An Overview of Wildlife Corridors

by Nicholas Bridgman

At Paso Pacífico, we talk a lot about wildlife corridors like the Paso del Istmo Wildlife Corridor. What is a wildlife corridor?

A wildlife corridor is a network of larger areas of wildlife habitat linked by another passage of habitat. Its goal is to counteract habitat fragmentation, a main cause of biodiversity decline. Fragmentation, such as by human development, leads to smaller and smaller islands being created, so that species become more and more isolated. This leads to a breakdown in ecological processes, since animals cannot travel to food, water, mates, and shelter, and plants cannot disperse their pollen and seeds to their full extent. This results in inbreeding and reduced genetic diversity. 

By connecting habitats, wildlife corridors enable migration, colonization, and interbreeding of plants and animals. Maintaining wildlife corridors as a network across both public and private lands can help mitigate some of the effects of fragmentation and aid landscape conservation efforts.

Corridors help prevent species from becoming endangered and stabilize populations in three main ways. First, they aid colonization, so that animals are able to move to new areas when food or natural resources are absent in their core habitat. Second, they aid migration, so that animals can effectively seasonally relocate. Third, they assist with interbreeding, so that animals can find mates in neighboring regions, which increases genetic diversity and positively impacts the overall population.

Corridors can be categorized according to their width. In general, wider corridors receive more use from species. However, proper construction and other design features, such as width-length ratio, also contribute to effectiveness, reducing suffering from edge effects such as weeds, predators, and chemicals. The main general corridor widths are:

1. Regional (>500 m wide), connecting major ecological gradients, such as migratory pathways
2. Sub-regional (>300 m wide), connecting larger vegetated landscape features, such as ridgelines and valley floors
3. Local (<50 m wide), connecting remnant patches of gullies, wetlands, and ridgelines

Paso Pacífico’s Paso del Istmo falls under the regional corridor width.

The effectiveness of wildlife corridors is generally well-regarded, although more study is needed. There are many cases of birds and butterflies successfully using the corridors, while less successful stories have come from other species such as deer. One reason for this may be that birds are highly migratory to begin with. In the Paso del Istmo, the corridor has helped jaguars to return, and prey species such as lowland pacas, peccaries, and tapirs are recovering. Overall, it can be hard to judge corridors in general, since each one must be observed on its own terms, with its own set of standards and goals, and its own unique mix of species and environmental factors.

The Paso del Istmo Wildlife Corridor

Paso Pacifico has applied the principle of wildlife corridors to the Paso del Istmo, a strip of land in Nicaragua between Lake Nicaragua and the Pacific Ocean. Deforestation and degradation have occurred here for decades, but even in spite of this, the area retains some of the region’s largest fragments of tropical dry forest. Without the wildlife corridor, plants and animals native to tropical dry forest could not travel north from Costa Rica, and rural farmers would suffer since their rivers would go dry and soils barren, lacking the protection and nutrients that trees and wildlife provide. Creating the corridor has been critical for connecting wildlife habitats and ensuring a healthy environment for local people.

The Paso del Istmo represents what most of the tropical world looks like, no longer virgin forest but rather fragmented habitats that are biologically diverse and need protection. Not surprisingly, Paso Pacífico’s work here translates well to work throughout the area. We first identify a corridor where we plan to work, observing and listening to the greatest needs, both so far as biodiversity and community wellbeing. Next, we identify specific urgent priorities, such as endangered species, degraded watersheds, and isolated habitat. Finally, we put these problems into a local context, enabling us to innovate solutions specific to the community and ecosystem’s needs. These steps can be successfully used in any geographic area, and already we are started work in El Salvador and are planning for other parts of the tropics.

An example of our work in the corridor and beyond is our partnerships with dozens of private landowners who commit their properties for biodiversity conservation. They give up profits that they could otherwise make from agriculture or infrastructure development, instead choosing to help protect the environment by maintaining the corridor. Some projects we have undertaken with their help include protecting almost 500 sea turtle nests, protecting a very rare frog, managing and supporting the growth of thousands of recently planted native trees, and protecting endangered primates. The landowners’ generous commitment helped make building the corridor a success.

What We Could Do in the Future

One main interest is continuing to help facilitate the development of the Mesoamerican Biological Corridor (MBC), established in 1997 by the governments of eight countries in the Mesoamerican region. The heart of the MBC is a wildlife corridor connecting habitats, but it is also more than that; the MBC is a system of land planning. It consists of four natural areas: core areas, exclusively for ecosystem conservation; buffer zones, areas with restricted use surrounding the core areas; corridor zones, which link habitats and facilitate species’ movement, dispersal, and migration; and multiple use areas, devoted to various activities including agriculture, fisheries, and forest management. The MBC works towards three main goals: maintaining biological diversity, reducing fragmentation, and promoting sustainable production processes that improve the quality of life of local human populations.

The MBC began with a strong focus on protected areas, but it has evolved towards integrating conservation interests with those of economic and rural development. Mesoamerica has over 600 protected areas that cover about one fifth of the area, but they virtually all have significant human populations, oftentimes indigenous. Thus, conservation of green areas requires focus on the needs of local peoples, millions of which depend on MBC-protected areas. The MBC itself also contributes to a culture of peace, bringing together countries in the region and focusing on international cooperation.

Paso Pacifico hopes to scale up its work on the Paso del Istmo to build corridors across Central America for the MBC. Many of the lessons we have learned in Nicaragua would greatly contribute to developing successful corridors throughout the region. For example, when we worked on coastal conservation in the Paso del Istmo, we observed how dwindling shellfish supplies impacted marginalized women who collected oysters. We found that a solution could be developing an oyster cooperative. By empowering local women, we enabled them to practice sustainable fishing and obtain a new economic opportunity, while at the same time enabling us to restore the native shellfish. This practice of observing, identifying priorities, and placing solutions in a local context could aid conservation efforts in corridors throughout Central America. Sustainable conservation practices and wildlife corridors can go hand in hand with providing strong economic opportunities and contributing to human well-being.

References

https://www.environment.nsw.gov.au/resources/nature/landholderNotes15WildlifeCorridors.pdf

https://www.sciencedaily.com/releases/2008/10/081020135221.htm

https://en.wikipedia.org/wiki/Wildlife_corridor

http://pasopacifico.org/wp-content/uploads/2016/07/2017-Paso-Pacifico-Annual-Report-Web.pdf

https://www.biodiversidad.gob.mx/v_ingles/corridor/mesoamericanCor.html

https://en.wikipedia.org/wiki/Mesoamerican_Biological_Corridor

http://www.tbpa.net/page.php?ndx=65

By Jason G. Goldman

Every year, millions of birds of prey migrate from summertime breeding grounds in North America to overwintering grounds in South America. One section of their pathway stretches nearly 2500 miles between central Texas and northwestern Colombia’s Chocó rainforests and is known as the Mesoamerican Land Corridor. More than five million raptors – the family of birds that includes vultures, hawks, eagles, and owls – can be seen making the journey each year. It’s the most important flyway for raptors in the Americas.

More than one million of them pass through a narrow stretch of southern Nicaragua, bounded on the west by Lago Cocibolca and on the east by Reserva Biológica Indio Maíz. That’s according to a survey conducted in 2019 on behalf of Paso Pacífico in San Miguelito. Over just twenty-three days of monitoring, biologists counted more than 1.2 million raptors passing overhead. Just over eight hundred thousand of them were turkey vultures. Also abundant were Swainson’s hawks and broad-winged hawks. In all, they documented sixteen different types of raptors.

Swainson’s hawk, cropped, by Tucker Hammerstrom on Flickr. Used under CC BY-ND 2.0

The importance of this region for raptors has been known since at least the year 1555, when a Spanish colonialist named Gonzalo Fernández de Oviedo y Valdés wrote about the seasonal movements of large flocks of raptors through eastern Panama. Nearly five hundred years later, there’s still a lot left for avian biologists to learn – especially about the section of the flyway that passes through Nicaragua.

With strict coronavirus protocols in place, the Paso Pacífico team returned to San Miguelito this year to repeat the raptor count. The effort has been extended from one to two months. Halfway through the study, the team reported early results: they again counted more than 1.2 million raptors in the first month of monitoring. As before, the most common species were turkey vultures, Swainson’s hawks, and broad-winged hawks.

Part of the 2020 raptor team, photo by Oswaldo Saballos.

“Everybody knew that the raptors were passing through Nicaragua,” says Sarah Otterstrom, executive director of Paso Pacífico. “It’s not like they’re disappearing between where they’re counted in Belize and where they’re counted again in Costa Rica and Panama,” she explains. But nobody had ever bothered to identify exactly how they are using Nicaraguan airspace, or what habitats they rely on as stopover sites.

That’s why Paso Pacífico intends to construct a permanent raptor monitoring station in the area. After completion, it will join a network of more than a dozen similar sites along the Mesoamerican Land Corridor that, together, will paint a complete picture of raptor movements in the Americas.

The station will be named in honor of Luis Fernando Díaz Chávez, a Paso Pacífico bird technician who pioneered the first year of the raptor monitoring study at San Miguelito. He died in June after spending nearly a month in and out of the hospital with COVID-19.

Luis Díaz Chávez during the 2019 raptor monitoring, photo by Marlon Sotelo.

Just thirty-one years old, Luis had been a regular contractor on Paso Pacífico’s bird projects for the last nine years. “He really loved raptors,” says Otterstrom. “He had written a draft of a Raptors of Nicaragua book, with his own photography, that we are trying to finish and publish for him.”

Luis came from a big family in Managua, where he shared a home with his parents, his grandparents, his brother, and many aunts, uncles, and cousins. Though his family did not have many financial resources, they helped him become first in his family to graduate college.

After his father died several years ago, Luis became a high school science teacher. The career move meant a more predictable salary than jumping from project to project as a bird technician for Paso Pacífico. “Luis would send most of his payments to his mother,” explains his colleague Oswaldo Saballos, who counted Luis as a friend and as a mentor. Anything left over would be spent on birding guides or other tools to fuel his passion.

Despite his full-time employment as a teacher, Luis still found time to lend his ornithological talents to Paso Pacífico when he could. Over the years, he taught more than five hundred children to observe birds. “He was one of the best birders in the country,” recalls Otterstrom, especially when it came to identifying birds based only on their songs and calls. “I think that his gentle, shy, quiet personality gave him this really supernatural ability to observe and perceive nature,” she says.

After the raptor monitoring station in Luis’s honor is completed, Otterstrom hopes it will attract birdwatchers and other tourists passionate about wildlife and nature. Local communities could therefore leverage the ecological value of the region for economic gain. “This area is where the Nicaraguan government wanted to run the canal. While that project is no longer a threat, it’s important for conservationists to put this space on the map in terms of its ecological value and importance,” she says. “We need to make sure we protect these migratory corridors for raptors and other wildlife.”

Panorama of the 2019 initial monitoring station located in Rivas, Nicaragua, photo by Vincent Romera.

Top photo: Turkey vultures (Cathartes aura) spotted during the 2019 raptor monitoring, photo by Vincent Romera