Biometric variability and sexual size dimorphism in the Great Knot Calidris tenuirostris

Figures & data

Figure 1. Location of bird ringing site in the Khairusova-Belogolovaya estuary (black dot). Dark grey area indicates the breeding range of the Great Knot (according to Tomkovich 2021).

Figure 2. Distribution of the most dimorphic trait, the wing length, of males (black bars) and females (grey bars) of adult and juvenile Great Knots. The median (dot) and interquartile range (rectangle) are given above.

Figure 3. Relationship between the two most dimorphic traits, the wing length, against the bill length in male (black dots) and female (white dots) Great Knots. The ellipses show the 95% prediction intervals for a single observation, given the parameter estimates for the bivariate distribution computed from the data for males (solid line) and females (dashed line).

Table I. Differences in mean linear measurements between male and female Great Knots, with the sexual dimorphism index (SDI) expressed in per cent according to the modified Lovich and Gibbons (1992) equation.

Measurement [mm]	Males			Females			t-test		SDI
	Mean	SD	N	Mean	SD	N	t	p
Adults
Wing length	187.7	4.06	565	193.1	3.86	117	13.10	<0.001*	2.9%
Tarsus length	35.99	1.15	537	36.07	1.13	116	0.69	0.491	0.2%
Bill length	42.00	1.71	566	42.48	1.80	117	2.76	0.006	1.1%
Head length	74.06	1.85	566	74.90	2.03	117	4.39	<0.001	1.1%
Juveniles
Wing length	181.7	4.31	137	187.3	3.93	92	10.03	<0.001	3.1%
Tarsus length	35.35	1.07	84	35.22	1.02	65	0.77	0.443	−0.4%
Bill length	36.10	1.98	137	36.11	2.06	92	0.02	0.988	<0.0%
Head length	67.68	2.28	137	67.59	2.44	92	0.28	0.780	−0.1%

* Cochran–Cox test results instead of t-test.

Table II. Age dimorphism index (ADI) in males and females of the Great Knot.

Measurement	Males	Females
Wing length	3.2%	3.0%
Tarsus length	1.8%	2.4%
Bill length	14.0%	15.0%
Head length	8.6%	9.8%

Table III. Equations for calculating discriminant scores. The percentage of birds correctly sexed is given according to squared mahalanobis distances from each sex-group centroid. WL – wing length, BL – bill length, THL – total head length.

Equation	Correctly sexed
	Males	Females	All
Adults
D1 = 0.265 WL − 0.237 BL − 41.397	75%	71%	74%
D2 = 0.244 WL − 0.026 THL − 48.037	75%	75%	75%
D3 = 0.248 WL − 46.824	76%	75%	76%
D4 = 0.869 BL − 31.281	54%	46%	53%
D5 = 0.531 THL − 39.406	58%	60%	58%
Juveniles
D6 = 0.240 WL − 44.195	76%	76%	76%

Tomkovich PS. 2021. Great Knot Calidris tenuirostris. In: Pavlov DC, editor. Red data book of the Russian Federation. Vol. Animals. 2nd ed. Moscow: All-Russian Research Institute for Environmental Protection (ARRIEP). pp. 738–739. (in Russian).

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Lovich JE, Gibbons JW. 1992. A review of techniques for quantifying sexual size dimorphism. Growth, Development and Aging 56:269–281.

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