• Kissner, Kelley J.
  • Weatherhead, Patrick J.


Understanding the trade‐off females make between offspring size and number requires knowing how neonatal size, and traits associated with size, affect survival. We studied neonatal survival in the northern watersnake Nerodia sipedon in outdoor enclosures with artificial hibernation sites. From a total of 950 neonates from 77 litters collected over 3 years, we found a survival rate of 65% between birth and hibernation and 47% during hibernation. Estimated survival from birth to the end of hibernation was 31%, comparable with indirect estimates for free‐living watersnakes. Consistent with the ‘bigger is better’ hypothesis, larger neonates and neonates heavier relative to their body length were more likely to survive both the pre‐hibernation and hibernation periods. Survival in the pre‐hibernation period also decreased with the duration of that period and varied among years. Survival during hibernation was higher in warmer winters. Mass change prior to hibernation did not affect survival during hibernation. These results suggest that an optimal reproductive strategy should exist for female watersnakes, producing a ‘consensus’ among females on the optimal size for offspring. This expectation stands in stark contrast to the pronounced variation in offspring size observed both within and among litters.


Artificial hibernation sites with enclosures were created at a beaver pond edge