ewer than 40,000 lions are left in Africa, perhaps 40% of which reside in Tanzania. Lions in East Africa are commonly killed in situations where they prey on livestock, either to retaliate for loss or avert future attacks. Among the Sukuma, Tanzania’s largest cattle-raising ethnic group, tradition allows a lion killer to visit households, perform a special dance, and demand rewards for ridding the area of a potentially dangerous predator. Here we document how this tradition of gift-giving provides sufficient economic incentive that lion killing continues to persist in the face of a near absence of livestock loss from lions. Contemporary lion killers no longer act as avengers, retaliating for loss or averting future attacks, but as hunters, pursuing non-threatening lions far from residential and grazing areas and often inside protected areas. Our study reveals that Sukuma householders are less likely to reward a lion dancer if they have received frequent visits from dancers (indicative of donor fatigue) and if they perceive change in motivation from avenging to hunting. These findings suggest that it may be possible to reduce illegal killing of lions by working through Sukuma institutions responsible for collective action within the local community, and to remove the economic incentive for killing non-problem lions. Keywords: Community-based conservation, Lion-killing, Panthera leo, Collective action, Retaliation, Sukuma, Tanzania.