Tortoise romance may be killed off by climate change
‘SINGLE female seeks relationship with male who must enjoy flowers … and cuddling up in desert caves’?
But such tortoise hook-ups may dry up due to climate change.
Wildlife biologists say an alarming number of female desert tortoise carcasses found earlier this year just outside the southern edge of Joshua Tree National Park in California may be the result of mothers fighting extinction by exhausting their water and energy to lay eggs, even under stress.
US Geological Survey biologist Jeffrey Lovich, who has monitored tortoises in and around the park for two decades, says the potentially lethal response to prolonged drought may become more common throughout the Southern California desert as temperatures rise and forage diminishes.
“This is still a hypothesis,” Lovich says. “But I believe these tortoises died after continuing to lay clutches of four eggs the size of ping pong balls year after year, using up vital resources they need to survive.
“It was an evolutionary gamble,” he says. “If it pays off, their genetic information will be passed on to a new generation of hatchlings in conditions more suitable for survival of the species.”
A research team led by Lovich was surveying a study area of several square miles on the northern flanks of the Orocopia Mountains when it discovered the remains of 14 female and three male tortoises, and 15 live animals, most of them males.
Death by drought
Judging from the deterioration of the carcasses and chalkiness of the bones, Lovich concluded the animals perished over the last five to 10 years, a period that included five consecutive years of drought regarded as the most severe in the state’s recorded history.
The find has stepped up concerns over the fate of tortoises within the more than 300,000ha national park, which recent rains made into a showcase lush with plants and flowers for the lumbering reptiles to fatten up on.
But vast swaths of terrain carpeted with daisies can only do so much, biologists say, in the face of longer droughts and climate change.
Despite its name, scruffy body armour and status as a symbol of the desert conservation movement, the tortoise is not well adapted to arid landscapes. It evolved thousands of years ago, when the region was cooler and dominated by lakes and marshes fringed with Joshua trees and junipers, Lovich says.
Over the past three decades, the park’s tortoise population has plummeted from roughly 30,000 to an all-time low of about 3,000, according to Michael Vamstad, a wildlife ecologist at the park.
A federal analysis determined that a viable population of tortoises must maintain an average minimum density of about 10 adults per square mile (or 250ha). The average density within the park today is about nine adults per square mile, Vamstad says.
“We’re at a point now where we expect tortoises to disappear in certain areas because there aren’t enough of them around to find a mate,” he says. “But we believe there will also be pockets with the right combinations of air temperature, moisture and forage to sustain tortoises for years to come.”
Over the past century, desert tortoises have been decimated by habitat loss, trampling by cows and sheep, shootings, vehicle strikes, disease, collecting, relocation efforts on military bases, and predation by ravens, coyotes, and dogs.
Now their deadliest foe is climate change, which is upsetting the delicate balance of life and death conditions for the species in an otherwise intensely managed expanse of habitat within a national park.
“The recent five-year drought is a window into the future of what climate change may look like across the South-Western United States,” says Cameron Barrows, a University of California, Riverside, ecologist who specialises in the park’s wildlife.
“In certain study plots where we found lots of tortoises even two years ago, we didn’t find any this year.”
Crush of tourists
Improving the odds of survival for tortoises hasn’t been easy at a time when record numbers of tourists are straining park roads, campsites and services, officials say. The park had 2.5 million visitors in 2016, twice the number seen five years ago, they say.
In the midst of a spectacular wildflower bloom in March that attracted both hungry tortoises and a crush of camera-toting tourists, three tortoises were struck and killed by cars in a single week.
Officials are considering roadside fencing, which is effective in reducing mortalities of tortoises and other reptiles. It is also controversial, however, because it is expensive to install and maintain, fragments habitat, and is an eyesore on federal lands set aside for their natural beauty.
“Climate change has no regard for traffic signs, speed limits, roadside barriers, or national park boundaries,” says Debra Hughson, a research biologist at the Mojave National Preserve, about 80km north-west of Joshua Tree park.
It’s not all bad news.
Under a hot morning sun on a recent weekday, park biologist Kristen Lalumiere is following telemetry pings across a desolate arroyo (a steep-sided gully cut by running water in an arid region) edged with cholla cactus to a radio-collared female desert tortoise the size of a volleyball emerging from a burrow to bask in the sunshine, dine on flowers and, perhaps, find a mate.
Lalumiere peers inside, then smiles and says, “You’re looking good, girl – clear eyes, clean nose, and flower stains all over your mouth.”
Adding a hopeful dose of anthropomorphism, she says, “Single female seeks relationship with strong male willing to fight to protect her. Must enjoy flowers, long slow walks, and cuddling up in desert caves.”
The tortoise biologists dubbed “Salsa Verde” stares back at her, then retreats into her burrow.
In a nearby burrow, a male tortoise known as “Scuter” is taking a siesta.
Whether or not they produce a new generation of tortoises will not be known for 15 to 20 years because that is how long it takes hatchlings to reach maturity, even in the best of times. – Los Angeles Times/Tribune News Service