This is the time of year when female Prairie rattlesnakes in Alberta, SK & Mont become pregnant. They mated last summer in July, Aug or Sep but they didn't become pregnant then. The sperm was stored in a cavity known as a spermathecae and was used to fertilize the ova right now.

The ova weren't mature at the time of mating but are at this time of year. Once the eggs are fertilized, the female leaves the over-wintering den and seeks out a birthing den or rookery where she spends her summer maturing the eggs developing within her body. In late summer,

when she believes her eggs are going to hatch (Aug or Sep) she'll shed her skin and then give birth to live offspring as the eggs hatch inside her, a process known as ovovivipary. She'll stay with her brood until they have shed their skin for the 1st time, usually within 2 weeks.

This is a photo of a gravid (pregnant) female Prairie rattlesnake at her rookery. She spent her time last summer moving between sun and shade (shade offered by broom or snake weed) or in a nearby hole to escape the sun, bad weather, or predators. Births occurred in late Aug.