Foraging Time Investment in an Urban Population of Watersnakes (Nerodia sipedon)

—In applying foraging theory to cryptic predators like many snakes, one of the most difficult variables to measure is effort spent in foraging. We estimated foraging effort from time invested in foraging using records for habitat use accumulated over a period of three years for 50 radio-tracked adult watersnakes (Nerodia sipedon). Because watersnakes eat predominantly aquatic prey, and limited prey records for the population studied were all fish, time spent foraging was estimated from the number of records in which snakes were found in water compared to the total number of records. Based on the data collected, this population of watersnakes devoted 1.43–2.38% of its time to foraging. Although the data do not permit allocation of foraging effort for most snakes to specific times, combining all relocation data suggests that adult watersnakes in this population forage infrequently. Opportunistic records of stomach contents regurgitated by captured snakes of all sizes suggest that these watersnakes find fish prey by active foraging and that the adult population benefits from periodic exploitation of dead or dying large fish (trout) following stocking. Foraging theory assumes that animals attempt to maximize caloric and critical resource intake while minimizing the energy expended to acquire these resources. The net result of this strategy should be to provide more energy for reproduction, hence maximizing fitness (e.g., Stephens and Krebs, 1986; Perry and Pianka, 1997). Applying the theory to any particular species requires, among other things, direct or indirect measures of foraging effort. For cryptic predators, even simple measures, such as time spent foraging, can be extraordinarily difficult to measure in the field, although a common perception is that ‘‘most wild animals must spend a large fraction of their waking hours locating food and extracting it from their environments’’ (Griffin, 1992). Here we provide one indirect measure of foraging effort for one population of snakes that suggests this perception may apply less widely than