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Water jewelsWhat every birdwatcher needs to know to understand our best-known and most charismatic birds Contributed by Eldon Greij
Published: September 1, 2008 Waterfowl have to be among the best known and most fascinating birds. They range from large, elegant swans to small, colorful teal. Their flights in both spring and fall are spectacular and awe-inspiring. And for many birdwatchers, the true harbingers of spring aren't crocuses or tulips but skeins of high-flying Canada Geese.
Distributed widely, waterfowl occur on all of the world's continents except Antarctica (though they are present on subantarctic islands). A few species utilize uplands, but most are associated with aquatic habitats, such as marshes, ponds, potholes, lakes, and rivers.
Waterfowl belong to a single family (which is known as Anatidae). Biologists divide Anatids into several subfamilies, three of which occur in North America: Whistling-Ducks (Dendrocygninae), Geese and Swans (Anserinae), and True Ducks (Anatinae).
Scientists further split the subfamilies into tribes. Geese and swans are placed in separate tribes, while True Ducks are divided four ways: into Dabblers (Mallards, pintails, and teal); Pochards or Inland Divers (Redheads, Canvasbacks, and scaup); Sea Ducks and Mergansers (eiders, scoters, and mergansers); and Stifftails (Ruddy and Masked Ducks).
Knowing differences between the tribes can be helpful in the field. Geese and swans, for example, ride high in the water, and most of them are large.
Among the True Ducks, the Inland Divers and Sea Ducks ride low, and their backs slope down to the surface. Dabblers, on the other hand, ride higher, and their backs are more horizontal, giving them a box-like shape.
Of course, ducks can be identified by their wings alone because of unique colors and patterns. In Dabblers, for example, the upper surface of the trailing edge of the inner wing (the speculum) is brightly colored and boldly patterned.
Bonds for life
Other major differences exist between tribes. Males and females are similar in appearance among geese, swans, and whistling-ducks. (That is, they are sexually monomorphic.) They typically have one annual molt, which occurs after the breeding season, and they maintain pair-bonds for several years - possibly for life. The fact that males remain with females after the young hatch is probably the reason that males help care for the young. Geese and swans tend to remain in family groups well into the fall, including migration.
The males and females of True Ducks, however, are markedly different in appearance - that is, they are sexually dimorphic, and especially so during the breeding season. They undergo not only a complete molt after the breeding season but also a partial molt, typically during the fall or winter. In males, this molt gives rise to colorful breeding (or alternate) plumage. Females, by contrast, wear shades of brown and black all year. Their plumage makes them less visible, especially during nesting.
Ducks' complete molt after the breeding season leaves them temporarily flightless, because they molt all wing feathers simultaneously (as do all waterfowl). In males, the result is a non-breeding (or basic) plumage that is dull brown and female-like. It is thought to provide camouflage when the males are flightless and vulnerable to predators.
In some cases, this plumage, called eclipse, is worn for only a matter of weeks before it is replaced by the new breeding plumage. The short duration allows males time to develop their breeding plumages before the onset of courtship.
Male Mallards, for example, begin courtship in early fall and are in eclipse plumage for only a month or two. Adult males enter fall migration in full breeding plumage.
Male Blue-winged Teal, on the other hand, look female-like during fall migration, except for a solid white bar in the speculum. (The bar is mottled on females.) They will acquire their breeding plumage in late winter, and courtship will follow. In fact, you can watch the courtship flights of teal (one female with several males) during spring migration.
Mix and match
When most species of True Ducks begin courtship, they are often in flocks containing birds from different regions of the country. Consequently, a female may select a male from almost any region, and they usually return to her nesting area. This behavior mixes the gene pool so effectively that individual birds are similar over a large range. Regional differences in the appearance of True Ducks rarely exist; subspecies, therefore, are not recognized.
Canada Geese, on the other hand, migrate in family units with other members of their breeding population. Because females select males from this group during courtship, members of the population possess a more uniform appearance and gene exchange between populations hardly occurs. As a result, differences can develop between populations. If the differences grow great enough, the populations are called subspecies. (And if subspecies become different enough, you can end up with different species. That's what happened in 2004, when small, tundra-nesting Cackling Goose was split from Canada Goose. Most biologists recognize four subspecies in Cackling Goose and seven in Canada Goose.)
The spectacular flights, incredible beauty and grace, and fascinating behaviors of waterfowl provide great enjoyment for birdwatchers. They are truly an amazing group of birds. |
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