Heading South

A look at five species’ amazing winter migrations and the threats they face along the way

Every autumn and winter, in a dramatic act of coordination and navigation, dozens of species across North America migrate vast distances for food, warmth or breeding. Monarch butterflies descend upon coastal California and central Mexico, turning trees into masses of orange, flickering wings. Deer, elk and pronghorn traverse mountains, valleys and highways in the Northern Rockies. Humpback whales cross thousands of miles of ocean from Alaska to the tropical waters of Hawaii. These migrations happen via air, land or water, each with their own obstacles, both natural and built. 

Without action to protect habitat and provide safe passageways for these, and other migrating species, there will be both economic harm and irreparable biological loss.

Monarch Butterflies

Monarch butterflies cover a vast range in North America, including southern Canada, the contiguous United States, and the entirety of Mexico. Monarchs are primarily divided by the Rocky Mountains, with the western population wintering along the central coast of California and the eastern population migrating down to mountainous regions outside of Mexico City. The western migrations tend to be shorter, traveling from places such as Utah and Idaho to California while the eastern migrations can stretch up to 3,000 miles from Canada to southern Mexico. 

monarch cluster
Each year, monarch numbers are estimated by the total overwintering area they occupy in Mexico. Credit: Pablo Leautaud/Creative Commons.

Over the past decades in California, there has been a well-documented and precipitous drop in monarch numbers. During the late 1990s, monarch counts were regularly above 500,000, however, in 2018 and 2019 there were under 30,000 counted, and in 2020, under 2,000. After the dangerously close call in 2020, this winter is an unexplained bright spot, with nearly 250,000 counted, yet this is not a sure sign of recovery and is still well below historic numbers. 

One of the primary threats to monarchs is the decline in the availability of milkweed, an essential food source for monarch caterpillars. In the mid-1990s, herbicide-resistant crops were developed, allowing for farmers to eradicate other plant life, including milkweed. Additionally, the increased occurrences of drought have killed milkweed, and warming temperatures can change the toxicity of milkweed, potentially rendering it too dangerous for monarchs. 

The loss of monarchs would not only be ecologically detrimental but culturally detrimental as well to the many communities and Tribal Nations who have valued this species for generations. It would also be a loss to the towns that rely on the tourism revenue that this amazing annual migration brings. 

A monarch butterfly on a showy milkweed plant
A monarch butterfly on a showy milkweed plant. Credit: USFWS

In recent years, the USDA’s Natural Resources Conservation Service has formed agreements with farmers and other private landowners to plant milkweed, making monarch and livestock-friendly improvements to wetlands and ranchlands along migratory pathways. 

You can help by planting native milkweed at home or in your community, participating in monarch counts if you live near wintering monarchs, and advocating for action on climate change.

Western Game Species – Elk, Mule Deer and Pronghorn

Wyoming and Idaho are home to three big-game species with arduous migrations: elk, mule deer, and pronghorn antelope. These three species typically spend the summers feeding on the grasses in high alpine environments before descending into warmer valleys for the winter months. These migrations occur across the West from Arizona and Nevada up through Idaho and Montana.

A net-wire fence severely impacts pronghorn movement.
A net-wire fence severely impacts pronghorn movement. Credit: Texas Parks and Wildlife

Each of their migrations can exceed 100 miles, and in the case of mule deer, up to 480 miles of challenging terrain. The main obstacle to the migration of these big-game species comes from development, which can take away roaming areas and cut off migratory corridors. Additional challenges stem from both climate change and invasive plant species upending native vegetation. In the case of development, highways and fencing are the primary concerns. Each highway poses a serious risk of collision with vehicles. Every year in Wyoming alone, there are approximately 6,000 collisions with big-game animals which cause an estimated $20-23 million in wildlife costs and $24-29 million in vehicular damage and injury. These collisions can kill up to 4% of the state’s mule deer population annually. 

Adding onto the risk from highways, barbed-wire fences can block access, injure wildlife, or delay migrations. Especially with pronghorn, who cannot leap very high, ranching fences either require many miles and valuable energy to bypass, or they must crawl under the fence which is often barbed and cuts into the animals. 

The National Wildlife Federation and the Nature Conservancy created a StoryMap, On the Move, which depicts pronghorns’ journey throughout the year and demonstrates how these common features can dramatically hinder migrations as they race towards warmer lands before winter arrives.

Northern Rockies states, the federal government, and private landowners have already made some progress in highlighting critical corridors, building wildlife crossings, and adapting fencing. In sections of Wyoming where wildlife crossings have been constructed, mule deer and vehicle collisions have dropped by 80%. 

A pronghorn uses a fence modification
A pronghorn uses a fence modification. Credit: Texas Parks and Wildlife Department

This success has been noted — the recent Infrastructure Investment and Jobs Act signed by President Biden provides $350 million for wildlife crossings, the largest investment in wildlife crossings ever. Yet this is just a start. Both in the Northern Rockies and nationwide, more attention is needed to ensure that habitat is connected across human development. If we can help game species overcome our built environment, it is a win for both human safety and wildlife survival.

Learn more about the National Wildlife Federation’s work to improve wildlife-friendly fencing across the West, and how you can get involved.

Humpback Whales

Majestic humpback whales are present across the world’s oceans and migrate along both the Atlantic and Pacific coasts of North America. In the Atlantic, humpbacks spend the summer in the north, along the Gulf of Maine and Newfoundland before wintering in the Caribbean and Cape Verde. 

Humpback whale off the coast of Maui.
Humpback whale off the coast of Maui. Credit: Peapix/Danita Delimon

On the Pacific side, the Mexican population summers along the coast from California to Alaska before wintering in Mexico, while the Hawaiian population summers in Alaska and winters around the Hawaiian islands. While these migrations cover vast distances, humpbacks travel quickly, in the case of Pacific migrations, they can cover 3,000 miles in a month. The colder waters up north are more productive and allow them to feed on thousands of pounds of crustaceans, plankton, and fish per day. In the winter, they breed in the warmer, shallower, and more protected water of the tropics. Since these waters are less productive than the northern habitat, humpbacks are very dependent on stored fat built up during summer to survive. 

Five populations of humpback whales are protected under the Endangered Species Act due to their near extinction from commercial hunting that lasted until the 1960s. Adding on to this problem, humpbacks today face a multitude of threats which include changing ocean conditions as a result of climate change, strikes from large commercial vessels, entanglement in fishing gear, as well as noise and pollution. 

An important tool for addressing these issues is the creation of Marine Protected Areas, that limit permitted commercial and recreation activities within certain bodies of water. This reduces the risk of collision, noise disturbance, entanglement, and localized ocean pollution. 

Two humpback whales spotted in Hawaiian Islands Humpback Whale National Marine Sanctuary.
Two humpback whales spotted in Hawaiian Islands Humpback Whale National Marine Sanctuary. Credit: Ed Lyman/NOAA 

The Hawaiian Islands Humpback Whale National Marine Sanctuary protects 1,400 square miles of water around the islands to provide safe breeding habitats and promote scientific research. In April of 2021, the Biden administration marked 156,000 square miles of ocean along the Pacific coast as critical habitat for humpback whales, which, under the Endangered Species Act, prohibits activities harmful to humpbacks. This is a clear step towards the administration’s long-term pledge to conserve 30% of US lands and waters by 2030, an ambitious yet critical goal. 

Apart from designating ocean areas for protection, economic and recreational activities must be managed in a way that promotes ecosystem health in marine environments. The Forage Fish Conservation Act, introduced in both the House and Senate, would protect fish such as herring and shad. These tiny fish support higher levels of the food chain, and responsibly managing their populations helps to promote sustainable fisheries and preserve other marine wildlife. 

This proposed legislation shifts the focus of fishery management from regulating fishing on a species-by-species basis, to Ecosystem-Based Management, which incorporates the dependency of other species, pollution levels, changes in habitat, and more. 

Lastly, pollution, including plastic and chemical, should be limited upstream as much as possible to mitigate the damage to aquatic ecosystems. A multi-pronged approach to protecting marine ecosystems is crucial for ensuring that humpback whales can continue to traverse our oceans. On an individual level, cutting down on plastic use, buying locally to reduce dependence on long-distance shipping, and if near the coasts, using eco-friendly cleaning supplies are all ways to reduce harm to humpbacks.

Moving Forward

Given how delicate these incredible migrations are, and the dangerous consequences of falling behind in winter weather, even the smallest hazards pose a great threat to these species’ continued existence. North America’s migratory species cannot thrive without free passage and ecosystems cannot thrive without migratory species. It’s essential that we invest in helping monarchs, game species, humpbacks, and others navigate our modern world.

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