Ornis Hungarica. vol.10. (2000) p.115-121.
The autumn migration of the Hume's Yellow Browed Warbler (Phylloscopus humei) in the Altai-Mountains, Mongolia
The aim of the study was to analyse the migration dynamics and biometrical characteristics of HumeÂ´s Yellow Browed Warblers (Phylloscopus humei). During a three month period (1 August - 10 October 1996), 2120 specimens were captured and 95 were recaptured in the Mongolian Altai, in the valley of river Khovd, in a willow bush habitat. The birds were mistnetted, at standard sites throughout of the study. Wing length, third primary length, wing formula, tail length, tarsus length, bill length, body mass and fat categories were measured. Age and sex determination was not possible. According to daily capture and recapture data, two migration waves (1st: 16 August - 17 September, 2nd: 18 September - 3 October) were identified. We examined whether (1) age, (2) population differences or (3) sex differences were responsible for the existence of two waves. (1) Moulting adults were captured only in the first wave, but many more birds were captured in the first wave then in the second one (1576, 544 respectively), which suggests that young birds arrived in the first wave. (2) The study site was close to the northern border of the breeding area of this species. Differences in size, and differences in wing shape indices were not found in the two waves. (3) A bimodality was found in the distribution of wing length. The birds belonging to the second wave were bigger in all parameters. The most likely hypothesis is that the two waves are caused by males migrating later than females.