The Birding Year in the Pacific Northwest
July: The Beginning of Fall
Written by Andy McCormick
Andy McCormick, Volunteer and Former Board President of Eastside Audubon
For birds, July marks the beginning of fall. I hear you thinking, “Didn’t the migrating birds just arrive and aren’t we getting ahead of ourselves?” Yes, but the breeding season for neotropical migrating birds is short. Western Sandpipers, Short-billed Dowitchers, Black-bellied Plovers, and Greater and Lesser Yellowlegs to name a few shorebirds, are long-distance migrants which breed in the Arctic tundra and boreal forest of Canada. Once the Earth passes the solstice, birds begin to stir. Just as birds respond to the length of daylight hours in spring and begin their northward migration, the reduction in the hours of daylight after the June solstice also stimulates birds to move.
In response to this change in available light, shorebirds are some of the first birds to begin heading south. Because Seattle is one of the most northly cities in the Lower 48 and consequently is closer the Arctic Circle than most other large American cities outside of Alaska, the early wave of shorebirds migrating south reaches the Pacific Northwest around the second half of July.
BIRDS ANTICIPATE THE SEASONS
We humans have used a set of facts based on the position of the Earth in relation to the sun to determine when the seasons begin and end. We have made a decision that spring in the Northern Hemisphere begins at the April equinox (April 20) and fall begins at the September equinox (September 21), the times of the year when the lengths of day and night are the same. We know from our own experience that spring flowers and warmer temperatures can occur before the date of April 20, and we can experience cooler and wetter days before September 21. Birds experience these same changes and respond very quickly to them.
Generations of birds over millennia have followed this pattern. Warblers, orioles, tanagers, and other neotropical birds, have migrated well before the onset of winter to complete the cycle of migration-breeding-migration and return to their tropical habitat in Central and South America. Our resident robins, sparrows, and nuthatches make a shorter migration of their own, usually moving down from high elevation to the lowlands where they will spend the winter.
THE STRESSFUL SEASON
Migrating shorebirds and neotropical birds are quite stressed by the time July rolls around. Many a robin looks a bit frazzled by late July. Their color will have faded, and their feathers will appear worn, with frayed edges, and sometimes broken. When we consider the daily obstacles and irritants birds encounter, it is amazing the feathers hold up as well as they do. The constant flow of air across the birds body, wings, and tail, exposure to rain and wind, and frequent contact with grass, leaves, and tree branches all take a toll on feathers. They have been through several taxing months. The energy toll expended to complete the northward spring migration, to breed and nurture young birds, and begin another long migration, is compounded by the pattern of their feather molt, that is, the process of losing aging feathers and growing new ones.
Birds are also exposed to the ultraviolet rays of the sun which over time can cause bleaching and weakening of their feathers. Pigments called melanin in the feathers and skin of birds add strength to the structure of feathers and provide protection by absorbing the sun’s rays. Gradually, the melanin become less effective, and feathers fade and weaken. In response, birds have evolved different annual strategies for growing new feathers.
FEATHER MOLT
The molt process includes both the loss of worn feathers and the growth of new ones and requires a large expenditure of energy. Bird species have evolved a variety of strategies to replace feathers, but a necessity for all birds is the presence of an adequate supply of suitable food for them during the molt period. Some birds molt feathers in stages of wing and tail feathers at one time of year, and body feathers at another time. Others, such as ducks, molt them all at once. The fall molt occurs in one of three typical patterns: Molting before, after, or during migration.
Molt before migration:
Smaller birds such as Red-eyed Vireo and Swainson’s Thrush can grow feathers rather quickly and will usually remain on the breeding grounds until they complete a feather molt. This process allows them to focus their energy on growing feathers before embarking on a long migration. Short-billed Dowitchers will also molt feathers on the breeding grounds and will have clean and sharp new feathers when they pass through the Puget Sound region.
Molt after migration:
Larger birds such as the Great Blue Heron take a much longer time to grow long feathers and most herons may begin molting on the breeding grounds and will suspend feather molt until after migration, completing the molt over the winter. This pattern allows herons to retain all their flight feathers for their migration. Long-billed Dowitchers migrate before molting and usually migrate inland and east of the Cascades. Worn feathers on a dowitcher in late summer can be a good indication that it is a Long-billed rather than Short-billed Dowitcher. Adult Woodpeckers are another family of birds which wait and molt after migration.
Molt during migration:
Researchers have become more aware that some families of birds will moderate their feather molt into stages. Eared Grebes, for example, will begin migration, but instead of completing the journey in one long series of flights, will move to a traditional intermediate location and molt their feathers there. Large flocks of Eared Grebes congregate at the Great Salt Lake and Mono Lake during their molt. There they feed on brine shrimp in the salty lakes. This stop is often referred to as a molt-migration location where birds can drop old feathers and grow new ones in a relatively safe area.
IDENTIFYING FALL SHOREBIRDS
Hatch-year birds, that is, baby birds from the current summer, will drop their downy feathers and grow new adult-looking feathers while still on the breeding range. This new set of feathers is called their basic plumage which is often referred to as winter plumage. When watching shorebirds in late summer and fall, birders will notice that the adults in fall will have feathers that are dull, worn, and frayed. In contrast, the later arriving juveniles will have plumage which is fresh with sharply defined edges and colors. This plumage difference is an important consideration when trying to identify a shorebird. The first step is to try to determine the bird’s age – adult or juvenile – by examining the condition of the bird’s feathers. Knowing the age of a shorebird helps us put the shape and color of the bird in the proper perspective. The bird’s behavior, habitat preference, and structure are often better clues to identification than the color of the feathers.
SUGGESTIONS FOR FURTHER READING
Lovette, Irby J. and John W. Fitzpatrick (2016). The Cornell Lab of Ornithology Handbook of Bird Biology, Third Edition. Cornell University.
Paulson, Dennis (1998). Shorebirds of the Pacific Northwest. Seattle: University of Washington Press.