Morphometrics and stable isotopes differentiate wintering populations of a migratory bird

Abstract

Background: Describing migratory connectivity in mobile animals is crucial for understanding the selective pressures acting on different populations throughout their life cycle. Tracking single individuals has provided valuable data, but for most species the data available are still spurious and usually limited to a few individuals. Since different populations of migratory birds can be distinguished by a combination of morphometric measurements and the isotopic composition of their feathers, it is possible to measure these parameters on a large sample to differentiate populations.

Methods: We studied northern wheatears, Oenanthe oenanthe, captured in their African wintering range and applied discriminant analyses on morphometric measurements and stable isotope signatures to determine whether birds found in different areas were distinguishable from each other.

Results: Morphometric and isotopic measurements alone were not sufficient to discriminate between the birds of ssp. oenanthe from different areas in Africa. When combining the two measurements, however, assignment to the different groups became substantially more accurate. Following the discriminant analysis of morphometrics and δ(2)H, δ(13)C, and δ(15)N isotopes signatures, 19 of 20 oenanthe from Kenya, 15 of 20 oenanthe from Mali/Mauritania, and 19 of 20 oenanthe from Niger were assigned correctly to their wintering area.

Conclusions: Our results show that birds at different wintering sites can be distinguished from each other when using a combination of markers. We discuss the possible breeding origins of these wintering birds.

Keywords: Connectivity; East Africa; Oenanthe oenanthe; Sahel; Wintering.

Fig. 1

Map of the study sites in sub-Saharan Africa. Area 1 represents Mauritania/Mali, area 2 represents Niger and area 3 represents Kenya. M1: Boucle de Baoulé (14.31°N; 8.18°W); M2: 30 km S of Nioro (15.03°N; 9.37°W); M3: 20 km N of Nioro (15.37°N; 9.43°W); M4: 80 km W of Ayoun (16.43°N; 10.36°W); M5: Massif de Bellar (17.38°N; 11.98°W); M6: 30 km E of Aleg (17.29°N; 13.71°W); N1: Tibiri (13.58°N; 7.04°E); N2: Takieta (13.69°N; 8.58°E); N3: Tanout (14.61°N; 8.75°E); N4: Abalak (15.42°N; 6.19°E); N5: Awillikiss (14.24°N; 5.36°E); K1: Mpala Research Centre (0.33°N; 36.90°E)

Fig. 2

Discriminant analysis ordination for oenanthe males from different study sites using morphometric measurements only or morphometric and isotopic measurements combined. Morphometrics only: LD1 = −0.54*Tarsus-0.08*Wing chord-0.84*Bill length-0.50*Bill width + 0.37*Bill depth-4.50*c2-0.53*c3; LD2 = −0.13*Tarsus + 0.22*Wing chord-0.41*Bill length-2.40*Bill width-1.86*Bill depth + 5.13*c2-0.27*c3. Morphmetrics and isotopes: LD1 = −0.26*Tarsus-0.27*Wing chord-1.03*Bill length-0.35*Bill width-0.91*Bill depth-1.09*c2-1.21*c3-0.09*δ²H + 0.26*δ¹⁵N + 0.02*δ¹³C; LD2 = 0.36*Tarsus + 0.13*Wing chord + 0.66*Bill length-0.80*Bill width-0.67*Bill depth + 5.97*c2 + 0.06*c3-0.04*δ²H + 0.25*δ¹⁵N + 0.15*δ¹³C. Red: Mauritania/Mali, blue: Niger, black: Kenya

Fig. 3

Discriminant analysis ordination for oenanthe females from different study sites using morphometric measurements only or morphometric and isotopic measurements combined. Morphometrics only: LD1 = −0.53*Tarsus-0.32*Wing chord-0.41*Bill length + 2.36*Bill width + 2.79*Bill depth-4.22*c2-0.57*c3; LD2 = 0.92*Tarsus-0.01*Wing chord-1.30*Bill length + 3.15*Bill width-2.78*Bill depth-2.36*c2 + 0.97*c3. Morphometrics and isotopes: LD1 = −2.68*Tarsus-0.01*Wing chord + 0.89*Bill length-1.31*Bill width + 1.97*Bill depth-5.63*c2-6.80*c3-0.10*δ²H + 0.56*δ¹⁵N + 0.00*δ¹³C; LD2 = 0.02*Tarsus + 0.09*Wing chord-0.89*Bill length-0.99*Bill width + 0.36*Bill depth + 2.90*c2-0.39*c3 + 0.04*δ²H + 0.54*δ¹⁵N-1.02*δ¹³C. Red: Mauritania/Mali, blue: Niger, black: Kenya