Northern Pacific Rattlesnakes mate bimodally. This means that they have two mating seasons: the spring and the fall. I was hoping to see mating activity last weekend, but instead I saw nothing. However, I did track several females to the exact same burrow as males. I found many male-female pairings and I found one two male-one female cluster. Although I could not see the snakes, I suspect they could be mating in shelter.
I also noticed that most of my snakes were hidden within rocky outcrops. This is strange for my site because there are very few of these. In the summer, snakes mainly hide in abundant squirrel burrows, but I did find that they tended to overwinter in the outcrops. This makes me wonder if they are moving to their overwintering sites early. Normally overwintering ("hibernation") begins in November and lasts through March. Check out the nice outcrops the snakes were in:
One snake in here:
One male and one female shacked up here:
TWO males, one female here:
The weekend wasn't a total loss though. We saw a nice little spider crossing the road and found that one of our females gave birth:
Tarantula!
A little baby outside its den:
Who knows what the snakes were up to? Maybe it was just too hot of a weekend. So much for me collecting venom...
Maybe they're using the dens to find each other? Western diamond-backed rattlesnakes also have a bimodal breeding season and mate in the spring as they emerge from their dens (when they den together). In the fall they mate before they head back to their den, but perhaps there's a reason your snakes need to arrive at the dens earlier. Anyway, interesting observation, although I'm sure it was a frustrating one to make!
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