Journal of Wildlife Management↗
USGS1999

A model to predict breeding-season productivity for multibrooded songbirds

Breeding-season productivity (the per capita number of offspring surviving to the end of the breeding season) is seldom estimated for multibrooded songbirds because of cost and logistical constraints. However, this parameter is critical for predictions of population growth rates and comparisons of seasonal productivity across geographic or temporal scales. We constructed a dynamic, stochastic, individual-based model of breeding-season productivity using demographic data from Wood Thrushes ( Hylocichla mustelina ) in central Georgia from 1993 to 1996. The model predicts breeding-season productivity as a function of adult survival, juvenile survival, nesting success, season length, renesting interval, and juvenile-care intervals. The model predicted that seasonal fecundity (number of fledglings produced) was 3.04, but only 2.04 juveniles per female survived to the end of the breeding season. Sensitivity analyses showed that differences in renesting interval, nesting success, fledglings per successful nest, and adult and juvenile survival caused variation in breeding-season productivity. Contrary to commonly held notions, season length and fledgling-care interval length did not cause variation in breeding-season productivity. This modeling exercise emphasizes the need for demographic data for songbird species, and we encourage biologists to use similar models to evaluate productivity in songbird populations.

The Auk↗
USGS1998

Effects of radio transmitters on migrating wood thrushes

We quantified the effects of radio transmitters on Wood Thrushes (Hylocichla mustelina) using 4 yr of banding and telemetry data from Piedmont National Wildlife Refuge, Georgia. Flight performance models suggest that the 1.6-g transmitter shortens the migratory range of Wood Thrushes by only 60 km, and the estimated migratory range is adequate to accomplish migration even with limited fat stores. We used two strengths of line, 5- and 9-kg test-strength braided Dacron, to attach the transmitters using the thigh-harness method. We recaptured 13 returning radio-marked Wood Thrushes, seven of which were still marked. Six of the seven birds marked with the 5-kg test harnesses lost their transmitters within 1 yr while all six of the 9-kg test harnesses were still attached up to 21 mo later. Radio-marking did not reduce the return rates of adults and immatures, and the transmitters did not cause radio-marked birds to lose more mass than banded-only birds. Wood Thrushes can successfully carry a transmitter during migration with no detectable negative effects. We recommend continued use of the thigh-harness method, but we encourage the use of 5-kg cotton line.

Journal of Field Ornithology↗