Of fifty warbler species regularly found throughout the U.S. and Canada, 11 make their way to Alaska each summer to breed. Like many other migratory birds, warblers take advantage of abundant insects and prime nesting habitat to raise young in the U.S. and Canada, before traveling to warmer areas like Mexico, Central and South America, and the Caribbean to spend the winter.
Migration is no easy task for any bird, let alone warblers, which average less than the weight of one AAA battery! Prior to our understanding of bird migration, people had many interesting ideas about where migratory birds went during the colder winter months. Centuries ago, people thought birds hibernated underground or underwater, while others proposed they transformed into new species (as people noticed seeing different birds at different times of the year). Some even thought birds flew to the moon and spent the winter there. The truth is that these minute creatures (made mostly of feathers and hollow bones) traverse the globe, some doubling their body weight to survive non-stop flights across oceans.
As birds go, Alaska is unique among North American states and provinces. Numerous species travel several flyways (migration routes) to meet in Alaska during the summer months. These migratory birds come from wintering grounds in the Americas, eastern Asia, Oceana, and Africa before arriving on their breeding grounds here in Alaska. And Alaska’s warblers are no exception to the incredible journeys and diversity of migratory routes and wintering locations.
Blackpoll Warblers are a summer breeder in the northern coniferous forests throughout Alaska and Canada. Males sport a striking black cap during summer (superficially similar to the Black-capped Chickadee) and sing an insect-like high pitch trill to attract a mate. Though not as flamboyant as other warbler species, it makes up for it with its fascinating migratory feats.
Attaching small devices known as geolocators, scientists tracked Blackpoll Warblers from their breeding grounds to their wintering grounds, uncovering one of the most impressive migrations among birds. Blackpoll Warblers that breed in Alaska travel up to 12,400 miles roundtrip each year, crossing the entire North American continent before making a non-stop 3–4 day transoceanic flight to northern South America.
Before they complete this amazing leap across the ocean, they spend a month fattening up along the eastern seaboard, doubling their body weight with fat reserves in order to survive the arduous oceanic crossing.
Blackpoll Warblers have lost over 90% of their population since the 1970s. Understanding where these birds go is critical to our understanding of what’s driving this population loss.
Wilson’s Warblers can be spotted in nearly all parts of the United States at some point during the calendar year.
These small bright yellow birds travel from their wintering grounds in Mexico and Central America up through both the eastern and western states before arriving at their breeding sites across mountain ranges and coastal areas in the western U.S., Canada, and nearly all of mainland Alaska.
Though tracking device technology is continually evolving, some species are still too small to carry these devices. Wilson’s Warblers weigh on average 8.5 grams (or half the weight of an empty soda pop can!), which is too light to carry a geolocator. So how do scientists learn about the migratory journey of this small bird? They use their feathers! More specifically, DNA from feather shafts.
With enough DNA samples across a species’ or population’s range, scientists can match individual birds to the breeding, migratory, and wintering locations, regardless of where those individuals were captured.
Using this technique, scientists discovered that Wilson’s Warbler that breed in Alaska and Alberta migrate through the western U.S. and disperse to central Mexico down through Panama. This is quite different from the Pacific Northwest and coastal California populations that winter exclusively in southern Baja and western Mexico.
Arctic Warblers are unique among all warblers in the Americas because they mainly breed across northern Europe and Asia, just barely extending into North America via Alaska. Due to their old-world origins, Arctic Warblers are not closely related to other warblers, but share the name “warbler” based on their structural similarities and general habits.
Given both its common and scientific name, it is fitting that Alaska is the only place in all the Americas where Arctic Warblers can be found. In their “new-world” range, they breed in sub-arctic forests across western and central Alaska, primarily in scrubby habitat and often near rivers.
Given this species’ old-world origins, it has a vastly different migratory strategy than other warblers that breed in Alaska. Though the exact migratory path of Alaska’s Arctic Warblers is still a mystery, we do know they winter in southeast Asia, mainly the Philippines. We also know they migrate over the Bering Strait and west over the Chukchi Sea.
Birds Connect Us
A glimpse here and there, a flicker of a leaf being expertly turned over to expose insects lurking underneath, with patience (and a sore neck) you may be rewarded with a sighting and a reminder of the incredible journeys these tiny charismatic birds undertake each year.
Here in Alaska we eagerly await the return of the birds to Alaska each spring, and the promise of the next generation. Rachel Carson said it well when she said:
“There is symbolic as well as actual beauty in the migration of the birds, the ebb and flow of the tides, the folded bud ready for the spring.”
Callie Gesmundo is an avian biologist for the U.S. Fish and Wildlife Service’s Migratory Bird Management Program in Alaska. Edited and formatted by Katrina Liebich, Digital Media Manager for Alaska.
In Alaska we are shared stewards of world renowned natural resources and our nation’s last true wild places. Our hope is that each generation has the opportunity to live with, live from, discover and enjoy the wildness of this awe-inspiring land and the people who love and depend on it.