Pheasant-tailed Jacana (Hydrophasianus chirurgus) have a polyandrous mating system, with females defending larger territories within which males compete for and defend smaller territories. The role of the sexes in territorial defense is therefore potentially complex yet remains poorly known. The sex-roles of defensive responses to intruders were monitored at Anawilundawa Ramsar site, North-Western Province, Sri Lanka, where birds encountered conspecifics and other potential predators: Purple Coots (Porphyrio porphyrio), aerial predators, and other waterbirds. Females contributed to defense, though males performed most defense. Females increased their propensity to defend as breeding progressed; by the chick-rearing phase defense was shared more or less equitably between the sexes. Females were more likely to defend against aerial predators than males, and males were more likely to defend against conspecifics than they were to other intruders. When defending against conspecifics, most male defense was directed at intruding males, and most female defense at intruding females. Defense in this polyandrous species relied on cooperation between the sexes but also on some defense specialization whereby females focussed on defending against aerial predators and conspecific females, perhaps because of their larger body size. Both female and male Pheasant-tailed Jacanas therefore contribute to parental care via their defensive activities.