title: Social and environmental factors modulate leucocyte profiles in free-living Greylag geese (Anser anser).
abstract: BACKGROUND
  Blood parameters such as haematocrit or leucocyte counts are indicators of immune status and health, which can be affected, in a complex way, by exogenous as well as endogenous factors. Additionally, social context is known to be among the most potent stressors in group living individuals, therefore potentially influencing haematological parameters. However, with few exceptions, this potential causal relationship received only moderate scientific attention.
  
  
  METHODS
  In a free-living and individually marked population of the highly social and long-lived Greylag goose,Anser anser, we relate variation in haematocrit (HCT), heterophils to lymphocytes ratio (H/L) and blood leucocyte counts to the following factors: intrinsic (sex, age, raising condition, i.e. goose- or hand-raised), social (pair-bond status, pair-bond duration and parental experience) and environmental (biologically relevant periods, ambient temperature) factors. Blood samples were collected repeatedly from a total of 105 focal birds during three biologically relevant seasons (winter flock, mating season, summer).
  
  
  RESULTS
  We found significant relationships between haematological parameters and social as well as environmental factors. During the mating season, unpaired individuals had higher HCT compared to paired and family individuals and this pattern reversed in fall. Similarly, H/L ratio was positively related to pair-bond status in a seasonally dependent way, with highest values during mating and successful pairs had higher H/L ratio than unsuccessful ones. Also, absolute number of leucocytes tended to vary depending on raising condition in a seasonally dependent way.
  
  
  CONCLUSIONS
  Haematology bears a great potential in ecological and behavioural studies on wild vertebrates. In sum, we found that HTC, H/L ratio and absolute number of leucocytes are modulated by social factors and conclude that they may be considered valid indicators of individual stress load.
authors.affiliation: Core Facility Konrad Lorenz Forschungsstelle for Behaviour and Cognition, University of Vienna, Grünau im Almtal, Austria; Department of Behavioural Biology, University of Vienna, Vienna, Austria.
authors.forename: Didone
authors.initials: D
authors.lastname: Frigerio
authors.affiliation: Core Facility Konrad Lorenz Forschungsstelle for Behaviour and Cognition, University of Vienna, Grünau im Almtal, Austria; Game & Wildlife Conservation Trust, The Coach House, Eggleston Hall, Barnard Castle, United Kingdom.
authors.forename: Sonja C
authors.initials: SC
authors.lastname: Ludwig
authors.affiliation: Core Facility Konrad Lorenz Forschungsstelle for Behaviour and Cognition, University of Vienna, Grünau im Almtal, Austria; Department of Behavioural Biology, University of Vienna, Vienna, Austria.
authors.forename: Josef
authors.initials: J
authors.lastname: Hemetsberger
authors.affiliation: Core Facility Konrad Lorenz Forschungsstelle for Behaviour and Cognition, University of Vienna, Grünau im Almtal, Austria; Department of Behavioural Biology, University of Vienna, Vienna, Austria.
authors.forename: Kurt
authors.initials: K
authors.lastname: Kotrschal
authors.affiliation: Core Facility Konrad Lorenz Forschungsstelle for Behaviour and Cognition, University of Vienna, Grünau im Almtal, Austria; Department of Life Sciences, Anglia Ruskin University, Cambridge, United Kingdom.
authors.forename: Claudia A F
authors.initials: CA
authors.lastname: Wascher
keywords: Age; Anser anser; Differential leucocyte count; Greylag geese; Haematocrit; Haematology; Seasonal patterns; Sex; Social status