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A new paper by BMRS reveals secrets of male and female Song Thrushes on their spring migration

By 23 lutego 2021 No Comments

In January 2021 BMRS team published a new paper: Sex-specific differences in spring migration timing of Song Thrush Turdus philomelos at the Baltic coast in relation to temperatures on the wintering grounds in an international scientific journal The European Zoological Journal. All the three authors: mgr Michał Redlisiak, prof. Magdalena Remisiewicz and mgr Aleksandra Mazur are the members of our team and the paper is a part of Michał’s PhD thesis. The research was based on data on Song Thrushes ringed at Hel, one of Operation Baltic field stations, during spring seasons between 1968 and 2019. The main topic of the article is protandry, which is the tendency of males to arrive at breeding grounds in spring earlier than females. This enables males to occupy favourable territories and attract later arriving females. This phenomenon was previously described in many dimorphic passerine species, but not in Song Thrush, which lacks sexual dimorphism in size or colour – thus males cannot be told from females in the field. Using the discriminant functions, derived from measurements of DNA-sexed individuals, which the same authors published in 2020 (Size dimorphism and sex determination in Song Thrush (Turdus philomelos) migrating through the southern Baltic coast ), it was possible to “calculate” the sex of 1154 adult Song Thrushes, captured at Hel since 1968, from their measurements taken in the past. Then the ringing dates of these males and females at Hel were correlated with temperatures at their wintering grounds in Western Europe in months preceding spring migration. The study confirmed the protandry in Song Thrush and showed changes in protandry with time. Over the 50 years  of studies the beginning of males’ arrival at Hel shifted earlier by 19 days on average, and females’ arrival by 12 days, thus the protandry increased by 7 days on an average. The responses of temperatures of winter months differed between the sexes. For males the warmer the winter, the earlier their spring migration. For females, only February temperatures had any effect, and the warmer the February, the earlier their migration started and the later it ended. These differences likely reflect different selection pressures on each sex. The article confirms the immense value of long-term data sets – such as Operation Baltic data – in studying the responses of migrant birds to climate change. The full text of the paper is available here HERE.

Arrival dates of Song Thrush males and females in the 50 years of study. The lines indicate the arrival of the first 10%, 50% and 90% of birds (from bottom to top of the chart). The shift of the beginning of migration is clearly visible, particularly for the males.

خرید vpn سرور مجازی ترکیه سرور مجازی آلمان

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