When migration and birds are discussed, the mental images of birds like geese, swallows, and birds of prey flying over long distances are immediately conjured. Around 40% of the world’s birds undergo some form of migration, meaning roughly 4,000 birds cover a certain distance throughout the year.
Firstly, Why Do Birds Migrate
Migration mainly occurs due to scarce resources like food and roosting spots. While cold weather is a factor, some birds, like hummingbirds and juncos, can survive if adequate food is available. It is believed that the tendency for birds to migrate evolved over the years when birds living in the north flew toward the south, searching for food.
Interestingly, the need to migrate is inherent in certain species. This has been confirmed by tagging juveniles migrating for the first time and verifying that they travel to the same destination as their predecessors. Even though, for many birds, the change in natural sunlight signifies the time to migrate, some birds, like sparrows and cuckoos, will do so at night, lowering the risk of predation and overheating.
Different Types of Bird Migration
There are three patterns of bird migration.
1. Long Distance Migration – When a bird migrates over a great distance, generally from a northern region to a southern one, it is categorized as a long-distance migration. This migration can occur in groups (storks or geese) or solo (Eurasian Blackcaps or Yellow-billed Cuckoos). Birds known to fly over long distances include the following.
Arctic Tern (covers the longest distance at a phenomenal 60,000 miles)
Sooty Shearwater
Short-tailed Shearwater
Pectoral Sandpiper
Northern Wheatear
Pied Wheatear
Adélie Penguin
Bar-tailed Godwit
Calliope Hummingbird
Great Snipe
Bar-headed Goose
Eurasian Wryneck
Red Knot
Orange-bellied Parrot
Sandhill Crane
Ruby-throated Hummingbird
Northern Pintail
Snow Goose
Barn Swallow
Amur Falcon
Osprey
Baltimore Oriole
Great Reed Warbler
Willow Warbler
Taiga Flycatcher
Gadwall
2. Short Distance (or Altitudinal) Migration – Altitudinal migration involves traversing small areas for food or moving to a different altitude if the weather becomes uncomfortable and is not dependent on the length of day. Alice Boyle gives a list of North American altitudinal migrants here. Some notable birds that are known to travel over short distances include:
Yellow-eyed Junco
Prairie Falcon
Wallcreeper
American Coot
American Dipper
Brewer’s Blackbird
Common Chiffchaff
Dusky Grouse
Eurasian Skylark
Greater Sage-grouse
Great Gray Owl
Hawaiian Goose
House Finch
Merlin
Mountain Quail
Northern Saw-whet Owl
Skylark
Snow Bunting
Western Bluebird
White-throated Dipper
Blue-fronted Redstart
Indian Pitta
White-browed Wagtail
3. Dispersal (or Irruptions) – An irruption occurs when birds are forced to travel beyond their normal range, as their usual destinations fail to provide them with the resources needed. Eventually, they may choose to migrate to their new destination regularly. Examples include redpolls and siskins traveling to certain locations in North America where they find more food in the winter.
Migratory Birds Flyways
Migratory birds commonly use predetermined “routes” called flyways to reach their destinations. These are the flyways followed by them:
Pacific Americas – This is one of three major flyways used by birds in North America, starting from the breeding grounds in Alaska and ending at Patagonia.
Central Americas – This flyway covers the flatlands of the Great Plains of North America, starting from the Canadian Prairies and ending at the Gulf of Mexico.
Atlantic Americas – This flyway generally starts from Greenland or Canada and goes to South America and the Caribbean. Sometimes, birds will join the route midway from the Appalachian mountains.
East Atlantic – While there are birds who start their journey on this flyway from Canada, most of the birds using this flyway are from northern Eurasia. Their final destination is southern Africa, though some will overwinter in western Europe.
Asian-East African – While little is known about the birds that use this flyway regularly, it covers over 60 countries, from Siberia in the north to South Africa in the south. Some birds recorded using this flyway include the Amur Falcon, the Barn Swallow, and the Steppe Buzzard.
Central Asian – The Indian subcontinent, the location of several wintering grounds for migratory birds, including the Rann of Kutch, is the final destination for those following the Central Asian Flyway. Like the Asian-East African Flyway, the birds on this route begin their journey from Siberia.
East Asian-Australasian – Ranging from the Taimyr Peninsula in Russia in the northeast to Australasia in the south, over 60 birds use this flyway regularly, including the Black-throated Robin and the Yellow-breasted Bunting.
Black Sea-Mediterranean – Birds travel from their breeding grounds in northern Europe and Asia to their feeding grounds in southern Europe and Africa via the Black Sea-Mediterranean Flyway. However, there has been a significant decline in birds on this flyway since 2003 due to overhunting.
Do Migratory Birds Face Any Risks
Despite the rewards, birds are at a lot of risk while migrating. Often, the entire flock fails to reach their final destination, with several of them dying. Reasons vary from lousy weather conditions, loss of stopover sites, and increased predation as the tired birds make easy prey. Humans have also significantly contributed to the drop in migratory birds’ numbers through the construction of tall buildings and windmills, climate change, oil spills, and commercial fishing. They are also often hunted for sport, especially in North America. As the migrating birds tend to be part of the breeding population, this hurts several species, especially those with low reproductive rates. Efforts have been put into place, like the Migratory Bird Treaty Act, which restricts the hunting of migratory species under its protection.
