Western U.S. Wildlife Migrations Spectacular but Endangered

Climate change, the paper indicates, is a leading threat and has the capacity to impact migrations in myriad ways – from the timing of insect emergences and flower blooms, to the amount of rainfall and snowpack.   Increased development, habitat loss, and human-made obstacles are other common threats discussed in the report.

The report, by WCS Senior Conservationist Keith Aune, solicited input from fish and wildlife biologists in 11 western states, including Alaska, on bird and mammal migration corridors most in need of conservation.  From 41 initial migrations evaluated, Aune ranked and profiled the “top” five terrestrial (land-based) and top three aerial (flight-based) events and the threats they face.

“The purpose of creating this list was to draw attention to these ecological wonders, and to the fact that they are rapidly disappearing,” said Aune. “In addition, by demonstrating the tremendous cultural, economic, and biological value of wildlife migrations, we are fostering public interest and support for the on-the-ground and policy activities necessary for their conservation.”

Of the five terrestrial mammal migrations profiled in the report, three involve caribou populations located in Alaska. These caribou face many threats as a result of energy development, and are extremely vulnerable to pending changes in climate and associated increases in precipitation.  Deeper winter snow and increased insect harassment will mean less access to food, decreased body fat, less reproductive success, and increased vulnerability to predators.

Other terrestrial migrations profiled include the migration of pronghorn occurring between northern Montana and Saskatchewan and the migration of mule deer and pronghorn in western Wyoming. Key threats to these migrations include cattle grazing and crop production, fencing, highways, railroads, housing development, and energy development.

The report credits the advent of new technologies (GPS collars and geolocators) with great strides made recently in understanding animal movements and the impediments to migration.  GPS collars affixed to migrating pronghorn were used by WCS and the National Park Service to document the longest known hoofed animal migration corridor in the contiguous U.S., which is now also the first federally designated migration corridor –  the “Path of the Pronghorn,” in Wyoming.

Aune said, “Within the last decade, we have developed superb tools to identify and map the detailed movements of migrating animals, from the largest to the smallest and lightest—including birds flying halfway around the world.”

The three top flight-based migrations profiled in the report included Swainson’s hawks–threatened primarily with loss of grassland habitat in North and South America; American golden plovers–threatened by agriculture, wind turbines and by climate change; and upland sandpipers–threatened by loss of habitat to agriculture, exurban development, and the spread of invasive knapweed in nesting sites.

Additionally, the report highlights three “unranked” migrations as special cases for their uniqueness–including pollinator bat migrations in the Southwestern U.S. and Mexico.  Plants within “nectar corridors” critical to bats face many threats, including invasive plants, fragmentation of desert wild lands, and herbicides.  Bats themselves are directly threatened by destruction of roosting and stop-over sites and increased harvest of agave flower buds for tequila. In addition, climate change may alter the timing of the flower blooms the bats use to fuel their migration, threatening not only the bats, but plant species that depend on the bat’s pollinating services.

Aune suggests that a successful framework for the conservation of these migrations would include: improving jurisdictional cooperation (as migration corridors often cross many borders); public education regarding the importance of ecological connectivity; increased funding to support conservation at key migratory stopovers, pinch points and bottlenecks; and increased field research efforts to identify important migrations and migratory pathways.

WCS North American Program Director Jodi Hilty said, “In order to keep wildlife populations healthy, we need to protect the pathways along which they migrate during a vulnerable time in their life cycles. WCS works with agencies and other NGOs to understand, connect, and protect the phenomenon of migration in an increasingly developed world.”