Stable isotopes reveal differences in diet among reed bunting subspecies that vary in bill size

Research output: Contribution to journalArticle

Abstract

Reed bunting Emberiza schoeniclus subspecies vary considerably in bill size and shape and seem to be at an early stage of speciation, in which bill might be indirectly causing reproductive isolation. Hence, we evaluated whether bill size, as well as age and sex, are associated with foraging niche in three west European subspecies of reed bunting: the thin-billed schoeniclus, the intermediate-billed lusitanica and the thick-billed witherbyi. Blood sampling was undertaken at three sites in southwest Europe during the winter (when these subspecies co-occur), and stable isotope analyses (carbon and nitrogen) were performed to assess their foraging niches. Stable isotope analyses of potential food items confirmed uniform baseline isotopic composition among sites. schoeniclus showed a significantly broader isotopic niche than lusitanica and witherbyi, which seemed otherwise similar despite the fact that witherbyi is more divergent in bill traits. Stable isotope ratios were consistent with the latter two subspecies feeding on C3-plant-feeding insects, whereas schoeniclus diet also included C4 plant material. Despite its lower sexual dimorphism, sex and age differences were found only in schoeniclus, but these differences vary between locations in a complex manner. Our results suggest that bill size and shape differentiated between northern, migratory and southern, resident subspecies as a consequence of natural selection through competition during the winter, which is now reflected in isotopic niche divergence between subspecies. The potential roles of sexual selection, reed thickness and summer temperature on the difference in bill size (and greater sexual dimorphism) between lusitanica and witherbyi are discussed.

Details

Authors
  • Júlio Manuel Neto
  • Luís de Oliveira Gordinho
  • Benjamin Vollot
  • Marcial Marín
  • Juan S. Monrós
  • Jason Newton
Organisations
External organisations
  • University of Porto
  • Lund University
  • Parc ornithologique de Pont-de-Gau
  • University of Valencia
  • University of Glasgow
Research areas and keywords

Subject classification (UKÄ) – MANDATORY

  • Evolutionary Biology
Original languageEnglish
Pages (from-to)284-294
JournalJournal of Avian Biology
Volume48
Issue number2
Early online date2016 Jul 29
Publication statusPublished - 2017 Feb
Publication categoryResearch
Peer-reviewedYes