Ducks, Geese, and Swans

Ducks, geese, swans, and other waterfowl forage on vegetation, controlling weeds on the banks of waterways and often clearing aquatic weeds and algae from small lakes, ponds, and canals. These animals have not been considered aquatic weed control agents. However, in Hawaii, 65 Chinese White goslings were placed in a 1-ha pond, completely covered with dense paragrass (BrachUzria mutica) and cattail (Typha spp.) that annually grew 1.8 m above the water. Despite the failure of mechanical and chemical controls to manage the weeds for several previous years, the geese cleared them out in 2* years.•

Ducks and geese are small, easily managed grazing animals, well-suited to aquatic areas and wet marshy land. They produce nutritious eggs and highly prized meat. Completely at home in shallow, productive waterways, they are potentially immediately applicable to aquatic weed control in developing countries.

With their waterproof feathering, ducks and geese are well-adapted to high rainfall regions, and ducks in particular are an excellent fowl for hot, humid climates. Both animals readily adapt to captivity and can be raised in small-farm culture. To raise ducks or geese as opposed to raising larger animals requires little investment. They are readily available worldwide, and their nutritive and management needs are well-known. They are excellent foragers and may find all their own food or need only a minimum of supplements. In the right areas they can be raised by farmers to provide an additional income with little extra work.

Domesticated ducks are already raised throughout the tropics, notably in Asia, especially in aquatic weed-prone, riverine areas, but their effect on the weed problem is seldom considered. Yet S-8 Muscovy ducks per hectare will control duckweed and some other aquatic plants. Coots (Fulica spp.) have controlled water hyacinth growing on sewage lagoons in the United States. In South Africa, as well, they are reported to eat the plant.

Geese are raised for their meat, which finds a ready market. Goose-farming is particularly important in Central Europe. For tropical developing countries, however, two breeds are known that could be more widely used: Chinese geese (White and Brown varieties), which are large birds (ganders can weigh

•Ross. 1971. (See Selected Readings.)

50 MAKING AQUATIC WEEDS USEFUL

over 5 kg) that are already raised in Southeast Asia; and Egyptian geese, which are about I kg lighter but are hardy birds and active foragers.

Geese provide a farmer not only with protein but also with large amounts of fat and goosedown. Although sometimes messy, they cause little trouble and require little expense for they range freely without restriction, feeding themselves and returning of their own accord. However, in some areas, fences or a caretaker may be needed. Though they cannot digest cellulose, they are almost entirely grazers and eat both terrestrial and aquatic weeds. They also grub for underwater roots, which is important because few other animals uproot aquatic plants.

The use of swans to control aquatic weeds is rare. Yet, in 1967, I 00 mute swans were added to Nissia Lake near Agras in northern Greece. The lake was being used to produce hydroelectricity, but the turbine inlets were clogged with aquatic vegetation. The swans (mostly unpaired singles) were first placed near the inlet area; they cleared it within a few weeks; They were then distributed about the lake.

The principal types of vegetation in the lake were reeds, Potamogeton spp., and chara (a submergent alga). The swans ate the young shoots and pulled the plants up to eat the tender roots. The chara was too deep for the swans to eat, so 60 pair of diving ducks (Netta mfina) were obtained to attack this problem.

Nevertheless, in the main body of the 900 ha lake the swans were less successful: Weed growth, bolstered by municipal wastewater, proved too

At a government training farm operated by teenagers near Port Moresby, Papua New Guinea, ducks are raised on duckweed and algae. These weeds grow on a small pond fertilized by sludge from a pig-manure methane generator (see Chapter 12). (N. D.

Vietmeyer)

DUCKS, GEESE, AND SWANS 51 great for them to have any appreciable effect. By 1976 the swan production had multiplied to perhaps 400 birds but was still inadequate to noticeably reduce the dense weed infestation.

Each winter the swans and ducks attract to the lake thousands of migrating waterfowl, including large numbers of coots, which also help control the weeds. But they all leave before summer when the weed problems are most severe.

The management of the swans is relatively simple: One wing is clipped to prevent them from flying away. The large lake provides plenty of vegetation, and no feed is given (in fact, they will not forage if they are fed). An advantage of swans over the other waterfowl was that they apparently needed no grain to supplement their diet of weeds.

Mute swans mature at about 5-7 kg and, while not commonly used for food in Europe-because of a reluctance to kill them-their flesh is as tasty as that of other waterfowl. In addition, they have a fme down, 2.5-5 cm, which can be woven into cloth.

While other swans might also be used for control of aquatic weeds, mute swans are the easiest to breed, producing about six young per year per pair.

However, their initial cost is high (the equivalent of about US$150 per pair in Central Europe).

It seems most likely that waterfowl can control aquatic weeds noticeably only in small bodies of water such as farm ponds; in a larger waterway the number of birds needed to "solve the weed problem" makes their use impractical. Nonetheless, even here waterfowl could be used to supplement other weed control efforts such as the use of herbivorous fish or mechanical harvesting.

The birds can clear submersed weeds only in waters shallow enough for them to grai.e the plant back severely so that its growth is retarded. In deeper waters their grazing will have little effect on weed growth.

Probably geese are best used to control grasslike aquatic weeds. They may be ineffective on the broad-leaved types.

Limitations

Ducks, geese, and swans may need a diet supplement (e.g., grain) if they grai.e certain aquatic weeds exclusively. The farmer must strike a balance: Too little supplement may cause the birds to die of malnutrition; too much, and they will not eat the weeds.

These birds can defend themselves well, but ducks in particular require the added protection of a fence. They may require shade in hot countries, for they do not adapt well to hot arid conditions.