With Contributions from: Zoe Finney, Aubrey Ellickson Fulsaas, and Don Quintenz
People have wondered where birds go during winter for thousands of years. Early theories included the idea of hibernation and even transmutation between species. One theory from the 1700s came close: it involved migration, but the birds’ destination was thought to be the moon.
Then, in the early 1800s, a German named Count von Bothmer discovered a stork with a spear lodged in its body while he was on his estate. He took the bird to a professor who said that it must have come from Africa. Over time, people found other birds with spears in their bodies, demonstrating that other storks were also flying from Africa. These discoveries paved the way for our current understanding of migration.
Migration is relatively new to our understanding, so there are still many mysteries surrounding it. Development of scientific instruments have just recently allowed researchers to pinpoint exactly where birds go during the migration cycle. This advancement has showed us how complex migration is and has brought forth even more questions. We do, however, now have a basic understanding of how it works.
Why Do Birds Migrate in the Fall?
When fall arrives in Wisconsin, migratory birds have finished nesting and raising young, the driving force motivating the birds to originally fly north. Once their young are grown, the birds return to where they came from in the spring. There are a number of factors causing birds to fly south for winter. A major one is food availability. By fall, insects that were plentiful in the spring and summer in the northern range are less abundant. But they are still plentiful in the warmer climate of the south. Birds must establish territories in the south to take advantage of this food source and gain strength to prepare to nest again.
Temperatures are getting colder at this time, and though many birds can survive the colder temperatures when food is available, most neo-tropical migrants can’t. The arriving cold signals that it’s time for the birds to go to warm climates. Later in the summer, the changing duration of light, called photoperiod, is also a deciding factor motivating the birds to search for more welcoming habitats. There is a genetic underpinning that tells many birds that it’s time to move on as well.
Differences Between Spring and Fall Migration
Fall migration is in many ways quite different from the spring event. Some birds take a different route back to their wintering grounds. Blackpoll Warblers, who have the longest migration of any warbler, fly up the Mississippi Flyway in spring but return to the tropics via the Atlantic Ocean.
Overall, fall migration is less distinct in nature compared to spring, and the timing of birds’ departure is more flexible. The main impetus for migration is less urgent, as birds aren’t trying to find a mate or to establish nests. Similarly, because they aren’t looking to pair up, male birds display less colorful plumage and they don’t sing in fall, just making various calls such as contact calls and alarm calls. It is very difficult to even tell some species of songbirds such as the warblers apart at this time of year, also partly due to their duller, non-breeding plumage. To confuse things even more, the less colorful juveniles and females fly south along with the males.
The Variety of Migratory Patterns
Birds in Wisconsin follow a number of migratory patterns. There are birds who don’t migrate at all, permanent residents who stay here year-round. One is the White-breasted Nuthatch, who you’ll see clinging to the trunks of trees eating insects all year. You’ll also find the Black-capped Chickadee foraging at the tips of branches. These birds, among other residents, often visit feeders in winter. Another pattern, short-distance migration, involves moving small distances, such as within one or between several states. Red-winged Blackbirds follow this behavior; their winter range is mostly in Illinois and farther south in the US.
Many of the spectacular birds that we look for in the spring, such as warblers and other songbirds, undergo long-distance migration. These are the neo-tropical migrants, breeding in the US and Canada and then wintering in Central and South America. They are considered true migrants and are pre-programmed to follow this pattern regardless of food availability or weather. Baltimore Orioles, Scarlet Tanagers, and Indigo Buntings are good examples, with these species migrating back to the tropics.
Alternate Migration Styles
Some birds follow out-of-the ordinary migratory styles. Species who are partial migrants will go to wintering grounds, but some will stay if the winter is mild. Crows are believed to be partial migrants, with some staying in their breeding grounds over winter and others migrating to locations of various distances. Partial migration is still not fully understood, however, and while an individual follows the same pattern over time, the species behavior is sometimes difficult to predict.
Nomadic migrants follow resources and are not tied to the causal factors of temperature, light, or genes. They are also not as strongly connected to a pre-determined destination when migrating. This is the case with Cedar Waxwings, who wander from place to place following food.
Waterfowl present an interesting facet to migration. Some waterfowl species’ winter destination is Milwaukee, as they are seeking the closest locations to their Canadian and Arctic homes offering open water. In Wisconsin, look for Common Goldeneye, with males having an all-white body and dark iridescent green head, and Greater Scaup, with dark head and chest and contrasting white sides, among others hunting in the waters of Lake Michigan through winter.
Bird Navigation
One question that people often ask is how birds find their way back to their wintering grounds. Birds navigate in many ways. They can follow the stars and track the sun’s movements. Birds are also aware of the earth’s magnetism and can recognize features of stopover sites and geographic markers as well.
Researchers believe many birds have an imprint of where they need to go encoded within. The Ruby-throated Hummingbird migrates to south of the Mexican border. But it is a solitary bird, so when a juvenile travels over the Gulf of Mexico for the first time to the exact location its ancestors came from, it does so with no assistance from other birds. Scientists think its destination must be genetically programmed.
The Procession of Species During Fall Migration
The earliest birds to return south are shorebirds. At the Center, look for shorebirds migrating beginning in July and peeking in August. They include the Solitary Sandpiper, with its blackish under-wings and white belly making it uniquely identifiable in flight, and the Killdeer, who like dry habitat. Their white belly and neck contrast the tawny wings and back and black ring around its lower neck.
Around August, viewers will begin to see songbirds migrating, including warblers. The majority of warblers will migrate later in the season, mostly in August and September, and are seen at the Center as late as October. Some of the warblers you will see include the Orange-crowned Warbler, whose wintering grounds are farther north than most warblers and whose migration is closely tied to food availability. The olive-colored, non-breeding Tennessee Warbler is easily confused with the Orange-crowned Warbler in appearance except for the white patch under its tail. It is found high in the trees and also migrates from September to October. Yellow-rumped Warblers, known for their streaky brown and yellow coloration, will fill up southern forests in the fall.
Also on the move at this time, kettles of Broad-winged Hawks and other raptors will fill the skies on the way to their winter destinations. On a nice blustery October day with strong northerly or northwesterly winds, look for hawks flying together in the hundreds or even thousands.
Observing birds throughout the year at the Center is a rewarding experience. Watch migration in fall, and then see the species that stay over winter. When spring arrives, look for bird species you saw during fall migration returning to their northern breeding grounds. In summer, observe nesting birds to complete the yearly cycle.
