Mineral contents of salt-lick water and mammal visitation to salt-lick in tropical rainforests of Peninsula Malaysia

Salt-licks are considered to be important places for conservation of animals; however, functions of salt-licks were still not well studied especially in Peninsular Malaysia. In order to examine the possible mineral-supplementing function of salt-licks of this area, we compared mineral concentration between the water from salt-licks mainly visited by herbivorous mammals to drink water and nearby streams, possible water sources for mammals at the area. We also analyzed the relationship between mineral concentration and salt-lick visit by mammals. Among analyzed minerals, only the concentrations of sodium and calcium were significantly higher in water from all studied salt-licks than those of nearby streams in both dry and rainy seasons, indicating that mammals could supplement these minerals by drinking salt-lick water. Herbivores most frequently visited the salt-lick with the sodium concentration significantly higher than other salt-licks. In contrast, omnivores and carnivores did not show such tendency. Red muntjac (Muntiacus muntjak) and sambar (Rusa unicolor), the first and second most-frequent visitors of salt-licks (41.7% and 20.8% of the visitation record by mammals, respectively), most frequently visited the salt-lick with highest sodium concentration. On the other hand, Malayan tapir (Tapirus indicus) and white-thighed langur (Presbytis siamensis), the third and fourth most-frequent visitors (15.1% and 5.4%, respectively), frequently visited the salt-lick with lower sodium concentration. The results are consistent with hypotheses that sodium supplementation is an important purpose of salt-lick visit by herbivores, and indicated that other factors which would vary by species, such as social interaction, also affect selection of salt-licks to visit by herbivores.


Introduction
In forests from temperate to tropical areas, there are specific sites where many terrestrial and some arboreal mammals have been recorded to eat soil and/or drink seeping water at these sites (Corlett 2009). These sites are called "salt-licks" (Molina et al. 2014), "mineral licks" (Moe 1993), "natural licks" (Matsubayashi et al. 2007a), or "mineral spring" (Bechtold 1996), etc. The salt-licks are considered to be important places for conservation of forest animals since various animals including endangered species are observed there. However, the functions of salt-lick visits for animals were still not well studied in many regions, especially in Southeastern Asia.
Several hypotheses on the functions of salt-lick visits have been proposed, such as mineral supplementation, detoxification of plant secondary compounds, or alleviation of gastrointestinal problems (Ayotte et al. 2006;Bechtold 1996;Wakibara et al. 2001). The mineral-supplementing function, in particular sodium supplementation, was suggested by a number of studies (Ayotte et al. 2006;Clayton and MacDonald 1999;Matsubayashi et al. 2011;Owen et al. 2014). This hypothesis supposes that herbivores need to supplement sodium at the salt-licks because plants do not contain enough sodium for animal physiological functioning (Corlett 2009).
In Southeastern Asia, Matsubayashi et al. (2007a) reported that various mammals in tropical rain forests of Borneo, including endangered species such as orangutan (Pongo pygmaeus), drank the salt-lick water with much minerals such as sodium and calcium, suggesting the mineral-supplementing function of the salt-licks and importance of the salt-licks in wildlife conservation. In protected rainforests of Peninsular Malaysia, the Department of Wildlife and National Parks (DWNP) introduced habitat enrichment program, involving maintenance of grazing field, forest replanting, clearance of the forest for new shoots, and maintenance of artificial salt-licks (Ali et al. 2021). The artificial salt-licks provide various minerals such as sodium, phosphorous, and calcium in the protected areas under the jurisdiction of DWNP (Magintan et al. 2015), supposing the mineral-supplementing function of the salt-licks. At these artificial salt-licks, some ungulate species such as wild boars (Sus scrofa), red muntjacs (Muntiacus muntjak), and Malayan tapirs (Tapirus indicus) were reported to drink water frequently (Simpson et al. 2020). On the function of natural salt-licks of this area, however, we still have limited studies.
At wet-type natural salt-licks in the tropical rainforests of Belum-Temengor Forest Complex (BTFC), Peninsular Malaysia, Tawa et al. (2022) showed that 95.3% of all records of animals at the salt-licks were herbivores, while the records of omnivores and carnivores were only 3.5% and 1.2%, respectively. In addition, they reported that water-drinking behaviors were recorded significantly more frequently in herbivores (73% of video captures) than in omnivores (28%) and carnivores (0%) at the salt-licks. Their results suggested that animals, especially herbivores, visited the salt-licks to supplement minerals which are deficient in plant-based diets and/or alleviate gastrointestinal acidosis related to plant-based diets by drinking the salt-lick water. It is still not clear, however, whether the water of these salt-licks contains a higher concentration of minerals and/ or bicarbonate which have been reported to alleviate gastrointestinal acidosis by neutralizing increased rumen acidity (Ayotte et al. 2008;Davies and Baillie 1988) than the water of other places.
In this study, to clarify whether the salt-licks in BTFC actually have the mineral-supplementing function for herbivorous mammals of this area and which minerals are important for their mineral supplementation, we compared the mineral concentrations of the water from the salt-licks and the reference sites. We also analyzed the relationship between mineral concentration and frequency of salt-lick visit by animals, supposing that herbivores would visit the salt-licks with higher concentration of more preferred minerals more frequently if mineral supplementation is a major reason for their salt-lick visits. In this study, we did not discuss the possible function of the salt-lick water to alleviate gastrointestinal acidosis of herbivores because we did not analyze bicarbonate concentration in the water.

Study area
This study was conducted in the Belum-Temengor Forest Complex (BTFC) located in the State of Perak in northern Peninsular Malaysia (5°30ʹ N, 101°20ʹ E) (Fig. 1), which is mainly covered by upland and lowland dipterocarp forests (Misni et al. 2017). The BTFC consists of two sections, the Royal Belum State Park (RBSP) in the north and Temengor Forest Reserve (TFR) in the south, separated by the East-West Highway (Gerik-Jeli Highway). The RBSP covers an area of 1175 km 2 (260-1533 m a.s.l.) and consists of primary forests. By contrast, TFR (1489 km 2 , 260-2160 m a.s.l.) is classified as a production forest where selective logging has been ongoing since the 1970s (Ching and Leong 2011). According to the data of rainfall at Kg. Lalang (about 30 km west of the study site) provided by Water Resources Management and Hydrology Division, the rainy season around BTFC was from April to December with the break from June to August during the study period (the graph of monthly rainfall is shown in Tawa et al. (2022) as Supplementary Information).

Locations of studied salt-licks
There are at least 12 salt-licks known by local people in the BTFC and some of them are shown in the sightseeing maps of this area. Automated infrared sensor cameras were established around four salt-licks easily accessible for humans. All the four salt-licks are of the "wet" type, i.e., salt-licks where water that may contain minerals is seeping or flowing from the ground. These salt-licks are relatively open areas surrounded by forest, lacking large trees, and where the underbrush is not very dense. One of the four studied salt-licks, called the Tersau salt-lick (5°19ʹ N, 101°22ʹ E), is located 16 m from the shoreline of Temengor Lake in TFR. This area is mainly covered by upland dipterocarp forest (Misni et al. 2017). The other three salt-licks are located along the Tiang River in RBSP. These salt-licks are called (A) Sira Kuak (5°42ʹ N, 101°27ʹ E), (B) Sira Batu (5°43ʹ N, 101°27ʹ E), and (C) Sira Tanah or Sira Dinding (5°43ʹ N, 101°27ʹ E) by the local people; however, in this study, we hereafter refer to them as "Tiang A," "Tiang B," and "Tiang C," respectively. This area is covered by mixture of upland and lowland dipterocarp forests (Misni et al. 2017). The detailed information on the studied salt-licks is described in Tawa et al. (2022) as Supplementary Information. The distance between Tiang A and Tiang B, Tiang A and Tiang C, and Tiang B and Tiang C is about 2.4 km, 2.2 km, and 0.4 km, respectively. Odden and Wegge (2007) estimated that the home range size of red muntjacs was 0.70 km 2 in males, and 0.59 km 2 in females (95% Fixed Kernel Density) on average in Nepal. Chatterjee et al. (2014) estimated that the home range size of sambars was 7.5 km 2 in males, and 4.3 km 2 in females (50% Fixed Kernel Density) on average in Western India. In addition, the present authors showed that one identified female Malayan tapir was recorded at all of the three salt-licks in the Tiang area by camera trapping (Tawa et al. 2021). Thus, the medium-large mammals in this area might easily move between Tiang B and C salt-licks. Besides, large ungulates such as sambar or Malayan tapir might access all of the three salt-licks in the Tiang area. In contrast, it is more than 40 km between the salt-licks in the Tersau area and those in the Tiang area which are also separated by a highway (Fig. 1). Thus, the Tersau salt-lick was probably visited by mammal populations different from those that visited the studied salt-licks in the Tiang area. Therefore, to analyze the relationship between mineral concentrations and frequency of salt-lick visit by medium-large mammals, we compared three salt-licks in the Tiang area, RBSP, excluding the salt-lick in the Tersau area, TFR.

Mineral analyses in the water of salt-licks
Mineral contents were compared between the water of the salt-licks and the nearby streams where mammals of those areas were likely to use for their usual water intake, and examine the possibility that water of the salt-licks could provide minerals which were not available from the stream water. The method of sample collection followed Matsubayashi et al. (2007a). The water samples were collected at four salt-licks and nearby streams on 4-5 February (dry season) and 18-19 November (rainy season) 2015. At the Tersau salt-lick, the water samples were collected right near the water-spring vents on the bottom of a puddle (about 1 m × 1 m size, 5 cm deep) from where the bubbles were rising up. At three salt-licks in the Tiang area, the waterspring vent was not detected, and thus, the water samples were collected randomly from the puddle. The four streams selected as the reference sites were at a distance of 10-20 m away from each salt-lick. Water samples of the streams were collected from the points on the same day as the sampling at the salt-lick, at a point where no surface inflow from the salt-lick was found upstream. Nine or 10 samples were collected using a syringe (Nipro syringe 20 mL 08753, Nipro Corporation, Osaka, Japan) at each salt-lick and stream. All the samples were filtered through a syringe filter of 0.20 μm pore size (Sartorius, Minisart 17597, Sartorius AG, Goettingen, Germany) to remove debris and particulates. The concentrations of sodium, potassium, magnesium, and calcium in the water samples were measured using an atomic absorption spectrometer (AAnalyst 800, Perkin Elmer, Shelton, USA). The water samples were collected and analyzed independently, without blending.

Camera trapping
We placed motion-sensitive infrared-triggered digital cameras at the four salt-licks between 25 February 2014 and Fig. 1 Location of Belum-Temengor Forest Complex (BTFC). The area of BTFC is about 320,000 ha which includes 17,200 ha Temengor Lake. The stars show the location of the Tersau salt-lick and three salt-licks in the Tiang area, respectively. The location of the three salt-licks in the Tiang area is shown by one star in this figure because they are closely located to each other. The locative relationship of the three salt-licks in the Tiang area is shown in Tawa et al. (2022) as Supplementary Information 24 February 2016 (730 days). At each of Tersau, Tiang A, and Tiang B salt-lick, three cameras were deployed. At Tiang C salt-lick, two cameras were deployed. The models of the cameras used in this study were Trophy Cam HD 2013 (Bushnell Outdoor Products, KS, USA), Stealth Cam Sniper Shadow STC-SNX1 (Stealth Cam LLC, TX, USA), and TREL 20 J (GISupply Co. Ltd., Hokkaido, Japan). The cameras were deployed originally to record the behaviors of Malayan tapirs in the other study by the present authors (Tawa et al. 2021). We used these cameras in video mode and collected 1-min-long videos per trigger event. The triggering interval was a minimum of 20 s. All camera units were mounted on trees at approximately 1 m above the ground to record medium-to large-sized mammals. Two or three cameras were placed at each salt-lick to cover a large portion of the open area; however, some parts of each saltlick were often not adequately covered due to issues with the faulty cameras, SD memory cards, or batteries.
In this study, videos recorded continuously at intervals of 30 min or less were considered to be not independent and counted as "one capture" to avoid repetitive count of many images by continuous shooting during a single visiting event by the same animals. Even if multiple cameras at the same salt-lick recorded an animal and/or group of animals walking into the salt-lick, the video records of this event were counted as "one capture," regardless of the group size. The capture frequencies (the number of captures per day with active camera) of each studied salt-lick and each species were calculated.
To analyze the relationship between mineral concentrations and frequency of salt-lick visit by medium-large mammals, we compared the mineral concentration in the saltlick water and the capture frequencies of animals among the three salt-licks closely located to each other in the Tiang area. The salt-lick in the Tersau area was excluded from the analysis because it is separated by a highway from other studied salt-licks.

Statistical analyses
The Wilcoxon rank sum test was used to compare the mineral concentration between the water from salt-licks and nearby streams. The Steel-Dwass test was used to compare the mineral concentration among the three salt-licks at the Tiang area. The Fisher's exact test was used to compare the record frequency of mammals among the three saltlicks at the Tiang area. These tests were computed in R version 4.2.0. For all tests, a p-value of < 0.05 was taken to indicate statistical significance. Data are presented as the mean ± standard deviation (SD).

Mineral concentration of the salt-lick water and stream water
Sodium concentrations were significantly higher at all four salt-licks studied than the average of stream water both in dry and rainy season (Wilcoxon rank sum test, p ≤ 0.004; Table 1). Calcium concentrations were also significantly higher at most salt-licks than the stream water in both seasons (p ≤ 0.001; Table 1), except at Tiang A in rainy season. On the other hand, potassium and magnesium concentrations were not always significantly higher at the salt-licks than the stream water. Thus, we focused on the concentrations of sodium and calcium in the rest of our analyses.

Relationship between mineral concentration and mammal records
Capture frequencies of mammals at each salt-lick ranged from 1.14 to 2.71 captures/day ( Table 2). The mammal species most frequently recorded at the studied salt-licks were red muntjac (41.7% of all animal captures, 0.633 captures/ day), followed by sambar (Rusa unicolor, 20.8%, 0.317 captures/day), Malayan tapir (15.1%, 0.230 captures/day), and white-thighed langur (Presbytis siamensis, 5.4%, 0.082 captures/day), as reported in Tawa et al. (2022). The red muntjacs and the Malayan tapirs were recorded at all the four studied salt-licks, while the sambars and white-thighed langurs were distributed only in RBSP and recorded at three salt-licks in the Tiang area. The percentage of red muntjacs, sambars, Malayan tapirs, and white-thighed langurs in the total animal captures at the three studied salt-licks in the Tiang area was 41.0%, 27.0%, 10.6%, and 7.0%, respectively.
The record frequency of mammals with each food habit was compared among the three salt-licks in the Tiang area (Fig. 3). The herbivores were recorded significantly more frequently at Tiang C salt-lick (590 captures, 2.67 captures/ day) with the highest sodium concentration than at Tiang A and B salt-licks (Fisher's exact test, p < 0.001 for both pairs of Tiang C-Tiang B and Tiang C-Tiang A), while omnivores and carnivores showed no such tendency. The omnivores were recorded significantly more frequently at Tiang A salt-lick (39 captures, 0.077 captures/day) than at Tiang B and C. The carnivores were recorded most frequently at Tiang B salt-lick (16 captures, 0.032 captures/day), though there was no significant difference among these salt-licks in the Tiang area (Fig. 3).
The red muntjacs and the sambars were recorded significantly more frequently at Tiang C salt-lick (352 captures, 1.59 captures/day, and 157 captures, 0.71 captures/ day, respectively) than at Tiang A and B salt-licks (Fisher's exact test, p < 0.001 for both pairs of Tiang C-Tiang B and Table 1 Mineral concentration of each salt-lick water and those of nearby stream water in each season The average concentration among four sites was calculated for streams. The asterisks (*) indicate that the mineral concentration of the salt-lick was higher than that of all stream sites at p < 0.05; double asterisks (**) at p < 0.001 (Wilcoxon rank sum test) Tiang C-Tiang A), in accordance to the difference in sodium concentration (Fig. 3). The Malayan tapirs, however, were recorded at Tiang B salt-lick significantly more frequently (163 captures, 0.327 captures/day) than at Tiang A and C salt-licks (Fisher's exact test, p < 0.001 and p = 0.00655, respectively). In addition, the white-thighed langurs were also significantly less recorded at Tiang A salt-lick than at Tiang B and C salt-licks (Fisher's exact test, p < 0.001 for both pairs) and there was no significant difference in the capture frequency between at Tiang B and Tiang C (Fisher's exact test, p = 0.130).

Discussion
Comparison of mineral concentration between salt-lick water and stream water in this study suggested that the herbivorous mammals could supplement sodium and/or calcium by drinking water at the studied salt-licks; the concentration of sodium in salt-lick water was higher than that of stream water regardless of seasons or sites, and that of calcium was also higher in most cases. On the other hand, those of potassium and magnesium in salt-lick water were not necessarily higher than in the stream water, suggesting that animals could not always supplement these minerals much more by drinking the salt-lick water than by stream water (Table 1). Some previous studies on wet-type salt-licks also reported higher mineral concentration (including sodium and calcium) in the salt-lick water than the reference-site water in various regions (Table 3) babirusa (Babyrousa babyrussa) in Sulawesi Island, Indonesia, reported higher concentration of sodium and calcium in the salt-lick water than in reference-site water. Matsubayashi et al. (2007a) who studied wet-type salt-licks in Borneo Island, Malaysia, also reported higher mineral concentration (sodium, potassium, magnesium, and calcium) of the salt-lick water. In addition, these authors compared animal visits between two adjacent salt-licks at a distance of only 16 m and reported that the sambars and bearded pigs (Sus barbatus) visited the salt-lick with higher concentration of all four minerals more frequently than the other. In this study, the herbivores most frequently visited the Tiang C salt-lick with the highest sodium concentration among the three salt-licks in the Tiang area, while the omnivores and carnivores did not show such tendency. Since omnivores and carnivores are thought to have less need for mineral supplementation than the herbivores, the result also suggests that the herbivores visited the salt-licks for supplementation of minerals, especially sodium.
Some previous studies also suggested that herbivores visited salt-licks mainly for sodium supplementation. Couturier and Barrette (1988) who studied salt-lick use by moose (Alces alces) in Quebec, Canada, reported that among the four wettype salt-licks where they observed moose, the one that had the most visits also had the highest sodium content. Moe (1993) who analyzed soils of dry-type salt-licks in southeastern Nepal showed that sodium concentration was significantly higher in soil from salt-licks than in reference soils, while other mineral concentrations were not. He also showed positive correlation between the sodium concentration and visit frequency by axis deer (Axis axis) using the data from 12 dry-type salt-licks in the study area. Holdø et al. (2002) who studied African elephants (Loxodonta africana) in a Kalahari-sand habitat, Zimbabwe, analyzed the mineral concentration of the food plants, drinking water, and soils of dry-type salt-licks the elephants ate. They estimated that the elephants could not ingest enough amount of sodium for their requirements from the food plants and drinking water, while they could take enough amount of calcium and magnesium. They also reported that the salt-lick soils contained higher concentration of sodium than other soils, while the calcium and magnesium concentrations of saltlick soils were lower than the food plants and drinking water, indicating that elephants supplement sodium, not calcium and magnesium, from salt-lick soils.
On the other hand, it is also reported that the salt-licks have an important role of supplementing not only sodium but also other minerals such as calcium for animals. Atwood and Weeks (2003), who studied the salt-lick use by white-tailed deer (Odocoileus virginianus) in Indiana, USA, reported that females visited salt-licks with various mineral contents more frequently than salt-licks with only sodium, pointing out that females during lactation might need minerals such as calcium and phosphorus in addition to sodium.

Table 3
Concentration of minerals in water drinking-type salt-licks The unit of mineral concentration is ppm. The asterisks (*) indicate that the mineral concentration of the salt-lick was higher than that of reference sites at p Reference (n = 18) 6.9 ± 2.4 (4.6-8.7) 1.6 ± 0.6 (1.5-1.8) 2.7 ± 1.0 (2.3-3.1) 13.8 ± 8.5 (5.6-20.4) Clayton and MacDonald (1999) The calcium concentration in salt-lick water (3.24 ± 1.54 ppm, range 0.51-12.79, n = 79) analyzed in this study, however, was much lower in absolute values compared to those reported by previous studies (Clayton and MacDonald 1999: 90 ppm;Matsubayashi et al. 2007a: 83.4 ± 50.0 ppm; Table 3). Therefore, the supplementation of sodium seems more important than that of calcium for animals that visited the salt-licks studied in this study. In addition, the herbivores (especially the red muntjacs and sambars, which were the main users of the salt-licks) most frequently visited the Tiang C salt-lick with the highest sodium concentration among the three salt-licks in the Tiang area, while the calcium concentration at Tiang C was not always higher than other salt-licks. This suggests that sodium is likely more important than calcium in mineral supplementation of herbivores at the salt-licks of this area. We cannot eliminate, however, the possibility that the animals supplement calcium at the salt-licks, because calcium concentration in the salt-lick water was higher than that in the stream water in most cases.
It also cannot be denied that the animals supplement some minerals other than sodium and calcium which were not measured in this study but critical for herbivore nutrition. Especially, phosphorous concentration and its relationship with salt-lick use by animals should be examined in future studies in this area because the artificial salt-licks containing phosphorous in addition to sodium and calcium succeeded to attract mammals in protected forests in Peninsular Malaysia (Magintan et al. 2015).
In contrast to the red muntjacs and sambars that visited Tiang C with the highest sodium concentration most frequently, the Malayan tapirs and the white-thighed langurs, the third and fourth most-frequent herbivorous visitors to the studied salt-licks in the Tiang area, did not visit Tiang C most frequently. The Malayan tapirs and the white-thighed langurs visited Tiang B more frequently than Tiang C while sodium concentration at Tiang B was significantly lower than at Tiang C, though the difference in the white-thighed langur was not significant (Fig. 3). These results indicate that not all the herbivore species visited the salt-lick with higher sodium concentration more frequently. Thus, other factors which may vary with species could influence the frequency of salt-lick visit by animals in addition to the sodium concentration.
The present authors studied the behavior of wild Malayan tapirs around the same salt-licks as this study, and observed male-female interaction such as chasing and vocalization, suggesting that they used the salt-licks as a place to meet potential mating partners in addition to drink water there (Tawa et al. 2021). Thus, such social interaction can affect selection of the salt-licks by tapirs. Matsubayashi et al. (2011), who studied the use of salt-licks by orangutans, also reported that multiple individuals such as two pairs of females with infants were recorded by sensor cameras in the same frame, suggesting that the salt-licks have secondary function as a communication site for them.
Since some carnivores, tigers (Panthera tigris jacksoni) and dholes (Cuon alpinus), and hunting behavior by dholes were recorded at the studied salt-licks (Tawa et al. 2022), difference in predation risk among the salt-licks could affect the salt-lick visit by herbivores. Griffiths et al. (2020), who conducted camera trapping survey at 52 salt-licks in the northeastern Peruvian Amazon, showed that three mammals (the paca Cuniculus paca, Brazilian porcupine Coendou prehensilis, and red brocket deer Mazama americana) were less likely to visit salt-licks during nights with bright moon probably due to a heightened risk of predation at the salt-licks when visibility was better for predators. Although it remains to be studied whether the visit frequency of prey mammal is affected by lunar cycles also in this study area, the lunar cycle could not cause the difference in visit frequency among three salt-licks in the Tiang area because the difference was observed during the same study period.
The micro-habitat preferences of each species were also considered to influence the visit frequency to the salt-licks by animals in this area. Razali et al. (2020) analyzed the relationships between the physical environments around the saltlicks and the visit frequency by animals in BTFC. And they suggested that ungulates preferred the salt-lick with dense understory foliage that could be their foraging site, and arboreal primates and birds preferred the salt-lick with closed canopy cover that could provide perching site for them. Lazarus et al. (2019) conducted camera trapping surveys at the same three salt-licks in the Tiang area as this study. Their results on the record frequency of red muntjac were not consistent with ours, while the results on sambar and Malayan tapir were consistent with this study. They reported that the red muntjacs were recorded significantly more frequently at Tiang A than the other two salt-licks based on the research of 6 months (the exact survey dates were not described), while in this study the red muntjacs were observed to visit Tiang C most frequently, followed by Tiang A and Tiang B based on the research of 2 years. Although they did not conduct mineral analysis of salt-lick water, they discussed that the red muntjacs might preferred Tiang A because of the thick, dense underbrush and vines around Tiang A where they could quickly hide from predators. They also speculated that the sambars were observed significantly more frequently at Tiang C because they can visit there in group due to the large open area in front of the water source in Tiang C.
Although it is still not clear why their results on red muntjacs are different from ours, the difference in survey season and studied period, however, could cause the difference because the red muntjacs could seasonally change the visit frequency to the salt-licks. In addition, the physiological demand for minerals could also seasonally change by pregnancy and lactation for example. Holdø et al. (2002) reported that the female African elephants spent more time than males for soil-eating at the dry-type licks. In Borneo, Matsubayashi et al. (2007b) reported that female sambars visited the wet-type salt-lick more frequently in rainy season than in dry season while visit frequency of males did not seasonally change. Couturier and Barrette (1988) showed that the various age-sex (yearling or adult, male or female) moose had different seasonal patterns of salt-lick use, suggesting possible differences in mineral needs related to molting, antler grows, calf growth, lactation, or estrus.
Some previous studies indicated that the seasonal changes in visit frequency to salt-licks are also relevant to the needs for alleviation of gastrointestinal problems, as shown in Ayotte et al. (2008). The possibility cannot be eliminated that herbivores visit the salt-licks in the purpose of bicarbonate ingestion to alleviate gastrointestinal problems also in this area because the concentration of bicarbonate in salt-lick water was not measured in this study.
This study did not examine the effects of factors other than some mineral contents of the salt-lick water; however, many other factors, such as unmeasured contents in salt-lick water, seasonal change in animal activity, and social interaction at the salt-licks, could affect the pattern of animal visitation to the salt-licks. In order to understand the functions of salt-licks for the mammals more precisely, we need to examine the effects of these factors on the salt-lick visit by mammals, which may vary by species, in future studies.
Mineral analyses of the salt-lick water by this study showed that the wet-type salt-licks studied in BTFC could provide the sodium and calcium supplementation for the herbivorous mammals. Especially, the high concentration of sodium was consistent with the hypothesis that the herbivorous mammals visit the salt-licks mainly for sodium supplementation. However, the results on relationship between the mineral concentration of salt-lick water and visit frequency by mammals suggest that the factors other than sodium concentration might also influence the selection of salt-licks by each species. The results of this study providing better understandings on the salt-lick functions can contribute to improve the design of artificial salt-licks and the plans for mammal conservation in this area.