Ecology of Sulawesi. Tony Whitten
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between crest and trough are small, minor differences in pore volume can produce major changes in the reaction of sand grains to a shearing force (Grant 1984).
Wading birds are often seen in mixed-species flocks which might be thought to be disadvantageous to the individuals by virtue of increased competition. In fact, more often than not, the birds are taking different foods and being together has the advantage that the more birds present the more likely it is that a predator, such as a bird of prey, will be seen. One particular species is usually first to settle on a certain stretch of beach having used visual clues to make its choice. Other species follow when it is clear that food is being found. A few species act as pirates taking food away from the other species. This is disadvantageous in that the birds which lose food have to spend more time feeding to compensate for the loss, but there are advantages in that feeding birds have their heads down searching for food whereas the pirate generally keeps its head up and serves an early warning of the approach of predators (Barnard and Thompson 1985).
In addition to the waders, other common large birds of the coast include the white-bellied sea eagle Haliaeetus leucogaster, the osprey Pandion halietus and Brahminy kite Haliastur indus all of which fish in the shallow waters and scavenge food along undisturbed beaches. There also various storks, herons, egrets and ducks seen around the shore and roosting and nesting in mangrove forest (fig. 2.30). Palopo Bay and the delta of the Cenrana River are good sites for seeing these birds (Uttley 1986). The milky stork Ibis cinereus is of particular interest because until a few years ago it was thought to be quite rare. Large numbers have now been found in Sumatra (Silvius et al. 1985) and they have also been observed, some in breeding plumage, in the Tiworo Straits between Muna Island and the mainland of Southeast Sulawesi (L. Clayton pers. comm.), near Ujung Pandang and in the Cenrana River delta (Uttley 1986).
Figure 2.30. Large birds seen feeding in or near mangrove forests, a - woolly-necked stork Cicortia episcopus; b - little egret Egretta garzetta; c - Chinese egret E. eulophotes; d - plumed egret E. intermedia; e - great egret E. alba; f - milky stork Ibis cinereus; g - grey heron Ardea sumatrana.
After King et al. 1975
Figure 2.31. Yellow-bellied sea snake Pelamis platurus.
After Tweedie 1983
Such fish-eating birds might occasionally encounter venomous sea snakes (p. 232) in the shallow waters of mudflats. One species, the yellow-bellied sea snake Pelamis platurus (fig. 2.31), is the most widely distributed species of snake, being found from south Siberia to Tasmania, and from the west coast of America to the Indian Ocean. It is about 1 m long and is often found near the water surface and eats mainly rabbitfish and mulletlike fish (Voris and Voris 1983). Young, hand-reared egrets and herons were presented with live and dead, poisonous and non-poisonous snakes, with and without their tails. The tails of sea snakes are very distinctive. The birds were most frightened by the yellow-bellied sea snake, even if its tail had been removed. This indicates a genetically-based response; they could not have learned that the snake was dangerous from experience (Caldwell and Rubinoff 1983).
Turtles
The sandy beaches of Sulawesi are used as nesting sites by four species of sea turtle which differ in size and in the shape of the carapace (fig. 2.32):
• green turtle Chelonia mydas which has an olive-brown carapace about 1 m long, can weigh 100 kg and feeds mainly on seagrass in shallow seas (p. 201);
• hawksbill turtle Eretochelys imbricata which has a dark-brown carapace about 90 cm long, weight up to 80 kg and feeds on invertebrates on coral reefs;
• loggerhead turtle Caretta caretta which has a brown carapace about 1 m long, a weight of about 100 kg and feeds on crustaceans and molluscs; and
• the enormous leatherback turtle Dermochelys coriacea which has a dark brown, ridged carapace up to 2.5 m long and can weigh up to a ton; perhaps surprisingly, this species feeds solely on jellyfish. It is a strong swimmer and can maintain a body temperature 18°C above the sea water temperature. Individuals migrate over large distances, in excess of 3,000 km, and although generally found in the tropics, they are have been found feeding inside the Arctic Circle.
Figure 2.32. The four species of turtle found around the coasts of Sulawesi, a - green turtle Chelonia mydas; b - hawksbill turtle Eretochelys imbricata; c - leatherback turtle Dermochelys coriacea; and d - loggerhead turtle Caretta caretta.
From Anon. 1979
The green turtle is more or less absent as a nesting species in South Sulawesi except on the remote Taka Bone Rate Atoll and the Sembilan Islands near Watampone (fig. 2.33; table 2.6). This may be the result of overhunting or overexploitation of eggs but the fact that the hawksbill turtle is present on the small islands in this province and the green turtle common in the other provinces, hints at an ecological factor being responsible. It has been suggested that hawksbill turtles favour small remote islands, even those with no vegetation, with beaches rather steeper than those favoured by green turtles (Nuitja and Uchida 1983). It is important to determine what factors make a beach acceptable so that human activities can be managed or controlled. A study in Australia found that nesting beaches tended to be protected from prevailing winds and to have sand moisture with a lower salinity than beaches not used for nesting (Johannes and Rimmer 1984). How the turtles detect these differences is not known.
Figure 2.33. Turtle nesting beaches. For key to numbers see table 2.6.
From Salm and Halim 1984
? = requires confirmation
After Salm and Halim 1984
Many turtle research and management programs have involved the taking of newly-laid eggs and hatching them with some form of protection from predators. These eggs have frequently been taken at the start of the laying season when the intensity of predation is greatest. It has been known for some years that the sex of hatchling turtles (and other reptiles, p. 303) is determined by temperature during incubation (Vogt and Bull 1982). The weather can very over the laying season causing the sex ratio of hatchlings to also vary. In the sub-tropics the percentage of females can change from 0% in the cooler, early parts of the season to 80% in the warmest month (Mrosovsky et al. 1984a). Even close to the equator effect is still noticeable and differences can be expected in sex ratio of clutches laid in different environments—in beach vegetation, in open beach with or without inundation by cool seawater during the critical middle third of incubation when sex is determined (Mrosovsky et al. 1984b). Where eggs are hatched under conservation management programs, great care must be taken not to unwittingly distort the sex ratio of the hatchlings.
The overexploitation of turtle eggs and adults for food makes the problem of survival for the turtle population progressively harder because the mass nesting behaviour of turtles is ecologically akin to the gregarious fruiting behaviour of dipterocarps (p. 368). Both act to satiate the appetites of their predators with the result that at least some of their eggs or seeds will get the chance to develop. The smaller the population of turtles, however, the large the proportion of eggs destroyed.
Maleo Birds
The maleo Macrocephalon maleo is a member of a small family of mound builders, or incubator birds (Megapodiidae), which with one exception is confined to eastern Indonesia, New Guinea, Australia, and Polynesia.14 The maleo itself, however, is found only in North, Central and Southeast Sulawesi. It is about the size of a domestic hen, weighing around 1.6 kg (Guillemard 1889), with striking black and rose-white plumage, an erect tail, and a head with a bare, helmeted cranium which may serve to keep the brain cool when it is on hot