December 3, 2022


From the Winter 2021 problem of Living Bird journal. Subscribe now.

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Part of the magic of migratory birds is their annual disappearing act—one autumn day there could be an oriole in a treetop, and the following day it’s gone, to not be seen once more till spring.

Back within the seventeenth century, scientists had a lot of concepts about the place birds go throughout winter within the Northern Hemisphere, together with one idea that they migrate to the moon. Today we all know Neotropical migratory birds are intercontinental vacationers, chasing summer season as they go away the North for the hotter climate and longer days of the New World tropics.

Birders within the U.S. and Canada are accustomed to saying that birds spend the winter down south, however as a result of the seasons are reversed on both facet of the equator, scientists choose to make use of the time period nonbreeding season. An ornithologist’s yr is comprised of 4 elements: prebreeding (spring) migration, breeding season, postbreeding (fall) migration, and the nonbreeding season.

But not all elements of a chook’s annual cycle are created equal. A Baltimore Oriole might spend 5 months from November to March in its nonbreeding-season vary, greater than twice so long as they reside of their breeding vary.

Scientists might not consider birds are moon vacationers anymore, however for a lot of the twentieth century they’d solely obscure notions of the place birds go on migration. In the outdated printed area guides, vary maps confirmed Baltimore Orioles overwintering wherever from Mexico to Colombia. For the previous 15 years, the Cornell Lab of Ornithology’s eBird Science crew has been onerous at work on the following era of vary maps. Through advances in big-data supercomputing, eBird is melding the observations of 120,000 birders with NASA satellite tv for pc imagery to point out exactly the place birds go throughout all 4 elements of their annual cycle—together with a nonbreeding-season map that exhibits most Baltimore Orioles overwintering within the core of Central America.

These eBird maps maintain solutions to one in every of humankind’s age-old questions: Where did the birds go? As it seems, that oriole might now be at a yard fruit feeder consuming bananas, bringing pleasure to a household in Costa Rica because it beneficial properties power for the journey again north.

Forest Birds of the North Become Forest Birds of the South

Though Neotropical migratory birds fly hundreds of miles south in the course of the nonbreeding season, they’re usually looking for climatic niches and habitat circumstances much like the locations they left up north.

Prothonotary warbler by Jillian Ditner; Coastal black mangrove photo by Nick Bayly. Source: L. Bulluck et al. “Habitat-dependent occupancy and movement in a migrant songbird ... in Panama and Colombia.” Ecology and Evolution, Sept. 2019.Prothonotary Warbler by Jillian Ditner; Coastal black mangrove photograph by Nick Bayly.

Prothonotary Warbler

Prothonotary Warblers (Protonotaria citrea) like one form of habitat—moist forests—they usually search it out wherever they’re from the breeding to the nonbreeding seasons, whether or not flooded woodlands within the southeastern U.S.A. (they’re known as “swamp warblers” in Georgia and the Carolinas) or mangroves in Panama and South America.

But these warblers don’t act the identical in each locations. While conducting area analysis in mangrove forests and lagoons alongside Colombia’s Caribbean coast, scientists noticed as much as 240 prothonotaries gathering collectively at nocturnal communal roosts. These birds house out on their breeding grounds up north, the place males aggressively defend territories and densities will be as little as three warblers per 100 acres. But on their overwintering grounds the place they often roost at night time, an acre of nonbreeding habitat can include greater than 10 occasions as many warblers as an acre of breeding habitat.

A prothonotary treasure trove alongside the Colombian coast

Research utilizing geolocators has proven that Prothonotary Warblers from Virginia, South Carolina, Arkansas, Ohio, and Louisiana fly south to northern Colombia and the Magdalena River Valley for the nonbreeding season. Salamanca National Park, which is stuffed with coastal mangrove forests, comprises the biggest identified abundance with as much as 48,000 overwintering prothonotaries, or 3% of the complete international inhabitants in a single spot.

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Source: L. Bulluck et al. (2019). Habitat-dependent occupancy and motion in a migrant songbird highlights the significance of mangroves and forested lagoons in Panama and Colombia. Ecology and Evolution.

Yellow Warbler by Jillian Ditner; Cacao farm photos by Warbler by Jillian Ditner; Cacao farm pictures by

Yellow Warbler

Yellow Warblers (Setophaga petechia) have an expansive breeding vary from Alaska to the southern Appalachians. During the nonbreeding season, Yellow Warblers cram into an overwintering vary that’s a lot smaller. eBird information evaluation exhibits that thousands and thousands of Yellow Warblers—13% of the worldwide inhabitants—overwinter in Nicaragua, the place they’re usually present in shade-coffee farms and different agroforestry operations.

Growing chocolate on farms that additionally feed warblers

Cacao Oro de Nicaragua is a cocoa plantation in Nicaragua that’s house to tens of hundreds of overwintering Yellow Warblers. After the farming lands have been devastated by hurricanes, the Cacao Oro farm was based as a large-scale agroforestry mannequin to rehabilitate greater than 3,000 hectares (or virtually 7,500 acres). By 2022, Cacao Oro will harvest about 4,000 metric tons of UTZ-certified sustainable cocoa, whereas restoring forest cowl and using native indigenous staff.

American Redstart by Jillian Ditner; Mayan biosphere photo by Viviana Ruiz Gutierrez.American Redstart by Jillian Ditner; Mayan biosphere photograph by Viviana Ruiz Gutierrez.

American Redstart

On their fall migration south, hordes of American Redstarts (Setophaga ruticilla) launch themselves off the coasts of Florida, Alabama, Mississippi, and Louisiana to fly throughout a whole lot of miles of open water within the Gulf of Mexico till they discover land once more on the Yucatan Peninsula. eBird information evaluation exhibits that a few third of the worldwide inhabitants of American Redstarts overwinters within the Yucatan areas of Mexico, Belize, and Guatemala.

Warblers amongst Mayan ruins

The Mayan Forest is the biggest tract of forest left in Central America, house to 21 species of migratory warblers from November by March—together with one-tenth of the world’s American Redstarts. In 2017, the Cornell Lab of Ornithology partnered with the Mexican authorities and the Wildlife Conservation Society to launch a neighborhood bird-monitoring and conservation mission right here. The analysis exhibits that cleared cattle pastures will be restored to forest and assist migratory birds inside only a few years.

Blackpoll Warbler by Jillian Ditner; photo of Villavicencio by Nick Bayly. Sources: N. Bayly et al. “There’s no place like home.” Animal Behaviour, April 2020.; C. Gomez et al. “Migratory connectivity then and now.Blackpoll Warbler by Jillian Ditner; photograph of Villavicencio by Nick Bayly.

Blackpoll Warbler

In their annual migrations between northern North America and South America, these long-distance athletes fly greater than 20,000 km (or 12,500 miles)—sufficient to earn a free journey in some airline frequent-flyer packages.

Though Blackpoll Warblers (Setophaga striata) breed all throughout North America from Alaska to the Canadian Maritimes, they cluster into northern South America for the nonbreeding season. These 4 months are essential to every Blackpoll Warbler’s survival, because it’s among the many forests of the Andes Mountains and Orinoco and Amazon River basins that they’ll feed and pack on weight to gasoline the journey again to their boreal forest breeding grounds.

La Guajira Peninsula on Colombia’s northern coast is the primary place many Blackpoll Warblers contact down after an unimaginable 1,800-mile flight south off the Atlantic Coast. It’s the longest recorded overwater journey of any songbird. When the Blackpolls arrive they’re emaciated, however they rapidly fatten again up, rising their physique mass by 20% in only a few days by gorging on caterpillars. The timing of the Blackpolls’ arrival is synced with a wet season in La Guajira, which spawns a livid green-up of timber—and a corresponding profusion of caterpillars. Migration-weary Yellow-billed Cuckoos and Prothonotary and Connecticut Warblers additionally take part with the Blackpolls to feast on caterpillars.

A warbler fueling station within the foothills of the Andes

Scientists have documented Blackpoll Warblers growing their physique mass by 40% on the finish of the nonbreeding season by feeding within the foothills across the metropolis of Villavicencio, a mixture of native forests and plantations for citrus fruits and cacao (for chocolate). A examine confirmed that the load Blackpoll Warblers placed on right here fueled nonstop northward flights of greater than 2,700 km (or 1,600 miles) to Cuba, Florida, even South Carolina—greater than half their spring migration again to Canada.

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Sources: N. Bayly et al. (2020). There’s no place like house: tropical overwintering websites might have a basic position in shaping migratory methods. Animal Behaviour; C. Gomez et al. (in evaluate). Migratory connectivity then and now. Proceedings of the Royal Society B; N. Bayly and Ok. Rosenberg. (2020). Discovery of an important hyperlink within the marathon migration of the Blackpoll Warbler. Partners in Flight.

Baltimore Oriole by Jillian Ditner; Coffee plantation photo by Jeffrey Arguedas. Sources: K. Sparrow et al. “Conditions on the Mexican moulting grounds influence feather colour and carotenoids in Bullock’s Orioles.” Ecology and Evolution, April 2017.Baltimore Oriole by Jillian Ditner; Coffee plantation photograph by Jeffrey Arguedas.

Baltimore Oriole

Orioles are a yard feeder favourite for North American birders in sum­mer. Set out an orange half and completely happy orioles will gorge like children on ice-cream sundaes. Where do the bright-orange birds get their candy tooths? During the 5 months of their nonbreeding season in Central and South America, their food regimen consists of foraging on orange and banana timber. So after they get again north to their breeding grounds, the orioles search for their favourite trop­ical fruits.

On their overwintering grounds in Central America, Baltimore Orioles (Icterus galbula) are frequent guests to shade-coffee farms. The orioles arrive simply because the espresso berries are turning pink. When the farmers see the orange-and-black birds within the timber, they realize it’s time to reap the espresso.

Backyard chook within the North and South

About 55% of the complete inhabitants of Baltimore Orioles overwinters in El Salvador, Honduras, Nicaragua, and Cos­ta Rica, the place they’re welcome guests in backyards. In Costa Rica individuals set out fruit on picket platforms, and the return of this colourful chook ev­ery yr indicators the approaching of the dry season.

Sources: Ok. Sparrow et al. (2017). Conditions on the Mexican moulting grounds affect feather color and carotenoids in Bullock’s Orioles. Ecology and Evolution.

Bullock's Oriole by Jillian Ditner; photo by??Bullock’s Oriole by Jillian Ditner; Photo of Chihuahua, Mexico, by Chris Corrigan.

Bullock’s Oriole

Baltimore and Bullock’s Orioles was once thought of the identical species (known as the “Northern Oriole”). But right now sci­entific analysis has proven that they’re two completely different birds, with Bullock’s Ori­oles (Icterus bullockii) having a definite DNA profile and completely different breeding vary within the West.

Like their jap cousins, Bull­ock’s Orioles will be seen on espresso farms throughout their nonbreeding sea­son, although their overwintering vary is farther northwest than that of Bal­timore Orioles. Bullock’s Orioles have been regularly seen throughout chook surveys on shade-coffee farms within the state of Chi­apas in southern Mexico.

A pit cease for Mexican monsoons makes for brighter feathers

Bullock’s Orioles make a two-part migration south in autumn. First, they cease off alongside the southwestern U.S. border and northern Mexico to benefit from the monsoon season. Whereas most songbirds molt on or close to their breeding grounds, Bullock’s Orioles develop new feathers throughout this mid-migration stopover. Recent analysis has proven that the place the orioles settle and what they eat throughout their molt interval in Mexico is straight related to plumage coloration. It seems that birds with a extra plant-based food regimen (seemingly consuming fruits wealthy in pink or orange carotenoids) are in a position to produce extra colourful plumage. The now-flashier orioles then proceed on so far as Guerrero and Oaxaca in southern Mexico for the 5 months of their nonbreeding season.

Epic Journeys

Raptors and shorebirds make the longest seasonal migrations down the Americas.

Broad-winged Hawk by Jillian Ditner; photo of Sapzurro by Nick Bayly. Sources: N. Bayly et al. “Migration of raptors ... through the Darien of Colombia.” Ornitologia Neotropical, 2014.Broad-winged Hawk by Jillian Ditner; photograph of Sapzurro, Colombia, by Nick Bayly.

Broad-winged Hawk

Each fall, spectacular kettles of Broad-winged Hawks (Buteo platypterus) by the a whole lot are a main attraction at hawkwatch websites in Pennsylvania and Minnesota. But their numbers and densities develop even excessive­er as they proceed farther south, enjoyable­neling down the narrowing hourglass landform of Central America and be a part of­ing with different species to type huge migratory flocks of hawks by the tens of hundreds—what’s been known as a “riv­er of raptors” flying by Veracruz, Mexico, and Panama.

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Scientists have used satellite tv for pc trans­mitters to trace Broad-winged Hawks as they traveled from Canada all the way in which all the way down to overwintering grounds within the Andean forests of Colombia and Bo­livia—a visit of greater than 4,000 miles, accomplished in increments of about 70 miles per day.

Above a small Colombian fishing village, one of many world’s busiest raptor highways

The little border city of Sapzurro, the place Panama meets Colombia, is one in every of solely six locations on the earth the place greater than half one million migrating raptors have been counted in a single season. Sapzurro lies close to the Darien Gap, so-called as a result of its rugged jungle is the one hole within the Pan-American Highway that runs from Alaska to Chile. The isthmus right here is simply about 100 miles large, and based on chook surveys carried out by the nonprofit science group SELVA, virtually 140,000 Broad-winged Hawks handed above Sapzurro within the fall of 2012.

Source: N. Bayly et al. (2014). Migration of raptors, swallows and different diurnal migratory birds by the Darien of Colombia. Ornitologia Neotropical.

A kettle of hawks in Sapzurro by Nick Bayly.A kettle of hawks in Sapzurro. Photo by Nick Bayly.
Snowy Plover by Jillian Ditner; photo of shorebird habitat by Osvel Hinojosa-Huerta.Snowy Plover by Jillian Ditner; photograph of shorebird habitat by Osvel Hinojosa-Huerta.

Snowy Plover

Snowy Plover (Charadrius nivosus) breeding populations are scattered alongside the Pacific and Gulf coasts, with just a few inland breeding teams at alkaline or saline lakes and reservoirs. In the nonbreeding season, Snowy Plovers cluster alongside the coasts of southern California, Texas, and Mexico. The Pacific Coast inhabitants of Snowy Plovers is protected below the U.S. Endangered Species Act resulting from habitat loss alongside seashores.

Return of the plovers

In the Nineteen Nineties, Snowy Plovers have been extirpated from the seashores round Ensenada, Mexico, on the Baja Peninsula. Mexican biologist Jonathan Vargas began a program in 2017 to deliver the Snowy Plovers again. In 2019, Vargas joined the Cornell Lab’s Coastal Solutions Fellows program and labored with native conservation teams to persuade town council to implement coverage rules that shield shorebird habitat. With fencing put in round plover areas on the seashores and groups of individuals maintaining watch in opposition to ATVs and disturbance, the Snowy Plovers returned. In the final two years, greater than 50 plover nests have hatched greater than 150 chicks. More than 80 banded plovers from southern California have been documented overwintering there.

Spotted Sandpiper by Jillian Ditner; photo of Amazon River by Ken Rosenberg.Spotted Sandpiper by Jillian Ditner; photograph of Amazon River by Ken Rosenberg.

Spotted Sandpiper

The dapper Spotted Sandpiper (Actitis macularius) is a com­mon chook in each hemispheres. It’s probably the most widespread breeding sandpiper in North America, and probably the most wide-ranging overwintering shorebirds in South America, from coastal seashores and mangroves to the Amazon Forest inside.

Sandpipers on the Amazon

The greatest time to rely birds in South America is August to April, as that’s when breeding birds there are singing and migratory birds from North Amer­ica have taken up residence for his or her nonbreeding seasons. Ken Rosen­berg, a Cornell Lab conservation sci­entist, says Spotted Sandpipers have been frequent birds throughout his survey expe­ditions deep into Peruvian rainforests. “Traveling by boat by the remot­est tributaries of the Amazon River, Spotted Sandpipers have been a well-recognized sight,” says Rosenberg. “We flushed Spotted Sandpipers alongside the sandy riverbanks at each bend within the river.”