lusitanius Yellow-legged Gull

(last update: 10-12-2013)

TABLE I & II: Comparison of basic call and mew call of three populations of Yellow-legged Gulls.
- the island of Oléron (pop. 1),
- the Camargue (pop. 2),
- Basque Country (pop. 3).

Data from:
Comparative study of four populations of Yellow-legged Gulls in Western Europe by Anne TEYSSEDRE
IN: L'Oiseau et R.F.O., V. 53, 1983, n° 1.

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Note: the difference is considered non-significant when ΔX << " Sp.

ΔX = │ X2-X1│

Sp = Sx * √ (n / n-1)

NS = non-significant difference

HS = highly significant difference ( ΔX > " Sp)

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1) Ethological study.

We have consistently observed the behaviour of nesting (pop. 1, 2 and 3) and recorded vocalizations from an hide placed near territories. From the wide variety of sounds in the colonies, we have studied statistically four vocalizations. It is the staccato alarm call ("staccato call" of TINBERGEN 1959) and three vocalizations expressed with high energy:

- The basic call ("call note"), a signal of varying intensity and meanings (call, alarm, attack);
- The "trumpeting" or "complete long call", a territorial call;
- The "mew call", a signal of recognition in the family (partner or parent).

Thirty vocalizations of each type delivered by thirty individuals in each of the two colonies, and eight by birds nesting of the island of Oléron were recorded and transcribed into sonograms.
For each sonogram, factor duration and frequency were measured (units in brackets):

- Total length (Dt), (10-2 sec.)
- Unit length (Du) for repetitive calls (10-2 sec.)
- Rate (C) for calls,
- Number of units (K) for the staccato calls,
- Duration of upward glissando (Da) and descending (Dd) ((10-2 sec.)
- Maximum fundamental frequency (FFmax) (Hz),
- Fundamental frequency of the level (FFP) for mew call, (Hz),
- Fundamental frequency at the glissando of the slide down (FFB), (Hz),
- Number of harmonics (nH).

Averages (x) and standard deviation (Sx) of these factors were calculated for each sample and estimated for the corresponding populations (Y, Sp). Averages were then compared by the Student t test to 95% confidence interval.

RESULTS

1) Ethological comparison.

There appeared to be no difference in behaviour between the three breeding populations. However, acoustic analysis brings new information (Tables I to IV and Fig. 1 and 2):
- When comparing Oléron and Camargue populations, there is no significant difference (t <2.0) in averages for all four vocalizations (24 factors analyzed).
- On the opposite, all four types of vocalizations significantly differ between all populations of Oléron and the Basque Country (as well as those of Camargue vs. Basque Country).
Especially, three calls with high-volume output – basic call, mew call and trumpeting - differ highly significantly regarding most of the analyzed factors (13 out of 18 factors).

The staccato calls are less dissimilar among the six factors compared here, only frequency (FFmax) differs significantly between these populations.