Mantled howling monkeys (Alouatta palliata

Primate Conservation and Behavioral EcologyAugust 2014

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14Paldino

Mantled howling monkey (Alouatta palliata) adult male versus female food consumption variations between morning and afternoonCecily N. Paldino

AbstractThis research aims to assess adult male and female mantled howling monkey consumption variation according to time of day at the El Zota Biological Field Station in Costa Rica. Food consumption includes both foraging and ingestion. Data collection on overall howling monkey activity through focal sampling suggested differences in feeding based on time of day and sex. This behavioral study revealed that mantled howling monkeys, on average, spend more time ingesting in the afternoon and foraging in the morning. Data also unveiled the distinctions between adult males and females; females consumed more both in the morning and afternoon than males. Mantled howling monkeys at El Zota, through this study, not only remain in familiar, respective home ranges, but also alternate most of their time between resting, traveling, and feeding, as well as exhibit differences in ingestion and foraging frequencies throughout the day.

IntroductionThe average mantled howling monkey troop contains 2 adult males, 2 adult females, and 2-3juveniles/infants (Bramblett, 1976)[endnoteRef:1]. Male howlers, when full-grown, are 20% larger than the full-grown female (Bramblett. 1976). When traveling, howling monkeys tend to use familiar, yet irregular pathways, traveling short distances throughout the day, averaging about 90 meters per hour (Bramblett, 1976). Howlers occupy extremely defined locations among the trees, due to their limited home ranges, implying that howlers have a narrow distribution of feeding sites (Bramblett, 1976). Foraging efficiency is measured by the net energy yield as well as optimal foraging time (Milton, 1980). There is a cost that accompanies foraging energy when searching for foods and the stress of exposure to potential predators (Milton, 1980)[endnoteRef:2]. A study on mantled howling monkey ranging, conducted by Milton in 1980, displays that howlers are goal-oriented in foraging in order to conserve maximum energy by using single-filed methods of travel. Howlers, on average, spend 65.54% resting, 16.24% foraging and consuming goods, and 10.23% traveling (Milton, 1980). [1: Bramblett, Claud A. 1976. Patterns of Primate Behavior, Primates in the field. pp. 113-155] [2: Milton, Katherine. 1980. The Foraging Strategy of Howler Monkeys: A Study in Primate Economics, Ranging. pp. 99-124]

Various studies have been done on mantled howling monkey feeding patterns and consumption rates. Feeding among howling monkeys is relatively unique in that they are selective in choosing specific leaves to eat based on nutritional quality and availability (Strier, 2011)[endnoteRef:3]. Mantled howling monkeys are primarily folivorous, meaning they consume leaves as a major staple in their diet; 63.6% of their diet includes leaves, 30.7% contains fruit and flowers (Janzen, 1983)[endnoteRef:4]. Of the leaves, howlers consume 44.2% new leaves and 19.4% mature leaves. Of the fruits and flowers, howlers consume 12.5% fruits and 18.2% flowers, with the remainder 5.7% consumption left for petioles and pulvines (Janzen, 1983). Research conducted by Glander in 1980 focused on the differences between new and mature leaf consumption, as the two differ greatly in dietary content. The reason new leaves are popular in mantled howler diet is due to their abundance in water and important nutrients (Janzen, 1983). New leaves contain less fiber and secondary compounds, but require more time to identify and harvest. Mature leaves require more search to locate, and they tend to contain excessive fiber and unwanted elements (Janzen, 1983). However, howlers select specific mature leaves that do not contain condensed compounds, such as tannins and alkaloids. The mature leaves that howlers do select and consume contain the most proteins, methionine, and the least amount of fiber (Janzen, 1983). This study by Glander expressed that mantled howling monkeys have a very specific diet and manner of foraging leaves to ingest, desiring the maximum amount of proteins and amino acids and the minimum amount of fibers and secondary compounds (Janzen, 1983). [3: Strier, Karn B. 2011. Primate Behavioral Ecology, Food, Foraging, and Females. pp. 146-167] [4: Janzen, Daniel H. 1983. Costa Rican Natural History, Mammals: Species Accounts. pp. 448-449]

The objective of this research was to examine El Zota Biological Field Station mantled howling monkey adult male versus female consumption variations between morning and afternoon. This study addressed whether or not howler monkeys have foraging and ingestion preferences based on time of day and sex. A prediction for this study was that the mantled howling monkeys will forage and consume more in the morning than the afternoon, thus allowing the howlers more resting time later in the day. Another inference was that because male howlers have a larger body size than females (Bramblett, 1976), they will consume more foods overall than females. Studying the feeding patterns of mantled howling monkeys at El Zota is not only beneficial in determining home range locations, but also to note specific species of trees that provide ample leaves for howler diet as well as foraging patterns that will aid in future conservation and reforestation tactics.

MethodsI. Study siteThis research was conducted at the El Zota Biological Field Station, located in the northeastern segment of Costa Rica, at coordinates 1057.6 N, and 8375.9 W (Pruetz and LaDuke, 2001)[endnoteRef:5]. El Zota is a privately owned biological research station that offers facilities to prospective students and returning researchers to pursue his or her studies on many diverse species of wildlife that thrive around the area. The site is a wet-lowland swamp forest, and is currently going through phases of reforestation (Pruetz and LaDuke, 2001). There are three species of primate that inhabit El Zota. They are: spider monkeys (Ateles geoffroyi), white-faced capuchins (Cebus capucinus), and the mantled howling monkey (Alouatta palliata). [5: Pruetz, J.D. and LaDuke, T.C. 2001. Neotropical Primates, New field site, preliminary census of primates at El Zota Biological Field Station, Costa Rica. 9:22-33]

II. Study subjectsMantled howling monkeys were the study subjects for the conducted research. The two howler troops that were observed for data inhabited the trails Sendero Rio Norte (SRN), Sendero Congo (SCo), and Sendero Swampo (SS). Occasionally, those two troops were contacted along the main road and at the El Zota headquarters. Adult male and adult females were the focal subjects of interest for data collected. Males were identified by their conspicuous white genitalia, while females lacked those identifiers.

III. Observational MethodsThis research used instantaneous focal sampling - one adult male or female was chosen at either in the morning or afternoon, and the sample was conducted with a 2-minute interval for a 30-minute time period per subject. The subjects were chosen based on first-initial sighting of the preferred sex subject of the day. When the subject of interest was out of sight (OS) for longer than 5 intervals, that subject was abandoned, and another subject of the same sex and age class replaced the original focal subject.

ResultsA total of 34 hours were spent in the field over a period of 6 days, between August 5th and August 10th, 2014. Total contact time was summed up to 11.8 hours, which evidently resulted in a total of 10 hours of data, with 5 hours in the morning and 5 hours in the afternoon. Overall, the mantled howlers observed spent 57.7% of their time resting, 26.5% ingesting food, 3.64% foraging, 11.3% traveling, and 0.9337% vocalizing (Table 3). In the morning, the howlers spent, on average, 52.5% resting, 18.96% ingesting, 7.03% foraging, 14.5% traveling, and 9.375% vocalizing (Table 1). In the afternoon, the howlers spent, on average, 52.95% resting, 40.63% ingesting, 9.375% foraging, 29.5% traveling, and no vocalizations occurred (Table 2). In the mornings, male howlers spent 60% resting, 16.25% ingesting, 3.75% vocalizing, and were out of sigh for 6.25% of the time observed (Figure 1, Pie Chart 1). Females spent 45% resting, 22.5% ingesting, 6.25% foraging, 18.75% traveling, and were out of sight for 7.5% of the time observed (Figure 1, Pie Chart 2). In the afternoons, male howlers spent 62.5% resting, 25% ingesting, 3.75% foraging, 3.75% traveling, and were out of sight for 5% of the time observed (Figure 1, Pie Chart 3). Females spent 50% resting, 36.25% ingesting, 10% traveling, and were out of sight for 3.75% of the time observed (Figure 1, Pie Chart 4).In total, mantled howlers spent the most time feeding in the afternoon at 57.1%, and 42.9% in the morning (Figure 2, Pie Chart 1). In the mornings, female howlers fed for 59% of the time, and males 41% (Figure 2, Pie Chart 2). In the afternoons, female howlers fed for 55.8% of the time and males 44.2% (Figure 2, Pie Chart 3). In terms of foraging, howlers spent more time foraging in the morning, 5% (Figure 3, Bar Graph 1) and less in the afternoon, 1.875% (Figure 3, Bar Graph 2). Females foraged more in the morning, 6.25% more than males, but less overall, males foraging 3.75% of the time in both morning and afternoon, and females were not recorded foraging at all in the afternoons.

FIGURE 1: Overall distribution of adult male and female activity between morning and afternoonPie Chart 1

Pie Chart 2

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FIGURE 2: Overall feeding variations based on time of day and sexPie Chart 1

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FIGURE 3: Overall percentages of mantled howler monkey activity between morning and afternoon

Bar Graph 1

Bar Graph 2

DiscussionBased on results of the data collected, feeding occurred the most in the afternoon. Between both adult male and female subjects, the females, overall, fed the most. These results refuted the hypotheses, allowing this research to reject the previous assumptions of greater feeding in the morning and afternoon by adult males. The male howlers spent the majority of their time resting when females were much more active in traveling than males, which supports the idea that because adult females were traveling more, there was a greater desire to consume and forage along the way. This does not dispute the fact that females still spend the most time resting they just do so less than males. Traveling occurred more often in the morning than the afternoon, which provides this research with yet another aspect of the data collected to analyze. Howlers spent less time traveling in the afternoon and more time alternating between resting and feeding. The howlers observed in the afternoon remained in one specific area during contact time. Because traveling is greater in the morning between both sexes, it may correlate with why howlers tend to focus on moving in the forest to a desired location for afternoon feed. This find supports Miltons 1980 study on howler ranging and the concept of goal-oriented foraging (Milton, 1980). The results of this study display distinctive feeding patterns of both the adult male and female howling monkey, as well as express the possibility that howler travel greatly affects consumption and forage.

ConclusionMantled howling monkeys at the El Zota Biological Field Station, based on data collected consumed more in the afternoon than in the morning. Adult females partake in over half of overall consumption, and they tend to travel more in both the morning and afternoon, when adult male resting is substantially over half. The results supported the hypotheses of this study to be incorrect, offering new questions and different perspectives on mantled howlers at El Zota. An issue that did arise throughout the study and may have caused data collection difficulties was the prevalence of out-of-sight cataloging, due to the heavy rainfall that hindered observer eyesight as well as instances of the howlers quick and sudden travel. Through this research, new questions surfaced, such as the effects of traveling and goal-oriented foraging (Milton, 1980) on mantled howler feeding. New research potential also arose; morning consumption variations do howlers consume more in early or late morning? Afternoon consumption variations do howlers consume more in early or late afternoon? Although this research cannot completely express accurate howler feeding patterns at the El Zota Biological Field Station, it does present great potential in future, longer-term studies on mantled howling monkey consumption variations based on time of day and sex, as well as travel and how that impacts the rate of consumption.