Alpine marmot hibernation can start as early as which month?

Alpine marmot hibernation can start as early as October.

The alpine marmot (Marmota marmota) is a large ground squirrel of the European mountains, especially the Alps, Carpathians, Tatras, and Northern Apennines. As summer ends, marmots gather dry stems and other old plant material to line their burrows. They then prepare for a winter in which food is scarce and temperatures are severe.

Hibernation may begin as early as October and can occupy much of the year; alpine marmots may spend up to nine months in their burrows. They seal the entrance with earth and faeces, creating a protected winter chamber. Before entering, they feed heavily and build fat reserves that sustain them through dormancy.

During hibernation, their heart rate can fall to about five beats per minute, while breathing slows to roughly one to three breaths per minute. Marmots huddle with nestmates, which helps conserve heat and improves survival. The species was also successfully reintroduced to the Pyrenees in 1948 after disappearing there near the end of the Pleistocene.