lecture 7: Bird sounds

pure tone vocalizations

on a single frequency at a time

harmonic vocalizatoins

at multiple, related frequencies

Oscillogram

displays amplitude versus time

sonogram/spectogram

displays frequency and amplitude versus time

physical properties of sound

• high frequencies propagate poorly compared to low frequencies

• pure tones propagate better in cluttered environments

• short duration, frequency modulated sounds are more locatable

• sounds with harmonics are more complex

• Bird sounds are adapted to their acoustical environment

calls

short simple vocalization, usually given by both sexes

songs

lengthy, complex, repeated vocal displays often performed by territorial males during the breeding season

syrinx

located near the junction of brochi at base of trachea, a vocal organ where sound is produced for calls/songs

1. interclavicular air sac in syrinx (distended)

2. syringeal muscels

3. internal tympaniform membrane

sound production and modulation control

• by tension on tympaniform membranes

• by air pressure

• by shape of air passage

Advantage of Bilateral symmetry on bird song

allows for possibility of different sides producing different sounds, i.e. two voices

→ ex: Wood and Hermit Thrushes

vocal repertoire

repertoire of structurally and functionally different types of vocalizations, includes songs (single element of repertoire) and variety of calls

Call

short simple vocalizations made by both sexes

→Ex: crow

Songs

lengthy. complex, repeated vocal displays often performed by males during the breeding season for the purpose of territorial defense and mate attraction

typical constituents of a repertoire

• song

• alarm calls

• warning calls

• contact calls

• courtship calls

• aggressive calls

pre-mating isolating mechanism

females only mate with individuals with sounds of their own species

individual recognition by sound

individuals recognize each other in situations where vision is not an option

Difference in Calls of Band and Rough-winged Swallows

• Bank swallows have complex, individually distinctive calls recognized individually by parents and offspring

• Rough-winged swallows have simple calls with no vocal recognition between parents and offspring

Ancient Murrelet - Communication

• nest in dark forest burrows where families rarely see one another, so parents and chicks rely on individually distinct calls to locate each other

• after hatching, parents guide their chicks hundreds of meter to the ocean using this vocal system to navigate a crowded nocturnal colony

song learning

vocal repertoire acquired by inheritance, learning, or by invention

song learning of non-passerine birds

typically have inherited (innate) songs and calls

song learning of inter-specific brood parasites

• cuckoos and cowbirds

• have innate songs

song learning of passerines

call often innate, while songs learned with predisposition of songs of own species

culture

behavior based on learned traditions

four phases of song learning

• critical leaning period

• silent period

• subsong period (babbling)

• song crystalizatoin

Anti-habituation hypothesis

one song is boring and listeners quickly lose interest, hence repetoires are required

→Heartshorne

Different functions hypothesis

different songs have different meaning or messages

→ in Black throated Green Warbler, one song is used for terriroy and another for mate attraction

Beau Geste Hypothesis

repertoire function to confuse neighbors about how many individuals occupy an area - hearing different songs indicates area is full

Badge of status hypothesis

large repertoire indicates experienced high quality male that would be formidable adversary - territorial defense function

location confusion hypothesis

having multiple song types is a way males prevent their neighbors from knowing their location

sexual selection hypothesis

song functions as an ornament used for mate attraction- more elaborate repertoire more attractive - leads to selection for males with largest repertoires

functionless epi-phenomenon hypothesis

song repertoires have no function - are simply an unselected consequence of birds having big brains, song learning ability, and spare time

song dialects

learning from conspecifics leads to accents or dialects

social signaling hypothesis

hypotheis of how song dialects developed: imitation of successful neighbors

→Payne

Ecological Hypothesis

hypothesis of how song dialects developed: dialects function to signal genetic adapted-ness to local environment