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6 Habitat Use Mammals do not make uniform use of their habitats. They tend to be very selective of their times of activity and their spatial use of habitat. This selectivity is a very important aspect of their ecology, and thus it continues to be studied frequently. Little more than a watch, pencil, and notebook is needed. The basic paper on sampling methods is by Altmann (1974). Additional comments are given in Clutton-Brock (1977, Appendix 1). TIME BUDGETS Two techniques are commonly used in primate field studies. In one, called the focal animal technique, the investigator focuses on a single animal for extended periods. He records the activity of that animal for a period of time, then switches to another animal and records its activities for another period. The second tech- nique is to scan the troop of primates at set intervals and record what each visible animal is doing at that time. This is the scan technique. In using either technique it is convenient to decide be- 128
Habitat Use 129 forehand on the categories of activity to be recorded: feeding, climbing, resting, sleeping, and so on. These categories can be as detailed as desired and should reflect the full range of activities being studied. When using the focal animal technique one should consider carefully beforehand how to analyze and present the data. In some studies, frequency is most useful (the number of figs con- sumed by a monkey or the number of interactions between ani- mals). Continuous recording may be essential to obtain data on the duration of eventsâhow long animals feed in fig trees or how much time during the day they spend foraging for insects. A sam- pling system can be used readily. For example, one can record every 2 min the major activities of the animal in the previous 2 min, tabulate the number of 2-min periods each hour in which different activities occurred, and use these data as estimates of frequency or of time spent in these activities, whichever is appro- priate. When using the scan technique one can make instantaneous observations (what each animal is doing the moment you look at it) or timed observations (look at each animal for 5 or 10 s, then record what it was doing). When scanning it is important to look at as many animals in a troop as possible and to be alert for bi- ases. It is always likely that some activities will be recorded infre- quently, only because it is more difficult to see the animals then. There may also be bias attributable to the shyness of certain indi- viduals (e.g., females with newborn young). Among social animals it is generally the case that males, fe- males, and juveniles use their time differently, so it is desirable that the data be collected separately for each class of animal. In scanning this also enables one to determine if one class of animals is harder to see than another and hence is being underrepresented in the samples. When using the focal animal technique, ran- domize the choice of the animal and be sure not to watch just ani- mals that are most easily observed. One should also check for other biases to make sure that adult males are not observed only on sunny days and females on rainy days or juveniles only when the troop is feeding on flowers. The shorter the study the greater the likelihood that some biases like these will occur, even though the selection of animals is randomized.
130 TECHNIQUES IN PRIMATE POPULATION ECOLOGY In many cases, primates' shyness makes it impossible to study them routinely. One can still use a scan technique, but the scan takes place when animals are first encountered, before they de- tect the observer. If one records the time, where they are, and what they are doing each time they are encountered, it is possible to gradually build up a good profile of their activities. However, if the encounter occurs at the same place or at the same time of day, the data will present a biased view of their total pattern of activ- ity. Thus, it is desirable to establish a series of transects, along established roads, trails, or waterways where necessary, and in other areas where possible. Off-trail transects can be followed easily, even at night, if they are laid out with a white string. One can proceed along these transects at different times of day or night collecting data whenever one encounters primates. If the transects are arranged in a grid, data will show spatial as well as temporal use of the habitat. USE OF SPACE DAILY RANGING How animals use space within their habitat can be studied in several ways. It is useful to know how far animals travel daily and over how large an area they range. This is best done by following the animals regularly, directly measuring the length of their pathâeither with a measuring tape or by pacing off the distanceâand by plotting their movements on a map (Richard, 1979). The home range is the area the animals cover in all their activities. The longer one watches animals, the larger their home range proves to be, but after a certain number of hours of obser- vation one usually knows most of the home range. There may be seasonal variation or changes in the home range, so it is fre- quently informative to compute the number of hectares used by the animals each month and to compare the areas used in dif- ferent seasons. The use of the home range is uneven. Frequently a core area is used much more often than are peripheral parts of the home range. This may be studied by dividing the home range into quadrats and recording how long the animals spend in each
Habitat Use 131 quadrat. For large primates the quadrats can probably be 1 ha (i.e., 100 m on a side). For small monkeys and prosimians it may be desirable to use smaller quadrats, perhaps 1/4 ha in size (Rud- ran, 1978). Even shy monkeys can be studied this way. Rather than recording the length of time they spend in each quadrat, one can record the number of times they are encountered in each quadrat (Rodman, 1978). With enough data of either type one can calculate the percentage of time the animals spend in each quadrat of their home range. These data can be compared with the types of resources found in each quadrat. Seasonal changes can also be documented. HEIGHT AND SUBSTRATE Another aspect of habitat use in a forest is the height above the ground at which the animals are found (Rodman, 1978; Suss- man, 1972). This can be estimated with a rangefinder, with the viewfinder of a camera, or by eye. In any case one should regu- larly check his estimates against known heights. Heights may be classified according to a system appropriate for the habitat. For example, in high forest the classes might be 0-5 m, 5-10 m, 10-20 m, 20-30 m, and more than 30 m. In analyzing the height data it is useful to categorize the heights of the different parts of the forest. In some areas the tallest trees may be only 20 m in height, whereas in other areas the first branches may be higher than 20 m. This information should be included with the analyses of the heights at which the monkeys feed, rest, sleep, or travel. It is also important to test whether the presence of the observer af- fects the height of the animals. Check to see if the animals are at the same height when first encountered and 5 min later. More refined studies of habitat use are becoming common. For example, it is of interest in some studies to record the sizes of the branches on which the primates move and feed (Fleagle, 1978) or the angles that they make to the horizontal (Rose, 1978). One makes these estimates from the ground, and with practice one can become quite accurate. Again, measurements are in classes. Angles are expressed in a range of degrees (e.g., 0-30Â°, 30-60Â°, 60-90Â°). Diameters are expressed in centimeters (e.g., 0-1 cm for twigs, 1-3 cm for small branches, 3-10 cm for large branches,
132 TECHNIQUES IN PRIMATE POPULATION ECOLOGY 10-20 cm, and so on). The size estimates can be facilitated by comparing the size of the branch with the size of the fingers, feet, and body of the primate being observed. FEEDING ECOLOGY The foods of primates can be studied in several ways. The most obvious way is to watch what they are feeding on. This is highly effective for fruit and leaf eaters if the observer knows the plants as well as the animals do. If he does not, the observer can still label the plant and return to it later to obtain samples for identifi- cation. Identifying insects that a monkey is popping into its mouth is more difficult, but it is sometimes possible to identify in- sects by the sounds they make (as in the case of cicadas), or to see fragments of insects that are dropped when insects that are being picked up are too small to be identified. It is undesirable to kill wild primates, but if dead animals are available, one can examine the stomach contents (Charles-Dominique, 1972; Fooden, 1965). These can be studied fresh or they can be fixed in 10% formalin or 70% alcohol. The stomach contents can be sorted, and frag- ments of leaves, fruits, seeds, and insects can be identified. It is sometimes possible to sort and weigh the components of the diet. Stomach contents can also be obtained from a captured anesthe- tized animal by inserting a tube down its throat into its stomach. Water is injected down the tube into the stomach, then sucked out again (G. G. Montgomery, personal communication). The sample can then be strained from the water. Be sure that the tube goes down the esophagus into the stomach and not down the tra- chea into the lungs. With the outer end of the tube held to one's ear, one can hear or feel the animal's breath if the other end of the tube is in the trachea. Be careful, because the animal will die very quickly if water is injected into the trachea or lungs. An astute naturalist can learn a great deal about the foods of animals just by examining the signs they leave behind. These in- clude partially eaten flowers, fruits, and leaves. Feces can be col- lected and examined for plant and insect fragments, seeds, and other evidence of foods eaten. They can also be examined for par- asites and parasite eggs, which may be clues to insect feeding. The feces can be preserved in formalin or alcohol, but it should
Habitat Use 133 be noted that many parasitologists do not like formalin preserva- tion of worms. Feeding studies have gradually become more detailed. It is commonly expected now that the investigator will record the spe- cies, the parts of a plant or animal that are eaten, and the phyto- phase or stage of each food item (Glander, 1978). Are the fruits ripe or green? Is it just the base of the flower that is being de- voured? Is it just the abdomen of the beetle that is favored? Are only small caterpillars eaten? These are some of the detailed questions that may be asked in feeding studies. Frequently, a much longer list of plant parts is discriminated, including those phenophases listed in Chapter 3 and such items as petioles, bark, tubers, and resin. Finally, the amount of each food item consumed can be esti- mated in various ways, the preferred way depending largely on the nature of observation conditions. Direct or indirect sampling measures are used, depending on whether visual contact can be maintained with individuals throughout the observation period. Ideally one might wish to know how much of each type of food an animal consumes throughout a day. This requires estimation of the number of items consumed and their weights. To estimate the number of items consumed, an animal is followed and the type and number of food items brought into the mouth are recorded for each minute of observation. The schedule followed depends on the amount and type of information required. Loss of informa- tion is minimized if one identified animal is followed from dawn to dusk and different individuals are followed on consecutive days for several days each month. In this way it is possible to accumu- late a series of feeding-day profiles and a record of seasonal varia- tion in the amounts of each food item consumed. Occasionally, continuous observation of a feeding animal is not possible, as when its back is turned to the observer or when it is hidden in the foliage. However, the amount of food consumed can be extrapolated if one knows the type of food being con- sumed, the time the animal spends in feeding, and the rate at which the food is ingested. The size of food items taken must be known in order to esti- mate the weight of comparable samples. For most food items (e.g., fruits, flowers, petioles) that are brought into the mouth
134 TECHNIQUES IN PRIMATE POPULATION ECOLOGY singly, the size is self-evident. When several food items, such as a bunch of leaves, are brought to the mouth with a handpicking motion, the number of leaves per bunch is estimated. Similarly, the size of "bites" from large food items may require estimation. To obtain accurate weights, food items should be collected in the field and placed into plastic bags to reduce the evaporation of moisture. Multiplication of the average weight of single or "bite- sized" food items by the number consumed yields the weight of each food item consumed per observation period. Once collected, food items may be analyzed for moisture content or nutritional content. The former involves simply drying the items slowly in an oven. The difference between the "wet" and "dry" weights yields the weight of water in the food items. Nutritional analyses require elaborate laboratory procedures that will not be considered here. Hladik (1977) described methods for collecting and preparing food items in the field for nutritional analyses. The food intake in terms of both quantity and quality may ulti- mately be correlated with the energy demands of foraging move- ments and energy needs for reproduction. Attempts to calculate energy expended and food intake on a seasonal basis have been undertaken with Alouatta, Ateles, and Papio (Altmann, 1974; Coehloef a/., 1979). The relationship between food selection and plant defense mechanisms involving secondary compounds is an active area of current research. Some authors are relating food preferences by species and season to the avoidance of toxic secondary com- pounds such as tannins, saponins, and alkaloids. The problems encountered by folivorous primates in feeding on potentially toxic compounds in leaves are shared by other arboreal mammals in- cluding marsupials and edentates (see McKey et al., 1978; Mont- gomery, 1978).