The first part of this outstanding introduction to the true water/ owl was begun in the last issue of the "Watchbird ''. It is from Frank Todd's forthcoming book, A Gathering of Waterfowl. In the last issue Mr. Todd explained the relative position of the family Anatidae to the other birds of the world. He mentioned how waterfowl are ancient birds that are found on all continents except Antartica.
Waterfowl have some very interesting features including their "duck bills", webbed feet, unusual variation in vocal organs, divergent coloration, extensive migratory habits, phenomenal navigational ability, and a summer moult that leaves the birds flightless for about two months. Of course, there are exceptions to every one of these characteristics.
The last section of this article ended with the spring migration when the waterfowl return to their northern homes to breed and rear their young.
Ducks, geese and swans are noted for their highly ritualized courtship behavior which may range from the very subtle and intricate to very elaborate. Mating usually takes place in the water and is often referred to as "treading" by aviculturists. Copulation is somewhat difficult for birds, and in the case of waterfowl, the act is complicated due to the unstability of the surface of the water. As a result, the males have developed a distinct, erectile penis which is lacking in most other avian species which merely need to bring together their cloacas for fertilization to result. However, penetration is required for waterfowl. Due to the presence of the penis, it is possible to accurately sex wildfowl by inspecting the vent.
Most anatids are monogamous; in fact, polygamy tends to be exceptional among waterfowl. The pair bond itself may vary from lifelong such as with the swans and geese to almost nonexistent such as with muscovies. Pair forming and courtship activities have received a great deal of attention from animal behaviorists in recent years. These highly stereotyped rituals are such that many of the sequences can be very complicated and difficult to interpret. Students of wildfowl behavior have coined special terms to describe specific displays, such as:
Triumph Ceremony, Display Shake, Billdown Display, Incite, Grunt-whistle, Head-throw, Kinked-neck Posture, Bowsprit, Rear-end Display, Salute, Curtsy, Pushing, Head-pumping, Bubbling, Burping, and Gesture of Repulsion. These terms are self descriptive and suggest the wide range of movements, often forming a kind of dance, with which the male seeks to attract the female. In some species, females initiate courtship by inciting the males. In other instances, females will flatten out on the surface of the water almost as if soliciting the attention of the drake.
Once the pair bond is established, nest building generally commences. However, in most non-tropical migratory species, pair formation may occur long before nesting and often far from nesting areas. In the far north the typical waterfowl nest is in a marshy area on rolling tundra near fresh water. Sometimes over a dozen species nest in relatively close proximity to one another. These immense concentrations frequently are located on small islands surrounded by the melting pack ice where they are afforded security from terrestrial predators such as arctic foxes. It is more common, however, for nests to be scattered because waterfowl are not particularly gregarious during nesting. Snow geese and some eiders, however, can be exceptions.
Many anatids nest in the open while others lay their eggs in the cavities of trees or in underground burrows. Swans, as well as some of the stiff-tails, construct elaborate nests. More typically, however, waterfowl nest construction is rather rudimentary. Wildfowl lack the instinct to carry nesting material. Generally they merely reach forward from the nest site, grasp a beakfull of material, pass it over their shoulders and drop it. As a rule, they use only material that is within their reach. However, at least one species, the South American blackheaded duck, does not construct a nest at all but rather is a parasitic nester, depositing its eggs in the nest of a host species.
Waterfowl eggs are never spotted or patterned and are generally white or off-white, pale green or brownish. Except for the magpie goose, black swan, some whistling ducks and the white-backed duck, the female alone incubates. Wildfowl incubation periods vary from 20 to 43 days. High latitude waterfowl tend to have shorter incubation periods than their tropical or temperate counterparts. The size of the bird does not appear to be related to the length of incubation as some northern geese have incubation periods as short as that of the much smaller teal. Incubation is obviously adapted to the very brief breeding season in the north, for the young must be fledged and capable of departing before the icy fingers of winter take hold.
Most anatids generally line the nest and cover their eggs, which are laid at one or two day intervals, with their own feathers which are heavily underlaid with thick down. Some swans and whistling duck males assist with incubation and in these cases, little down is used. Lining sometimes commences as the clutch is being set although most species wait until the final egg is laid and incubation commences. It is interesting that most of the down is dark for species nesting in the open and whose eggs require a protective cover. Cavity or hole nesters like the American merganser have little need to conceal their eggs and consequently, their down is white. The down of a closely related ground nester, the red-breasted merganser, is dark brown.
During incubation, the nests are protected in a variety of ways. Some species cover the eggs with down, as previously noted, to provide warmth and camouflage while others depend on their drab disruptive plumage to keep them concealed during incubation. Still others attempt to draw off an intruder by feigning an injury such as a broken wing; the broken wing technique has been reported for at least 58 wildfowl species. Swans and some geese will stand and fight intruders. These tactics are not always successful because egg predation is surprisingly high. To compensate for such losses many wildfowl lay large clutches. If frightened off the nest, many ducks defecate on the eggs. The foul odor may serve to discourage predation, or it may function as a camouflage mechanism, or both.
In most cases, once incubation commences the hens are reluctant to depart the nest. Some northern species fast during the entire incubation period and will not desert the nest unless ejected by an intruder. More commonly, the females cautiously sneak away from the nest briefly during the early morning or late afternoon to feed. As hatching approaches, the diligent hens flee the nest only as a last resort. Recent evidence suggests that just prior to pipping some communication between the incubating adult and the unhatched egg may take place. Thus, it is not inconceivable that a form of audio imprinting occurs before the young are even hatched.
There is usually an inverval of 16 to 18 hours or more between pipping and emergence although up to 24 hours may be required. Since incubation of the total clutch commences at the same time, most of the eggs hatch within a day or two of each other. This synchronized timing increases the survival potential. The young are extremely appealing and are covered with thick down which may be strikingly colored and patterned. They hatch with their eggs open and they become active as soon as they dry off and fluff up. While dependent on their parents for protection, they are not nearly as helpless as the blind and naked chicks of other avian groups such as the passerines, woodpeckers, or hummingbirds. Down covered young....