Social environment and immunity in male red jungle fowl

We examined the relationship between social dominance, immune response, and ornamentation in captive red jungle fowl by comparing these variables in males housed individually with a single female to those in the same males after they were placed in flocks with an unfamiliar male and three unfamiliar females. Males with larger combs before being placed in the flocks were more likely to become dominant, and dominant males’ combs grew after flock formation, whereas subordinate males’ combs shrank. Immune response as reflected in hematocrit, immunoglobulin levels, and wing web swelling (a measure of cell-mediated immunity) was stronger in males that later became dominant, both before and after flock formation, although the difference between dominant and subordinate birds was more pronounced after males were housed in the multi-male groups. Dominant and subordinate males also differed in the relationship between comb length and wing web swelling. Among dominant males, individuals with larger combs had significantly larger swellings after flock formation, whereas within the subordinate males, those with relatively larger combs had worse cell-mediated immunity than those with smaller combs. These results suggest that males of different quality pay different costs to maintain both ornamentation and immune defense.