Kinds of vocalization:

Song: relatively long, complex vocalization given during male-male interactions, territorial advertisement, courtship of females

Calls: relatively short, less complex vocalizations given in other contexts/ with other functions:

• distress (being handled, picked up by a predator)
• begging (nestling calls)
• alarm (a predator is nearby)
• may be different alarm calls for different predators (hawk vs. terrestrial predator)
• alarm calls of different species similar; accoustic properties make hard to locate
• social contact within flocks
• mobbing (a group of birds fly at and call at a potential predator)

Aspects of sound:

• amplitude (loudness)
• frequency (pitch)
• pure tones vs. frequency modulation
• temporal pattern

• plot of frequency (kHz) vs. time of the song.  Figure 1 shows an example.

Production: syrinx; some association between song complexity and syrinx complexity

• oscines have most complex syrinx; can produce most complex vocalizations
• however some oscines produce very simple vocalizations
• the double voice phenomenon: the parts of the syrinx in the different bronchi can act somewhat independently.  Figure 2 shows an example.

Song Development

Learning and song development:

• most orders: assumed or known to be innate (genetic, not learned) (ex: Columbiformes; doves raised in isolation develop normal vocalizations)
• learned vocalizations known from: Psittaciformes, Apodiformes, possibly some Galliformes, possibly some Piciformes,  Passeriformes
• within Passeriformes:
• many oscines shown to have some form of song learning
• some suboscines shown not to learn songs; lack of variability in many described species suggests suboscines have little/no song learning

• specific details of song are often learned from other individuals, but birds raised in acoustic isolation will still develop some of the species typical characteristics of song
• example: song sparrows and swamp sparrows raised in acoustic isolation showed species typical differences in repertoire, repetition of syllables, details of syllable structure, but did not develop normal details of song
• learning is often most likely during a sensitive phase, not necessarily when the bird is singing
• birds may learn specific details of song from other birds (e.g. white-crowned sparrows) or develop songs that differ from those of other birds, but require exposure to conspecific song to develop normal song (e.g. dark-eyed juncos)
• species vary in what they will learn from tape recordings:
• white-crowned sparrows: preferentially learn conspecific song
• meadowlarks: will learn conspecific and other song
• social interaction with "tutor" is often important in learning
• indigo buntings will not learn songs from recordings in the lab; they will learn songs in the lab from individuals with whom they interact
• white-crowned sparrows will learn songs of different species if they interact with them socially; will learn from tutor over wider range of time
• brood parasites: indigobirds -- learn song of host; female identifies appropriate species based on song of host.  Brown-headed cowbirds: interaction with female important in learning normal song.

Hypotheses of social function:

• decrease aggression towards individuals that sing a bird's own song
• deceptive mimicry: young birds sing the song of older birds and by mimicing the older birds compete better with other young birds

Song Repertoires

• discrete vs. continuous song
• extreme inter- and intra- specific variation in song repertoire size.  Examples:
• white-crowned sparrow, common grackle, indigo bunting: 1 song type
• many warblers, yellow-headed blackbirds,... 2 song types
• western meadowlarks: 7 - 10 song types
• eastern meadowlarks: 60 - 80 song types
• thrashers, mockingbirds: continuous song, can be over 1,000 syllable types

• birds that sing a lot may have large repertoires to avoid habituation their listeners (but then need to explain why some species sing more than others)

• large repertoire associated with polygyny among wren species, monogamy among old-world warbler and old-world bunting species; no association in blackbirds
• large repertoires and territory defense: Great Tit (Paridae): playback of more than one song from a male's territory deters intruding males for longer than playback of just one song
• large repertoires and female attraction/ male quality: Great Reed Warbler (European species, not a parulid -- in the thrush relatives group) -- social mate chosen by female related to both territory quality and song repertoire size; extra-pair matings occur with neighboring males with LARGER song repertoires; survival of offspring related to the repertoire size of the genetic father.  Suggests larger repertoires indicate good male quality inherited by offspring.