The Aye-Aye Lemur of Madagascar: Feeding Ecology, Social Behavior, and Microhabitat

Eleanor Sterling, PhD Candidate
Betsy Carlson, MFS '89¹

Four hundred kilometers off the southeast coast of Africa lies the isolated island continent of Madagascar. Having separated from the African mainland at least 200 million years ago, Madagascar appears to have been in its present relative position for the last 120 million years (Rabinowitz et al. 1983). It is unlikely that plants or terrestrial animals have crossed the channel between Madagascar and Africa for at least 40 million years. This long isolation from the mainland along with the wide diversity of available habitats on Madagascar have resulted in the survival and radiation of ancient genetic lineages. Ninety-three percent of the island's primates and 80% of its flowering plant species are found nowhere else in the world (Jenkins 1987). Tragically, forest habitat on this unique island is fast disappearing, even before some of the most preliminary of field studies can be completed. At least 14 lemur species have become extinct since humans arrived about 1500 years ago (Dewar 1984), with approximately 24 species remaining on the island. All but the four smallest living species are listed as threatened in the IUCN Red Data Book (IUCN 1980-1985).

One such species is the aye-aye (Daubentonia madagascariensis), the only living member of the primate family Daubentoniidae. An animal of great taxonomic interest, the aye-aye displays a suite of morphological features which distinguish it from all others. Once described as being made from “the spare parts of other animals,” the aye-aye's peculiar morphology includes bat-like ears, rodent-like continuously growing incisors, claws on all digits but the first toe, a fox-like tail, a foreshortened face, and a filiform middle finger. It is about the size of a house cat and weighs 2.5 kilograms. This combination of features resulted in arguments over the aye aye's taxonomic position for nearly a century following its discovery by scientists in 1780. Owen's (1863) anatomical study finally placed the aye-aye in the Order Primates.

As a consequence of its taxonomic uniqueness and endangered status, conservationists consider the protection of the aye-aye one of the highest conservation priorities in the world. This profile describes an on-going two-part study based on the PhD thesis work of Eleanor Sterling. It combines a study of aye-aye feeding behavior and ecology with a botanical evaluation of its microhabitat preferences.

The study area is the Special Reserve of Nosy Mangabe, an island located in the Bay of Antongil off the northeast coast of Madagascar. This 520-hectare reserve was set aside in 1965 as an enclave of natural habitat for the aye-aye, then thought to be verging on extinction. In 1967, nine aye-ayes captured in forests on the mainland were released on the island by Dr. Jean-Jaques Petter and colleagues. The island supports a moderately high forest canopy (30-35 meters), and evidence collected from this study thus far suggests that the founder population has thrived. The rain forest is characterized by steep slopes, boulder-strewn ravines, and thick liana tangles. Many tree species in this diverse flora are from such families as Lauraceae, Burseraceae (Canarium), Clusiaceae (Garcinia), Sapindaceae, Sapotaceae, Rubiaceae, and Ebenaceae (20 or more species of ebony, Diopyros). A variety of mammals shares the forest habitat with the aye-aye, including four other primate species.

Despite the aye-aye's endangered status and unique morphology, no long-term study has been undertaken of this animal in the wild. The main objective of this work is to investigate the behavioral ecology and social system of the aye-aye over a period of eighteen months. Eleanor Sterling is focusing on the role of the aye-aye's digits and dentition in food acquisition, its diet in the wild, and its social interactions. In collaboration with Betsy Carlson (MPS '89), microhabitat preferences and population density of aye-aye are being assessed on Nosy Mangabe, as well as in nearby forested regions on the mainland of Madagascar. This study will contribute to our understanding of four general issues in primate ecology: 1) the interaction between morphological and ecological specialization; 2) the relationship between body size and diet; 3) the degree of sociality in nocturnal primates; and 4) seasonal patterns of fruiting and flowering in tropical plants. Data collected will also be useful for developing a conservation management plan for this endangered species.

Figure 1. Daubentonia madagascariensis

To assess aye-aye ecology and feeding behavior, Sterling and two field assistants conduct all-night focal animal samplings of radio collared individuals. So far, five animals have been captured and affixed with collars, and the trapping effort continues. Ethological data are recorded on the minute at five minute intervals. Size, height and nature of supports are noted to determine patterns of substrate use. The researchers then retrace their steps during the day in order to plot activity ranges and confirm identification of food sources. As many animals as possible are tracked each day to their nest sites to aid in detennination of home ranges and sleeping associations. Samples of all food sources are being collected for identification and subsequent nutritional analysis.

A series of 10x10 m plots are being surveyed to evaluate the forest structure. One set of plots is being placed at aye-aye nesting and feeding sites, and the other set is being placed randomly within the study area. The availability of different microhabitat types will be assessed using the latter, and will be expressed as a proportion of total forested area on the island. Plots established around feeding and sleeping sites will be compared to these estimates of microhabitat availability in order to determine microhabitat selectivity by aye ayes. Within the plots, each tree over 10 cm dbh (diameter at breast height) is identified, mapped, and measured for height, crown diameter, and dbh. Forest structure is described by combining these measurements with an inventory of seedlings, small trees, dead trees, lianas, and epiphytes. A comparison will be made with neighboring mainland forests using similar methods.

Phenology–time of leaf formation, flowering and fruit formation–is a major determinant of food availability. This aspect of the botanical study focuses on tree species already known to be important to other lemurs on Nosy Managabe, particularly Varecia variagata variagata. A permanent phenology trial has been established by marking individuals of these and other common species. Food sources utilized by aye-aye are added to the study as they are discovered by Sterling. Flowering, fruiting and leaf-flush times are recorded monthly to provide a general picture of seasonality and insight into possible keystone food species of this tropical forest. This information is supplemented by plant materials collected every two weeks from fruit traps placed throughout the study area. The construction of the trials and collection of first year phenological data have been done in collaboration with Dr. George Schatz of the Missouri Botanical Garden, who is currently working on a flora of Nosy Mangabe.

One of the most important forest trees found on Nosy Mangabe is Canarium (Burseraceae). This tree is used extensively by humans and by a variety of wildlife. Local people cut boles for the construction of dugout canoes and process sap to make a glue for patching wooden boats. The fruits are heavily consumed by humans, lemurs, and wild boars. The branches provide sleeping sites for some lemurs. Because of Canarium's value as a food source, Carlson is taking a closer look at the fruit production of this species. Thus far, the understanding of Canarium in Madagascar is poor; its taxonomy needs revision and its phenology is unrecorded.

The analysis of forest structure and phenology will facilitate the estimation of the distribution and relative abundance in space and time of different food sources, as well as the availability of different microhabitat types. Together, these data and observations of the behavior of the animals themselves will be used to answer basic questions about aye-aye ecology and to identify variables important in the selection of habitat by aye-ayes. This information is also important as it can be used in developing potential translocation schemes for individuals threatened by hunting or habitat destruction on the mainland.

References

Buffon, Comte de. 1789. Histoire Naurelle, Generale et Particuliere, Supp. vol. 7, Imprimerie rovale, Paris.

Dewar, R. 1984. Recent extinctions in Madagascar: the loss of subfossil fauna. in Quaternary Extinctions. Ed. by P.S. Martin and RG Klein. University of Arizona Press. Tuscon. pp. 57-93.

Gmelin, B. 1790. Systema Natura. International Union for Conservation of Nature and Natural Resources (IUCN). 1980-1985. Red Data Book IUCN. Cambridge, MA.

Jenkins, M.D. 1987. Madagascar: an Environmental Profile. International Union for Conservation of Nature and Natural Resources. Gland.

Owen, R. 1863. On the Aye-aye. Trans Zoological Society. London 33: 101.

Rabinowitz. P.D., M.F. Coffin, and D. Falvey, 1983. The separation of Madagascar and Africa. Science 220: 67-69.

Sonnerat. C. 1782. Voyage aux Indes Orientales et a la Chine. depuis 177 4 jusqu 'en 1781. Paris.

Van der Hoeven, J. 1858. Handbook of Zoology. vol. VII.

Citation of Original Article

Sterling, E. and Carlson, B. 1990. The Aye-Aye Lemur of Madagascar: Feeding Ecology, Social Behavior, and Microhabitat. TRI News 8, 3–5.