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Why birds sing
A Red－eyed Vireo sings more than 20，000 songs a day． A Pileated Woodpecker drums on a tree at 15 beats per second． A Wilson's Snipe dives through the air， the feathers on its wings vibrating to produce a winnowing sound， hu－hu－hu．．．Why? Birds put a lot of effort into singing， drumming， winnowing， and otherwise displaying． They are trying to impress mates and proclaim territories．Songs are often loud and repetitive， so they tend to be noticed more than other bird sounds． One observer commented that a Winter Wren sings "with remarkable vehemence，" as if he were "trying to burst [his] lungs．" This tiny songster weighs just one－third of an ounce， but it sings with 10 times the power of a crowing rooster， per unit weight． Birds may sing their songs thousands of times throughout the day． Dickcissels may spend as much as 70 percent of the day singing while establishing territories and courting females．Some birds have large repertoires－－the Brown Thrasher can sing as many as 2，000 distinct songs． Other species， such as the Henslow’s Sparrow， seem to have only one song． In North America， we hear mostly males singing， because they typically take the lead in defending territories and attracting mates． However， especially in the tropics， some species sing duets involving both the male and female．Courtship serenades
How do scientists know why birds sing? Experiments with recorded songs have shown that birds sing to attract mates． House Wren songs broadcast near nest boxes will attract female House Wrens， for example． Female birds may also judge the quality of a male's song when selecting a mate． Some studies have shown that males with extra food on their territories are the most persistent singers， and in some species， the most persistent singers attract females the soonest．Playback experiments have also shown that songs are important in defending a territory． For example， male House Wrens respond aggressively to the recording of another male's song， sometimes even attacking the loudspeaker． In other tests， researchers temporarily removed male birds from their territories but played songs through speakers on some of the territories． Neighboring males were less likely to invade territories from which songs were broadcast， showing that song means "Keep out！" to other birds．Song is not the only "keep out" signal that birds use． Although Northern Mockingbirds sing complex songs on their territories during the breeding season， they use only a loud chuck sound to declare their winter feeding territory． Some warblers also use just a simple call note on their winter feeding territory．Singing on the wing
Some birds sing while in flight， especially species that nest in open areas such as grasslands or the Arctic tundra．
Male Western Sandpipers arrive in Alaska several days before the females and make frequent display flights over their territories as they utter their flight song． Some display flights last up to five minutes and cover the sandpiper's territory． Others are rapid flights low over the tundra， followed by an abrupt ascent．
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