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 m ales housed individually with a single female to those in the same males af ter they were placed in flocks with an unfamiliar male and three unfamiliar females. Males with larger combs before being placed in the flocks were mo re likely to become dominant, and dominant males' combs grew after flock Fo rmation, whereas subordinate males' combs shrank. Immune response as reflec ted 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 do minant 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 mal es, individuals with larger combs had significantly larger swellings after flock formation, whereas within the subordinate males, those with relativel y larger combs had worse cell-mediated immunity than those with smaller com bs. These results suggest that males of different quality pay different cos ts to maintain both ornamentation and immune defense.