The trade-off theory between reproductive effort and parasite defense predicts that parasite intensity would increase with increment of reproductive cost. A breeding population of the Bull-headed Shrike Lanius bucephalus on Minami-daito Island in subtropical region have exhibited much higher prevalence of avian malaria parasites (96.2%, n = 78) than that of a northern population in Nagano Prefecture, Japan (5.6%, n = 54). In addition, we found that 58.7％ of breeding shrikes (n = 75) on Minami-daito Island had the throat swelling perhaps caused by Hamatospiculum sp. (Nematode). The size of the swelling was positively correlated with parasite intensity of avian malaria parasites in both sexes. In male Bull-headed Shrikes, the parasite intensity of avian malaria infection increased as the number of fledglings increased. On the contrary, in females, the parasite intensity decreased with increase of the number of fledglings. The mechanisms underlying the trade-off between reproductive efforts and parasite defense may be sex-specific. These findings are important to understand the impact of infectious diseases on life-history evolution.