Housing developments, major highways, expanding farmlands and general urban sprawl have made it harder and harder for wildlife to move around freely. These human-made barriers especially impact predators, which are naturally inclined to roam long distances in search of prey. Other large mammals, such as deer, might find themselves separated from a water source or grazing ground by a highway or a brand-new suburban neighborhood.

The solution is to create wildlife corridors where animals can move from place to place without interference. These "nature highways" are now being established all around the world. They are primarily focused on the movements of larger animals, but smaller creatures, including insects, can also benefit. Ideally, these "wildlife bridges" can help entire ecosystems expand and thrive despite their close proximity to humans.

1. Terai Arc Landscape

Elephants, tigers and rhinos move between the national parks that are a part of the Terai ArcElephants, tigers and rhinos move between the national parks that are a part of the Terai Arc. (Photo: Utopia_88/Shutterstock)

The Terai Arc Landscape covers 14 different protected areas in India and Nepal. The grasslands, forests and river valleys here are important habitats for a number of species including rare Indian rhinos, Asian elephants and Bengal tigers. The Terai stretches from the Bagmati River in Nepal to India's Yamuna River. Alone, the parks and preserves, such as Chitwan National Park in Nepal and Rajaji National Park in India, are not big enough to sustain a healthy population of large mammals. Linked, however, the 14 areas provide more than enough habitat.

The issues that surround the Terai are much different from those that affect wildlife corridors in the U.S. and Europe. Despite being rural, the region is densely populated, especially on the Indian side of the border. Poverty is a problem here, so activities like poaching, slash-and-burn farming and overusing natural resources are common. The government of India has undertaken several initiatives, including paying farmers in the area to grow flowers instead of less-sustainable food crops.

2. Banff Wildlife Bridges

Wildlife overpasses in Banff allow animals to cross over the Trans Canada HighwayWildlife overpasses in Banff allow animals to cross over the Trans Canada Highway. (Photo: Robert Crum/Shutterstock)

Not all wildlife corridors require decades to develop. Some are meant to address an immediate need rather than work on a "big picture." That was the case with the wildlife bridges in Banff National Park. Built across the Trans Canada Highway, these overpasses and underpasses are meant to solve the problem of frequent car-wildlife collisions. More than three million people visit the national park each year, and an additional four to five million drive the Alberta section of the highway without stopping.

The park has built six wildlife overpasses and several dozen underpasses. Thus far, naturalists have documented 140,000 animals crossing the highway using either the bridges or the underpasses.

3. Lower Rio Grande Valley National Wildlife Refuge

Two ibis birds migrate to the Lower Rio Grande Valley.Rare birds, including the ibis, migrate to the Lower Rio Grande Valley. (Photo: Lower Rio Grande Valley/U.S. Fish & Wildlife Service)

Southeastern Texas is among the fastest-growing regions in the U.S. Housing developments, commercial buildings, farms and roadways now crisscross the landscapes here, and the city of Houston continues to spread outwards. The Lower Rio Grande Valley, from the Falcon Dam (right on the border with Mexico) to the Gulf of Mexico, is right in the middle of all this development.

The Lower Rio Grande Valley National Wildlife Refuge has actually been working with conservation groups for more than three decades to create a wildlife corridor along the river valley. This often involves purchasing land from farmers and then replanting the fields with natural foliage. The wildlife along the Lower Rio that benefits from these efforts includes migrating birds and rare mammals like the ocelot.

4. Christmas Island crab bridge and tunnels

Not all animal crossings are designed for large mammals. On Australia's Christmas Island, an annual crab migration has inspired a series of "crab crossings." The crabs live deep in the island's forests, but migrate en masse to the ocean to breed and lay their eggs each year. Population estimates vary from about 50 million to well over 100 million. The crustaceans literally carpets the island (and its roadways) as they move from forest to ocean. It is impossible for people to avoid them as they drive on the roads. Naturalists estimate that at least 500,000 crabs die each year during the journey.

The island now houses a center where undocumented immigrants are detained. The influx of these refugees, and the authorities who process them, has increased the island's population. At least one new crab bridge has been built to help limit the number of casualties during the migration.

5. Sawantwadi-Dodamarg Wildlife Corridor

The Sawantwadi-Dodamarg Wildlife Corridor links protected preserves and sanctuaries in Southwestern India. The Western Ghats, a wildlife-rich mountain range that towers over this region of the subcontinent, has also been the focus of the mining industry. In addition to Bengal tigers, bears and elephants, the Ghats are home to many of the natural medicinal herbs used in traditional Ayurvedic medicine.

With the help of the Mumbai-based Awaaz Foundation, a charitable trust that focuses on environmental issues and conservation, the lands inside the Sawantwadi-Dodamarg Corridor have been designated as part of an "ecologically sensitive area." Because of this, mining companies cannot stake any claims here.

6. Oslo, Norway's Bee Highway

Norway's capital is developing a different kind of wildlife corridor. Oslo is known as a clean city, but it lacks the urban parklands and plants that pollinators such as bees need to survive and thrive. A new "bee corridor" gives the insects a network of pollen-producing plants. The bees can forage in one place before moving onto the next pit stop along the "highway."

The bee-friendly venues include rooftop gardens and balconies where flowering plants are kept. The goal is to have pollen-rich habitats every 800 feet, so bees can enjoy a movable feast as they travel through Oslo.

7. Highway 93 Wildlife Crossings, Montana

A white-tailed deer exits from one of the Highway 93 Wildlife Crossing tunnels in MontanaA white-tailed deer exits from one of the Highway 93 Wildlife Crossing tunnels in Montana (Photo: The People's Way Partnership)

U.S. Highway 93 is known as the "People’s Way." It might also be apt to call it the "Wildlife Way." The highway in Montana has been the site of one of the most extensive safe-crossing efforts in the country. A total of 41 crossing structures, both underpasses and overpasses, were created along a 56-miles stretch of road. Fencing was installed along portions of the highway to funnel the wildlife into the safe corridors.

Special cameras have caught a number of creatures using these passageways and bridges. There is photographic evidence of grizzly bears, deer, elk and cougars using the structures to bypass the road.

8. Burnham Wildlife Corridor

Burnham Park sits on a prime piece of real estate along Chicago's Lakeshore area. The Burnham Wildlife Corridor is a 100-acre landscape within the park featuring the prairie and woodland ecosystems that are native to this part of the Central U.S. The corridor runs right through the heart of the city. It is mainly used as a refuge for the three million migratory birds that pass through the Windy City each year. Members of the public have been able to take part in the clearing and planting of these new habitats.

9. European Green Belt

This section of the European Green Belt sits on the former border between East and West Germany This section of the European Green Belt sits on the former border between East and West Germany. (Photo: Nickel van Duijvenboden/Wikimedia Commons)

The idea for the European Green Belt started in Germany shortly after the fall of the Berlin Wall. Over the years, it has expanded through a series of agreements. It now runs from the Finnish-Russian border all the way through the Balkans. The corridor is located roughly where the so-called Iron Curtain used to be. For this reason, the Green Belt has cultural and historic significance as well as serving to protect wildlife.

Actually, the fact that nature still thrives in these particular areas is a happy side-effect of the Cold War. With little economic activity along the borderlands, nature developed uninhibited for decades. In Finland, for example, old growth forests still dominate the landscape. In Germany and the rest of Central Europe, endangered species have been given a literal lifeline by the Green Belt.

10. The Netherlands' 'ecoducts'

The Zanderij Crailoo Nature BridgeThe Zanderij Crailoo Nature Bridge is the longest wildlife crossing in the Netherlands. (Photo: Globe-trotter/Wikimedia Commons)

When it comes to wildlife corridors, the Netherlands is second to none. The European nation has more than 600 crossings that allow animals to safely get from one side of a highway to the other. Some of these are quite modest, while others are huge. The largest, the Natuurbrug Zanderij Crailoo, stretches for almost half a mile. The "ecoducts" allow safe passage for deer, wild boar and other mammals, including the endangered European badger.