Assessing the impact of spring hunting on waterfowl populations

Harvesting prior to the breeding season is widely considered 'unwise' since it has the bearing of deducting from the capital. However, spring hunting is still a common practice in many parts of the world, and its true effects remain uninvestigated. We present a model to investigate the range of poss ible effects of spring harvesting on waterfowl populations. The cost of spr ing harvesting is defined as corresponding loss in harvest opportunities in autumn; this cost may be sex-specific. Factors increasing the cost are mon ogamy, high breeding output, high summer survival and weak density dependen ce in summer, such that the population is mainly regulated through winter c onditions. If the relative success of unpaired individuals is high (as in p olygynous species if males are abundantly available after spring hunting), the cost of killing females may increase while that of killing males is red uced. Spring sex ratios may be more important in determining the cost than whether hunting occurs before of after pairing. Killing males can have surp risingly high costs and they may even exceed the cost of killing females if sex ratios are female-biased.