Sunning themselves in heaps, knots, and snarls: the extraordinary abundance and demography of island watersnakes

Snakes represent a sizable fraction of vertebrate biodiversity but until recently, data on their demography has been sparse. Consequently, generalizations regarding patterns of variation are weak and the potential for population projections are limited. We address this information gap through an analysis of spatial and temporal variation in demography (population size, annual survival, realized population growth) of the Lake Erie Watersnake, Nerodia sipedon insularum, and a review of snake survival more generally. Our study spans a period during which the Lake Erie Watersnake was listed as threatened under the U.S. Endangered Species Act, recovered and was delisted. We collected capture-mark-recapture data at 14 study sites over 20 years, accruing 20,000 captures of 13,800 individually marked adults. Lake Erie Watersnakes achieve extraordinary abundance, averaging 520 adults/km of shoreline (ca. 260 adult/ha) at our study sites (range = 160-1600 adults/km; ca. 80-800 adults/ha) and surp...