title: A protocol to correct for intra- and interspecific variation in tail hair growth to align isotope signatures of segmentally cut tail hair to a common time line.
abstract: BACKGROUND
  In recent years, segmental stable isotope analysis of hair has been a focus of research in animal dietary ecology and migration. To correctly assign tail hair segments to seasons or even Julian dates, information on tail hair growth rates is a key parameter, but is lacking for most species.
  
  
  METHODS
  We (a) reviewed the literature on tail hair growth rates in mammals; b) made own measurements of three captive equid species; (c) measured δ(2)H, δ(13)C and δ(15)N values in sequentially cut tail hairs of three sympatric, free-ranging equids from the Mongolian Gobi, using isotope ratio mass spectrometry (IRMS); and (d) collected environmental background data on seasonal variation by measuring δ(2)H values in precipitation by IRMS and by compiling pasture productivity measured by remote sensing via the normalized difference vegetation index (NDVI).
  
  
  RESULTS
  Tail hair growth rates showed significant inter- and intra-specific variation making temporal alignment problematic. In the Mongolian Gobi, high seasonal variation of δ(2)H values in precipitation results in winter lows and summer highs of δ(2)H values of available water sources. In water-dependent equids, this seasonality is reflected in the isotope signatures of sequentially cut tails hairs.
  
  
  CONCLUSIONS
  In regions which are subject to strong seasonal patterns we suggest identifying key isotopes which show strong seasonal variation in the environment and can be expected to be reflected in the animal tissue. The known interval between the maxima and minima of these isotope values can then be used to correctly temporally align the segmental stable isotope signature for each individual animal.
authors.affiliation: Research Institute of Wildlife Ecology, University of Veterinary Medicine, Vienna, Austria.
authors.forename: Martina
authors.identifier: http://orcid.org/0000-0002-3198-1687
authors.initials: M
authors.lastname: Burnik Šturm
authors.affiliation: Smithsonian Conservation Biology Institute, Front Royal, Virginia, USA.
authors.forename: Budhan
authors.initials: B
authors.lastname: Pukazhenthi
authors.affiliation: Smithsonian Conservation Biology Institute, Front Royal, Virginia, USA.
authors.forename: Dolores
authors.initials: D
authors.lastname: Reed
authors.affiliation: Great Gobi B Strictly Protected Area Administration & Department of Zoology, School of Biology and Biotechnology, National University of Mongolia, Ulan Bator, Mongolia.
authors.forename: Oyunsaikhan
authors.initials: O
authors.lastname: Ganbaatar
authors.affiliation: Oslarija, Institute for Donkey Breeding and Research, Komen, Slovenia.
authors.forename: Stane
authors.initials: S
authors.lastname: Sušnik
authors.affiliation: Research Institute of Wildlife Ecology, University of Veterinary Medicine, Vienna, Austria.
authors.forename: Agnes
authors.initials: A
authors.lastname: Haymerle
authors.affiliation: Leibniz Institute for Zoo and Wildlife Research (IZW), Berlin, Germany.
authors.forename: Christian C
authors.initials: CC
authors.lastname: Voigt
authors.affiliation: Research Institute of Wildlife Ecology, University of Veterinary Medicine, Vienna, Austria.
authors.forename: Petra
authors.initials: P
authors.lastname: Kaczensky
mesh_terms: D000818:Animals; D002247:Carbon Isotopes / Q000032:analysis*; D003903:Deuterium / Q000032:analysis*; D018397:Equidae; D006197:Hair / Q000737:chemistry* / Q000254:growth & development*; D013058:Mass Spectrometry; D009587:Nitrogen Isotopes / Q000032:analysis*; D012377:Rodentia; D012621:Seasons; D013623:Tail / Q000737:chemistry* / Q000254:growth & development
chemical_list: D002247:Carbon Isotopes; D009587:Nitrogen Isotopes; D003903:Deuterium