The winter dens pine snakes left and returned to

Following individuals across decades

Joanna Burger and Robert Zappalorti followed winter-den use from 1986 through 2012. Their 2015 analysis included 120 snakes of known age encountered at least twice. Only 23 percent always returned to the same hibernation site. Females showed greater fidelity than males, and older snakes were more likely to have changed sites. Burger and Zappalorti, hibernation-site philopatry (2015).

The denominator matters. These were repeatedly encountered individuals, not every snake in the Pines. A snake missing from a monitored den might have died or moved elsewhere. The researchers explicitly discuss that uncertainty, which prevents a simple conversion of absence into a mortality count. Burger and Zappalorti, hibernation-site philopatry (2015).

An empty den was not necessarily abandoned

A separate study followed seven hibernacula from 1986 through 2011. Some sites went unused for years, with gaps as long as a decade, before snakes occupied them again. A den without snakes in one monitored year was occupied the next year in 22 of 58 observed cases. Apparent abandonment sometimes followed intrusion by a predator. The authors argued that the long intervals made short surveys a poor guide to a den’s lasting value. Burger and colleagues, long-term hibernaculum use (2012).

These were intensively monitored research dens, some with reconstructed chambers. Researchers excavated them each spring, returned snakes to the tunnels, and withheld exact locations because of collection risk. The findings should not be read as a random survey of every possible den in the Pines. Burger and colleagues, study methods.

Together the studies distinguish loyalty by an individual snake from continued use of a place by a population. A den can remain valuable even as its occupants change, and an animal can return after intervening winters elsewhere. That is a conservation lesson grounded in repeated observation rather than a claim that every snake returns to one permanent underground home. Burger and colleagues, long-term hibernaculum use (2012).