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Occasional posts - from the quirky to the momentous - on the life and times of the Methow Conservancy.
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Monday, March 19, 2018

Herpetology Course - Class #4 Rattlesnakes

Our 4-part 2018 "Conservation Course" started February 12th. Below are notes taken by Kristen Kirkby. See notes and videos from the previous classes here:
Class #1 - Herpetology Overview
Class #2 - Methow Reptiles

Class #3 - Methow Amphibians

Learn more about the Herp Course here

Class #4 -Rattlesnakes & the Methow's Northern Pacific Rattlesnake with John Rohrer, March 12, 2018


Watch and listen to the 1.75 hour lecture portion of the class on this video




Cool Terms ~ Ecdysis: Process of skin shedding
~ Ectothermic: only get heat from environment, don’t generate their own
          Thigmothermic: heat from contact with a warmer object
          Heliothermic: heat from the sun
~ Solenoglyphs: snakes with hinged front fangs
~ Viviparous: give birth to live young
~ Oviparous: young hatched from eggs


Class: Reptilia – Snakes, lizards, turtles
     Order: Squamata – Snakes and Lizards
          Suborder: Serpentes – Snakes
               Family: Viperidae – Pit vipers
                    Genera: Crotalus and Sistrurus – Rattlesnakes

There are 32 species of rattlesnakes in the world - of those 16 are in US (and territories). There are also 32 subspecies among the species.

In WA: only the Northern Pacific Rattlesnake (Crotalus oreganus oreganus), which is a subspecies of the Western Rattlesnake (Crotalus oreganus).

Federally listed (Endangered Species Act) rattlers:
~ New Mexican Ridge-Nosed (threatened) (AZ, NM)
~ Aruba Island Rattlesnake (threatened) (Aruba)
~ Eastern Massasauga (threatened) (Midwest US)

State Listed (species of concern):
~ Timber Rattlesnake (East of the Mississippi)
~ Eastern Diamondback (Southeast US)

The Rattle:The rattle is thought to have evolved as a warning to large animals, like deer and elk, so that the snakes wouldn't get stepped on. They still use the rattle as a warning today. A muscle at the end of the tail vibrates at 50x/second, shaking the "buttons" (made of keratin similar to our fingernails). The buttons are loosely connected so they shake against each other and make noise. A new segment or button is revealed each time the snake sheds it's skin. Shedding depends on growth (multiple times/year in warm, productive areas versus only 1x/year further north like in the Methow).

Food Acquisition:
~ Pit vipers have paired heat sensing organs and can detect tiny temperature differences (0.002 degrees F) at close range
~ Short-sighted, see varying shades of heat
~ Use venom to subdue prey; venom glands behind eyes give triangular shaped head
~ Venom is a mix of hemotoxin (destroys blood cells) and neurotoxin (affects nerves)
~ Sit and wait to ambush predators, then reach out, strike, and inject venom, then sit back and wait for the venom to take affect (less opportunity for injury from fighting prey). Then they use their tongue to smell/track prey down, and eat it whole.
~ Primarily eat rodents (baby rattlers eat lizards)

There are approx. 9000 venom bites/year in US (all venomous snakes not just rattlers); most happen in the Southeast, and most people are trying to catch or kill the snake. Of these, there are only about 5 fatalities per year, and this is typically because these victims choose not to get treatment or delayed it too long. 25-50% of rattlesnake strikes are dry (no venom). Treatment is antivenin

Snake Fungal Disease (Ophidiomyces ophidiicola) was identified in 2006 in Timber Rattlers in New Hampshire, found mostly in the East, and Midwest; it has not yet found in West. The disease may be linked to a warming climate, 5-15 degrees C is too cold for fungus growth, but folks have seen outbreaks in warmer dens.

North Pacific Rattlesnake (Crotalus oreganus oreganus)

Lives in British Columbia, WA, OR, ID, and CA. There are no protections in any state, so anyone can kill them anytime.

Live primarily east of the Cascades; in the Methow they live valley bottom (core habitat), and somewhat up in the hills (peripheral habitat)

Tan to green coloring, with blotches on dorsal surface; broad triangular head; typically 30-40” long and up to 60” (largest found in the Methow was 47”, 1093 grams).

They are ectothermic, so they only get heat from their environment; they can't generate their own heat like we can. But this also means they use and need a lot less energy (food). They use 1/5 to 1/10 of the energy requirement of a similar sized "endotherm" (a creature like a mammal or bird that). Consequently, they have a much broader range of suitable body temperatures, however they do need to maintain a temp above freezing (and 85-90 degrees is the optimal body temperature, physiologically).

So, they are challenged in northern latitudes: There's a short growing season; they need winter refuge (underground den), and they have a seasonal migration.

They den from roughly mid-September to mid-April, and dozens to hundreds of snakes are in a communal den. Individuals generally use the same den their whole lives. Den sites are 6-8 feet underground (under frost line). They need air flow and shelter from precipitation, so they require unique conditions. Most local dens are on talus slopes with rock outcroppings (~35 dens are known in the Methow).

Historical documents outline people killing 350-400 rattlesnakes from a den in Pateros (1930), even 1000 at one site. In 1952, someone documented killing 259 in one day at a site on Leecher Mountain.

Methow Research
John and others wanted to find dens, so they started radio-tagging rattlers with a transmitter to detect their location, and sometimes with an internal sensor to log body temperature.

They found that rattlers are active with temperatures of 60 degrees and sun. Individuals start coming out of their dens in April, but only a subset (15-20%) will come out of the den each day to sun nearby, and all leave their dens by mid-May.

Females always return to the same den, but males forage until mid-July, and then search out the track of a female to follow her back to her den and to mate.

Females give birth to 4-10 babies for the first time at 6-9 years old, and then every 1-3 years (need recovery time). Methow Valley females reproduce after 8 sheds. They give birth in late-August to early-Sept, and while it was once thought that the young were immediately on their own, research now shows that mom stays with the baby snakes for a week to 10 days, then she goes back to her communal den (if she's not already there), and the young snakes follow the mom’s smell to the den and imprint on it.

A rookery is a group of pregnant females that hang out and stay warm together.

N.P. Rattlers live up to 20 years (Timber Rattlers found to live up to 45 years)

Males have longer tales (length from vent), usually 3.5 cm+
Females have body constriction at vent, tail less than 3.5 cm
Other study findings:
~ Nuisance snakes that were relocated to new dens had the same recapture rate as snakes native to a den~ Dens affected by fires (e.g. Carlton Complex) showed no difference in growth rate than unaffected dens the following year, but rattlesnakes in fire areas were smaller (meaning larger snakes may have died), and showed some burn scars
~ Some difference in crypticism and color between females and males from Methow and Columbia, but not statistically significant findings.

Respect and appreciate your snake neighbors!

1 comment:

  1. nice blog
    great information.
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