Alaska’s Songbirds

Wandering Warblers

Tiny Migrant Songbirds with Arctic Aspirations

Townsend’s Warbler (Setophaga townsendi) is arguably the most striking warbler species that breeds in Alaska. 📷 Intermountain Bird Observatory/Zak Pohlen

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.

Several species of warbler breed in Arctic National Wildlife Refuge in the summer, all using the treed or shrubby habitats found in the southern portion as well as the Brooks Range and its foothills. Here, Arctic Refuge’s Porcupine River cuts through the surrounding boreal forest creating picturesque cliffs and canyons. 📷 USFWS/Callie Gesmundo

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.

In the 17tth century an English educator named Charles Morton wrote the first extensive work on bird migration, in which he wrongly suggested birds migrate to the moon. 📷 Michele Lamberti via Flickr

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

Blackpoll Warbler (Setophaga striata). 📷 USFWS/Zak Pohlen

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.

This map shows animated weekly abundances of Blackpoll Warblers throughout the calendar year. The data used to create this animation was collected by citizen scientists who submitted sightings of Blackpoll Warblers to eBird.

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.

Scientists use geolocators to collect light level data (i.e. daylight) to estimate an individual’s location. In order to collect the location data, the geolocator must be retrieved from the tagged individual, downloaded, and analyzed. 📷 USFWS/Zak Pohlen

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.

Birds do not grow feathers on every part of their body, but rather in uniformed sections called feather tracts or pterylae. Scientists check a bird’s condition by lightly blowing along the featherless spaces (called apteria) to check the amount of muscle and fat present. 📷 Intermountain Bird Observatory/Callie Gesmundo

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 Warbler

Wilson’s Warblers can be spotted in nearly all parts of the United States at some point during the calendar year.

Wilson’s Warbler (Cardellina pusilla). 📷 USFWS/Zak Pohlen

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.

This map depicts the range of Wilson’s Warblers in the Americas throughout the calendar year, with red depicting their breeding range, yellow their migratory range, and blue their winter range. The data used to create this map was collected by citizen scientists who submitted sightings of Wilson’s Warblers to eBird.

Male Wilson’s Warbler in Anchorage, Alaska 📷 USFWS/Laura McDuffie

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.

Portrait of Wilson’s Warbler. 📷 Michigan State Bird Observatory/Zak Pohlen

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.

This map shows animated weekly abundances of Wilson’s Warblers throughout the calendar year. Citizen scientists helped collect the data used to create this animation by submitting sightings of Wilson’s Warblers to eBird.

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

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.

Arctic Warbler Phylloscopus borealis. 📷 USFWS/Zak Pohlen

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.

This map shows animated weekly abundances of Arctic Warblers throughout the calendar year. The data used to create this animation was collected by citizen scientists who submitted sightings of Arctic Warblers to eBird.

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.

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