President Trump has vowed to build a hardened wall along the entirety of the U.S.-Mexico border to keep out illegal crossers and drug smugglers. But experts say it will likely do a better job of keeping out animals — many of which are already endangered. They say the existing border fence authorized under the Bush administration already has negatively impacted wildlife even though it doesn't cover the whole 1,900-mile border. The area ranks among the most biodiverse places in North America — particularly the Rio Grande Valley in South Texas. We visited the Valley to see the fence for ourselves and talk to people about its impacts. 

Sonia Najera, grassland manager for the Nature Conservancy, stands in sabal palm forest at the Lennox Foundation Southmost Preserve. The 1,100-acre preserve is home to some of the land remaining patches of sabal palm forest in the United States.It is prime habitat for the endangered ocelot, a small cat that looks like a tiny leopard.
Sonia Najera, grassland manager for the Nature Conservancy, stands in a sabal palm forest at the Lennox Foundation Southmost Preserve. Sabal palms are more majestic than the ones you'd see in Beverly Hills, and the 1,100-acre preserve is home to some of the last remaining patches of them in the United States. The subtropical forest is prime habitat for the endangered ocelot, a small cat that looks like a tiny leopard. The conservancy has seen fewer ocelots on the preserve since the border fence was completed in 2010.  Callie Richmond for The Texas Tribune
The Nature Conservancy has been working for years to restore the threatened sabal palm forest. Staffers recover sabal palm and other seeds from coyote scat and germinate them in an on-site nursery.
The Nature Conservancy has been working for years to restore the threatened sabal palm forest. Staffers recover sabal palm and other seeds from coyote scat and germinate them in an onsite nursery. Callie Richmond for The Texas Tribune
The federal government did do some things to try to help endangered species when it built the border fence, including rerouting some sections. At a segment near Brownsville that runs through a private nature preserve, there are small openings at the base of the fence every 500 feet or so meant to let small wild cats through — particularly the ocelot, whose numbers have dwindled to fewer than 100 in the United States.
The federal government did do some things to try to help endangered species when it built the border fence, including rerouting some sections. At the segment that runs through the Lennox Foundation Southmost Preserve, there are small openings at the base of the fence every 500 feet or so meant to let small wild cats through — particularly the ocelot, whose numbers have dwindled to fewer than 100 in the United States. Callie Richmond for The Texas Tribune
Pamela Taylor has lived in a house on the Texas-Mexico border since the 1950s. It's on American soil, but now sits south of the border fence in an area critics refer to as a
Pamela Taylor has lived in a house on the Texas-Mexico border since the 1950s. It's on American soil but now sits south of the border fence in an area critics refer to as a "no-man's-land." Taylor said she doesn't think Trump will build his proposed wall. "He doesn't know us from a hole in the ground," she said.  Callie Richmond for The Texas Tribune
Pamela Taylor put up this sign at the beginning of her driveway, which U.S. Customs and Border Patrol Agents use to access the Rio Grande River.
Pamela Taylor put up this sign at the beginning of her driveway, which U.S. Customs and Border Protection agents use to access the Rio Grande. Callie Richmond for The Texas Tribune
Taylor leaves out food and water for border crossers, but always reports them to Border Patrol.
Taylor leaves out food and water for border crossers but says she always reports them to the Border Patrol. Callie Richmond for The Texas Tribune
The Rio Grande River is less than a mile from Taylor's house. On a recent weekday, undercover Border Patrol agents said they were expecting people to cross at any moment.
The Rio Grande is less than a mile from Taylor's house. On a recent weekday, undercover Border Patrol agents said they were expecting people to cross at any moment. Callie Richmond for The Texas Tribune
A group of Wisconsinites on the lookout for birds and other wildlife at Resaca de la Palma State Park and World Birding Center in the Rio Grande Valley. The region is one of the preeminent birding and ecotourism locales in the Unites States, drawing some 685,000 visitors last year.
A group of Wisconsinites looks out for birds and other wildlife at Resaca de la Palma State Park and World Birding Center in the Rio Grande Valley. The Valley is one of the pre-eminent birding and ecotourism locales in the Unites States, drawing some 685,000 visitors last year.  Callie Richmond for The Texas Tribune
A kiskadee at Resaca de la Palma State Park and World Birding Center near Brownsville. Two major migratory bird paths converge in the area, and several tropical bird species there can’t be found anywhere else in the United States.
A kiskadee at Resaca de la Palma State Park and World Birding Center in the Rio Grande Valley. Two major migratory bird paths converge in the region, and several tropical bird species there can’t be found anywhere else in the United States. Scientists say low-flying birds are impacted by border barriers and others would suffer if their habitat is damaged.  Callie Richmond for The Texas Tribune
Muddy handprints cover the rusty, iron posts on this section of border fence in far South Texas. The 18-foot-tall barrier, which runs between a national wildlife refuge and a local nature center, ends abruptly less than a mile down the road. Still, somebody clearly thought it was best to cross here.
Muddy handprints cover the rusty, iron posts on this section of border fence in Hidalgo. The 18-foot-tall barrier, which runs between a national wildlife refuge and a local nature center, ends abruptly less than a mile down the road. Still, somebody clearly thought it was best to cross here.  Callie Richmond for The Texas Tribune
Before the border fence was even a topic, the federal government was buying up land along the border to protect endangered species. Environmentalists and conservation groups say the border fence has compromised the federal government’s own efforts to protect those animls, pitting the U.S. Department of Homeland Security against the U.S. Fish and Wildlife Service.
Decades before the border fence was even an issue, the federal government was buying up land along the border to protect endangered species. Environmentalists and conservation groups say the border fence has compromised the federal government’s own efforts to protect those animals, pitting the U.S. Department of Homeland Security against the U.S. Fish and Wildlife Service. Callie Richmond for The Texas Tribune
Scott Nicol, co-chair of the Sierra Club's Borderlands Campaign, says the fence has kept some animals out but not people.
Scott Nicol, co-chair of the Sierra Club's Borderlands Campaign, says the fence has kept some animals out but not people. "People can build a ladder and it's not any big deal. But for anything that can't hammer and nail stuff together, that stops them completely," he said. Callie Richmond for The Texas Tribune

Disclosure: The Nature Conservancy has been a financial supporter of The Texas Tribune. A complete list of Tribune donors and sponsors is available here.

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