Among birds vocal sound is one of the best methods of communication to aid them to survive successfully in their environment. Its results are most evident in escaping from danger and success in breeding, which directly govern the survival of a species.

Some birds which do not produce vocal sounds (e.g. Storks, in the family Ciconiidae) produce non-vocal sounds with the bill. Some bird species produce both vocal and non-vocal sounds.

Bird vocalizations can be recognized as two types, calls and songs, by examining the structure of a sound and the benefit related to it.

A call is a note or a phrase of very few notes for communication between a pair or among a family or flock, usually uttered to be in contact, indicate the approach of danger, the availability of food, or hunger by nestlings.

A song is a phrase of very few to many notes which is repeated at regular intervals. It is uttered mostly by the male, and is important in breeding behaviour, establishing and defending territories, and attracting mates. Females join males, sometimes in singing to defend territory, and regularly in duetting: see below. Often different types of behaviour or postures are seen with different types of song in the same species.

Songs of the true songbirds, who are all Passerines*, are pleasant and “musical”, and usually complex and varied–examples are larks, thrushes, robins, and some flycatchers among Sri Lankan birds. The songs of most Sri Lankan Passerines other than true songbirds are varied though not so complex–examples are ioras, leafebirds, bulbuls, warblers, drongos and orioles.  Many Passerines include in their songs mimicry of calls or songs (in part or whole) of other birds, or this is uttered separately–examples are the White-bellied drongo and Jerdon’s Leafbird, the former mimicking the domestic cat and Shikra, the latter the Shikra and other birds. Most Non-Passerine† birds do not have complex or varied songs, but some do have pleasant and musical songs–examples are the cuckoos.

* In Sri Lanka, Families of birds from Pittidae (Indian Pitta) to Emberizidae (buntings).

† In Sri Lanka, Families of birds from Phasianidae (junglefowl, peafowl, etc.) to Picidae (woodpeckers).

Distinct types of calls are:

Contact calls, to maintain contact between a pair, especially when they are some distance apart, and within members of a family or flock, e.g. made by the Yellow-billed Babbler.

Flight calls, made in flight to maintain contact within flocks of Whistling Ducks  and shorebirds, and among individuals of some species while taking wing, e.g. wagtails, pipits, mynas.

Aggressive calls, uttered at other birds of the same species, or sometimes at other bird species or animals, to threaten them, e.g. Oriental Magpie Robin, Black-hooded Oriole, Blyth’s Reed Warbler.

Scolding and alarm calls, to announce danger in the vicinity, a typical alarm call often being a rapidly uttered single note announcing the approach of danger with high risk, e.g. Red-vented Bulbul.

copulation calls, uttered while copulating, only by a few species, e.g. the Shikra.

Distinct types of songs are:

Advertising songs, to announce the ownership of a territory or to attract a mate.

Territorial songs, to announce the ownership of a territory – with the same song/s being used for both purposes above by most species.

Courtship songs, to attract a female after approaching her or to entice her to copulate.

Aggressive songs, to threaten an intruder, usually a male, of the same species approaching a territory (see no. 11) – again, most species using the same song/s for both the above purposes.

Duetting songs or duets, territorial songs in which both birds of a pair sing, in the same session, the same phrase or different phrases; in some duets this is so close in succession that this is heard like a continuous song sung by one bird–e.g. by the Sri Lanka Spurfowl, Brown Fish Owl, and Sri Lanka Scimitar Babbler.

Subsongs­, males of many Passerine birds sing long phrases of softly uttered notes during the non-breeding season. This is usually done while sitting quietly on a less exposed low branch of a tree. This kind of singing seems to provide practice for the adult males before they sing their loud, full songs in the breeding season. Young males babble phrases somewhat reminiscent of full songs of their adults in their practice of singing songs. E.g. Oriental Magpie Robin and Blyth’s Reed Warbler.

In many species the song of the male and the female differ only or mostly by the pitch, with the same or very similar phrase –e.g. Greater Coucal, Owls (Collared Scops Owl, Brown Hawk Owl and Brown Fish Owls.

In all Non-Passerine, and some Passerine, species, it can be difficult to make out whether certain vocalizations are calls or songs.

Non-vocal sounds related to territorial and breeding behaviour are known in bioacoustics as mechanical sounds–examples in Sri Lanka are bill clattering in storks, wing clapping by the Junglefowl, pigeons and doves, and the drumming of woodpeckers by very rapid striking of the bill on a resonant tree.