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At least 937 records · Page 52Linked to original sources
USGS1955

Fifty-fifth Christmas Bird Count. 159. Ocean City, Md

The distribution of dynamic pressure behind a Harris' hawk's wing was sampled using a wake rake consisting of 15 pitot tubes and one static tube. The hawk was holding on to a perch, but at an air speed and gliding angle at which it was capable of gliding. The perch was instrumented, so that the lift developed by the wing was known and the lift coefficient could be calculated. The mean of 92 estimates of profile drag coefficient was 0.0207, with standard deviation 0.0079. Lift coefficients ranged from 0.51 to 1.08. Reynolds numbers were nearly all in the range 143000-194000. The estimates of profile drag coefficient were reconcilable with previous estimates of the wing profile drag of the same bird, obtained by the subtractive method, and also with values predicted by the ?Airfoil-ii? program for designing aerofoils, based on a digitized wing profile from the ulnar region of the wing. The thickness of the wake suggested that the boundary layer was mostly or fully turbulent in most observations and separated in some, possibly as an active means of creating drag for control purposes. It appears that the bird could momentarily either increase or decrease the profile drag of specific parts of the wing, by active changes of shape, and it appeared to use the carpo-metacarpal region especially for such control movements. Further investigation in a low turbulence wind tunnel would help to resolve doubts about the possible influence of airstream turbulence on the behaviour of the boundary layer.

Audubon Field Notes↗
USGS1999

Fifty-eighth Christmas Bird Count. 166. Ocean City, Md

Gauging the impact of manipulative activities, such as rehabilitation or management, on wetlands requires having a notion of the unmanipulated condition as a reference. An understanding of the reference condition requires knowledge of dominant factors influencing ecosystem processes and biological communities. In this paper, we focus on natural physical factors (conditions and processes) that drive coastal wetland ecosystems of the Laurentian Great Lakes. Great Lakes coastal wetlands develop under conditions of large-lake hydrology and disturbance imposed at a hierarchy of spatial and temporal scales and contain biotic communities adapted to unstable and unpredictable conditions. Coastal wetlands are configured along a continuum of hydrogeomorphic types: open coastal wetlands, drowned river mouth and flooded delta wetlands, and protected wetlands, each developing distinct ecosystem properties and biotic communities. Hydrogeomorphic factors associated with the lake and watershed operate at a hierarchy of scales: a) local and short-term (seiches and ice action), b) watershed / lakewide / annual (seasonal water- level change), and c) larger or year-to-year and longer ( regional and/or greater than one-year). Other physical factors include the unique water quality features of each lake. The aim of this paper is to provide scientists and managers with a framework for considering regional and site-specific geomorphometry and a hierarchy of physical processes in planning management and conservation projects.

Wetlands↗
USGS1983

Fifty-ninth Christmas Bird Count. 176. Ocean City, Md

Some organophosphorus insecticides have been reported to interfere with reproduction and even cause the decline of small mammal populations. The effects of such anticholinesterases on plasma LH concentrations were examined in male mice (Peromyscus leucopus noveboracensis) intubated with water (OW) or acephate (50 and 100 mg/kg) and sacrificed after 4 h. Brain acetylcholinesterase (AChE) activity was inhibited by 45 and 56%, and basal LH levels were reduced by 29 and 25% in mice receiving the 2 doses of acephate. Responsiveness to LHRH did not appear to be affected 4 h after intubation with 100 mg/kg acephate, as 5 ug/kg LHRH ip evoked a comparable rise in plasma LH after 30 min (2.4 and 3.6 fold) in OW-control and treated mice. Subchronic dietary exposure to 0, 25, 100, and 400 ppm acephate for 5 days resulted in a dose-dependent decline in brain AChE activity (23, 42, and 57%), but did not affect LH concentration or the weights of testes and seminal vesicles. These findings suggest that acute exposure to organophosphorus insecticides may impair reproductive function by altering LH secretion.

American Zoologist↗