The Robert L.B. Tobin Land Bridge connects the once divided Phil Hardberger Park.
Photo courtesy of Phil Hardberger Park Conservancy and Airborne Aerial Photography.
Teresa Shumaker, Alamo Area Master Naturalist and Associate Director of the Phil Hardberger Park Conservancy, wrote this piece.
When the land for Phil Hardberger Park was purchased in 2008, Wurzbach Parkway bisected the property with six lanes of traffic, isolating wildlife from the other half of the park. Development of the park plan involved architects, engineers, and a lot of community input. The wildlife crossing that resulted from that planning was unique. They designed a land bridge to accommodate BOTH people and wildlife. This was the first mixed-use wildlife crossing of its kind. After a decade of planning, the Robert L.B. Tobin Land Bridge was completed in December 2020. It now provides a safe passageway for wildlife to access all 330 acres of the park and the Salado Greenway Trail corridor.
Wildlife Use the Land Bridge
In April 2021 — four months after the Land Bridge’s completion — a study was launched by Park Naturalists to determine wildlife activity on the Land Bridge. By the first anniversary in December 2021, ALL 12 species of mammals, known to reside within the park, had been photographed on the Land Bridge. The wildlife crossing is working, providing safe passage to the two sides of the park.
Careful research and consideration went into the design of the Land Bridge to make wildlife feel safe to cross, despite the presence of humans. The U.S Department of Transportation’s publication, “Wildlife Crossing Structure Handbook – Design and Evaluation in North America,” strongly influenced the design of the Land Bridge. It contains the most successful elements of wildlife crossings worldwide, such as how wide the crossing needs to be and what features will encourage wildlife to explore, then use, the bridge.
The elements that were implemented to benefit wildlife in San Antonio’s Land Bridge include:
- Space: The Wildlife Crossing Handbook recommended that the crossing be between 50 to 80 feet wide. The Land Bridge is 150-feet-wide at its narrowest point.
- Shelter: The trail for people is located to one side of the Land Bridge, allowing a corridor behind an earth berm for wildlife to navigate, partially obscured from human traffic. This is important to provide visual cover for wildlife, especially white-tailed deer, to make them feel safe to cross during the day.
- Water: There are two water bubblers on the Land Bridge that provide an important source of water for wildlife. A water bubbler is a water feature that has a small basin for water to pool in for wildlife to drink and bathe in. It also includes a water fountain that makes a splashing sound. The sound of water hitting a surface can be widely heard by animals, attracting them to the feature.
- Vegetation: Native plants were installed to provide food and cover for wildlife while crossing. While the vegetation was being established, construction crews placed brush piles along the corridor to provide temporary shelter.
The selection of species of plants was carefully considered by the design team for hardiness in the local climate and the ecological services within the surrounding habitat. By doing so, the vegetation not only provides cover, it also extends the suitable wildlife habitat. Many insects, especially moths and butterflies, need specific plants to reproduce. And, many species of small mammals and birds rely on insects as a food source.
History of Wildlife Crossings
The first instance of wildlife crossings were fish ladders that date back to 17th century France. The wildlife crossings we are accustomed to today, which go over or under roadways, date back to France in the 1950s. It wasn’t until the late 1980s that wildlife crossings were attempted in North America. Parks Canada led the way by building over- and underpasses along the Trans-Canada Highway, which runs through Banff National Park. Despite the initial public skepticism, the six overpasses and 38 underpasses have been a success story leading the way to many more wildlife crossings throughout North America.
What is Habitat Fragmentation?
As humans continue to develop the natural world, they break up habitat and routes that animals use to find food, water, shelter, and mates. This fragmentation is one of the greatest threats to wildlife conservation, with roadways being the most lethal. This has impacted our wildlife in Texas. Many species of animals need to move between large tracts of land in order to find unoccupied territories or mates. The large cats that were once common in parts of South Texas are an unfortunate example. The last sighting of a Jaguar in Texas dates back to 1948; the last Jaguarundi was seen in 1986. Both are now considered extinct in Texas. They were lost in part due to overhunting, however habitat loss and fragmentation were contributing factors. Ocelots are now nearing extinction — despite their protection on the endangered species list. It is estimated that only 100 are left. They too need to roam far and have been strongly affected by habitat fragmentation. In 2017, 15 underpasses were built along Highway 100 to reconnect important areas of habitat. In 2020, an ocelot was caught on camera using one of the culverts.
On the Robert L.B. Bridge, bobcats, coyotes, raccoon and white-tailed are likely to benefit the most from this safe passage. They roam large areas and safe pathways to access disconnected natural areas within the city are very important for their survival.
We are running out of wild habitat and as we continue to develop the land for the growing needs of humans. There is only one logical solution. The only way to conserve wildlife is to learn how to live WITH it. Wildlife crossings provide a sustainable compromise between the needs of wildlife and humans.
What is a Wildlife Crossing?
Wildlife crossings are known by many names: animal bridges, ecoducts, wildlife tunnels, underpasses, culverts, overpasses, viaducts, green bridges, canopy bridges, and more.
They are planned passageways built in key areas where wildlife is known to travel in order to give wildlife safe options for crossing dangerous barriers. The two most common types of wildlife crossings are land bridges that go OVER roadways and culverts that go UNDER. However, there are a wide variety of wildlife crossings, such as rope ladders for monkeys and squirrels, fish ladders made of piles of sticks in streams, green roofs that offer food and rest points for pollinators, amphibian tunnels, and more.
Notable Land Bridges around the world
- Banff National Park, Canada
- Collier and Lee Counties in Florida
- Ecoducts, Netherlands
- Slaty Creek Wildlife Underpass, Calder Freeway, Black Forest, Australia
- I-70 Vail Pass, Colorado
- I-90 Snoqualmie Pass East, Washington
- Interstate 80 in Parleys Canyon, Utah
Robert L.B. Tobin Land Bridge Features
- Accessibility: The trail over Land Bridge is ADA Accessible; the slope is gradual and it feels like climbing a gentle hill.
- Sound barrier: There are 8-foot tall steel walls that mute road noise. When standing on top of the Land Bridge, one can barely hear the traffic below.
- Skywalk: The one-of-a-kind Skywalk is an elevated walkway that travels 480 feet from the Water Loop Trail, gently climbs through the treetops, and ends at the top of the bridge. This elevated view is excellent for those wishing to see small birds, such as warblers and other small birds that stay up in the canopy. There is a landing with a bench for those who would like to stay a moment and marvel at the beauty of life up high in the trees.
- Habitat reclamation: In addition to connecting fragmented habitat, the Land Bridge also reclaims habitat over Wurzbach Parkway. Local soil and native vegetation have restored some of the habitat lost when the roadway was built.
- Water reclamation and erosion control: The Land Bridge has a 250,000-gallon cistern that collects rainwater to be used as irrigation for the plants on top of the bridge. During heavy rain events, underground French drains inside the bridge divert excess stormwater off the Land Bridge and into the cistern.
- Wildlife viewing blinds: Two wildlife viewing blinds provide opportunities to see elusive animals that usually avoid people. At each viewing blind there is a water bubbler that will draw wildlife in. These blinds are a great place to stop to see what might stop by. Each wildlife blind is also covered in public art, in partnership with San Antonio’s Public Art Department. They were designed separately by artists Ashley Mireles and Cade Bradshaw. Both artists worked closely with STIMSON Landscape Architects to transform these wildlife blinds into art.
- The southern wildlife viewing blind is called “Innature.” Ashley Morales designed cutout silhouettes of native plants found in the park.
- The northern wildlife viewing blind is called “Lightbox,” designed by Cade Bradshaw. There are hundreds of small circular cutouts that mimic the topography of the area. Hidden in the topography are silhouettes of wildlife that could be seen in the area.
- Water for wildlife: There is a water bubbler at each wildlife blind. Water is an important and sometimes scarce resource in Central Texas. The two bubblers not only provide a reliable source of water for wildlife, but they provide the sound of water hitting rock which can be heard far and wide. That sound draws wildlife to discover the Land Bridge. Once there, they might learn that they can also use the bridge to access the whole park safely.
Robert L.B. Tobin Land Bridge Interesting Facts
- The Land Bridge is 150 ft. wide at the top, 165 ft. wide at the base
- The skeleton of the bridge contains 16 steel girders, each weighing 80,000 lbs.
- It is reinforced with 450 tons of rebar
- The form was made using 5,000 cubic yards of concrete
- The top of the bridge contains 120,000 cubic yards of soil
- The Land Bridge was designed by Stimson Landscape Architects and Rialto Studios.
- Arup, the engineers who created the “instructions” to build the Land Bridge, also worked on the Sydney Opera House
- SpawGlass constructed the Land Bridge