Vultures on the beach

Taking a lesson from the Oroville dam almost-catastrophe, water levels in the Vasona reservoir south of San Jose, CA, have been lowered substantially prior to the next series of storms expected this weekend.

Vasona Reservoir, CA

The water in Vasona Reservoir is quite muddy, with a high volume coming in from highly eroded banks upstream.  The lake level is low enough now to expose some minor gravel islands, though.

Apparently, fish stranded in some of the back channels of the reservoir became fodder for the local bird life.  Turkey Vultures, seagulls, crows, and even a rarely seen Bald Eagle have been spotted feeding on the fish carcasses the past couple of days.

A “venue of Vultures” (I.e., a group of them) were still present picking over the last remains of a few fish this morning.

Turkey Vultures, Vasona reservoir, CA

Turkey Vultures:  where you see one, you usually find many

The weather wasn’t chilly, but when the sun emerged from behind some low clouds, the Vultures immediately began basking, backs to the sun and spreading their wings wide.  First one, then another and another…

Turkey Vultures basking

Does one Turkey Vulture copy another?  Coordinated basking behavior…

Turkey Vultures basking

Turkey Vulture show-off  — “I’m so pretty, oh, so pretty…”

Turkey Vulture take-off

Turkey Vulture taking off.  If you can ignore the naked red head, they are kind of pretty, especially those long, black and white wings.

Basking for warmth

It’s difficult to get any warmth out of a January sun at this latitude, especially on days when the high temperature for the day is in the negative digits.  The squirrels finally made an appearance in the backyard by late morning, but they favored clinging to vertical surfaces where they could maximize the amount of sun hitting them.

gray squirrel with amur maple seeds-

After collecting a few of the Amur Maple seeds still present on a nearby tree, this gray squirrel paused for several minutes to warm up, pressing its body tightly to the trunk of a walnut tree.  Oops, it looks like one seed escaped and has fallen out of the squirrel’s mouth (behind its ears).

gray squirrel eating amur maple seeds-

Assuming the Nuthatch posture (head down), the squirrel proceeded to eat (or husk) the seeds). I wonder if it was warmer in this position?

I’ve often seen squirrels performing this kind of behavioral thermoregulation on extremely cold days.  In fact, you often see humans do the same thing, while waiting at a bus stop in cold weather — turning their backs to the sun to soak up the heat. Increasing their surface area by pressing their bodies flat on the tree trunk probably helps the squirrels gain a few extra quanta of heat from that weak sun.

Basking tree

The trunk and top branches of the Buckeye tree outside my (somewhat dirty) porch windows are brightly illuminated with the morning sun, making it the perfect place to bask in whatever heat the sunlight can provide on this chilly morning.

A chilly start...

A chilly start…

Early in the morning, I’ve noticed a variety of birds and squirrels using the buckeye as a basking spot.

You don't normally see White-breasted Nuthatches at rest in this posture (head up).  Notice how the bird is plastered right up next to the trunk of the tree with its feathers maximally fluffed.  Is it possible that the tree surface is actually "warm"?

You don’t normally see White-breasted Nuthatches at rest in this posture (head up). Notice how the bird is plastered right up next to the trunk of the tree with its feathers maximally fluffed. Is it possible that the tree surface is actually “warm”? (well, probably warmer than the air…)

Red-bellied Woodpeckers apparently like the buckeye as a basking spot as well.

Red-bellied Woodpeckers apparently like the buckeye as a basking spot as well.  This bird was sitting at rest, not foraging in this spot.

Even the much, much larger-bodied Gray Squirrels enjoy a little basking time on the trunk of the tree when the temperatures dip into the -20 F range.

Even the much larger-bodied Gray Squirrels enjoy a little basking time on the trunk of the tree when the temperatures dip into the -20 F range. Belly and tail are plastered tightly to the trunk of the tree to soak up whatever warmth it can provide.

Usually we associate basking behavior with reptilian thermoregulation — sun-loving turtles and lizards, for example.  Even crocodilians lie around in the sun letting its heat warm them while they digest their latest meal.  But basking becomes important to birds and mammals as a means of economizing on the high metabolic expense of staying warm in extreme cold.

Here's a bird that specializes in basking to warm up on cool mornings.

Here’s a bird that specializes in basking to warm up on cool mornings.

Basking squirrels

Even though the air temperature was well below 0F for most of the day, the squirrels were out looking for goodies.  Unlike their usual ground foraging activity, today their efforts seemed to be restricted to the trees.  Something I have never seen these squirrels do before:  flatten themselves against the tree and sit still for several minutes at a time.  I think they must have been trying to pick up some heat from solar radiation.

basking gray squirrel

This squirrel stayed in this position for more than 10 minutes.

This squirrel stayed in this position for more than 10 minutes.

I couldn’t find much in the science literature about basking behavior in gray squirrels, but there are other species of squirrels that definitely use this strategy to reduce metabolic costs in extreme cold weather.  Rather than remain inactive in their nest, the squirrels have opted to utilize whatever warmth the weak sunlight provides and hope they can remember where they stashed a few of their nuts for a quick snack.

Turtle-day

A balmy 70 degree day with bright sun brought the turtles out of the pond mud en masse.  Rounding the corner of the pond just 200 yards from my back door, I came across this sight.

On every limb hanging over or dipping into the pond, Painted Turtles were stacked up like coins, with heads pointed upward.

Basking to increase their body temperature helps turtles digest food, grow quickly, mature their eggs, etc.  Usually they orient themselves perpendicular to the incoming solar radiation to maximize their heat gain.  As they heat up, they might change position to reduce heat gain and regulate a steady body temperature.

You can just barely see the red edging on their upper (carapace) shell and there is a hint of the red that covers their bottom (plastron) shell, which gives them their name — painted turtle.  Here is a better shot of that colorful part of their anatomy from the National Park Service website for reptiles on Niobrara Prairie in Nebraska (http://www.nps.gov/niob/naturescience/reptiles.htm)

Painted turtles are probably the most common freshwater turtle species in North America, found in slow moving fresh water from southern Canada to Mexico, and from the west to east coasts.  They are omnivorous, consuming algae as well as crustacean prey.  Adults are relatively immune to predation themselves as they withdraw all their vulnerable parts into their shell, but their eggs and hatchlings are favorite food items of all sorts of mammalian predators (fox, raccoon, etc.).

Although superbly adapted to an aquatic existence, even in winter when they “bruminate” in the mud of the lake bottom, females must leave their ponds or streams to lay a clutch of eggs in a sandy nest in early summer.  This might require crossing a road or field to find an appropriate nest spot, and some of them end up under the wheels of passing cars in the process.  Nevertheless, judging from the number of turtles basking on the shoreline of this small pond, the population seems to be doing quite well.