Evidence of a dominance hierarchy in captive Caribbean flamingos and its relation to pair bonding and physiological measures of health

• Captive flamingos are capable of forming semi-linear dominance hierarchies.
• Flamingos that instigate agonistic encounters are more likely to win those encounters.
• Paired flamingos maintaining strong pair bonds were more dominant within the flock.
• Dominant Caribbean flamingos appeared to be less stressed than subdominant birds.

Caribbean flamingo social structure, how pair bonds affect the structure of the flock, and how social stress affects health measured by heterophil to lymphocyte ratios (H/L) were investigated at the Philadelphia Zoo. It was hypothesized that a hierarchy may become apparent by analyzing agonistic interactions and that paired individuals would share similar places within the hierarchy. Furthermore, it was hypothesized that a negative relationship between H/L ratio and dominance would exist. Forty observations were conducted and in 70% of interactions instigating bird(s) won the encounter, suggesting either some advantage for instigating birds or a prior expectation of an encounter's outcome based upon an understanding of the flock's hierarchy. The flock possessed a semi-linear hierarchy (in terms of wins/losses) and birds with higher pair-bond strengths maintained dominant positions, suggesting that pair-bonding may help individuals become more successful in agonistic encounters. Birds who won more often had higher lymphocytes percentages and analyses suggested a trend indicating dominant birds may be less stressed. A semi-linear hierarchy was also found in terms of initiation/being targeted, and a bird's rank on the dominance (wins/losses) and initiate/target hierarchies were positively correlated, suggesting that subdominant birds were targeted by dominant birds more frequently than vice versa.