Density
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A male Black-throated Blue
Warbler caught in a mist-net after responding to a tape recording
of another male's song (photo by M. Cline). Shortly thereafter,
the bird was safely removed from the net, given leg bands,
weighed and measured, and released unharmed. |
The final piece of data required for the
purposes of this module is warbler density. In order to determine
the number of Black-throated Blue Warblers within the study area,
the researchers have to mark each individual so that the same one
isn't counted twice. A standard protocol in bird studies is to capture
birds in mist-nets (see photo) and to place a numbered aluminum and
several colored plastic bands on their legs in a unique combination.
The bands are of negligible weight and do not impede the birds' movements.
They are essential for the purposes of this study because individuals
can then be identified by looking at them through a pair of binoculars
and noting what band combination they have - for instance, red-aluminum-white-blue
or black-aluminum-blue-black. Usually, males are caught early in the
season when they are defending their territories, luring them into
a net by playing a recording of another male's song. Females don't
respond to playback as readily, so they are usually caught later in
the season while they are getting on or off their nest. In the end,
the total number of individually-marked birds within the study area
is used as a measure of warbler density.
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