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G.V.N. Powell

Publications and source records attributed to G.V.N. Powell.

10 recordsLinked to original sources
USGS2002

Overwinter survival of neotropical migratory birds in early-successional and mature tropical forests

Many Neotropical migratory species inhabit both mature and earty-successional forests on their wintering grounds, yet comparisons of survival rates between habitats are lacking. Consequently, the factors affecting habitat suitability for Neotropical migrants and the potential effects of tropical deforestation on migrants are not well understood. We estimated overwinter survival and capture probabilities of Wood Thrush ( Hylochichla mustelina ), Ovenbird ( Seiurus aurocapillus ), Hooded Warbler ( Wilsonia citrina ), and Kentucky Warbler ( Oporornis formosus ) inhabiting two common tropical habitat types, mature and early-successional forest. Our results suggest that large differences (for example, ratio of survival rates (γ) ≤ 0.85) in overwinter survival between these habitats do not exist for any of these species. Age ratios did not differ between habitats, but males were more common in forest habitats and females more common in successional habitats for Hooded Warblers and Kentucky Warblers. Future research on overwinter survival should address the need for age- and sex-specific survival estimates before we can draw strong conclusions regarding winter habitat suitability. Our estimates of overwinter survival extrapolated to annual survival rates that were generally lower than previous estimates of annual survival of migratory birds. Capture probability differed between habitats for Kentucky Warblers, but our results provide strong evidence against large differences in capture probability between habitats for Wood Thrush, Hooded Warblers, and Ovenbirds. We found no temporal or among-site differences in survival or capture probability for any of the four species. Additional research is needed to examine the effects of winter habitat use on survival during migration and between-winter survival.

Conservation Biology↗
USGS1997

A rop net and removable walkway used to quantitatively sample fishes over wetland surfaces in the dwarf mangrove of the Southern Everglades

We describe a 9 m 2 drop net and removable walkways designed to quantify densities of small fishes in wetland habitats with low to moderate vegetation density. The method permits the collection of small, quantitative, discrete samples in ecologically sensitive areas by combining rapid net deployment from fixed sites with the carefully contained use of the fish toxicant rotenone. This method requires very little contact with the substrate, causes minimal alteration to the habitat being sampled, samples small fishes in an unbiased manner, and allows for differential sampling of microhabitats within a wetland. When used in dwarf red mangrove ( Rhizophora mangle ) habitat in southern Everglades National Park and adjacent areas (September 1990 to March 1993), we achieved high recovery efficiencies (78&ndash;90%) for five common species <110 mm in length. We captured 20,193 individuals of 26 species. The most abundant fishes were sheepshead minnow Cyprinodon variegatus , goldspotted killifish Floridichthys carpio , rainwater killifish Lucania parva , sailfin molly Poecilia latipinna , and the exotic Mayan cichlid Cichlasoma urophthalmus . The 9 m 2 drop net and associated removable walkways are versatile and can be used in a variety of wetland types, including both interior and coastal wetlands with either herbaceous or woody vegetation.

Wetlands↗
USGS1989

A 107-year-old coral from Florida Bay: barometer of natural and man- induced catastrophes?

The 107-yr growth history of a massive coral Solenastrea bournoni from Florida Bay was reconstructed with X-ray imagery from a single 4 in. diameter (10 cm) core that penetrated the exact epicenter of the 95.3 cm high colony. Growth increments totalled 952.9 mm, averaging 8.9 mm/yr over the life of the coral. Growth rate trends in the Florida Bay coral were compared to those in a Montastraea annularis of similar age from a nearby patch reef on the Atlantic Ocean side of the Florida Keys. It was concluded that growth rate, at least in these specimens, is a questionable indicator of past hurricanes and freezes. There does appear to be, however, a possible cause-and-effect relationship between major man-induced environmental perturbations and a prolonged reduction in growth rate in each coral's growth record. -from Authors

Bulletin of Marine Science↗
USGS1984

Reproduction by an altricial songbird, the red-winged blackbird, in fields treated with the organophosphate insecticide fenthion

(1) Breeding red-winged blackbirds were used as a model to study the effects of a single application of an organophosphate insecticide, fenthion, on reproduction of altricial songbirds. (2) The insecticide had no significant effect on frequency of nest abandonment, clutch size, hatching success, or fledgling success. (3) Growth rates of young nestlings were lower in nests on one of two treated areas, but overall growth rates of survivors were not significantly different from controls in nests on nearby unsprayed areas. (4) The insecticide had no measured effect on male spatial organization. (5) Measures of abundance of the principal nestling food item, noctuid larvae, showed that one application of the insecticide significantly reduced the abundance of the food supply, but the reduction of food supply did not result in a decrease in nestling growth rates or fledgling success.

Wyoming↗
USGS1983

Industrial effluents as a source of mercury contamination in terrestrial riparian vertebrates

Eight species of piscivorous and insectivorous birds and one species of bat collected along Virginia's North Fork of the Holston River contained elevated mercury residues. The ubiquitous occurrence of mercury in riparian insectivores implicates aquatic insects as a vehicle for spreading mercury contamination from one ecosystem to another and expands the ecological ramifications of mercury-contaminated industrial effluents.

Virginia↗
USGS1982

A field evaluation of frogs as a potential source of secondary organophosphorus insecticide poisoning

Because amphibians are relatively resistant to organophosphorus insecticides and can bioaccumulate residues to high levels, they may be a source of secondary poisoning for vertebrates that feed on them. This hypothesis was tested by determining residues in breeding upland chorus frogs Pseudacris triseriata, that were collected from ponds treated with the organophosphorus insecticide fenthion. Frogs were collected up to 3-days posttreatment in four areas that were treated with fenthion formulated in either diesel oil or water. No residues of fenthion were detected above the 0.01 ppm level of analytical sensitivity. These results indicate that the frogs were not a likely source of secondary poisoning for predatory vertebrates.

Canadian Journal of Zoology↗
USGS1982

Care of nestlings by wild female starlings exposed to an organophosphate pesticide

(1) Our objective was to determine the effect of exposure to an organophosphate pesticide (OP), dicrotophos (3-hydroxy- N,N -dimethyl- cis -scrotonamide dimethyl phosphate), on care of nestlings by wild female starlings ( Sturnus vulgaris ). (2) We selected twelve pairs of active nests based on synchrony in the reproductive cycle. When nestlings were 10 days old (day 10), adult males were captured and killed and brood size was adjusted to four. The frequency and temporal distribution of sorties made by each pair of females to feed their young were recorded for 2 h at 18.00 hours on day 11 and 06.00 hours on day 12. One female from each pair was given a single oral dose of dicrotophos (2.5 mg/kg of body weight) dissolved in corn oil; the second female received an equivalent exposure of pure corn oil. Birds were released and their nestlings weighed. Parental care was again monitored between 18.00 and 20.00 hours on day 12 and 06.00 and 08.00 hours on day 13. Females were then captured and they with their young were weighed and killed. Changes in parental care in OP-dosed and control females were compared using paired t-tests. (3) The OP-dosed females made significantly ( P < 0.5) fewer sorties to feed their young and remained away from their boxes for longer periods of time than controls. Nestlings of OP-treated females lost significantly more weight ( X̄ = 9.3%) than nestlings of controls ( X̄ = 3.2%). Brain ChE activity in OP-treated females was inhibited an average of 50.7% compared with controls. Weight changes in OP-dosed ( X̄ = -8.9%) and control females ( X̄ = -8.3%) were similar. (4) Results indicate that parental care may be significantly reduced in songbirds receiving severe but sublethal exposure to organophosphate pesticides. The potential for a reduction or modification in parental care to alter reproductive success in passerines is discussed. (5) Techniques utilized, or modifications thereof, may be useful in collecting the additional data needed to adequately assess the impact of OPs on songbird reproduction.

Journal of Applied Ecology↗