Phytohaemagglutinin skin-swelling test in scarlet rosefinch males: low-quality birds respond more strongly

► We performed phytohaemagglutinin test in scarlet rosefinch (Carpodacus erythrinus). ► The swelling response to PHA was dependent on basophil activity. ► The response was positively associated to size and mean growth bar width. ► The response was negatively related to carotenoid-based ornament coloration. ► Our data indicate stronger responsiveness in inferior males.