This week marks a significant milestone in the conservation and recovery of the endangered whooping crane. On March 11 and 13, the U.S. Geological Survey’s Patuxent Wildlife Research Center transferred its last two cranes of the approximately 75 that were in its flock to other institutions, closing out more than 50 years of the center’s whooping crane research and captive breeding success.
Researchers at the center pioneered the science informing much of the birds’ recovery to date, including assessing dietary needs, developing breeding methods and techniques for raising chicks, and preparing birds for reintroduction into their natural habitats. Over the years, the program at Patuxent has naturally transitioned to a more operational role of producing chicks for reintroduction. With other institutions capable of filling that role, the USGS has transferred the birds to organizations in North America interested in continuing the captive breeding and reintroduction efforts, allowing the USGS to focus its resources on other species at risk and in need of scientific research.
“Whooping cranes are still endangered, but the overall population has grown more than tenfold in the last 50 years since Patuxent’s program began,” said John French, a USGS biologist and director of the USGS Patuxent Wildlife Research Center. “The end of the USGS program is an indication of just how far we’ve come in our research and recovery efforts and is a tribute to the numerous researchers from the U.S. Geological Survey and numerous collaborators and partners who dedicated five decades to help chart the course for the recovery of this iconic species.”
Whooping cranes are North America’s largest bird and a longtime symbol of the American conservation movement. They are native to North America and their current population is estimated at more than 700 birds. In 1942, the entire population declined to 22 birds. This decline was primarily due to human actions, such as overhunting and the development of shorelines and farmland that led to habitat loss.
The Start of the Largest Whooping Crane Captive Breeding Program
The captive breeding program began in 1967 when biologists from the U.S. Fish and Wildlife Service captured a young whooping crane and collected 12 eggs from the wild in Canada. All were sent to the Patuxent center, which was then under the USFWS. The center was transferred to the USGS in 1996. The overall conservation goal for the species has been to help establish new populations in places where the large, majestic birds once lived. The Patuxent effort became the world’s largest whooping crane captive breeding program, and a model for science-based reintroduction of endangered species.
USGS Role in Breeding and Raising Whooping Crane Chicks
“When the staff at Patuxent first got involved in whooping crane recovery, new scientific research was needed on just about every aspect of whooping crane biology,” said French. “That research was used to establish captive breeding programs, to develop methods of reintroduction and, more recently, to assess how the reintroduced populations are faring.”
Scientists sought ways to increase the number of eggs laid and chicks hatched. In the wild, whooping cranes typically lay two eggs at a time and only one clutch (group) per year. If the eggs don’t survive or are lost to predators, a whooping crane may lay a second or even a third clutch that year. In captivity at Patuxent, scientists removed eggs from the parents’ nests for incubation in the lab, which encouraged re-nesting and increased the total number of eggs and chicks produced. Sandhill cranes were often used to incubate the extra eggs.
Methods developed at Patuxent for artificial insemination of breeding females have allowed the production of chicks with a healthy genetic heritage and allowed the preservation of genetic diversity in the captive flock.
From the moment a whooper chick hatched, technicians interacted with them only when wearing a crane costume. Costumed technicians taught the chicks how to find food, purred or played brood calls to the chicks like their parents would, and introduced them to wetland habitats. The costume prevented chicks from imprinting on—or attaching themselves to—humans. This is especially valuable after release, as it is beneficial for the chicks to act as natural in their habitat as possible.
Various methods were also developed for preparing whooping crane chicks for reintroduction to the wild. Federal scientists and partners developed and improved the method of training young crane chicks to follow an ultralight aircraft, which was used to teach the fledglings a migration route south for their first winter.
The Next Phase and Transferring Cranes
Patuxent’s cranes were transferred to other institutions that can produce chicks for reintroduction. These institutions are the Smithsonian Conservation Biology Institute in Front Royal, Virginia; the White Oak Wildlife Conservation in Yulee, Florida; the International Crane Foundation in Baraboo, Wisconsin; the Dallas, Houston, Abilene and San Antonio Zoos in Texas; the Oklahoma City Zoo in Oklahoma; the Omaha Zoo in Nebraska; the Freeport-McMoRan Audubon Species Survival Center in Louisiana; and the Calgary Zoo and the African Lion Safari in Canada.
Conservation and Recovery Plan
Whooping crane captive breeding for reintroduction in North America is one part of the strategy for conservation and restoration of the species. A joint U.S.-Canada International Recovery Team develops and guides the strategy for whooping crane management, which is detailed in the International Recovery Plan for the Whooping Crane. The team also oversees the management of wild and reintroduced populations of whooping cranes.
Click here to access the paper from the paywall at PNAS.org (Kimberley T. Davis, Solomon Z. Dobrowski, Philip E. Higuera, Zachary A. Holden, Thomas T. Veblen, Monica T. Rother, Sean A. Parks, Anna Sala, and Marco P. Maneta). Here’s the abstract:
Changes in climate and disturbance regimes may cause abrupt shifts in vegetation communities. Identifying climatic conditions that can limit tree regeneration is important for understanding when and where wildfires may catalyze such changes. This study quantified relationships between annual climate conditions and regeneration of Pinus ponderosa (ponderosa pine) and Pseudotsuga menziesii (Douglas-fir), two ecologically and economically important conifer species in low-elevation forests of western North America. We found that regeneration exhibited a threshold response to annual climate conditions and the forests we sampled crossed these climate thresholds in the past 20 years, resulting in fewer recruitment opportunities through time. In areas that have crossed climatic thresholds for regeneration, stand-replacing fires may result in abrupt ecosystem transitions to nonforest states.
Climate change is increasing fire activity in the western United States, which has the potential to accelerate climate-induced shifts in vegetation communities. Wildfire can catalyze vegetation change by killing adult trees that could otherwise persist in climate conditions no longer suitable for seedling establishment and survival. Recently documented declines in postfire conifer recruitment in the western United States may be an example of this phenomenon. However, the role of annual climate variation and its interaction with long-term climate trends in driving these changes is poorly resolved. Here we examine the relationship between annual climate and postfire tree regeneration of two dominant, low-elevation conifers (ponderosa pine and Douglas-fir) using annually resolved establishment dates from 2,935 destructively sampled trees from 33 wildfires across four regions in the western United States. We show that regeneration had a nonlinear response to annual climate conditions, with distinct thresholds for recruitment based on vapor pressure deficit, soil moisture, and maximum surface temperature. At dry sites across our study region, seasonal to annual climate conditions over the past 20 years have crossed these thresholds, such that conditions have become increasingly unsuitable for regeneration. High fire severity and low seed availability further reduced the probability of postfire regeneration. Together, our results demonstrate that climate change combined with high severity fire is leading to increasingly fewer opportunities for seedlings to establish after wildfires and may lead to ecosystem transitions in low-elevation ponderosa pine and Douglas-fir forests across the western United States.
Forests around the world face being permanently wiped out because climate change is making them unable to recover from devastating wildfires.
Solomon Dobrowski at the University of Montana and colleagues painstakingly dug up approximately 3,000 small trees from 90 burn sites across the western US to look at the ability of forests to regenerate after a wild fire.
They found that before the 1990s, low-lying forests could grow back after being burned, but between the early 1990s and 2015 there was a sharp drop in the ability of seeds to regenerate a forest at most sites.
The team used tree ring dating to see which year their trees had germinated since a fire, and used those samples to build a model of how forests would likely recover in different conditions.
Climate change appears to have changed soil moisture and surface temperatures so much that the forests have passed a threshold where conditions no longer favour new growth after a fire. Unlike mature trees, seedlings’ roots are too shallow to reach water deeper underground.
Climate scientists have warned for years of the possibility of such abrupt responses to higher temperatures, such as the rapidly-accelerating loss of ice sheets.
“These dramatic disturbance events, the changes we will see over the landscape won’t be gradual over decades, they will happen very quickly,” says Dobrowski.
The study looked at just two types of conifers, ponderosa pine and Douglas-fir. But Dobrowski said the findings were also relevant to similar semi-arid forests around the world, such as those of southern Europe.
That would be bad both in terms of the ecosystem services those forests provide, but also limiting future climate change.
Human interventions could help some of these burned forests grow back, for example by reintroducing seedlings when they are 2-3 years old and have roots long enough to reach water underground. But this costs money and time.
“Bergen Park” was painted by John Frederick Kensett circa 1870. The painting illustrates the open, spatially-variable structure of a ponderosa pine stand with an open understory typical of some Front Range forests at that time. (Bergen Park, at an elevation of 7800 ft., is located near Evergreen, CO, 25 miles west of Denver.) via Rocky Mountain Research Station
Pinon and juniper forests that burned in the early 2000s show little sign of regeneration. Pony Fire, Happy Camp, Siskiyou County, California. Photo credit AWeekOrAWeekend.com.
Piñon pine (Juniperus_occidentalis). Photo credit: Wikimedia
The rescue project is on the Scott M. Matheson Wetlands Preserve, a property owned by The Nature Conservancy on the fringes of Moab alongside the Colorado River. Over the last few weeks, construction crews have been creating a special side-channel that will carry river-water into the wetlands during periods of higher water. It’s designed to mimic – on a small scale – the natural system of annual spring flooding that’s been disrupted over the last century or so by dams, diversions and other human activity.
“We don’t have the same magnitude of flood events, or the same duration, or even the same timing,” said Zach Ahrens, a fish biologist for the Utah Division of Wildlife Resources, one of several agencies that have partnered on the project.
In the spring, the suckers spawn and hatch tiny babies in the main current of the river. The plan is to divert the higher spring flows through the new channel into a large pond in the Matheson wetlands. Actually, in recent years it hasn’t really resembled a pond because it contains so little water. The new channel is aimed at refilling it from time to time to give the larvae of razorback suckers an alternative, temporary habitat.
“Away from the main channel allows for a little bit warmer water, which allows the fish to grow more quickly,” Ahrens said. “It also allows them some refuge from the turbulent currents that occur during spring runoff.”
If they stay out in the main channel of the river, the larvae are highly vulnerable to being eaten by non-native fish that have taken over the Colorado. “They’re maybe a half an inch long,” Ahrens said. “They’re tiny little translucent noodle-looking things.”
But if they can spend a few months in an off-stream nursery, they can come out big and strong.
“If we can bring them into a safe harbor, into a nursery and give them the months they need to grow to a sufficient size, and then release them back into the river, then they can compete” Whitham said.
When they re-enter the Colorado River, they’ll have a better chance of stand up to hungry non-native predators that were accidentally or deliberately introduced in the last few decades.
“If we can help bring back these populations of native fish, who have been around for millions of years, and get them to sufficient sizes, then we’ll know that we’re doing something right,” Whitham said.
The project is being built in phases because all the funding hasn’t been lined up yet. The Nature Conservancy hopes to fill the gap with state and federal grants as well as private contributions.
Ron Rogers biologist with Bio-West Inc., holds a large razorback sucker captured in Lake Mead near the Colorado River inflow area
From the South Fork Republican River Restoration Coalition via The Yuma Pioneer:
Bonny Reservoir, once a popular camping, boating and fishing destination located in extreme southeastern Yuma County, was drained years ago to help Colorado get into compliance with the Republican River Compact with Kansas and Nebraska.
However, efforts by a coalition of county governments and other organizations — named the South Fork Republican River Restoration Coalition — still remain underway to at least partially restore it to its formal usage.
There have been a series of public meetings since last year. The next is being planned for Thursday, March 14, in a joint meeting with the Colorado Agriculture Preservation Association. It will be at Idalia School from 5 to 6:30 p.m., followed by CAPA’s annual meeting.
The coalition has been working on the project for the past two years. Yuma County and Kit Carson County are part of the group, along with Three Rivers Alliance, the Republican River Water Conservation District, Colorado Parks & Wildlife and The Nature Conservancy.
Yuma County Commissioner Robin Wiley told the Pioneer he believes the group is making headway in a positive direction. He stressed that plans do include necessarily refilling the lake, but restoring the stream flow and possibly establishing some non-water and small water recreational activities in and around the old lake bed.
The coalition secured a grant in January 2018 from the Colorado Water Conservation Board for $99,000, with The Nature Conservancy giving the cash match.
Wiley said the money is being used to do Phase I of the project, planning and design.
The coalition has hired Otak Engineering to do channel design and engineering. A firm named Stillwater is doing the habitat restoration planning, and CHM has been hired to do an economic analysis of possible recreational activities.
It had a landowner meeting last August in Idalia to tell the landowners, up and down the South Fork of the Republican River, what the coalition is trying to do and ask for their cooperation.
Last November there were two meetings, one in Idalia and one in Burlington, to get input from the public on the project.
Now comes the March 14 meeting in Idalia. All interested members of the public are invited to attend.
Bonney Reservoir back in the day. Photo credit: Colorado Parks and Wildlife.
FromYale 360 (Jim Robbins). Here’s an excerpt click through for the photos and to read the whole article:
The Colorado River has been dammed, diverted, and slowed by reservoirs, strangling the life out of a once-thriving ecosystem. But in the U.S. and Mexico, efforts are underway to revive sections of the river and restore vital riparian habitat for native plants, fish, and wildlife. Fifth in a series.
From the air, the last gasp of the Colorado River is sudden and dramatic. The pale green river flows smack into the Morelos Dam on the U.S.-Mexico border, and virtually all of it is immediately diverted into a large irrigation canal that waters a mosaic of hundreds of fields — alfalfa, asparagus, lettuce, and other vegetables, their vivid green color clashing against the sere desert. The slender thread of water that remains in the Colorado’s channel continues to flow south, but is soon swallowed up by a sea of sand, far short of its delta, which lies 100 miles farther on.
The Colorado River once surged through the delta during high flows, carrying so much water at times that shallow draft steamboats chugged hundreds of miles up the river into the U.S. with loads of freight. The water in the delta nourished a vast fertile landscape, a fitting end to a river known as the Nile of North America.
“The river was everywhere and nowhere,” the naturalist Aldo Leopold wrote during a 1922 canoe trip to the delta, describing the waterway as it ebbed, flowed, braided, and stalled into pools, nourishing a rich and diverse ecosystem of “a hundred green lagoons,” a “milk and honey wilderness” with thick stands of cottonwoods and willows that provided habitat for hundreds of species of birds. The delta’s marshes, mudflats, and white sand beaches were home to clapper rails, bitterns, mallards, teal, and clouds of egrets.
Bobcats, puma, deer, and wild boar wandered the delta’s forests. Leopold was searching for the jaguar that roamed there, but didn’t see any…
As a natural river, before it was dammed, the Colorado was a massive, dynamic waterway. It flowed from elevations above 14,000 feet in the Colorado Rockies, then dropped to sea level, which meant that it moved at high water with tremendous force, liquid sandpaper carving out red rock canyons. It flooded the desert plains, carving new channels and braids with every inundation. When it receded, it left behind a mosaic of fecund marshes, wetlands, and ponds.
In its natural state, the Colorado had more extreme flows than any river in the U.S., ranging from lows of 2,500 cubic feet per second in the winter to 100,000 cubic feet per second in the summer. In 1884, an all-time historical peak flow reached 384,000 cubic feet per second in Arizona.
But extreme flows are too capricious to support a civilization, so over the past century or so humans have built a network of expensive dams and reservoirs, pipelines, canals, flumes, and aqueducts to tame and divert the flow. Yet these projects also strangled the life out of a once-thriving ecosystem. By design, the river will never again function as a free-flowing stream.
Now, however, experts and environmentalists are rethinking this technological marvel of a river, and looking at ways a natural Colorado can flourish — to some degree, and in some places — with the permission of the engineers. One of those places is in the delta.
The water that flowed in the once-lush delta has been replaced by sand, and the cottonwoods and willows have surrendered their turf to widespread invasive salt cedar and arrowweed. Without the river and its load of nutrients, marine productivity in the Gulf of California — where the Colorado River once ended — has fallen by up to 95 percent. But despite the dismal forecast for the future of water on the Colorado, some conservationists are hoping to return at least a portion of the delta to its former glory.
“We are trying to restore a network of sites that creates a functional ecosystem,” said Francisco Zamora, who manages the project for the Sonoran Institute. “We’ve acquired water rights, but use them for habitat instead of cotton or wheat.”
The delta is one of a disconnected series of restoration projects that government agencies, local groups, and environmental organizations are undertaking along the Colorado. Numerous efforts are focused on tributaries to the main stem of the river, seeking to enhance resiliency by increasing the flow of water and protecting and restoring riparian habitat for fish and other wildlife.
For example, a coalition of groups — including state agencies, nonprofits, and the Arizona cities of Buckeye and Agua Fria — have been removing invasive salt cedar, planting native species, and building levees to reclaim a 17-mile stretch of the Gila River. Invasive salt cedars are a region-wide problem on the lower Colorado, with a single tree sucking up 300 gallons a day. The invasive forest on this stretch of the river uses enough water to serve 200,000 households.
In the upper basin, meanwhile, a number of groups and local landowners are working to restore a 15-mile-long floodplain with globally significant biodiversity on a narrow section of the Yampa River, another Colorado tributary. Called Morgan Bottom, the section has been damaged by deforestation and poor agricultural practices, threatening bald eagles and greater sand hill cranes, as well as a rare riparian forest of narrowleaf cottonwood and red osier dogwood.
But there are limits to how natural the Colorado River can become, especially along the river’s main stem. “We should not kid ourselves that we are making it natural again,” said John Fleck, the director of the University of New Mexico’s water resources program and the author of a book about the restoration of the Colorado. “We are creating an intensively managed system to mimic some nature because we value it.”
Because of the Colorado’s extensive infrastructure, serious disruption of the river’s ecology is inevitable.
Indeed, some of the remaining naturalness on the Colorado is, paradoxically, because of the human-made system. “The geography of the Colorado gives it hope because L.A. and southern California, which everybody loves to hate, guarantee that a lot of water stays in the system through the Grand Canyon,” says Jack Schmidt, a professor at Utah State University and a member of the Colorado River Research Group. “The best friend endangered fish ever had in the Colorado River Basin is that giant sucking sound” of California withdrawing water.
Widespread protection efforts are focused on native fish in the Colorado. The river once was home to an unusual number of endemic fish. But dams, irrigation, and the introduction of bullhead, carp, and catfish did them in. While the upper basin still has 14 native fish species, the lower basin, according to one study, “has the dubious distinction of being among the few major rivers of the world with an entirely introduced fish fauna.”
The Colorado pike minnow — something of a misnomer for a fish that historically grew to 6 feet in length and weighed up to 80 pounds — once swam through the entire system from Wyoming to Mexico. It is now listed as endangered, with two distinct populations remaining in the upper Colorado and the Green River.
The humpback chub lived in various canyon sections, and though once seriously endangered, it has fared better in recent years through transplantation efforts, growing from 2,000 to 3,000 fish to 11,000. Officials say it may soon be taken off the endangered list.
Razorback suckers, once common, are now rare. The bonytail, a type of chub that is one of North America’s most endangered fish, no longer exists in the wild. A handful of these fish exist in hatcheries, and attempts are underway to restock them in the river throughout the basin.
Because of the Colorado’s extensive infrastructure, serious disruption of the river’s ecology is inevitable. Dams trap most of the river’s sediment in reservoirs, which means there is no material to rebuild beaches, sandbars, and important fish habitat downstream.
Dams also deprive the river downstream of nutrients, such as phosphorous and nitrogen, and stratify water temperatures. The native fish in the Colorado adapted to a wide range of temperatures, from cold to very warm. They also evolved to tolerate high flood flows along with extremely dry periods. Now, the water is cold in the summer for miles below the dams, and the humpback chub and other fish that had adapted to a range of water temperatures and flows suffer.
Something called hydro-peaking also has had serious impacts on the food web. Dams generate power according to demand. As people come home from work and switch on the stove, air conditioning, and lights, demand soars and dams release more water to produce power. “Prior to the construction of dams, there were almost no major daily changes in river levels,” said David Lytle, a professor of integrative biology at Oregon State University. When fluctuations in water levels occur, they “can interrupt the egg-laying practices of some species. It’s a serious problem.”
Insects lay their eggs just below the water level, and if levels drop rapidly it can dry them out. A recent study found that below the Hoover and Glen Canyon dams, there was a complete absence of stoneflies, mayflies, and other species — insects that are vital food for fish, bats, birds, and other creatures.
Because of the ecological effects of the Glen Canyon Dam, the Grand Canyon stretch of the Colorado is one of the least productive sections of river in the world. The Colorado here will always be highly unnatural, a novel, human-created ecosystem with some natural elements.
Today, there is a large and growing backlash against dams in America and elsewhere as the immense damages they have inflicted on rivers become manifest. Few dams, though, are as reviled as the Glen Canyon, which was built in 1963 and took 17 years to fill Lake Powell.
Before the Glen Canyon was dammed, those who saw it say it was not unlike the Grand Canyon, with towering walls of red, tan, and ochre. Early Native American sites were plentiful. Environmental activist Edward Abbey decried the dam, and in his novel the Monkey Wrench Gang fantasized about using houseboats packed with explosives to blow it up. In 1981, members of Earth First!, a radical environmental group with a connection to Abbey, rolled a black plastic “crack” down the face of the dam to symbolize its demise.
Removing the dam was part of the reason the Glen Canyon Institute was formed, but activists have now dropped that idea, says Rich Ingebretsen, a Salt Lake City physician who founded the group. Today, he advocates draining Lake Powell to fill Lake Mead, which is downstream and where the need for water is by far the greatest. The “Fill Mead First” campaign would restore a free-running Colorado River to what was once Lake Powell.
“You’d get much of Glen Canyon back,” said Ingebretsen. “A free-flowing river through the Grand Canyon means you’d restore the river — riparian zones, animals that belong there, a beautiful canyon with arches and bridges and waterfalls. Much of that would come back very quickly.” There would also be increased water in the river, he says, because so much of the Colorado is now lost from Lake Powell; scientists estimate that the lake loses three times Nevada’s allotment of water because of evaporation. As levels in Lake Mead drop due to prolonged drought, a growing number of people are taking this idea more seriously.
Paradoxically, two of the Colorado River’s most important wetlands for wildlife are the product of runoff from irrigated farm fields — and are now at risk from a changing climate and agreements to reduce water use.
In the Sonoran Desert of northwestern Mexico, the 40,000-acre La Cienega de Santa Clara wetland was inadvertently created in the 1970s when U.S. officials built a canal to dispose of salty wastewater from agricultural fields in Arizona. As the water began spilling into the desert, myriad forms of life began to appear. Now its cattail-studded marshes and mudflats are considered one of the most important wetlands in North America, home to 280 species of birds — including the endangered Ridgeways rail — on what was once hard-baked desert.
Meanwhile, in California, the Salton Sea was once a shallow inland lake whose levels routinely fluctuated. In 1905, an effort to increase Colorado River flow into the Imperial Valley led farmers to allow too much river water into their irrigation canal, overwhelming their system; for two years the water poured into the 35-mile-long, 15-mile-wide Salton Sea and expanded it.
But as less water becomes available to agriculture and rising temperatures cause more water to evaporate, scientists are concerned that these wetlands will dry and shrink faster than they already have. A 2003 agreement, for example, allows agricultural water in the Imperial Valley to be sent to San Diego for municipal uses. That could cause water levels in the Salton Sea to drop by more than 40 percent, dramatically reducing bird habitat and increasing toxic dust because wetlands would dry out. Local, state, and federal officials have devised a plan — still not fully funded — to restore 15,000 acres of wetlands, at a cost of more than $700 million.
The largest project to restore some semblance of nature to the Colorado River, though, is in the delta. An unusual agreement in 2012 between the U.S. and Mexico, called Minute 319, mandated that the two countries would provide water and funding to revive sections of the delta and release a one-time pulse of 105,000 acre-feet to again connect the river to the delta temporarily. Scientists would then study the effects.
In 2014, for the first time in decades, the river flowed again in Mexico — for eight weeks. San Luis Rio Colorado — once a Colorado River town, but now a dusty desert settlement — became a river town for two months, to the delight of locals, many of whom had never seen the river. The pulse offered a glimpse of what reclamation efforts might look like. “It gave us an idea of how the river behaves, and the best sites for restoration,” said Zamora.
Minute 319 and its 2017 replacement, Minute 323, have funded the restoration of sections of the river. A group of nonprofits — including the National Audubon Society, the Sonoran Institute, The Nature Conservancy, and a Mexican group called Pronatura Noroeste — is working on a project called Raise the River to revive a significant swath of the delta.
In 2008, the group secured rights to 1,200 acres along the desiccated river channel. Since then, local residents have torn out acres of salt cedar and planted irrigated fields of cottonwood, willow, and other endemic species — more than 200,000 trees in all. A small supply of water mandated by the treaty, along with excess water that flows off of irrigated fields, have been dedicated to the restoration.
On a recent visit, I joined Zamora and botanist Celia Alvarado on a short boat ride to Laguna Grande, a 6-mile section of restored river and estuary. We skimmed across still water the color of weak tea, minnows darting away from our paddles. Thick groves of cottonwoods and willows lined the river. Zamora remarked that bobcats and beaver lived there now, along with blue grosbeaks and yellow-billed cuckoos. “Impacting the target species is key,” he said.
And what about the jaguar? I asked. It has not returned, he said. Will it come back?
“Yes,” said Zamora, smiling. “Someday. If they allow me to introduce them.”
The restoration site is one of three south of the U.S.-Mexico border, in the riparian corridor along the last miles of the Colorado River. There, in the delta, a small amount of water has been reserved for nature, returned to an overallocated river whose flow has otherwise been claimed by cities and farms.
Although water snakes through an agricultural canal system to irrigate the restoration sites, another source is increasingly important for restoring these patches of nature in the delta’s riparian corridor: groundwater.
Scientists who monitor restoration in the delta wrote in a November 2018 report that a shallow water table, one with higher groundwater levels, is essential to the survival of riparian vegetation in the broad expanses of the delta.
“The trees, the cottonwoods and willows, they need to be connected to the groundwater directly,” said Osvel Hinojosa-Huerta, a scientist at the Cornell Lab of Ornithology who has worked to restore pockets of the delta for over 20 years with the non-profit Pronatura Noroeste. “They have shallow roots so the groundwater level is very important to their survival.”
But groundwater levels have declined, much like the river’s surface flows that once flowed into the Gulf of California. Some of the declines may be due to drought, some to overpumping and some to the loss of agricultural runoff as farmers become more efficient.
Historically, so much water poured into the aquifer that it overflowed, creating a vast wetland, said Eloise Kendy, a scientist at the Nature Conservancy who worked on the 2018 study.
Now, researchers warn that a groundwater “depletion zone,” where levels have dropped too far to support riparian vegetation, is extending both upriver and downriver from an area near the border. Such zones are created when the groundwater pumped out exceeds what is replaced, either naturally or through artificial recharge.
“If (groundwater levels) continue to go down there’s not going to be enough water to fulfill the restoration objectives,” Hinojosa-Huerta said, while stressing there’s currently still “amazing opportunities for restoration” in key areas in of delta.
Although restoration efforts in the delta have shown progress, habitat within the riparian corridor is more and more vulnerable to declining groundwater levels, according to a 2017 report that assessed the vulnerability and sustainability of the region under different scenarios.
When groundwater levels are deeper, trees like cottonwoods need more time to sink their roots into the water table, which means they’ll need to be irrigated for longer, Hinojosa-Huerta said. In some cases, they’ll have to be irrigated forever.
The Laramie Foothill Bison Conservation Herd at Soapstone Prarie Open Space. May 10, 2016
The Laramie Foothills Bison Conservation Herd, a genetically pure, Brucella abortus-free bison herd is released in the City of Fort Collins Soapstone Prairie Natural Area and Larimer County Red Mountain Open Space, November 1, 2015, National Bison Day.
Yellowstone Bison at the Soapstone Prairie near Fort Collins November 2015.
It was not always certain that bison could rebound. Once numbering in the tens of millions, they dominated the Great Plains landscape until the late 1800s, anchoring a remarkable ecosystem that contained perhaps the greatest concentration of mammals on Earth. That abundance was wiped out as settlers and the U.S. government engaged in a brutally effective campaign to eradicate the ecosystem and the native cultures that relied on it.
Bison were shot by the millions, sometimes for “sport,” sometimes for profit, and ultimately to deprive Native Americans of vital resources. By 1890 fewer than 1,000 bison were left, and the outlook for them was bleak. Two small wild populations remained, in Yellowstone National Park and northern Alberta, Canada; and a few individuals survived in zoos and on private ranches.
Remarkably, a movement developed to save the bison and ultimately became a conservation success story. Some former bison hunters, including prominent figures like William “Buffalo Bill” Cody and future President Theodore Roosevelt, gathered the few surviving animals, promoted captive breeding and eventually reintroduced them to the natural landscape.
With the establishment of additional populations on public and private lands across the Great Plains, the species was saved from immediate extinction. By 1920 it numbered about 12,000.
Bison remained out of sight and out of mind for most Americans over the next half-century, but in the 1960s diverse groups began to consider the species’ place on the landscape. Native Americans wanted bison back on their ancestral lands. Conservationists wanted to restore parts of the Plains ecosystems. And ranchers started to view bison as an alternative to cattle production.
More ranches began raising bison, and Native American tribes started their own herds. Federal, state, tribal and private organizations established new conservation areas focusing in part on bison restoration, a process that continues today in locations such as the Tallgrass Prairie National Preserve in Kansas and the Fort Peck Reservation in Montana.
By the early 2000s, the total North American population had expanded to 500,000, with about 90 percent being raised as livestock – but often in relatively natural conditions – and the rest in public parks and preserves. For scientists, this process has been an opportunity to learn how bison interact with their habitat.
Improving prairie landscapes
Bison feed almost exclusively on grasses, which, because they grow rapidly, tend to out-compete other plants. Bison’s selective grazing behavior produces higher biodiversity because it helps plants that normally are dominated by grasses to coexist.
Because they tend to graze intensively on recently burned zones and leave other areas relatively untouched, bison create a diverse mosaic of habitats. They also like to move, spreading their impacts over large areas. The variety they produce is key to the survival of imperiled species such as the greater prairie chicken (Tympanuchus cupido) that prefer to use different patches for different behaviors, such as mating and nesting.
Bison impacts don’t stop there. They often kill woody vegetation by rubbing their bodies and horns on it. And by digesting vegetation and excreting their waste across large areas, they spread nutrients over the landscape. This can produce higher-quality vegetation that benefits other animals.