Figure 3. Overall percentage of time spent feeding on different dietary items by season for aye-ayes on Nosy Mangabe from November 1989 to April 1991. Averages of six individuals were used to calculate seasonal means. Seasons are: hot, wet (HW); cold, wet (CW); and hot, dry (HD). Seeds = Canarium spp., T. catappa; other = fungus, ants, unidentified food sources (Sterling, 1994a). Used with permission from S. Karger AG, Basel.
below 250 m above sea level. Aye-ayes eat Canarium seeds by removing the endocarp with their long anterior teeth and then extracting the cotyledon with their slender middle finger (Iwano and Iwakawa, 1988). Individual trees of both species are large-crowned and abundant on the island, and one study showed the lowland Canarium species to have the third-highest stem density of all the plants sampled (Sterling, 1994a). Aye-ayes sometimes spent more than 30% of their feeding time consuming Canarium seeds, and they appeared to prefer fruits of the lowland species when they were available. Fruit from one species or the other is available throughout the year, although both are less abundant during the coldest of the three seasons. The preferred lowland species is less common during the wet, hot season, causing aye-ayes to turn to fallen, and to a lesser extent, upland Canarium.
To gain access to another of their preferred foods, aye-ayes remove cankers from a leguminous tree, Intsia bijuga, and then scrape a waxy substance from the underlying cambium with their anterior teeth. The growths are found most commonly on secondary branches and on trunks with more exposure to light and air; it is either a fungus or a gall, but botanists, entomologists, and local forest specialists have not been able to identify it further. This resource is patchily distributed and is restricted to lower elevations on Nosy Mangabe (less than 270 m above sea level). Aye-ayes eat this food most frequently during the cold season, when Canarium fruits are less abundant.
Nectar from Ravenala madagascariensis (Strelitziaceae) flowers provides a high-energy food source for foraging aye-ayes. The animals scoop the viscous liquid out of the flowers with rapid back-and-forth movements of their thin middle finger. Ravenala inflorescenses are few per tree, but the trees are often clumped together in groups of 3 to 12. On Nosy Mangabe, they tend to be most common at higher elevations. In addition, aye-ayes open Ravenala fruits to access an unknown food source inside the fruit. The fruit contains seeds that are about 2 cm in length and covered with a blue aril, but aye-ayes do not eat these. Aye-ayes probably open the fruit to reach insects from a diverse array of families (Bruchidae, Pyralidae, Cerambycidae, and Tenebrionidae) that can be found inside the fruits in both adult and larval forms. Larvae (Diptera) have also been found in the Ravenala nectar that aye-ayes exploit.
The aye-aye is well-known for its ability to locate and extract wood-boring larvae from several different families with a characteristic behavior called tap-foraging. As it moves along wood surfaces, the aye-aye taps the wood with its middle finger, keeping its nose near the wood and its large ears pointing forward. When it senses a cavity, the aye-aye anchors its upper incisors in the wood and uses the scooping action of its lower incisors to gouge a pit. Larvae from a diverse array of families (Cerambycidae: Lamiinae, Prioninae; Scarabidae: Dynastinae; Passalidae; Pyralidae: Phycitinae) are retrieved from the cavity and brought to the mouth with the slender middle finger (Figure 4). Rich sources of larvae include fallen dead wood, dead branches on a living tree, living trees, dead and living lianas, the underside of bark on living trees, and the insides of bamboo stalks and parasitized seeds. Aye-ayes extract larvae from dead trees, lianas, and the bark of live trees
more often than from any other host types, and they are known to remove larvae from at least 29 different tree species (Figure 5). The periodicity of larval resources is difficult to measure, but large larvae have been found in the bark of medium- to large-sized Canarium trees during every month of the year. Bark beetle larvae that live under the first centimeter of bark are also available year-round. Density of larvae resources appears to be high, as aye-ayes eat larvae from beneath the bark of several species that have high stem densities in the forest. Although aye-ayes eat a wide variety of foods throughout the year, insects may represent a stable resource during times when the availability of other resources fluctuates more.
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