Data from: Baseline immune activity is associated with date rather than with moult stage in the Arctic-breeding barnacle goose (Branta leucopsis)

Variation in immune defence in birds is often explained either by external
factors such as food availability and disease pressure or by internal
factors such as moult and reproductive effort. We explored these factors
together in one sampling design by measuring immune activity over the time
frame of the moulting period of Arctic-breeding barnacle geese (Branta
leucopsis). We assessed baseline innate immunity by measuring levels of
complement-mediated lysis and natural antibody-mediated agglutination
together with total and differential leukocyte counts. Variation in immune
activity during moult was strongly associated with calendar date and to a
smaller degree with the growth stage of wing feathers. We suggest that the
association with calendar date reflected temporal changes in the external
environment. This environmental factor was further explored by comparing
the immune activity of geese in the Arctic population with conspecifics in
the temperate climate zone at comparable moult stages. In the Arctic
environment, which has a lower expected disease load, geese exhibited
significantly lower values of complement-mediated lysis, their blood
contained fewer leukocytes, and levels of phagocytic cells and reactive
leukocytes were relatively low. This suggests that lower baseline immune
activity could be associated with lower disease pressure. We conclude that
in our study species, external factors such as food availability and
disease pressure have a greater effect on temporal variation of baseline
immune activity than internal factors such as moult stage.