Sex-related migration distances in the dimorphic Eurasian Bittern Botaurus stellaris breeding in The Netherlands
van der Winden, J.; Hogeweg, N.; Shamoun-Baranes, J.; Piersma, T. (2019). Sex-related migration distances in the dimorphic Eurasian Bittern Botaurus stellaris breeding in The Netherlands. Ardea 107(3): 283-290. https://doi.org/10.5253/arde.v107i3.a1
In: Ardea. Nederlandse Ornithologische Unie: Arnhem & Leiden. ISSN 0373-2266; e-ISSN 2213-1175, meer
In many bird species intraspecific variation in migration strategies is related tosex or size. The Eurasian Bittern Botaurus stellaris is a sexually size-dimorphicheron species with a vast breeding and wintering range spanning a range ofclimates. Ringing data show that Bitterns from northern populations migratewestwards or southwards over thousands of kilometres, while Bitterns fromsouthern or temperate breeding areas migrate much shorter distances or remainresident. So far, any differences in the migrations of males and females haveremained unstudied. In temperate climates, relatively benign winters alternatewith the occasional harsh winter, and under these conditions, males as thelarger sex might take the risk to stay rather than show seasonal migration. In theyears 2010–2012 we equipped three females and three males from breedingareas in The Netherlands with a tracking device, recording their movementsover periods of 2–5 years. All three males and one female stayed within or nearthe breeding area during the non-breeding season, but two females moved todistant wintering sites. One female migrated 4900 km to The Gambia providingthe first direct evidence for trans-Saharan migration in this species. Anotherfemale migrated 700 km to winter in Devon, UK, for five consecutive years. TheBitterns were site-faithful to their breeding area and, mostly, to their winteringareas as well, although one male and one female progressively wintered closerto the breeding area in three successive years. Our results suggest that largermales from The Netherlands, a breeding area with fluctuating winter conditions,are predominantly resident, while the females are partial migrants with individuallydifferent and flexible strategies.
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