SEEN - SE European Bird Migration Network
Sex determination of robins migrating through the Soutern Baltic coast according to biometric measurements

Małgorzata Ginter1 and Michał Kaszuba2
1Bird Migration Research Station, University of Gdańsk, Przebendowo, 84-210 Choczewo, Poland
2Department of Molecular Cytogenetics, Institute of Genetics and Animal Breeding Polish Academy of Sciences, Jastrzębiec, ul. Postępu 1, 05-552 Wolka Kosowska, Poland

Robins migrating through the Polish Baltic coast were sexed by gonadal inspection (119 dead birds found in years 2001-2006) and molecular techniques (189 feather samples from birds caught in 2006). Linear measurements were taken (wing length, tail length, wing formula, bill length, total head length, tarsus length) and amount of greyness on head and side was determined. Feathers from some dead birds were also used to genetic analysis and repeatability of sexing by these two method was checked. The aim of this study was to propose measurements which could be helpful in sex determination of migrating Robins. Percentage distribution of different measurements in both sex groups was presented and averages of all measurements between sexes were compared by t-test or Mann-Whitney U-test respectively. Next conceptual models to explore possibility of sex determination based on combination of different measurements were presented by GLM method. Analysis was done for both age groups jointly as well as only for immatures and for birds sexed by both methods as well as for each method separately. The results showed that wing, tail and total head length differred significantly between sex groups (p<0.001). Among these three measurements only wing length and total head length were a decisive criterion in sexing immature birds. Ranking of models in GLM method showed that also tarsus length improved sex determination of Robins. Tarsus length and total head length index is recommended as a better indicator of body shape than total head length itself and it could be more useful in sex determination. In Fennoscandian Robins differences between sexes refer to wing length and tarsus length. In Robins migrating through the Polish Baltic coast tarsus length undirectly differ between sex groups. The results showed that females were smaller than males but they had longer tarsus. Combination of body size and body shape parameters could improve sex determination of Robins.

Created by Pronetix 2006