Early home ranges and other news

Good news: On 25 April, I came across our Female 39, who’s transmitter had failed prematurely 19 days before. She was captured, her transmitter was surgically replaced, and she was released the next day. At her initial capture last July, she weighed 365 grams (12.9 oz) and she produced a litter of kids a couple of months later. When recaptured last weekend, she weighed 404 grams! She clearly has been hunting successfully and is in great shape to reproduce again this year. While tropical pit vipers often reproduce annually, pit vipers in temperate climates like ours often require a year or two to replenish body fat before they can sustain another pregnancy.

But annual births are not unheard of this far north. In fact, we had a female rattlesnake produce litters three years in a row in El Dorado County a few years ago. After her third litter, however, she was skin and bones and we didn’t think she would survive the winter. But she did and might have pulled through if she had not been nailed by a raptor the following spring.

One day we found her radio signal to be weak and coming from far down a canyon, well outside her typical home range. Because thick manzanita and chamise made getting to her signal very difficult, I didn’t investigate right away. Eventually, when her signal didn’t change, we burrowed through the chaparral until we got to a large live oak that stood by itself on a hillside. The snake’s transmitter was laying in the leaves under the tree, completely clean and undamaged – as if it had been surgically removed and washed! I have had telemetered rattlesnakes eaten by coyotes before but coyotes chew the transmitters. The undamaged transmitter under a lone large tree far from the snake’s last location just screamed raptor. The area was full of red-tailed hawks and there were certainly owls at night.

Back to our current study, just two males, 36 and 37, remain loose with failed transmitters. I recently shipped the other five faulty transmitters back to the manufacturer for evaluation and repair.

Last week I found one of the hollow logs frequently used by our telemetered rattlesnakes freshly ripped apart (photo below).


I’m not sure what kind of animal, besides a person or a black bear, might have ripped a log apart like that. While it is certainly not impossible for a bear to stray this far downstream, it would also be attracting attention in more obvious ways. Having encountered a visitor with a snake hook off-trail a few weeks ago, I thought this might be a good time to reiterate why I am no longer publishing plots of the study animals’ travels (as I did last year) or providing more details about where they are hanging out. Too many rattlesnake researchers have had study animals captured or killed after they disclosed their locations.

But I do want to share how far the telemetered rattlesnakes have been roaming during the first six weeks of the season. The illustration below shows the home ranges used by the seven rattlesnakes with working transmitters so far this year. The solid lines are the males and dashed lines are the females. The Effie Yeaw visitor center is in the top center and the EYNC parking lot is in the top left corner of the Google Earth photo.

HRs 02May15

The most interesting finding to me is that Females 41 and 47 have been moving as much as any of the males and much farther than some. Also remember that we lost almost three weeks’ movement on Female 39 when her transmitter failed. Male 35 had a small home range last year, primarily because he hung around in the elderberry and redbud thicket next to the bike rack for so much of the summer. He spent most of the rest of his time in the meadow – and that’s where he is again. Male 40 was the last to leave his winter shelter this spring, has not moved as frequently as the other males, and I have not found him courting any females. He has always been quite under weight for his length. He is an old guy, based on his untapered rattle and an impressive collection of scars, but he seems to be getting by.

Courtship seems to have slowed a bit in the past week, with most animals by themselves and apparently hunting, at least when I have visited. Nonetheless, there should be another month or so of courtship before the summer hiatus.







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