CAPÍTULO II MARCO TEÓRICO
C) Las diversas aproximaciones teóricas respecto al autoconcepto
birds in the New Zealand sites were recorded. The patterns 1 of geographic variation for groups of syllables were
■ ; modelled by Lynch at al (1989), who suggested that the I transmission within and between populations of these
"memes" depends upon the number of syllables linked i I
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together. The balance of the processes of miscopying songs and immigration may vary between populations, especially if migration of birds occurs in one place but not another, or if dispersal distances differ for any reason.
It is the object of the present study to investigate the effect of habitat upon the time-frequency structure of chaffinch song. That habitat may affect song in the
chaffinch is suggested by the songs of chaffinches in New Zealand (Galbraith 1977, Jenkins & Baker 1984) . The species was introduced there about a century ago; although most song types are similar in terms of the number of phrases and endphrase syllables to those described in Britain, about 10% of New Zealand song types were found to be
unusual. In some of these songs the syllables have becdme elaborated, and the pitch altered.
The trill part of New Zealand songs is commonly
simpler, and the end phrase more complex, possibly because elaborate end phrases should degrade less from * reverberations in the dense coniferous forests where New Zealand chaffinches are typically found (Jenkins & Baker 1984). In Europe chaffinches more often live in mixed deciduous woods (Glas 1960), or at least ear1ief studies- a
have been in such woods; their songs may not be adapted to the transmission characteristics of coniferous woods.
The following predictions of the acoustic adaptation hypothesis were tested by recording songs from coniferous woods and open scrub habitats:
1) The frequencies used in a dense habitat (coniferous wood) should be lower than in an open scrub habitat.
This is because high frequencies will be scattered more by obstructions in the transmission path. This can be tested both with the maximum frequency found on sonagrams, and with the frequency at which most energy is concentrated. The latter measure is the frequency - of maximal amplitude measured on a power spectrum of a song or a part thereof.
2) Given (1) and that the minimum frequency should be as low as possible in all habitats, the range of
frequencies used should be smaller in the coniferous woods than in the open scrub.
3) The effect of reverberations, which interfere with the transmission of the amplitude structure of sounds, is greater in dense habitats. It should be minimised by spacing sounds out in time more in the coniferous woods than in the open scrub. In addition, the effect of irregular amplitude fluctuations, which are
expected to be more common in open habitats, will lead to selection for sounds in this habitat which are only separated by short gaps. This combined effect can be measured as the gap between syllables, or as the ratio
syllable cadence
The cadence is the sum of the duration of the syllable and the gap between successive syllables.
The methods used to record, measure, and analyse songs are given in chapter 4.
Chapter 4
l8 Ghaffinoh aong adapted for transmission
through the habitats in which it is sung ?
Chapters 2 and 3 have reviewed the literature on the acoustic adaptation hypothesis and on the song of the
chaffinch. The predictions made from the hypothesis at the end of chapter 3 are tested below on chaffinch songs
recorded in Scotland.
4.1 Habitat descriptions
Recordings were, made from two main habitat types; open
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scrub, and coniferous woodland. In addition, recordings | were made in the Abernethy forest around Loch Garten, which .;|’ ■ : ' i
is an area of ancient Scots Pine {Pinus sylvestris) f to enable comparison between natural coniferous woodland and
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with plantations. To examine whether background ^
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environmental noise might have an influence on song ;;
• . 4
Structure, songs were recorded from an area of mixed
deciduous woodland in the gorge of the Birks of Aberfeldy, a set of waterfalls and rapids. Songs were recorded in an open deciduous area near Dunkeld for comparison with the
■ ■ 4
Aberfeldy sample. Map references below are given to four 3
,4 4
figure accuracy only as recordings were made over a larger area than is implied by a six figure reference.
4.1.1 Open scrub 4
These sites were characterised by an open aspect and, " i ' - 4 especially where gorse {Ulex europaeus) was present (Foret
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Hill, Largo Law, and St Andrews Links), by a lack of
vegetation over about 1.0-1.5m in height. Chaffinches are scarce in very open areas, so the sample size was increased by recording in some rural villages and hedgerows (Logie, Gauldry and Kingsbarns). Those birds which lived in the gorse areas usually sang at the tops of the bushes, or in any trees (usually elder Sambuccus niger) which were
present. The paucity of birds in this habitat is possibly j because trees are very important to them: Goodfellow (1988) .1 4 showed that the size of territories of chaffinches was 41-
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