Vocalization

Bats use different calls for communication and echolocation.  In communication calls, bats determine information content but in echolocation, signal parameters depend on environment. Social calls differ in duration, frequency, and pattern of frequency change over time. They generally use lower frequency sounds to minimize attenuation, and are more often audible to people. In colony roosting bats, there may be group-specific and individual-specific calls.

Communication vocalizations have not been as well studied as echolocation, but many species have a wide repertoire of calls.  For example, Phyllostomus discolor uses one echolocation call and 20 social calls.  Communication calls tend to be longer, highly complex, and broadband.  They are thought to be genetically determined, but are highly influenced by behavioral state and mood

Bats change their calls when flying with conspecifics, possibly to avoid jamming. Enhanced communication may also be a reason that echolocation calls change when several bats are flying together (Fenton 2003).

Bats known as whispering bats glean prey from cluttered environments and produce weak calls. Bats that forage in open areas tend to produce intense calls (Jones and Holderied 2008).

Eastern Forest Bat. Photo courtesy of Laura Street.

Signals are shaped by both environmental factors and phylogenetic constraints. Bats tend to use specific signal designs in specific ecological situations (such as open or cluttered) but can also change signals as they move from one habitat to another (Holderied et al. 2008). Call features such as frequency, bandwidth, duration, and pulse interval are all related to ecological niche.

Brain regions involved with vocalization include the anterior cingulate cortex. Several experiments have elicited both echolocation and social calls by stimulating this portion of the brain. The periaqueductal gray is also functionally involved in vocal control. This region is active during vocalization in many vertebrates including fishes, cats, birds, and frogs. (Fenzl and Schuller 2007).
See Neurobiology

Image used with permission from Moss

(A) Different vocalization call types FM and CF-FM. (B) An example of a feeding buzz while pusuing an insect. Although call design is different, the series of vocalizations are very similar, increasing in repetition rate and decreasing in duration rate (Moss and Sinha 2003)

Image used with permission from Smotherman.

(A) A spectrogram of horseshoebat calls and echoes illustrating Doppler shift compensation during vocalization. During the first 600 ms, echo mimic bat calls were played back at twice the rate of breathin g, and the bats themselves began calling faster. However, when echo mimics were played at a normal rate, bats resumed calling and breathing at a normal rate as well (Smotherman 2007)