Our Founder, Garry, and Senior Ecologist Scott have recently returned from a short trip to the Mojave Desert in Southern California, to explore Desert Tortoise Conservation and the impact of humans on a changing landscape was no more obvious than deep within Joshua Tree National Park.
As we sat in the car park of Barkers Dam within the park, our presence was graced by a Raven. The bird sat less than 5 meters from us without a care in the World.
Being from the UK this was a grand experience, as Ravens are few and far between. Without, mentioning the fact they are seriously difficult to get close to.
But what reason would a scavenging corvid have to be in the driest desert in North America, and the hot waterless landscape of the Mojave Desert?
As we researched further, we found that the number of ravens has exploded in recent years. Partly due to their ability to thrive in developed areas.
As humans moved into the desert for recreation and hiking they introduced new sources of food and water for ravens. Such as illegal landfills, unsecured dumpsters, and trash bins, roadkill, man-made ponds, and irrigation systems.
Booming desert communities offered the ravens plenty of places to nest. Billboards, telephone poles, bridges and buildings, and of course littering to name a few.
With more people – came more ravens.
With a keen appetite for hatchlings, it made a serious dent in the population of endangered desert tortoises.
Ravens are everywhere in the Mojave Desert.
Fifty years ago, these large black corvids were relatively uncommon in this hostile environment. Nowadays, Raven populations are soaring, up 700 percent in the West Mojave Desert alone over the past 25 years.
Ravens are now abundant, year-round residents of the Mojave.
Found only within the desert’s fragile ecosystems of the Mojave and Sonoran deserts of South West American and Northern Mexico the Desert Tortoise populations are rapidly diminishing; and in some places, they have disappeared altogether.
Desert tortoises have lived in the deserts of California, Arizona, Nevada, and Utah since the Pleistocene and history shows that they have survived alongside humans, in particular, the indigenous Aha Makhav (Mohave) native American tribes, in the Mojave desert for over 10,000 years with little to no impact on their ecology.
Even when European settlers first arrived in California, In the early years of the 20th century, the tortoise thrived within the Southwest’s arid landscapes: As many as 1,000 tortoises per square mile once inhabited the Mojave.
The presence of the Joshua trees, which are native only to the Mojave Desert was seeming, as the settlers thought, the only vegetation available within the region.
That was until during the 1860’s gold was discovered in the Vanderbilt area and the settlers moved in to reap the financial rewards.
Initially, with just small impacts, however, as the gold dried up the area became a hot spot for visitors. By the 1970’s Joshua Tree National Park, became the go-to place for hikers and climbers from all over the world.
But by the end of the century, this population of the desert tortoise was listed as a threatened species under the Endangered Species Act, and now as little as 5 desert tortoise survive per squire mile.
Though the desert tortoises are well-adapted to their environments, it’s becoming increasingly clear that they’re unable to cope with the fast-paced and increasingly widespread and intensive changes humans have wrought on their ecosystems in recent decades.
Habitat has been lost or damaged from mining, livestock grazing, development of desert lands for agriculture, sub-divisions, high-ways, industrial uses, and in particular off-road vehicle use are all having detrimental effects on the desert tortoise populations.
Many of these human activities have fragmented habitat within fragile desert ecosystems, Exacerbating natural impacts, such as disease and Raven predation, which affect desert tortoise populations, reducing their numbers by 90 percent in recent years.
The U.S. Fish & Wildlife Service biologists believe there are an estimated 650,000 tortoises in the four-state Mojave range. But the relatively high number of tortoises can be deceptive, considering they are spread over such a large area (124,000 km²).
Desert tortoises are difficult to find and count because they are scattered across the Southwest and spend 95% of their lives in burrows underground, and some ecologists believe that the estimates are way below this figure.
Raven’s, of course, is not the only threat brought to the desert tortoise by the increase in humans settling in the desert.
The desert ecosystem is extremely vulnerable to impacts from off-highway vehicle (OHV) use and even light use can cause significant damage to the soil, plants, and wildlife. With prolonged vehicle use, hardened soil and reduced availability of nutrients, such as nitrogen, impede the growth of native plants. Compacted soils are also less capable of absorbing water, and thus adjacent areas are prone to erosion.
Young tortoises are as small as 2” in shell length, soft-shelled, camouflaged, and active during the very seasons and times favoured for off-highway vehicle use. Their small size makes them almost impossible to tell from rocks and gravel, thus they are vulnerable to being struck and killed.
Adult tortoises, though larger and more visible than juveniles, are still at risk of injury and death from vehicle collisions, especially in rolling terrain and dusty conditions when visibility is reduced.
In fact, our first sighting of a Desert Tortoise was along a dirt road in the Kelso Dunes of the Mojave.
The tortoise was walking in the middle of the road with an oncoming off-road 4×4 hurtling toward it. Luckily, we’d been traveling in the opposite direction and was able to rescue the animal before it was crushed.
In addition, a number of diseases have been identified in desert tortoise populations, including upper respiratory tract disease (URTD), shell disease, and herpesvirus. While the disease is a natural phenomenon within the wildlife, some tortoise diseases were unnecessarily introduced via the release of captive tortoises. Since the late 1980s, the disease has been a major concern for the conservation and recovery of desert tortoise populations throughout their range.
In 1994 the U.S Fish & Wildlife Service created a Desert Tortoise Recovery Plan, which was updated in 2011. The Recovery Plan described a strategy for recovering the desert tortoise, which included the identification of six recovery units, recommendations for a system of Desert Wildlife Management Areas (DWMAs) within the recovery units, and development and implementation of specific recovery actions focused within the DWMAs.
Along with the DWMA’s, the fight to save the desert tortoise in the Mojave Region has seen some amazing innovational creations. Biologist Tim Sheilds and his team at Hardshell Labs Inc. (a conservation technology program attempting to repopulate desert tortoises in the Mojave, whose species has been preyed on by ravens) have created a 3-D printed tortoiseshell, painted to offer a more believable look.
The plan for the fake tortoise shells is to fill them with foods known to make ravens nauseous, and early tests are proving really effective.
Other tools that the biologists are using for their active ecological management plan include green light lasers, rovers, and drones. They serve as makeshift bodyguards for tortoises, following them around and deterring ravens from snagging a bite.
Ecologically, the conservation efforts from various angles are starting to work but we have the ask the question, how can we allow a species, which, has been on earth for millions of years suddenly in the last 50 years, start to decline at such a rate, that without huge ecological science & conservation efforts soon become extinct?