Functions of Birdsong: Why Do Birds Sing?

By Ana Gabrielle Alcantara

The wondrous sounds of birds fill us with joy as we take our daily walks and commute.  Birdwatching and hiking trips are all the more enjoyable when we hear a cacophony of warbles and melodies across the trees early in the morning.  As we bask in the natural world around us, we may start to wonder:  why do birds tweet and sing in the first place?  To whom are the songs directed to?  What is the message we are hearing from them?

This article explores the singing behavior in birds and provides insights into the different roles a song can play between individuals and different species.

Species recognition

Recognition is an important aspect of birdsong and is considered the ability of a bird to recognize its own species.  Song recognition occurs between individuals, which includes the ability to recognize both intra- and interspecies variation in song features.  This is highly important for parents to recognize their offspring, for neighbors to ward off their rivals, and for breeding individuals to attract mates.

As such, calls are important methods to locate a bird amongst the hundreds of birds within a flock, even amongst dense background noise, despite travelling long distances and encountering different landscape features during their migration.  It allows for more complex social interactions within the flock, which include cooperative breeding and group decision-making processes.

Fighting and territorial defense

It is the male birds that are known to do most of the singing we hear.  Males need to sing in order to defend the territory they occupy.  They can recognize the songs of their neighbors and determine if they’re from the same species or not.  They are seen to respond to the songs of other birds as either trespassers or competitors.

Territorial defense refers to how birds use calls as an aggressive display towards the same or different species that intrude on their territory.  Thus, a territorial song is dubbed as a singing action that ensures the protection of their food resources and can act as a predator defense mechanism.

Vocal duals can be observed and this zealous singing can intensify into aggression.  It was found that muted males are more prone to invaders and had a slower time obtaining a territory.  With this singing disability, male birds may resort to visual signals as compensation and reinforcement of territorial integrity.  This indicates that songs can transmit messages about a male’s ability and motivation to fight that can dissuade a rival into a retreat.

Courtship and mating

Songs can provide a subtle indication of a male’s suitability as a potential mate for female birds during the breeding season.  Females choose their mates by assessing a male’s favorability for mating and reproduction.  Their fitness and good health, their ability to feed potential young, and their efficiency in maintaining a territory all come into play when a female prefers a male over other candidates.

Visual cues, such as plumage coloration or mating dance, can provide an additional basis for a female’s favorability.  Likewise, birdsongs contain information that relays a male’s quality and advertises their fitness for mating during courtship.

Female song preferences differ from species to species.  This sensory bias can be seen when some females prefer males who can sing a specific song sequence, often fitting their acoustic sensitivity.  Some prefer males who have a larger vocal repertoire and can sing more complex songs, as this tends to be correlated with male age and indicates a higher likelihood of the individual’s good condition, greater breeding experience, and survivability probability.

Song familiarity is also an important factor for certain species.  Birds may choose mates who sing songs familiar to them, such as a neighbor’s local song compared to a stranger’s.  This can be a result from a female’s favorability towards their own species’ song features which can fit their species-specific song template.  Hence, high quality vocal performance and sensory bias stimulate female attraction in choosing between potential mates from the rest of the flock.

Conclusion

The functions of birdsong are often studied in avian behavioral ecology and bioacoustics.  Individual vocal characteristics are seen in birdsongs and are a gold mine of information for researchers and birdwatchers alike.

Songs and calls can be used for species recognition, territorial defense, and courtship purposes.  

Recognition through birdsong enables group cohesion among members of the same flock or family unit and allows them to stay together during migratory periods or resource hunting.

Territorial defense involves establishing boundaries between different bird species or individuals within the same species in order to protect and secure their resources from competitors.

Mate attraction and courtship occur when females choose a potential partner by judging males through their songs as part of courtship rituals.

Much is still needed to know about the singing behavior of birdsong, especially for Philippine birds.  Observation of their behavior and analysis of their acoustic signals are necessary to understand the purpose of the different song features and gain insight into why birds behave in certain ways.

References

Catchpole, Clive K., and Peter JB Slater. Bird song: biological themes and variations. Cambridge university press, 2003.

Kroodsma, Donald E. Singing life of birds. Houghton Mifflin, 2005.

Marler, Peter R., and Hans Slabbekoorn. Nature’s music: the science of birdsong. Elsevier, 2004.