Although they may occasionally sing during the night, blackbirds are diurnal. During migration and winter, many species form flocks—sometimes huge flocks—when they are both foraging and roosting. In the mid-1970s, there were 723 major roosting flocks in the United States containing an estimated 438 million blackbirds. An estimated 200 million icterids winter in Arkansas, Louisiana, Tennessee, and Mississippi. In the west, particularly in rice growing areas of east Texas and California, another 139 million icterids winter, and in North Carolina about 76 million winter. There are advantages to the birds in these large roosting flocks. There is strength in numbers: there are more birds to sight potential predators, and it can be dangerous for flying predators to enter a large flock of birds. There is also protection from rain, wind, and heat loss in a large flock. A disadvantage is that there is not sufficient food close to a large roost to feed the large numbers of birds present, and some individuals must travel up to 60 mi (100 km) each direction every day to reach feeding areas where the food has not already been depleted. Migrating and wintering blackbirds often forage in flocks as well, but foraging flocks are generally smaller than roosting ones. New World blackbirds walk rather than hop on the ground.

Blackbirds perform a wide variety of displays, many of which are quite interesting to watch. One common and widespread icterid display is the "song-spread" (or "rough-out") display. In this display, the bird (most commonly a male, but females of some species also do this) spreads its wings somewhat, and raises the feathers on its shoulders, back, and neck; on the red-winged blackbird this displays the bright red epaulets prominently. Some birds, such as some of the cow-birds (Molothrus), have a neck ruff that is exaggerated during this display. The "song-spread" display is accompanied by song. The "song-spread" appears to function both in territorial defense and for mate attraction. The "bill-tilt" display is another display that many blackbirds use. In this display, the feathers are sleeked, and the bill, head, and body are pointed upward. "Bill-tilting" is aggressive, and is used during encounters both within and between sexes. Many blackbirds have "flight-song" displays, and in some species these displays can be spectacular. Male white-browed blackbirds (Sturnella superciliaris) fly to a height of about 60 ft (20 m) and para-

Baltimore oriole (Icterus galbula) female builds her nest. (Photo by Gregory K. Scott. Photo Researchers, Inc. Reproduced by permission.)

chute to the ground while giving their song. The "flight-song" of the bobolink is also spectacular. The male, with a fluttery flight and wings bowed—not rising above the horizontal, and tail pointed downward, fly up to perhaps 30 ft (10 m) from the ground while uttering their bubbling song. Male red-winged blackbirds commonly give a rapid series of notes, "tseee tch-tch-tch-tch chee-chee-chee" while in flight. Female blackbirds characteristically arch their backs, and with their heads down raise their tails and shiver their wings in a pre-copulatory display. Injury feigning distractions are given by some blackbirds, but are not common in the family. Male oropendolas perform a "bow-display." In this display, the male sits on a branch, partially opens his wings, thrusts his head downward and tail upward, until he is completely upside down, with his tail at right a right angle to his body, then rights himself as he finishes his song, and shakes his wings.

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