CAPÍTULO II MARCO TEÓRICO
D) Dificultades en la comprensión lectora
trees. Recordings were made at five open sites 1 (i) Foret Hill and Logie (NO 3920 & 4020).
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i (ii) Gauldry (NO 3723)(iii) Kingsbarns (NO 5912) |
(iv) Largo Law (NO 4204) \
(v) St Andrews Links and Kinkell Braes (NO 4918 & 5215)
4.1.2 Coniferous woods (plantations) I
In general these woodlands are characterised by their
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greater density of vegetation (mean density 6.6-8.2
trees/5m ) compared to the open sites, and a lack of ground ' flora apart from some bracken (Pteridium aquillnum), mosses ; and grasses. The ground cover was rarely more than half a t metre high, and in no case was it more than a metre. Often 4 the ground was covered with just a carpet of needles, and : sometimes small branches. It was impossible to obtain clean J recordings of songs in the very densest of woods, as it was
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not possible to get close to the birds without disturbing
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; ■ jthem, therefore recordings were mainly made in slightly older woods which had been brashed and thinned. The trees present were sitka spruce {Picea sitchensis) at Dunkeld, Paddockmuir, and Priorwell wood, and lodgepole pine {Pinus
contorta) at St Ford Links, Tentsmuir and St Michael's
wood. Recordings were made at six sites: (i) Dunkeld (NN 0342)
(ii) Paddockmuir (NO 2120) (iii) Priorwell wood (NO 3523) (iv) St Ford Links (NO 4600)
(v) St Michael's Wood (NO 4423) 5
1 (vi) Tentsmuir (NO 4829)
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4.1.3 Loch Garten (NT 9617) ,3
This is a large area of mature Scots pine woodland. It | is more open (mean density 2.3 trees/5m^) than the | plantation woods, and has a ground flora of heather
{Calluna vulgaris), bilberry (Vaccinium myrtillus), with i
various herb, grass and moss species. The ground cover was
usually between 25cm - 75cm tall. Some regeneration of the | pines was noted, but these young trees were mainly small 1
(up to 3m). Recordings were made between 1®^ - 4^^ May 1 1990. Since all the recordings at Loch Garten were counted î as being from the same site the assumption that variation ;| between areas within the general area did not occur had to
be made.
4.1.4 Aberfeldy & Dunkeld
Recordings were made in the immediate vicinity of the waterfall and rapids at Aberfeldy (NN 8547) by following the path to the waterfall at the top of the gorge. The trees were mainly beech {Fagus sylvatica) and birch {Betula
sp.) f with a small amount of ground cover, mainly of herbs,
grasses, and dead leaves. Recordings were made on the 6^^
April 1988. 1
The Dunkeld (NN 0343) sample was recorded in an open area of deciduous woodland, mainly beech, birch and
sycamore (Acer pseudoplatanus), beside the road from
1 Dunkeld to the Loch of the Lowes. As with Aberfeldy, the | ground cover was mainly herbs and grasses. Recordings were i
made on the 1^^ June 1988.
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4.2 Recording equipment and methods
The songs were recorded using either a Sony Walkman Professional (WM-D6C) or a Marantz CP430, in most cases
using a Sennheiser MD 400 supercardoid microphone in an - 1 Atherstone 50cm fibreglass parabolic refector. In
conditions where the wind speed was greater than about Beaufort force 2 a windshield (Rycote Ltd) was used over the parabola. A few of the songs at Tentsmuir were recorded
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using a gun microphone (Sennheiser MKH 816 in a tubular j 4 shock mount) and the Marantz recorder, and the songs at
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Loch Garten (plus a few of those at Largo Law) were | recorded with a Telinga Pro III parabolic reflector (60cm
diameter) and mono microphone, with the bass filter
switched off, connected to the Sony Walkman recorder. All
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recordings were made on Type I (normal) tape (TDK D60, Sony H60, Maxell UR60).
In all cases recordings were made as close as possible to the singing bird (estimated <30m, modal distance about 10 - 15m), with a minimum of intervening vegetation.
Recordings were made between 05:30 and 11:00 BST on clear days with a minimum of wind (_ Beaufort force 3), and no rain. An attempt was made to record as many song types as possible by recording from as many different birds as possible. This was achieved by moving from one to another
if two or more were countersinging or, if not, moving about 100m between recording birds. This distance is
approximately the diameter of a territory: Marier (1956b) 2
calculated mean territory size as 6700 m . Songs were recorded until the bird either flew off, stopped singing, or I estimated that it had cycled through its song types. No attempt was made to record all the birds at a site. Recordings were made between 9^^ March - 2^^ July in 1988, and 17th March - 16^^ June in 1989.
4.3 Sonagraphic analysis
A survey of the song types possessed by each bird was made by viewing them with a Unigon 4512 real time FFT
analyser and SCI waterfall display screen, and making a catalogue of sonagrams. In 1988 and 1989, a Kay Elemetrics 7800 Digital Sonagraph was used, but in 1990, a new
machine, a Kay Elemetrics DSP 5500 became available. After the initial survey, a representative song for each song type was chosen for the measurements. The songs actually
analysed were chosen visually on the basis of having minimal background noise and degradation.
Two sonagrams (wide and narrow band) were made for each song type. Measurements for time variables were taken from wide band (300Hz filter width) sonagrams, and for frequency variables from narrow band (45Hz filter width) sonagrams. All sonagrams were made using the 0-8kHz range, and settings (especially the print darkness) were
standardised to ensure that the sonagrams were as far as
possible directly comparable. With the sonagrams prepared 4? by the 7800 Sonagraph, a program written in Turbo Pascal 4, ïj J in conjunction with a graphics pad (Cherry Mk III)
I connected to a Zenith 159-13 PC, was used to digitise | points and convert them to time and frequency measures. .
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Points were digitised with an accuracy of ± 0.5mm, thissonagraph allows measurement of variables using cursors on the screen, so measurements taken in 1990 used this
facility. The time cursors are moved in steps of 3ms when a two second time base is used for display of a sonagram.
..'j distance equates to ± 4ms, and ± 40Hz. The DSP 5500
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4.3.1 Definitions of the parts of a song
The definitions below describe the terms used for the 1 W measurements taken, and are based on those of Slater & Ince i
■i (1979), and Slater et al (1984). They are shown in 4
graphical form in Figure 4.1. 1
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Element : a continuous trace on a wide band sonagram, ■ Syllable : a group of elements (sometimes, given the
definition of a phrase below, a syllable was defined as
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just one element). There is usually no repetition of elements within a syllable, but see section 6.3 for more details.
Phrase : a sequence of repeated syllables.
Transitional syllable : a group of elements which is not repeated.
End phrase (flourish) : the terminal part of the song which contains no repeated syllables. There is one syllable type (Figure 4.1) which when present is always found at the end of the song. Though this syllable type may be repeated it is defined as being part of the flourish, as it can occur after more than one unrepeated syllable.
Song type : a unique sequence of syllables and end phrase
4.3.2 Measurements taken
Within each song type 1 measured the last syllable in the first phrase, and the first syllable in subsequent phrases. This is because in the first phrase it is often very difficult to measure the first syllable, as birds usually start singing quietly, and increase the amplitude
of the song as the first phrase proceeds. This can be seen | i in Figure 4.1: the syllables in the first phrase become j ■I better defined as the phrase proceeds. However, since there |
is variability both within and between birds in the number of repetitions of a syllable within a phrase (see chapter 6
for more details), it is better to measure the first j 1 syllable, and this was done for phrases subsequent to the 1 first.
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♦--- 1 I--- 1 X 3» O C <0 3 C7 0> -4 -3 2 1 I J ,1
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0.1s h~iElement Syllable Transitional
Syllable
Figure 4.1 A sonagram of a chaffinch song. Note that phrase 1 becomes better defined as it is sung, and that the syllable type marked * only occurs in the endphrase part of the song.