If you saw this on a drive down a quiet country road, what would you think?
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----------------------------------------------- A Followup: ---------------------------------------------
A few days ago, I invited readers to share their thoughts about the above photo. Responses here and ones I otherwise received speculated this situation was the result of humans persecuting animals, a giant shrike or other predator taking advantage of a barbed wire fence, even witchcraft (see comment section below). Let me share the specific facts as I heard them, biological facts as I've learned them, and unmask this story of predators.
That is a bobcat carcass hanging on a barbed wire fence. I did not stage that photo. It is exactly how I found it.
A few days ago, a ranger told me he was driving around the curve at the Alpine Road corral and was surprised to see a very large bird flush off the road. It was dragging a spotted carcass in its talons and having a hard time getting airborne. As it swooped over a steep road bank, it barely cleared a barbed wire fence and the carcass snagged on the top strand. The dark bird kept flying without its payload, and the ranger assumed it would come back later for its dangling meal.
He was certain the bird was a golden eagle because of its large size and overall dark color. I was not surprised to hear that a golden eagle was seen in the neighborhood. On December 23, I was washing dishes and heard a red-tailed hawk screaming so loudly, I figured I'd better investigate. I headed outside wiping my hands on my apron (not really), and looked up to see a red-tail hawk chasing a large dark bird. Compared to the red-tail, this bird was huge. It made a few wide turns over the farmyard with slow beats of its solid wings without once acknowledging the irate hawk. I hurriedly pulled out the camera I always keep in my apron pocket and got a few blurry photos before it steered its bulk towards Devil's Canyon, then Monte Bello Ridge. My cross-canyon neighbors tell me they see golden eagles fly into Devil's Ridge in the springtime and they think the eagles might be checking the cliffs. I briefly considered tossing my house cats out in the yard to attract the magnificent bird back (a moment of premonition?).
By color and size, I was pretty sure the large bird flying over my kitchen was a golden eagle, and checking my photos later, I could make out the characteristic golden color of its lower nape. This eagle had a distinct, white semi-circle on its right shoulder (lesser secondary coverts). In January, another ranger saw a golden eagle on a deer carcass (probably roadkill) in Russian Ridge Open Space Preserve. I checked his early morning photos and that bird appeared to be a different eagle since it did not have a white shoulder patch. It did have some white streaks in its underwings and was possibly a subadult. Golden eagle sightings are occasionally listed on the Peninsula Birding Group for the Santa Cruz Mountains including recent sightings of a "hatch-year" and two adults.
After assessing the ranger's Alpine Road eagle report as reliable, I impatiently worked through a dayload of meetings. The ranger told me about this incident two days after he witnessed it, and I wasn't sure there would be any signs left. When I finally got down to the Alpine Road corral late that afternoon, I found the spotted carcass hanging on a fence high above the road just as the ranger had described it.
I speculated the bobcat had been hit by a car and the golden eagle was feeding on the roadside carrion. It also occurred to me that this could be the remains of a bobcat I had seen 4 days earlier on the Dipper Ranch cautiously sneaking towards a steer carcass. The family of 3 coyotes who frequently showed up on the wildlife cameras I installed at the steer carcass, or even the mountain lion that dragged the heavy carcass one night, might have decided to eliminate the smaller bobcat as competition for carrion which can be an important food source in the winter before the grassland herbivores start popping out meals on tiny hoofs and paws. In either case, I assumed the golden eagle scavenged the bobcat and did not originally kill it.
|Coyote scavenging on steer carcass|
and trying to locate sound of shutter clicking on wildlife camera
Slipping into my recently acquired dead-wildlife detective mode, I sensed something odd about the bobcat carcass. The front legs and back pelt were undamaged and attached to the stripped yet fully articulated backbone. The rear legs and tail were gone. Between the front legs hung a solid, bloody bulk and the ribs were snapped off at different lengths. I looked around in the nearby bushes and hollows to see if I could find more of the carcass but I didn't find any guts, other bones, or any type of digging or recent soil disturbance. I returned to the carcass and eventually recognized the stubs of ears and nostrils on the unfurred bulk hanging between the legs which turned out to be a partially defleshed skull. Despite my attempt to be an objective observer, I was feeling creeped out as the sun set, so I took a stick and loosened the torn body from the fence and gently wrapped it around the base of a T-post where the predators could finish their meal out of eyesight from the road.
I spent the next few days reflecting on the sad fate of the bobcat, its beautiful lifeless paws, and decided to learn more about golden eagles. Since they are large birds admired by some, despised predators to others, and they range across North America, Asia, northern Africa and Europe, they have been frequently studied. Golden eagles are top predators and many were previously killed in rural western states because of the belief that they took large amounts of livestock. Although their diet varies by location, in most places, their prey primarily consists of rabbits and ground squirrels. Lagomorphs (rabbits, hares and pikas) represented 85% of the diet of nesting golden eagles studied in Northern California, and 87% and 91% in similar studies in Utah and Colorado (Bloom and Hawks). A dense population of golden eagles in the Altamont Pass area near the city of Livermore, California, eat primarily California ground squirrels (Santa Cruz Predatory Bird Research Group). Golden eagles also hunt deer, coyote, snakes, frogs, fish, other birds and will feed on carrion.
They have been known to take small domestic livestock such as lambs and calves. In the same Northern California study, the remains of livestock found in golden eagle nests in a rangeland area were less than 1% of their total diet. Over the six-year study period, the remains of 3 total calves were found in the nests (20 average nests were checked each year) and at least one was determined to be collected as carrion because it contained crushed bones that were too big for golden eagles to smash. The researchers found sheep wool in the nests, were not able to determine the number of sheep collected, but their estimated biomass represented a small fraction of other prey items consumed.
Shooting or even collecting feathers from bald and golden eagles is illegal unless you have received permission as a Native American for religious purposes, for some scientific purposes, or if authorized by the Secretary of Interior for the protection of wildlife or agricultural interests under certain circumstances. If convicted of a violation under the Bald and Golden Eagle Protection Act, you can be fined $5000 to $10,000 and imprisoned up to two years for each incident, and additionally lose your permit to graze domestic livestock on federal land. The golden eagle was added to the Eagle Protection Act in 1962 because "Whereas the population of the golden eagle has declined at such an alarming rate that is is now threatened with extinction; and Whereas the golden eagle should be preserved because of its value to agriculture in the control of rodents."
|The fence did it.|
It was while reading an account of eagle-feeding habits on the Internet Center for Wildlife Damage Management, that I realized how chillingly close their description was to what I saw on the fence:
"Eagles skin out carcasses, turning the hide inside out while leaving much of the skeleton intact, with the lower legs and skull still joined to the hide. On very young animals, however, the ribs often are neatly clipped off close to the backbone and eaten. Eagles frequently do not eat the breast bone, but some clip off and eat the lower jaw, nose, and ears. Quite often, they remove the palate and floor pan of the skull and eat the brain."
|Deer carcass fed on by coyotes with evidence of|
gnawing, canine punctures in scapula, and pulled hair
I went back through my photos of the bobcat carcass on the fence and realized why the carcass had seemed so odd to me - it was too clean for a carcass fed on by coyotes. Thin bones that coyotes usually crunch and scrape were still intact and picked neatly clean. I had also never seen a carcass with skin pulled back over curved surfaces rather than ripped open and torn free. Because it was hanging on a fence out of the reach of coyotes for two days, this gruesome sight which we found emotionally upsetting and imagined the cruel actions of humans was actually a near perfect visual representation of how large avian predators eat.
In eulogy of the bobcat, I want to recognize its status as a mesopredator - a mammalian carnivore of medium size, sometimes with highly adaptive behaviors. Some ecologists have theorized and found many potential examples that as apex predators are eliminated by humans, out of fear, competition for food, or through alteration of habitat, this may result in an increase in the predators the next size and trophic level down in that ecosystem (Praugh et al.). One might assume that the elimination of apex predators would result in an increase in prey species (e.g. deer), however, if the removal of top-predator competition allows the subsequent rise of mesopredators, and these are more efficient at reproduction and predation, then the overall amount of prey may actually be reduced in the absence of large apex predators.
Just as I would recommend a rancher not assume livestock was killed by a particular predator until evidence is carefully examined, so I recommend we not assume humans are always responsible for the death of wildlife. There are a lot of predators out there and they've gotta eat. Let's learn more about predator ecology before we tumble into emotional skewering of either wildlife predators or human predators.
|The new fencelines have barbed strands (green) on the top to hold cattle|
and unbarbed strands (silver) on the bottom for the wildlife to pass under.
Golden Eagle, Aquila chrysaetos, The Birds of North America - Online, Cornell University.
Food Habits of Nesting Golden Eagles in Northeast California and Northwest Nevada, Peter Bloom, California State University - Long Beach, and Stephen Hawks, Bureau of Land Management, 1982.
The Rise of the Mesopredator, Laura R. Praugh, et al., Bioscience, October 2009.