Gestation has begun for pregnant females

Just a brief update to report that three or our six telemetered females (41, 39 and 53) have returned to the shelters where they have delivered broods in past years and all look quite heavy. Another, Female 66, is also stationary in a hollow log with a full abdomen but she did not reproduce last year and, since 2016 was our first year monitoring her, we don’t know where she has gestated in the past. Female 75, who did produce kids last year, is not heavy, still on the move, and looks like she will skip this year. Female 80 was on the hillside at the bluff but I have recently lost her radio signal. She was heavy and I could not palpate embryos when I replaced her transmitter in early June but she had lots of material in her GI tract which complicates the exam. Hopefully, her new transmitter has not failed…

Female 41 in the same hollow log where she gestated and delivered broods in 2014 and 2015. She took last year off and hunted throughout the summer. These images are made with our BurrowCam (actually an inspection camera made by Rigid Tools).
Radio signals from Females 39 and 53 are currently coming from this hollow log. Female 39 produced broods here in 2014 and 2015. She hung around here last year but we are not sure she produced kids; she was never very large and we never spotted babies but she behaved like she reproduced. We’re just not sure. Female 53 produced offspring here in 2015 and gestated here for a while in 2016 before moving to a shelter in the dry riverbed to give birth. Since we cannot see the rattles on these two, it is impossible to tell if these are Females 39 and 53, since other pregnant females often share this shelter. Photo with the Rigid BurrowCam.

 

Our females continue to often produce offspring during consecutive years, sometimes three years in a row before taking a year off. As mentioned before, this is not the norm for temperate-latitude pitvipers. While annual reproduction is common in the tropics where it never gets cold, the shorter warm season this far from the equator usually means that females need a year or two between broods to replace body fat before they can reproduce again. Conditions for our rattlesnakes are obviously quite good (even in past “drought” years), allowing them to replenish their weight quickly after losing 30%–50% of their body mass when they give birth.

Finally, I thought you’d find this photo interesting. Our big beautiful Male 37 was just in for his transmitter change two days ago and had obviously consumed a ground squirrel just before I captured him.

Male 37 anesthetized for surgery yesterday morning. I was surprised at how much of his meal he digested overnight… the squirrel was better defined and the bulge was even larger just a day before. This was probably a half-grown ground squirrel pup. These pups are everywhere right now, are easier for the rattlesnakes to kill, and an adult squirrel would have made a really enormous bulge in the snake. Just for reference, the rule is a “meter stick” and the snake is about 40 inches long. The small bump on his left side behind the squirrel is a bit of shed skin (actually just the corneal layer of the skin) stuck in the scar from his last transmitter surgery. Shortly after this photo, he received his fourth transmitter and was released yesterday back into the EYNC preserve.

5 thoughts on “Gestation has begun for pregnant females”

  1. Mike,
    Thank you so much for these “family” stories. It is another teaching technique to explain to visitors that we have a healthy rattlesnake population and we hardly ever see them. But they do their job well of keeping down the squirrel population.
    We will miss your reports.
    jackie delu

  2. Great information Mike. What a wonderful care taker of our Rattlesnake population. Thanks for all your effort. Bob McCleary

  3. Thanks for the always interesting updates furthering the knowledge of what we know about rattlesnakes in the wild

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