That is a great account and pics. I would agree with Dave L. that it is a
Western Terrestrial Gartersnake (which will have the western dropped off
its name soon I believe - *Thamnophis elegans*)). Most snakes will climb,
many better than others, but especially the colubrids. The aquatic snakes
will as well (the Natricinae subfamily, or family now). I worked on Guam
with the brown tree snake for a few years and they are truly arboreal with
a prehensile tail (they can raise themselves straight up from the vent to
the tip of the tail - most snakes can't perform that feat). They could
climb trees like nothing - most species struggle a bit.
You were wondering what attracted the snake. They have a keen sense of
smell and cells sluffed by the chicks and adults that drop below the nest
and in the wind attract them to the site. With brown tree snakes, an
invasive species on Guam that wiped out 9 of the 11 forest birds, trapping
was found to be much more efficient with live mice than dead mice or any
type of lure (they would eat anything - found with rib bones in them and so
on). It was attributed to the cells continually sluffed and reinforcing
the smell below the nest. The wind helps it spread giving them an
indication where it is coming from by the amount they can smell. They are
able to see and hear prey, but smell is their forte.
I also have a recent story - I was in the Dominican Republic and a
Hispaniolan Boa which was consuming, what I believed to be, a White-crowned
Pigeon (just the dark tail fan was sticking out). The boa was maybe 5-6
feet without much of a girth and fifteen feet up a tree. It was hanging
half out of a tree swallowing the pigeon which looked to be at least four
times wider than its body. Dave did a great job explaining the "hows," but
I am always amazed how efficient they are.
Great story - nature is amazing!
Fort Collins, CO
On Monday, July 9, 2018 at 1:05:14 PM UTC-6, <mvjo......> wrote:
> Yesterday some friends and I saw a shocking sight that I will not soon
> forget. I was hiking and birding at the Great Sand Dunes with some friends
> when we spotted bird activity at eye level in an aspen tree on the side of
> the trail 15 feet ahead. Flitting around the tree was a pair of alarmed
> Dusky Flycatchers. Soon, we spotted a small nest in the tree, about 4 feet
> up, with something odd sticking out of the nest. My friend said “It’s a
> snake!” Sure enough there was a 14 inch Western Garter Snake coiled around
> the nest and in its mouth was one of the three nestlings! What a shocking
> sight to see! It was quite disturbing to watch but then again, this goes on
> all the time in nature, and is rarely witnessed. We had to swallow hard,
> and watch the drama unfold. The snake stayed on the nest for a good 20
> minutes and continued to grapple with the nestling which was long since
> deceased. The bird seemed so much bigger than this small snake could
> handle. We left the scene after watching this disturbing yet amazing event
> and headed up the Mosca Pass Trail.
> Upon our return 45 minutes later, we saw the snake at the base of the tree
> with the bird nearly devoured. We left the scene under the mixed emotions
> of grief, sadness and amazement all chaotically working inside us as we
> strolled down the trail to the vehicle.
> The event sparked a number of questions. First, I never knew Western
> Garter Snakes could climb a tree so well and skillfully. I had always
> pictured them as ground-hunting predators, slinking through the grasses and
> brush. To see one in a tree definitely shattered my long-held belief.
> Secondly, how did the snake know there was food in that direction? Was it
> a keen sense of smell? Or was it the sound of chirping babies on the nest?
> I am not exactly sure.
> Thirdly, the snake was not large, being about 14 inches in length…not big
> as garter snakes go. But this snake successfully devoured the chick which
> was the size of a ping pong ball! It did take considerable time for the act
> to be completed, but I never knew snakes had such an extreme ability to
> accomplish such a feat.
> John Rawinski
> Monte Vista, CO