Mantled howling monkeys (Alouatta palliata
Primate Conservation and Behavioral EcologyAugust 2014
[Type text][Type text][Type text]
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
Pie Chart 3
Pie Chart 4
FIGURE 2: Overall feeding variations based on time of day and
sexPie Chart 1
Pie Chart 2
Pie Chart 3
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.