available statistics biometrics

Available Statistics on Biometrics

Introduction

The biometrics of michahellis and atlantis are well-established in the literature. Some six sources have been found for the biometrics of michahellis and ten for atlantis. These are shown in Tables 1 and 2 respectively. Where a range is given for a measurement, the first figure is for females and the second for males. A single figure indicates that the source only provided an average value over both sexes.

	michahellis
Country		France	France	Spain	Morocco
Locality	Medi-terranean	Camargue	Camargue	Balearic Islands	Islas Charafinas	Medi-terranean	Average female	Average male	Average overall
Source	Cramp (1983)	Isenmann (1973)	Van Swelm (2002)	Carrera (1987)	Carrera (1987)	Faber et al (2001)
wing	438-460	440-465	420.5	447	457	454.6	439.0	462.5	446.8
tail	169-179	-	172.2	-	178	-	169.0	179.0	174.7
bill	51.5-56.6	56-61	55.5	57.4	56.6	57.0	53.8	58.8	56.5
tarsus	64.5-70.6	67-72	69.8	70.3	68.5	69.6	65.8	71.3	69.2
toe	59.2-65.4	-	66.5	-	-	-	59.2	65.4	64.4

Table 1: Biometrics for michahellis from six sources

	atlantis
Loc-ality	W Iberia	NW Iberia	Portugal	NW Africa	Macro-nesia	Canaries	Canaries	Azores	Azores	Azores
Source	Cramp (1983)	Carrera et al (1987)	Van Swelm (2002)	Urban et al (1986)	Cramp (1983)	Banner-man (1963)	Volsøe (1951)	Dwight (1922)	Dwight (1925)	Vaurie (1965)	Average female	Average male	Average overall
wing	401-431	419	425.1	420-439	423-437	401-418	417-440	401-423	402-421	418-438	410.4	430.9	420.9
tail	158-169	-	169.7	162-170	165-173	162-170	-	162-170	162-171	-	161.8	170.5	166.7
bill	49.5-53.6	54.8	51.0	49.4-55.7	49.1-51.5	46.5-54	-	50.3-55.1	50.2-54.3	-	49.2	54.0	51.9
tarsus	60.3-64.4	65.6	61.7	61.6-65.0	62.7-64.7	62.5-65.5	-	61.7-66.6	61.6-66.3	-	61.7	65.4	62.3
toe	55.2-59.3	-	61.2	-	58.7-60.3	-	-	52.3-56.0	52.2-55.2	-	54.6	57.7	57.1

Table 2: Biometrics for atlantis from ten sources

Average Biometrics

Table 3 shows the average biometrics (across both sexes) for three populations of atlantis: Iberian, Southern (NW Africa and Macronesia/Canaries) and Azorean The NW Africa population of Southern atlantis has been given separately to show the details for the Moroccan population alongside other Southern populations. The Macronesian totals may include some Azores individuals.

Form	atlantis					micha-hellis	graellsii	argenteus
Locality/ Source	Iberian	NW Africa	Macro/Canary	Azorean	atlantis overall	overall	Cramp (1983)	Cramp (1983)
wing	420.0	429.5	422.7	417.2	420.9	446.8	416.5	414.5
tail	166.6	166.0	167.5	166.3	166.7	174.7	158.0	165.0
bill	52.4	52.5	50.3	52.5	51.9	56.5	49.9	50.9
tarsus	59.9	63.3	63.9	64.0	62.3	69.2	62.7	62.8
toe	59.2	-	59.5	53.9	57.1	64.4	54.4	59.1

Table 3: Comparison of Biometrics within atlantis populations and of atlantis overall with michahellis, graellsii and argenteus.

Observations

There is remarkable homogeneity between the various atlantis forms. No separation of the forms is possible on the biometrics alone. The Azores form is not differentiated at all from the other forms of atlantis on biometrics.
There is remarkable similarity between the overall data for atlantis and the data for graellsii and argenteus.
There is a substantial difference between the overall data for atlantis and the data for michahellis. Compared to michahellis, atlantis is:

5.8% shorter in wing;
4.6% shorter in tail;
8.2% shorter in bill length;
10.0% shorter in tarsus;
11.3% shorter in toe.

Direct comparisons between michahellis and atlantis

These are particularly useful because they should avoid the uncertainty caused by slight differences in measuring techniques.

Carrera et al (1987) found Galician birds (Iberian atlantis) on average to be about 17% lighter in weight, 6% shorter in the wing, 4% shorter in the bill and 6% shorter in the tarsus than michahellis breeding in the Balearic Islands and the Charafinas Islands.

Van Swelm (2002) found using statistical tests that Berlengas birds (Iberian atlantis) were significantly smaller than Camargue birds (michahellis). In respect of weight, tarsus, middle toe, head + bill, bill height at gonys and bill height at base, van Swelm found that the differences were significant between birds of the same sex at the 0.001 level using ANCOVA tests. Three measurements, tarsus, bill height at base and tarsus + toe were significant at the 0.010 level across both sexes.

Conclusions

The biometric evidence is compelling for treating atlantis and michahellis as separate taxon.
The shorter tarsus, bill length and bill height at base of atlantis appear to be useful field marks for identification purposes.
The geographical definition of atlantis adopted in this study is supported by the homogeneity in biometrics across the whole region including the Azorean form.

atlantis is similar to graellsii and argenteus in biometrics.

Further work:

Biometrics for cantabricans would be very useful for comparison with Iberian atlantis and argenteus.

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