ENDANGERED SPECIES: Three Examples of Waterfowl

Abstract

The nene or Hawaiian goose (Branta sandvicensis), Hawaiian or koloa duck (Anas wyvil/iana), and the Laysan teal (Anas laysanensis) are considered endangered species in the wild. Coincidentally, all three are noted for limited insular or island distribution, a condition which no doubt contributed to their precarious state. Endemic insular flora and fauna are often ultra-specialized and as such, generally react adversely to rapid environmental changes. If these changes are natural and minor and occur slowly, the plants and animals are often able to adapt. On the other hand, if the changes are sudden and of a large magnitude, then the adaptive changes cannot occur; some species all to frequently disappear altogether. In the past, changes of great magnitude were usually associated with volcanic eruptions, etc.; in some cases, entire islands disappeared, thus eliminating the life forms associated with that island. However, in historic times, it has been the arrival of man to the often remote islands which had created biological havoc.

A case in point is the nene goose. It is probable that no more than 25,000 individuals ever existed but in recent years (since the 1900's), the population has declined dramatically. The nene goose inhabits the slopes of Mauna Kea, Mauno Loa and Hualalai volcanos, on the big island of Hawaii. This habitat is unique and is characterized by heavy precipitation but no permanent water areas. The birds have adapted their life styles to fit this environment. Interestingly, they are among the very few species of waterfowl that normally copulates ashore. They are nonmigratory, a unique distinction for a northern goose. It is suggested that they evolved from the mainland Canada goose. The legs have become stronger along with the nails and the webbing of the feet has become much reduced, enabling the birds to negotiate lava-covered areas.

Once modern man discovered the islands, changes were rapid and dramatic. Introduction of new species, i.e., rats, dogs, cats, pigs and the mongoose, com-

bined with over-hunting, brought about their present plight. The geese were hunted as a source of food and the introduced animals preyed on their eggs and young. ln the early 1940's, biologists became quite concerned and estimated that there were less than 40 geese left. A local rancher, Richard Shipman, had protected a number of the birds on his property located on the island of Hawaii. ln 1950, three birds were sent to the Wildfowl Trust in England in an attempt to get them established in captivity. As of 1979, this effort, combined with that of the Hawaiian Division of Fish and Game, zoos and private aviculturists has resulted in well over 2,000 individuals being reared throughout the world. Many of the geese have now been re-introduced back into the wild on both the islands of Hawaii and Maui.

In collections, nene are relatively easy to maintain and are only mildly aggressive during the breeding season. Fortunately, captive propagation presents no real challenge. Nesting either in the open or under sparse cover, the clutch consists of 3 to 5 buff colored eggs. While the female alone incubates for 29 days, the gander guards the nest and this is when they can become aggressive. At Sea World in San Diego, all eggs are removed from the nest after a full clutch is laid in late winter or early spring (January or March). The eggs are incubated in a Petersime at 99.5°F dry bulb, 84° to 86°F wet bulb. Fertility has not proved to be a problem. Upon hatching, the goslings are placed in a bank brooder for four to six days and fed Purina Startina and fresh ground lettuce, ad. lib. Once out of the brooder they are moved to indoor rearing pens. The amount of protein offered is reduced drastically at this time; if not, splayed legs and, later, drooping wings will result. The birds are maintained to fledging on a diet consisting almost entirely of lettuce with small amounts of Startina and meal worms. lt is best if they are kept on grass. If large numbers of young are in a single rearing unit, care must be taken to insure that larger, dominant birds do not pick at the

backs of the less aggressive youngsters.

The Hawaiian or koloa duck occupies the low-lying wetlands of the island group. Their former range was apparently all of the islands except Lanai and Kahoolwe but they are now apparently confined to the few remaining wetlands and rivers of Kaui. As is the case with many endangered species, habitat destruction has been extremely detrimental. Like the nene, they probably were never abundant. It is estimated that there are approximately 3,000 individuals existing in the wild. Delacour gives an account of a population census in both 1923 and 1946-47, compiled by Schwartz. Mr. Woodhouse of the Kekaha Sugar Company estimated that the six square mile Mana Marsh of Kaui contained approximately 2,400 birds prior to its drainage in 1923. When Schwartz surveyed the same area in 1946-47, only 30 birds remained. Hunting, without a doubt, helped to further reduce the population.

In appearance they are nondescript and are distinctly smaller than the common mallard. The female being redder than the female mallard which the male hints at the drake mallard in eclipse plumage. In essence, they can best be described as degenerate, insular mallards.

In the wild they are semi-solitary, often observed singularly or in pairs, although there are accounts in the early 1900's of Hawaiian ducks forming flocks. Like their mainland counterparts,they are ground nesters and lay 6 to 12 pale greenish eggs. The female alone incubates for 26 to 29 days. In 1951, the San Diego Zoo and the Wildfowl Trust received birds which had been reared at the Honolulu Zoo and bred them that same year. Many aviculturists and zoos are reluctant to bother with them due to their tendency to hybridize and their overall dull plumage. At Sea World many young have been reared over the years. Hybridization is a definite problem and birds must be watched continuously if maintained in a mixed collection. It is my opinion that this species must be isolated from closely related species to alleviate this problem. As is the case with all waterfowl species at Sea World, eggs are collected and young are reared by hand. The eggs are incubated at 99.5°F dry bulb reading, and 84° to 86°F wet bulb, in a Petersime Model 4 incubator. A bank brooder is used for the first ten days after which they are transferred to indoor I outdoor runs. The ducklings are offered Startina chow and lettuce as well as meal worms.

Laysan Island is located approximately 700 miles northwest of Oahu, Hawaii, and is the ancestral home of the Laysan teal.