Experiment:
Hacienda La Pacifica, Cañas,
Costa Rica [1976] (Clara B. Jones, Ph.D.)
WHO:
This post describes an unsuccesful attempt to manipulate food
dispersion (distribution of food in time and space) using a
Neotropical primate. The target species was the mantled howler monkey
(Alouatta palliata Gray), a predominately arboreal monkey
that is exclusively herbivorous, preferring new leaves, flowers, and
fruit. The diet of mantled howlers, also, includes mature leaves of
many plant species (mostly tree and some shrubs and vines); as well,
old leaves may be eaten in due course as well as "fallback"
foods, eaten when preferred food items are not available, rare in
time and space, or dispersed in a manner making foraging for them
energetically and/or temporally expensive, ceteris paribus.
As described by Milton in her 1980 book, the foraging behavior of
mantled howlers is "rule-governed", and the method
described here is probably most useful with animals whose foraging
behavior is tactical and strategic (e.g., animals following
particular routes depending upon distribution, abundance, and/or
quality of food) rather than opportunistic or "random". The
method described herein should apply to animals feeding on food
occurring in discrete packages (e.g., trees, termite mounds,
carcasses) and/or in patches. In general, the method has utility with
non-volant and non-aquatic animals.
WHAT:
Foraging behavior of one mantled howler group in Costa Rican tropical
dry forest was followed before manipulation for 3 d in dry season.
Dry season was selected as the time of year when many preferred foods
are most likely to flower and fruit, and the particular procedure
employed (see below), required the absence of rain. A medium-sized,
relatively abundant tree (Tabebuia neocrysantha: see image)
was flowering at its peak during the study week and was selected as
the target food item for logistic and practical reasons. In addition,
the manipulation was performed in a relatively small patch of forest
on the monkeys' home range (see below) to allow for selected
post-manipulation data collection. The 3 d window of observation was
selected to minimize the chance that flower quality would
deteriorate, decreasing salience of the food item for the animals.
DESIGN
AND APPARATUS: Two T. neocrysantha trees were selected for
experimental manipulation. Close observation of the animals' foraging
behavior in the days prior to the manipulation permitted confident
knowledge of the group's location relative to the test site and
relatively confident prediction that the group would utilize the
trees selected as well as the approximate time of day of feeding. The
objective of this field experiment was to record group movement(s),
including routes taken, and feeding behavior(s) before and after
manipulation, in particular, "decisions" regarding food
type (flowers, fruit, new leaves, and/or mature leaves), distance
traveled from feeding site of origin, route taken to next feeding
station, etc. The manipulation entailed spraying the target trees
with a liquid substance gustatorially, and, possibly, olfactorily,
aversive to the animals. Based upon the suggestion of a rancher,
quinine (Qualaquin, see link) was selected as the substance employed
because of its low cost, because of the low likelihood that it would
harm the animals, and because it was water-soluble. Furthermore, in
Costa Rica, quinine is available "across the counter". The
particular ratio of quinine to water should be as high as possible to
ensure its effectiveness as a deterrent/avoidant substance to the
animals from the food source; however, the particular ratio of
aversive substance to water will be a function of body size, type of
aversive product, and, possibly, other factors. The vehicle for
delivery of the liquid substance was an inexpensive, plastic spray
container generally employed for delivery of insecticide.
OUTCOME:
The success of the project descrtbed was limited as a completed study
primarily because of the small number of field assistants used with
whom to divide tasks, an obvious contingency unfortunately not
considered in sufficient detail before beginning what must be termed
a pre-test.
BENEFITS
AND COSTS: Each researcher must determine for her/himself the
relative benefits and costs of the design described here. However,
inherent to any experiment, whether field or laboratory, is the
requirement to stress organisms in order to obtain veridical
results/data. This principle applies, also, to human research.
ADDITIONAL
QUESTIONS THAT MIGHT BE ADDRESSED WITH DESCRIBED METHOD:
1.
travel efficiency/costs pre- and post-manipulation
2.
movements in relation to cognitive complexity requiring evaluation of
foraging tactics/strategies
3.
assesment of possible decision hierarchy regarding food selectivity
and is pre- and post-manipulation foraging "rule-governed
4.
assessment of consequences of manipulation as ecological constraint
(e.g., does manipulation induce fissioning or other changes in social
organization)
5.
does manipulation increase/decrease competition/aggression
6.
which, if any subject, emerges as leader to alternative food
station(s) (e.g., topics related to coordination and control at
individual, sub-group, and group levels)
7.
do temporal and/or spatial (e.g., detours, alternate routes)
patterning of movements change from pre- to post-manipulation
8.
do animals continue to utilize or reject food item(s); if reject, for
how long; if reject, what stimuli salient (color, food type, etc.);
do they generalize these cues to other food items
The
attached link displays a published report of a foraging experiment
using two baboon groups as subjects: