title: Seasonal rainfall at long-term migratory staging sites is associated with altered carry-over effects in a Palearctic-African migratory bird.
abstract: An understanding of year-round habitat use is essential for determining how carry-over effects shape population dynamics in long-distance migratory songbirds. The recent discovery of long-term migratory staging sites in many species, prior to arrival at final wintering sites, adds complexity to efforts to decipher non-breeding habitat use and connections between sites. We investigated whether habitat conditions during migratory staging carry over to influence great reed warbler (Acrocephalus arundinaceus) body condition at final wintering sites in Zambia. We asked whether the presence/absence and strength of such carry-over effects were modified by contrasting rainfall conditions during 2 years.
  
  
  
  First, we found that individuals staging in a dry year had higher corticosterone (CORTf) and stable nitrogen isotope values (suggesting higher aridity) than birds staging in a wet year, indicating that regional weather affected staging conditions. Second, we found that carry-over effects from staging habitat conditions (measured via carbon and nitrogen isotopes) to final winter site body condition (measured via scaled mass index and β-hydroxybutyrate) were only present in a dry year, suggesting that environmental factors have consequences for the strength of carry-over effects. Our results also suggest that wet conditions at final winter sites may buffer the effects of poor staging conditions, at least in the short term, since individuals that staged in a dry year had higher scaled mass indices in Zambia than individuals that staged in a wet year.
  
  
  
  This study provides a first insight into the connections between long-term migratory staging sites and final wintering sites, and suggests that local environmental factors can modify the strength of carry-over effects for long-distance migratory birds.
authors.affiliation: Department of Zoology, University of Cambridge, Cambridge, CB2 3EJ, UK. marjoriesorensen@gmail.com.
authors.forename: Marjorie C
authors.identifier: 0000-0002-5556-0502
authors.initials: MC
authors.lastname: Sorensen
authors.affiliation: Department of Biology, University of Saskatchewan, Saskatoon, S7N 5E2, Canada.
authors.forename: Graham D
authors.initials: GD
authors.lastname: Fairhurst
authors.affiliation: Swiss Ornithological Institute, Sempach, Switzerland.
authors.forename: Susanne
authors.initials: S
authors.lastname: Jenni-Eiermann
authors.affiliation: NERC Life Sciences Mass Spectrometry Facility, Scottish Universities Environmental Research Centre, Rankine Avenue, East Kilbride, G75 0QF, UK.
authors.forename: Jason
authors.initials: J
authors.lastname: Newton
authors.affiliation: Limnological Institute, University of Konstanz, Mainaustrasse 252, 78464, Constance, Germany.
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Yohannes
authors.affiliation: Department of Zoology, University of Cambridge, Cambridge, CB2 3EJ, UK.|DST-NRF Centre of Excellence at the FitzPatrick Institute, University of Cape Town, Cape Town, South Africa.
authors.forename: Claire N
authors.initials: CN
authors.lastname: Spottiswoode
mesh_terms: D025041:Animal Migration; D000818:Animals; D017753:Ecosystem; D005260:Female; D008297:Male; D011157:Population Dynamics; D011891:Rain / Q000737:chemistry; D012621:Seasons; D020308:Songbirds / Q000502:physiology*
keywords: Great reed warblers; Long-term staging; Migration; Plasma metabolites; Stable isotopes