The Bone Yard

Deer skull in the Bone Yard

The ground is covered with bright green grass which germinated in the fall rains.  Most days have been cool, so the new grass is still short.  The Roper taught me the cattleman's 100-degree rule:  if the sum of the daytime maximum temperature and the nighttime minimum temperature is more than 100 degrees Fahrenheit, then the grass keeps growing.  Conversely, if the sum is less than 100, the grass stops growing.  For example, last week the nighttime lows were in the 30s and the daytime highs were in the 50s, which adds up to the 80s.  No prolonged freezing weather, so the grass didn't die, it just stayed short.  For the next few weeks, any bones lying about the grasslands stand out in stark contrast to the bold green turf alluding to prior struggles between predator and prey.

There's a field below the house I call the Bone Yard.  On the edge of a dark oak forest, it is littered with a collection of white-grey bones old enough to have been separated and scattered into what I imagine are chewing piles.  Bones of a large cow, several deer and even a coyote skull suggest that this is some type of wildlife 'killing zone'.

Please note:  the remainder of this blog post contains some graphic descriptions and photos of a carcass.  Do not select "Read More" below if you do not want to see these. If you are interested in amateur wildlife detective challenges, press on.

Old lumbar vertebrae of a cow at the Bone Yard

On a recent morning when I was shaking out rugs in the backyard, I got distracted by a vulture sunning its spread wings near the Bone Yard.  It caught my attention because, after a summer of vulture visits, the buzzards have been largely absent since the weather turned cold.  Then I noticed the bobbing heads of several more vultures in an adjacent dip.  They were perched on some type of dark carcass.

A new carcass added to the peaceful hillside

I hiked the long way around the base of the hill and tried to sneak up on the vultures, but they flapped off as soon as I peeked over the small rise below them.  They had been feeding on a dead steer which was lying on its right side in a shallow seasonal drainage.  I paused to evaluate the scene, wanting to find clues to how the steer died.  This black steer, as all 70-some cattle recently arrived on the Dipper Ranch, was not full grown and was approximately 500 pounds.

Steer carcass on the first morning of discovery

To the west was a flat area we call the Golf Tee, a favorite grazing grounds for the cattle this time of year.  Cowboy V currently has the cattle confined to a 25-acre area around the Golf Tee that has no water trough or ponds, but shallow water flows in its seasonal drainages during wet winters.  During the dry summer when there is no nearby water, the cattle bypass the Golf Tee, so Cowboy V is trying to get them to graze it down now while water is available.  The dead steer was laid out at the toe of a gently sloped hoofprint-covered bench, apparently a pathway the cattle take from the Golf Tee to water.  

The pathway down to the water from the Golf Tee.
Carcass is at lower left corner.

Predators had started feeding on the carcass.  I guessed from the bright red color of the exposed flesh, the absence of the smell of decay, and the small amount of flies, that the steer had been dead for less than two days, perhaps had even succumbed the night before.  The belly of the steer had been ripped open with most of its internal organs gone and I could see partially digested grass still of a greenish-brown color in its gut.  The top ribs were mostly stripped of flesh.  The left shoulder area was eaten, and the humerus bone was nearly dislocated from both its scapula and radius ends.  The left eye and ear were gone.  The tongue was severed with a straight cut and was lying on the ground next to the mouth.

The scapula rests below the ribs and above the head.
The humerus bone further to the right is nearly dislocated.

I carefully looked for tracks before walking near the carcass.  I found both canine and feline tracks.  The canine tracks were probably coyotes, although domestic dogs sometimes harass stock animals.  These tracks were too big to be fox.  As for wild felines, both bobcat and mountain lion reside in the Santa Cruz Mountains.  Later that day, the Labrador Ranger applied her hunting skills and found more feline tracks around the carcass, and she reminded me to measure them.

A feline track at the steer carcass with the toes pointing towards the pen.

You can tell the difference between canine and feline tracks primarily by the overall shape and by the arrangement of the toes around the palm or metacarpal pad.  Feline tracks are rounder than canine tracks with a more asymmetrical arrangement of the toes around the top and sides of the palm pad.  The negative space between the toes and the palm pad of a feline track is shaped like a "C" that has fallen to the right to 'face' the palm.  Think "C" for cat.

A canine track at the steer carcass with the toes pointing to the left of the photo.
Note the claw marks sinking into the mud.

Canine tracks are more oval and more frequently show claw marks.  With the the toes symmetrically arranged around the front of the palm pad, an "X" can be drawn in the negative space between the outside and inside toes and along the edge of the opposite side of the palm pad.  See drawings and photos of Canine vs. Feline Tracks by Kim Cabrera at Beartracker's Animal Tracks Den, and at the Mountain Lion Foundation.

The size of a track can also help determine its owner.  In his Mammal Tracks and Sign book, Mark Elbroch states that the palm pad width ranges from 1 to 1-9/16 inches for a bobcat, and 1-9/16  to 2-7/8 inches for a mountain lion.  I measured the width of the fresh feline palm pad at the steer carcass and it was 2-3/4 inches wide, possibly a mountain lion track.

Distinct feeding patterns can indicate what predators are visiting the carcass.  Mountain lions usually slit open the belly of their prey from the backside of the ribs, pull out and set aside the stomach and intestines in a neat pile, and then eat the heart, lungs and liver which are rich with protein, fat and vitamins.  If they continue eating, they may move onto the large muscle areas like the rear flank.  When they are done feasting for the night, they will often cache the remains - drag the carcass under brush, up a tree and/or cover it with leaves or dirt.

Coyotes usually feed at the hind end of the carcass first and work their way up to the ribs.  Since one coyote usually means more coyotes, soon a carcass will be ripped apart and scattered about as each coyote tears off its share and eats at a comfortable distance from the frenzy, or stashes parts for later.

These are general patterns of feeding behavior by mountain lions and coyotes.  Individual animals and the circumstances of each kill can result in variances.  I have seen many fresh deer carcasses at Rancho San Antonio Open Space Preserve that were clearly mountain lion kills as evidenced by the gut pile precisely removed and set aside of the feeding area, however, there was no attempt to cache the carcass.  Rancho San Antonio has one of the highest human visitation levels of any wildlands in the Santa Cruz Mountains, so it is possible that the mountain lions that hunt the plentiful deer there are either scared off their kill by the early morning joggers or have learned to eat and run in this type of environment.

An older cow pelvis at the Bone Yard.

Once a large animal is killed, its carcass is usually fed upon by many different types of scavengers.  Within a short period of time, sign upon sign cover each other and it becomes difficult to determine which predator originally brought the prey down.

On the first day I saw the steer carcass, it appeared freshly killed, however, coyotes, some type of cat, ravens and vultures had already started to mark the carcass.  The absence of a gut pile or caching suggested the steer was not killed by a mountain lion.  The relatively large size of the steer, the belly-focus pattern of feeding, and the nearly severed joints of large bones suggested it might be a lion.  I decided to set up a wildlife camera at the carcass to determine which predators returned and provide more clues to this most recent death at the Bone Yard.

Next: what wildlife cameras revealed at the Bone Yard.