A chirp uttered by the species resembles crickets. Goslings chirp or whistle lightly, and adults hiss if threatened or angered. They are known to chirp, chortle, and emit other distinctly unusual vocalizations when stimulated. All three species have the ability to emit a loud chirp if irritated. The female frog will not "chirp" or "croak" as often as males, but do sometimes. Females chirp in response to the shrill of the males. The tree swallow's song consists of three parts&colon; the chirp, the whine, and the gurgle. They can scan a series of high frequencies using a chirp transmitter. Typical excitation signals can be classed as impulse, broadband, swept sine, chirp, and possibly others. As with a linear chirp, pulse compression is achieved through intercorrelation. Recently he has analyzed Chirp Transmitter signals using the coupled system of receivers. It is based on spread spectrum modulation techniques derived from chirp spread spectrum (CSS) technology. The parents often use the chirp call to stimulate nestlings to beg. When the scopes were switched on a pulsing chirp sound effect was used. Viewers follow Peep, Chirp, and Quack as they investigate and explore the world around them.