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Student essays

Song is an important part of avian behavior and is striking to human observers.
Some bird species have repertoire of distinct song types, which they use in different context. I investigated which song type occurs in the determinate situation, and what does it mean for other individuals.
In many songbird species in the temperate zone only males sing.
Functions of the male song:
- territorial defence against other males
- mate attraction and stimulation.
The ability to sing is genetically encoded into the nervous system, and the birds also learn to sing.
A song contains qualities specific to the species, and may also contain qualities that are specific to the individual.
In some birds, males have only a single, simple and stereotyped song, which they repeat monotonously. For some species, the individual variation of song consists of variation in note structure within song -> the male possesses a repertoire of distinct song type –
or individual variation consists of variation in quantity -> how many songs are produced (DeVoogd and Székely).

What is the function of different songs?
Song types can provide several information about the singer to both males and females.

Messages encoded in different songs:

Chestnut-sided warbler song repertoires contain two distinct categories of song: accented –ending (AE) and unaccented – ending (UE) songs. The song categories encode information about the singer’s location, mating status and future behaviour.
Males use AE songs: when they are unmated, at the close of the dawn, in the centre of the territory, will not advance to a territorial border, will avoid conflict with other males, will interact with females (and the opposite holds for males using UE song) (Byers 1996).

Different interactions between males based on different answers:

Song matching: when one bird replies to another bird’s song by a similar song. Often occurs between territorial neighbours. If song matching functions as a directed signal, then birds should benefit from being able to match their songs (Burt et al. 2002).
Armstrong (1973) suggested: naming an opponent in song duels.
Bertram (1970): flinging it back at the rival.

Song matching has several types:

Repertoire - matching: In many songbird species neighbours share song types. The bird replies to the neighbour by a shared song type.

Type - matching: the bird replies by the same song type that he heard (Beecher et al. 2000).

Broad-sense form of song matching: In many populations neighbours do not share song types, and therefore cannot type-match. Hypothesis: birds lacking a true type match could still match songs by a song from their repertoire that is similar in some way (Burt et al. 2002).

Neighbouring male song sparrows share song types and respond to neighbour song by type matching or repertoire matching (Beecher et al. 2000).

The mechanism of song sharing: a young male learns several songs from 3 or 4 older, established males in a particular area; furthermore, the young bird attempts to set up his own territory close to his tutors ? song sharing. This provides several advantages for the birds ? they can recognize each other by singing a song type, that they share with their neighbours (repertoire matching) ? decreasing aggressive interactions (Beecher et al. 1996).

According to the threat hypothesis, type matching is a threat signal ? a bird will be more likely to escalate when type-matched by his neighbour than when repertoire matched. When type-matched, birds who escalate will continue to sing type-matching, while those who de-escalate will switch off the matched type or stop singing (Burt et al. 2001).
Furthermore, birds are more likely to type-match early in the breeding season when territory boundaries are new, and more likely to repertoire-match later in the season, once boundaries become established (Beecher et el. 2000).

In the population investigated by Beecher (2000), where sharing between neighbours is high on average, there are still neighbours who share few or no song ? may still have song types that are similar enough to be used in song matching. In a playback experiment song matching using the two different song classes as playback stimuli (double-buzz song, speed-up song) was examined. Birds replied to playback of double-buzz songs or speed-up songs by their own double-buzz song or speed-up song respectively. So, where neighbours do not share song types, broad-sense song matching might still be possible (Burt et al. 2002).

Females recognize males based on different songs:

Song sparrow females responded to songs recorded from their mates, neighbouring males or stranger males in different ways. Females responded most strongly to songs of their mates, less strongly to songs of neighbouring males and least strongly to songs of stranger males ? females have the ability to discriminate between males on the basis of their songs.
Among the stranger songs females preferred songs similar to their mate’s song.
Females had more exposure to the songs of mates and neighbours than to the songs of stranger.
The spontaneous song rate by males is 100 songs/h. When defending territorial boundaries it could be over 200 songs/h. ? females are more exposed to songs of mates than of neighbouring males.
Furthermore, the greater the similarity between songs of the stranger and mate, the more likely the female to respond. Probably, females simply confused the songs of strangers and mates. In operant song classification studies in laboratory, males initially confused similar song types (Beecher et al. 1994).
Deceptive mimicry models propose that locally shared songs are beneficial to males in attracting mates (Payne 1981). Females may be preferentially attracted to males with locally shared songs ? such males are likely to have established territories and on average to be older, more experienced males.
Under these circumstances, natural selection is expected to favour young males that learn local neighbourhood songs when setting up a territory. These young males should have an advantage in attracting females because they sound like older males (O Loghlen and Beecher 1999).

References:

Beecher, M. D., Campbell, S. L. and Burt, J. M. 1994b. Song percepion in the song sparrows: birds classify by song type but not by singer. Animal Behaviour, 47, 1343-1351.

Beecher, M. D., Stoddard, P. K., Campbell, S. L. and Horning, C. L. 1996. Repertoire matching between neighbouring song sparrows. Animal Behaviour, 51, 917-923.

Beecher, M. D., Campbell, S. L., Burt, J. M., Hill, C. E. and Nordby, J. C. 2000. Song type matching between neighbouring song sparrows. Animal Behaviour, 59, 21-27.

Burt, J. M., Campbell, S. L. and Beecher, M. D. 2001. Song type matching as threat: a test using interactive playback. Animal Behaviour, 62, 1163-1170.

Burt, J. M., Bard, S. C., Campbell, S. L. and Beecher, M. D. 2002. Alternative forms of song
matching in song sparrows. Animal Behaviour, 63, 1143-1151.

Byers, B. E. 1996. Messages encoded in the songs of chestnut-sided warblers. Animal Behaviour, 52, 691-705.

O Loghen, A. L., Beecher, M. D. 1999. Mate, neighbour and strangers song: a female song sparrow perspective. Animal Behaviour, 58, 13-20.

Bird Song 1995. Eds: Catchpole, C. K. and Slater, P. J. B. Part 8:Themes and variations, Matched countersinging.

Animal Cognition in Nature 1998. Eds: DeVoogd, T. J. and Székely, T., Part12: Causes of Avian Song Using Neurobiology to Integrate Proximate and Ultimate Levels of Analysis