If you want to make the most of the fall bird migration, you need to know when the peak of migration is in your area. The exact times of fall migration vary, but there are plenty of clues birders can watch for in order to learn when their best fall birds will be arriving.
The actual dates of autumn vary based on your local geography, altitude, and climate. In the Northern Hemisphere, autumn occurs from early to mid-September through mid- to late November or early December. In the Southern Hemisphere, autumn is from mid- to late March through late May or early June. Birds do not have calendars, however, and they rely on different factors to determine when fall commences and it is time for migration.
Factors Affecting Migration
Many different factors affect when birds migrate in the fall, and they use different clues to determine when the time is right to move from their breeding range to their wintering range. Factors that affect birds’ fall migration include:
- Light: Light levels and the overall daily angle of the sun are strong clues for the change of seasons. As the days grow shorter and light angles shallower birds know the time is right to begin migration.
- Temperature and Climate: Cooler temperatures are another indication of the change of seasons. In some climates, the onset of more rains (the rainy season) is another factor that influences the timing of migration.
- Food: As summer crops are consumed and less food is regionally available, birds know it is time to move on to areas that have more resources available. In years of severe drought or when other factors have reduced food sources, birds may migrate earlier than normal.
- Offspring: Birds will not migrate until their offspring are mature enough to care for themselves or to begin their first migration journey. Birds that breed later in summer will also typically migrate later, but as the baby birds mature, the time for fall migration is at hand.
- Location: Where birds are located dramatically impacts when they begin fall migration. Shorebirds that nest in the Arctic may begin their autumn journey as early as July, while passerines in areas closer to the equator may not start migrating until late September.
With so many different factors affecting the timing of migration, how is it possible to know when your local migration is underway? As birds travel from breeding ranges to wintering ranges, they can cover great distances in a single day, and birders who aren’t aware of migration patterns can miss spectacular opportunities as birds move through their region. Fortunately, there are many local clues you can use to determine exactly when birds are migrating in your area.
- Fall Festivals: Birding festivals in autumn are often planned to coincide with peak migration periods with the greatest diversity of visiting migrants. If you know of local festivals, start watching for migrating birds a few weeks before the festival dates to see what new arrivals are in the area as the seasons change.
- Hunting Season: Game bird hunting is often timed during peak migration. Being familiar with local hunting seasons for ducks, geese, quail, doves, and other game birds can help birders recognize the most productive birding times.
- Backyard Species: Watching your familiar backyard birds carefully year after year can teach you about their seasonal migration habits. Use a calendar or birding journal to note when you last see certain bird species each autumn, and within a few years, you will be able to reliably predict when their seasonal migration will begin.
- Flocks: Many migratory birds, particularly swifts and swallows, will form tremendous flocks in the fall just before leaving on their migration journey. When these flocks begin to form on wires or at popular roosts, migration is about to begin.
- Plumage: Many male songbirds, such as American goldfinches, molt into non-breeding plumages that are duller and more camouflaged than their familiar breeding brilliance. Even if those birds do not migrate themselves, their change of attire can indicate the change of seasons and the onset of fall migration. Similarly, watch juvenile birds as they mature, and the more they begin to resemble their parents, the closer fall migration will be.
- Genders: In dimorphic species, watch each gender carefully to see when one leaves the other behind. In rufous hummingbirds, for example, mature males migrate a week or two before females, and their disappearance can be a clue that migration has begun.
No matter when your fall migration takes place, you need to be ready to take advantage of its great birding opportunities.
- Plan your bird-friendly landscaping with migration in mind and opt for flowers that bloom in late summer and early fall to help attract and nourish migrating birds.
- Leave berries, fruits, and seed-bearing flowers intact, rather than dead-heading, late in fall to provide a refueling stop for migrants. These foods will also be welcome for winter visitors.
- Avoid pruning trees and shrubs in autumn if possible to provide additional shelter for migrating birds. If the pruning is necessary, add the cuttings to a brush pile for easy shelter.
- Attract birds using leaf litter that you leave on your lawn or underneath shrubs to provide a rich foraging area for ground-feeding birds such as sparrows, doves, thrushes, and quail.
- Winterize your birdhouses in late fall to convert them to roosting boxes for late-season migrants and winter residents.
- Go birding frequently, particularly in areas that cater to fall birds’ needs for food and shelter, to note any new arrivals and to enjoy the last glimpse of departing summer species.
By learning what to look for to time fall migration, it is easy for every birder to enjoy this rich, productive birding season.