birds inhale, air is passed from the mouth, through the trachea, which forks into two bronchii connecting to the lungs. The primary vocal organ of birds is called the syrinx, which is located at the fork of the trachea, and is not present in mammals. As air passes through the respiratory tract, the syrinx and the membranes within vibrate to produce sound. Birds are capable of producing continuous song during both inhalation and exhalation, and may sing continuously for several minutes. For example, the skylark (Alauda arvensis) is capable of producing non-stop song for up to one hour. Some birds change their song characteristics during inhalation versus exhalation. The Brewer's sparrow (Spizella breweri) alternates between rapid trilling during exhalation interspersed with lower-rate trills during short inhalations. The two halves of the syrinx connect to separate lungs, and can be controlled independently, allowing some birds to produce two separate notes simultaneously. Insects Insects such as crickets (family Gryllidae) are well known for their ability to produce loud song, however the mechanism of sound production differs greatly from most other animals. Many insects generate sound by mechanical rubbing of body structures, a mechanism known as stridulation. Orthopteran insects, including crickets and katydids (family Tettigoniidae), have been especially well-studied for sound production. These insects use scraper-like structures on one wing to sweep over file-structures on an opposing wing to create vibrations, producing a variety of trilling and chirping sounds. Locusts and other grasshoppers (suborder Caelifera) stridulate by rubbing hind legs against pegs on wing surfaces in an up and downward motion. Cicadas (superfamily Cicadoidea) produce sound at much greater volumes than Orthopterans, relying on a pair of organs called tymbals on the base of the abdomen behind the wings. Muscle contraction rapidly deforms the tymbal membrane, emitting several different types of sounds. Insects thus produce a variety of sounds, using various mechanisms distinct from other animals. Functions of vocalizations Vocalizations can play a wide variety of different roles. In groups such as anurans and birds, several distinct types of notes are incorporated to form songs, which are sung in different situations and serve distinct functions. For example, many frogs may use trilling notes in mate attraction, but switch to different vocal patterns in aggressive territorial displays. In some species, a single song incorporates several note types which serve different purposes, with one type of note eliciting responses from females, and another note of