Hybrids between mallards and black ducks sometimes have partially green heads with the plumage of the black duck except for speculums similar to the mallard.
Puddle ducks, also known as dabblers, are in a group that tips up the tail when stretching down to feed.
They have large, powerful wings for vertical take-off, and their legs are positioned near the center of the body for easier movement on land.
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Area around ear opening. Synonym(s): auricular. In picture it is referred to as auricular.
early forest succession
The biotic (or life) community that develops immediately following the removal or destruction of vegetation in an area. For instance, grasses may be the first plants to grow in an area that was burned.
Rounded, earlike areas on the face. Synonym(s): facial discs. In picture it is referred to as facial discs
Periodic movement of the Earth's crust caused by gravitational interactions between the Sun, Moon, and Earth.
East Africa Coast Current
Same as Somali Current.
East Australian Current
A South Pacific Ocean current setting southward and then southwestward along the east coast of Greenland.
East Greenland Current
A North Atlantic Ocean current setting southward and then southwestward along the east coast of Greenland.
Average set of the current at ebb strength.
ebb current (ebb)
The movement of a tidal current away from shore or down a tidal river or estuary. In the mixed type of reversing tidal current, the terms greater ebb and lesser ebb and are applied respectively to ebb tidal currents of greater and lesser speed each day. The terms maximum ebb and minimum ebb are applied to the maximum and minimum speeds of a current running continuously ebb, the speed alternately increasing and decreasing with coming to a slack or reversing. The expression maximum ebb is also applicable to any ebb current at the time of greatest speed. See ebb strength.
The interval between the transit of the Moon over the meridian of a place and the time of the following ebb strength.
ebb strength (strength of ebb)
Phase of the ebb tidal current at the time of maximum speed. Also, the speed at this time. See strength of current.
ebb tidal delta
The bulge of sand formed at the seaward mouth of tidal inlets as a result of interaction between tidal currents and waves. Also called inlet-associated bars and estuary entrance shoals.
A nontechnical term used for falling tide or EBB CURRENT. The portion of the tidal cycle between high water and the following low water.
eccentricity of orbit
Ratio of the distance from center to focus of orbit to the semimajor axis. The eccentricity of orbit = square root (1 - (B / A)
In acoustics, a signal which has been reflected or otherwise returned with sufficient magnitude and time delay to be detected as a signal distinct from that directly transmitted
The determination of distance by measuring the time interval between transmission of a radiant energy signal (sound) and the return of its echo.
An instrument for determining the depth of water by measuring the time of travel of a sound-pulse from the surface of a body of water to the bottom and back.
Determination of the depth of water by measuring the time interval between emission of a sonic or ultrasonic signal and the return of its echo from the bottom.
The intersection of the plane of the Earth's orbit with celestial sphere.
An approach to natural resource management that considers the relationships among all organisms, including humans, and their environment.
managed areas that attract wildlife because they appear to be suitable (i.e., for nesting), but become population sinks because of predation or human disturbance.
The interrelationships of living things to one another and to their environment, or the study of these interrelationships.
An area over which the climate is sufficiently uniform to permit development of similar ecosystems on sites that have similar properties. Ecoregions contain many landscapes with different spatial patterns of ecosystems.
An arrangement of living and non-living things and the forces that move among them. Living things include plants and animals. Non-living parts of ecosystems may be rocks and minerals. Weather and wildfire are two of the forces that act within ecosystems.
The living organisms and the nonliving environment interacting in a given area.
An ecological approach to natural resource management to assure productive, healthy ecosystems by blending social, economic, physical, and biological needs and values
The transition zone between two biotic communities, such as between the Ponderosa pine forest type and the mixed conifer forest, which is found at higher elevations than the pine.
A population of a species in a given ecosystem that is adapted to a particular set of environmental conditions.
A current of air, water, or any fluid, forming on the side of the main current, especially one moving in a circle; in extreme cases a whirlpool.
The margin where two or more vegetation patches meet, such as a meadow opening next to a mature forest stand, or a ponderosa pine stand next to an aspen stand.
Waves moving between zones of high and low breakers along the shoreline. Edge waves contribute to changes in water level along the shoreface which helps to control the spacing of rip currents. See longshore current and rip current.
A submerged marine plant with very long narrow leaves.
In fish, the term egg usually refers to female haploid gametes. In reptiles, birds, amphibians and insects the term egg refers to a fertilized ovum with protective and nutritive tissues.
Resultant flow at right angles to and to the right of the wind direction (in the northern hemisphere) referred to as upwelling and downwelling.
A logarithmic spiral (when projected on a horizontal plane) formed by current velocity vectors at increasing depth intervals. The current vectors become progressively smaller with depth. They spiral to the right (looking in the direction of flow) in the Northern Hemisphere and to the left in the Southern with increasing depth. Theoretically, the surface current vector sets 45
electric tape gauge
A gauge consisting of a graduated Monel metal tape on a metal reel (with supporting frame)., voltmeter, and battery. Heights can be measured directly by unreeling the tape into its stilling well . When contact is made with the water's surface, the circuit is completed and the voltmeter needle moves. At that moment the length of tape is read against an index mark, the mark having a known elevation relative to the bench marks.
element (of ecosystems)
An identifiable component, process, or condition of an ecosystem.
Some part of a fin higher than the adjacent parts of the fin or body.
The distance of a point above a specified surface of constant potential; the distance is measured along the direction of gravity between the point and the surface.
One of the final processes in the harmonic analysis of tides in which preliminary values for the harmonic constants of a number of constituents are cleared of the residual effects each other.
The process by which a granular material can be sorted into its constituent particle sizes by means of a moving stream of fluid (usually air or water). Elutriators are extensively used in studies of sediments for determining particle size distribution. Under certain circumstances wind, rivers and streams may act as natural elutriating agents.
An artificial bank, mound, dike, or the like, built to hold back water or to carry a roadway.
Formed into a bay or bays; as an embayed shore.
(1) An indentation in a shoreline forming an open bay. (2) The formation of a bay.
A coast in which land formerly under water has recently been placed above sea level, either by uplift of the land or by a drop in sea level.
An immature insect that is "emerging"
A plant or animal that is in danger of extinction throughout all or a significant portion of its range. Endangered species are identified by the Secretary of the Interior in accordance with the Endangered Species Act of 1973.
Native to a specific geographic area.
A plant or animal that occurs naturally in a certain region and whose distribution is relatively limited geographically.
The scientific study of insects
An analysis of alternative actions and their predictable long and short-term environmental effects. Environmental analyses include physical, biological, social, and economic factors.
A brief version of an Environmental Impact Statement. (See Environmental Impact Statement.)
Environmental Impact Statement
A statement of environmental effects of a proposed action and alternatives to it. The EIS is released to other agencies and the public for comment and review.
Streams that flow only as the direct result of rainfall or snowmelt. They have no permanent flow.
(1) Also known as phase lag. Angular retardation of the maximum of a constituent of the observed tide (or tidal current) behind the corresponding maximum of the same constituent of the theoretical equilibrium tide. It may also be defined as the phase difference between a tidal constituent and its equilibrium argument. As referred to the local equilibrium argument, its symbol is k. When referred to the corresponding Greenwich equilibrium argument, it is called the Greenwich epoch that has been modified to adjust to a particular time meridian for convenience in the prediction of tides is represented by g or by k'. The relations between these epochs may be expressed by the following formula:
G = k + pL
g = k' = G - aS / 15
in which L is the longitude of the place and S is the longitude of the time meridian, these being taken as positive for west longitude and negative for east longitude; p is the number of constituent periods in the constituent day and is equal to 0 for all long-period constituents, 1 for diurnal constituents, 2 for semidiurnal constituents, and so forth; and a is the hourly speed of the constituent, all angular measurements being expressed in degrees. (2) As used in tidal datum determination, it is 19-year cycle over which tidal height observations are meaned in order to establish the various datums. As there are periodic and apparent secular trends in sea level, a specific 19-year cycle (the National Tidal Datum Epoch) is selected so that all tidal datum determinations throughout the United States, its territories, Commonwealth of Puerto Rico, and Trust Territory of the Pacific Islands, will have a common reference. See National Tidal Datum Epoch.
equation of time
Difference between mean and apparent time. From the beginning of the year until near the middle of April, mean time is ahead of apparent time, the difference reaching a maximum of about 15 minutes near the middle of February. From the middle of April to the middle of June, mean time is behind apparent time but the difference is less than 5 minutes. From the middle of June to the first part of September, mean time is again ahead of apparent time with maximum difference less than 7 minutes. From the first of September until the later part of December, mean time is again behind apparent time, the difference reaching a maximum of nearly 17 minutes in the early part of November. The equation of time for each day in the year is given in the American Ephemeris and Nautical Almanac.
A current setting eastward between the North and South Equatorial Currents of the Atlantic, Pacific, and Indian (in northern winter) Oceans. In the Atlantic and Pacific, its axis lies about latitude 7
(1) Ocean currents flowing westerly near the equator. There are two such currents in both the Atlantic and Pacific Oceans. The one to the north of the equator is called the North Equatorial Current and the one to the south is called the South Equatorial Current. Between these two currents there is an easterly flowing stream known as the Equatorial Countercurrent. (2) Tidal currents occurring semimonthly as a result of the moon being over the equator. At these times the tendency of the moon to produce diurnal inequality in the current is at a minimum.
Moon to Tides occurring semimonthly as a result of the Moon being over the Equator. At these times the tendency of the produce a diurnal inequality in the tide is at a minimum.
A subsurface current setting eastward along the Equator in the Pacific, Atlantic, and Indian Oceans. In the Pacific, its core of maximum velocity lies at a depth of about 100 meters within the South Equatorial Current.
The theoretical phase of a constituent of the equilibrium tide. It is usually represented by the expression (V + u), in which V is a uniformly changing angular quantity involving multiples of the hour angle of the mean Sun, the mean longitudes of the Moon and Sun, and the mean longitude of lunar or solar perigee; and u is a slowly changing angle depending upon the longitude of the Moon's node. When pertaining to an initial instant of time, such as the beginning of a series of observations, it is expressed by (Vo + u).
A model under which it is assumed that the waters covering the face of the Earth instantly respond to the tide-producing forces of the Moon and Sun to form a surface of equilibrium under the action of these forces. The model disregards friction, inertia, and the irregular distribution of the land masses of the Earth. The theoretical tide formed under these conditions is known as the equilibrium tide.
Hypothetical tide due to the tide producing forces under the equilibrium theory. Also known as gravitational tide.
The celestial equator.
Tides occurring near the times of the equinoxes.
The two points in the celestial sphere where the celestial equator intersects the ecliptic; also, the times when the Sun crosses the equator at these points. The vernal equinox is the point where the Sun crosses the Equator from south to north and it occurs about March 21. Celestial longitude is reckoned eastward from the vernal equinox. The autumnal equinox is the point where the Sun crosses the Equator from north to south and it occurs about September 23.
Same as geopotential surface.
Wearing away of the land by natural forces. On a beach, the carrying away of beach material by wave action, tidal currents or by deflation. (2) (SMP) The wearing away of land by the action of natural forces.
Vegetation of sufficient size and density to hide an animal, or an area used by animals to escape from predators.
A more or less continuous line of cliffs or steep slopes facing in one general direction which are caused by erosion or faulting, also called scarp.
establishment of the port
Also known as high water, full and change (HWF&C). Average high water interval on days of the new and full Moon. This interval is also sometimes called the common or vulgar establishment to distinguish it from the corrected establishment, the latter being the mean of all the high water intervals. The latter is usually 10 to 15 minutes less than the common establishment.
A water passage where the tide meets a river current; especially : an arm of the sea at the lower end of a river.
Observation of a current with a device fixed relative to the flow.
That part of the littoral zone less than 50 m in depth.
eustatic sea level rate
The worldwide change of sea level elevation with time. The changes are due to such causes as glacial melting or formation, thermal expansion or contraction of sea water, etc.
A perturbation of the Moon depending upon the alternate increase and decrease of the eccentricity of its orbit, which is always a maximum when the Sun is passing the Moon's line of apsides and a minimum when the Sun is at right angles to it. The principal constituents in the tide resulting from the evectional inequality are 2, 2, and 1.
even aged management
Timber management actions that result in the creation of stands of trees in which the trees are essentially the same age.
An occurrence meeting specified conditions, e.g. damage, a threshold wave height or a threshold water level.
segments of biological diversity that contain the potential for a unique evloutionary future.
wildlife species which are not native to the place where they are found. North American examples include bullfrogs, European starlings, wild boar, nutria, and Persian wild goat.
extreme high water
The highest elevation reached by the sea as recorded by a tide gauge during a given period. The National Ocean Service routinely documents monthly and yearly extreme high waters for its control stations.
extreme low water
The lowest elevation reached by the sea as recorded by a tide gauge during a given period. The National Ocean Service routinely documents monthly and yearly extreme low water for its control stations.
In vertebrates, a jelly-filled ball with a photosensitive layer (retina) at the back; also
The loop at the end of a hook shank
line- Line of feathers in front of and behind the eye.
ring- Pale-colored feathers encircling the eye.
Line of feathers above the eye. Synonym(s): supercilium, superciliary line. In picture it is referred to as supercilium.