Geophagy amongst Formosan Macaques at Mt. Longevity, Taiwan

 Published in Folia Primatologica 72:339-341 (2001)

Geophagy amongst Formosan Macaques at Mt. Longevity, Taiwan

Minna J. Hsu ^a, Govindasamy Agoramoorthy ^a, Jin Fu Lin ^b

^a Department of Biological Sciences, National Sun Yat-sen University, Kaohsiung, Taiwan

^b Shi-Pu Junior High School, Kaohsiung, Taiwan

Running head: Geophagy in Formosan macaques

Key Words

Behaviour . Diet . Geochemistry . Iron . Macaca cyclopis . Soil mining

Corresponding author:

Dr. Minna J. Hsu, Department of Biological Sciences,

National Sun Yat-sen University,

P.O. Box 59-157, Kaohsiung 80424, Taiwan

Tel. +886 7 5252000 ext. 3623, Fax ++ 886 7 5253623

E-Mail hsumin@mail.nsysu.edu.tw

The behaviour of soil-eating, or geophagy, has been reported in 39 species of non-human primates.   Six hypotheses have been proposed to explain the function of this behaviour, four relate to alleviating gastrointestinal disorders and two relate to mineral supplementation [1]. This paper is the first report of soil-eating by the wild Formosan macaques that inhabit Mt. Longevity in Taiwan and includes a geochemical analysis of the soil.

Materials and Methods

Details of the long-term field research on Formosan macaques, Macaca cyclopis, and the habitat and seasonality at the study site on Mt. Longevity are described elsewhere [2-3]. Demographic and behavioural observations were carried out on 15 social groups of macaques between January1999 and December 2000, four days per week. Feeding behaviour, including soil ingestion, was recorded using the all-occurrences sampling technique [4]. Soil samples were collected from 23 mine sites immediately after monkeys dug or ingested soil, and these were compared with 8 random soil samples from the study site. The concentrations of 15 major, minor and trace elements in the soil samples were analysed using Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) in the Department of Chemistry.

Results and Discussion

Formosan macaques at Mt. Longevity were observed to excavate dozens of mine sites. Both males and females belonging to all age classes were observed eating soil  and the youngest was just 3 months old. A total of 138 soil-eating events among the 15 groups were recorded in 82 days (Fig. 1). The majority of the soil-eating occurred between August and February (74.64%), with a peak in August and September (31.88%), and it decreased during May and June (4.35%). No sexual difference was found in the frequency of soil eating (X² test, p>0.05), but 35.29% adult females alone concentrated to eat soil in the month of August.

Seven elements (iron, chromium, manganese, arsenic, cerium, neodymium and samarium) were significantly higher in soil from mining sites than in the random topsoil samples (Table 1). However, the concentrations of three major elements (magnesium, aluminum and calcium) were significantly lower in soil from mining sites than in the random samples (Table 1). No difference in concentration of the remaining five elements (copper, strontium, barium, lanthanum and ytterbium) was found between the two groups of soil samples.

Overall, the majority of the macaques’ diet at Mt. Longevity is fruit (45.54%) and plant parts (flowers, leaves, stems and roots, 42.48%).  In addition, they take a small portion of insects (7.10%) and soils (4.87%). However, between September and February, plant parts accounted for 60.2% of the macaques’ diet, while between April and June, fruits accounted for 56.92% of the diet, with plant parts making up 25.13% and insects 15.38%.

Formosan macaques ate soil all year round with a peak at the end of the rainy season (August) that continued through the dry season (November to March) and ended in April. Although our data are consistent with the hypothesis that seasonal folivory could favour geophagy in the dry season when fruits and insects are scarce, either as a mineral supplement or as a secondary compound absorbent [4], this cannot explain the elevated frequency of soil use that occurred in August and September.

Formosan macaques are seasonal breeders and mating usually starts in August [2]. Iron, at a concentration of >5% in the mining sites observed in our study, should be nutritionally useful if it is available for absorption. It appears that by ingesting soil, adult females may absorb mineral supplements, especially iron, which have the potential to help them physiologically during the periods of menstrual cycle and pregnancy. Furthermore, fighting among rival males as well as among females during the mating season has been reported to result in wounding among, for instance, Tibetan macaques, M. thibetana, [5] and Formosan macaques [6]. Thus the geophagic stimulation may also have the potential to boost erythrocytes in the blood of wounded individuals.

Acknowledgments

This research was partially funded by the National Science Council’s grant (NSC 88-2313-B- 020-023) awarded to G. Agoramoorthy and M.J. Hsu.

References

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2        Hsu MJ, Agoramoorthy G and Lin JF: Birth seasonality and interbirth intervals in free-ranging Formosan macaques, Macaca cyclopis, at Mt. Longevity, Taiwan. Primates 2001;42:15-25.

3        Hsu MJ and Lin JF: Troop size and structure in free-ranging Formosan macaques (Macaca cyclopis) at Mt. Longevity, Taiwan. Zool Studies 2001;40:49-60.

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5        Mahaney WC, Aufreiter S, Hancock RGV: Mountain gorilla geophagy: A possible seasonal behavior for dealing with the effects of dietary changes. Int J Primatol 1995;16:475-488.

6         Zhao QK: Mating competition and intergroup transfer of males in Tibetan macaques (Macaca thibetana) at Mt. Emei, China. Primates 1994;35:57-68.