Spix's Owl Monkey (Aotus vociferans)
Spix's owl monkey has a grooming claw on the fourth digit of both feet. Members of the genus Aotus are the only nocturnal New World primate. The legs of this species are longer than the arms, which assists in leaping. Spix's owl monkey has large eyes, but lacks the tapetum typical of the nocturnal prosimians. The average body mass for this species is 1 kilogram, and no difference exists in body mass between males and females (Ford and Davis, 1992).
Spix's owl monkey is found in Southern Colombia, Eastern Ecuador, Northeastern Peru, and Northwestern Brazil (Nowak, 1999). This species lives in forests where the trees are evenly dispersed. This species favors lowland forests over highland forests, possibly because the greater abundance of softwood trees in lowland forests used for sleeping sites (Aquino and Encarnacion, 1988).
Spix's owl monkey is a frugivorous species that also eats leaves and insects. Spix's owl monkey prefers to eat small ripe fruit (Kinzey, 1997). An advantage of foraging at night is decreased competition from diurnal frugivores and the presence of larger nocturnal insects (Wright, 1989).This species spends all of its life up in the trees (Kinzey, 1997). Spix's owl monkey becomes more active when the moon is bright (Wright, 1984), and they travel the same route during the night, so they may memorize routes when they travel when the moon is brighter (Wright, 1989). This species sleeps during the day in tree holes, with the family group sleeping together (Aquino and Encarnacion, 1986). The tree holes are found on the trunk or branches of dry senescent and mature trees (Puertas et al., 1995). This species uses the following tree species as sleeping sites: Eschweilera sp., Calycophyllum spruceanum, Buchenavia, and Macrolobium acaciifolium (Puertas et al., 1995). This species cohabitates with other species during the day, that Spix's owl monkey shares the sleeping site with other species (Puertas et al., 1995). Some of the species that the sleeping site is shared with are the kinkajou, Potos flavus, the yellow-crowned brush-tailed rat, Isothrix bistriatus, and chiropteran spp. (Puertas et al., 1995). These shared sleeping sites are often in trees with wide and deep cavities, and have more than one access hole and are surrounded by hemiepiphytes and hemiparasites (Puertas et al., 1995). The average group size for this species is 3.3 individuals, with a range from 2 to 5 (Aquino et al., 1990).
Spix's owl monkey moves through the forest quadrupedally in the trees, but also can leap from tree to tree (Fleagle, 1988).
The basic group of Spix's owl monkeys is composed of a breeding pair and their offspring, which usually numbers two (Aquino et al., 1990). This species has a monogamous mating system (Kinzey, 1997). The monogamous mating system is correlated with having males present to help raise offspring and having food resources in predictable, uniform patches (Wright, 1986). As opposed to Aotus nancymae, only adult male offspring are tolerated within the family group (Aquino et al., 1990). Both males and females disperse in this species (Kinzey, 1997). The young stay with their birth group until between 2.5 and 3.5 years old, then they disperse (Kinzey, 1997). Social grooming is not common for members of this genus (Fleagle, 1988). In this species the father becomes the main carrier of the infant and only gives the infant to the mother to suckle (Jantschke et al., 1998).
hoot call: This is a long, low call, of between 200-400 hertz, emitted by an individual, and can be heard for 500 meters (Wright, 1985). Each hoot is made up of 2 long sounds and 2 to 5
short sounds, with brief intervals, making them sound all like one note (Moynihan, 1964). Hoot bouts occur
singly or in a series from 2 to 4 (Moynihan, 1964). During each bout the mouth is slightly opened, then
closed between bouts (Moynihan, 1964). This call is used to communicate sexual advertisement, and is used
by females or subadult males when looking for mates (Kinzey, 1997). This call is also emitted by a
separated juvenile, or by an adult if its mate has been separated (Kinzey, 1997).
resonant whoop: This call consists of a series of 10-17 low grunts which build up in intensity to a
climax, and is used to communicate defense of a fruit tree used for feeding (Kinzey, 1997). This call starts
low and soft, softer than gruff-grunt (Moynihan, 1964). Then the succeeding notes became louder,
rapidly, and during the middle of the call the notes are much louder than gruff-grunt and take on a
resonating quality that lasts for a few notes (Moynihan, 1964). The last part of the call the notes
decrescendo, becoming softer, lower, and slower (Moynihan, 1964). The notes of this call are monosyllabic
in nature (Moynihan, 1964). An individual performing this call will go into back-arch, and then stop
when the call is completed (Moynihan, 1964). The elbows also move during this call, going in (towards the
body) when the note is uttered and going out (away from the body) between the notes (Moynihan, 1964).
This pumping action of the elbows may help to increase air flowage moving in and out, which would assist
in sound production (Moynihan, 1964). This call may also be emitted during hostile situations, functioning
as a threat display (Moynihan, 1964).
gruff-grunt: This call is low-pitched, moderately long, and moderately loud in nature (Moynihan,
1964). The call is uttered singly or in a short series of 2 to 5 notes (Moynihan, 1964). When occurring in
series, several series may be emitted which are separated by long pauses (Moynihan, 1964). The mouth is
closed or almost completely closed when this call is emitted (Moynihan, 1964). This call is emitted during
hostile encounters, during intraspecific disputes, and as a reaction to a predator or a potential predator
(Moynihan, 1964). When emitted during intraspecific disputes, the call occurs before or after an attack
(Moynihan, 1964). This is essentially a threat call (Moynihan, 1964).
scream: This call is high in pitch but wavering, and can be quite prolonged (Moynihan, 1964).
When the call is uttered the mouth is usually wide open (Moynihan, 1964). This call functions to startle a
predator or potential predator, giving the individual time to escape (Moynihan, 1964). When this call is
emitted by infants or young juveniles this call is softer and more plaintive in tone (Moynihan,
low trill: This is described as "a 'bubbling' series of short low-pitched notes. uttered very rapidly
one right after the other but still distinguishable by the human ear" (Moynihan, 1964). The individual notes
of the call are described as being slightly plaintive in tone (Moynihan, 1964). The number of notes varies
from 2 to 12 in a series and successive notes tend to rise in pitch (Moynihan, 1964). This call is done with
the mouth closed or almost closed (Moynihan, 1964). This call is emitted during initial greeting ceremonies
between individuals, and when this occurs between members of the opposite sex, the female will emit this
call more frequently than the male (Moynihan, 1964).During the greeting, this call will often occur before
or during social sniffing (Moynihan, 1964). The call may serve to function as a threat between
novel individuals (Moynihan, 1964). This call may also function as an appeasement display (Moynihan,
1964). This call is heard in association with moan and sneeze-grunt (Moynihan,
moan: This call is brief, soft, and described as plaintive sounding (Moynihan, 1964). The mouth is
closed when this call is emitted (Moynihan, 1964). This call serves the same function as low trills
do, and also when two mates are separated and brought back together (Moynihan, 1964). This call is also
heard during the first parts of a precopulatory sequence (Moynihan, 1964). This call is heard in association
with low trill, gulp, and sneeze-grunt (Moynihan, 1964). This call may occur when
hostile and nonhostile stimuli occur simutaneously (Moynihan, 1964). This call also function as an
appeasement call (Moynihan, 1964).
gulp: This call is moderately loud and "liquid" in nature, sounding like a human belch (Moynihan,
1964). The mouth remains closed during this call, but the throat swells up (Moynihan, 1964). The call is
uttered in a series of 2 to 5 notes, with 2 or 3 being the most common (Moynihan, 1964). This call was
heard in captivity during vigorous locomotory activity, and may function as being a contact call (Moynihan,
1964). Contact calls would be important for this species because of the need to maintain contact during the
night when moving and/or foraging (Moynihan, 1964).
sneeze-grunt: This call is described as being sounding like a sneeze superimposed upon a gruff-
grunt (Moynihan, 1964). The call is sharp and abrupt, and has a slightly nasal tone (Moynihan, 1964).
Usually this call is emitted singly, but sometimes two are emitted in a quick succession (Moynihan, 1964).
The mouth is closed or nearly closed when this call is uttered (Moynihan, 1964). This call occurs in
association with gulp, moan, and low trill (Moynihan, 1964). This call may function
as a contact call like gulp (Moynihan, 1964).
squeak: This call is made up of two to three sounds with short intervals in between them and are
brief and relatively high in pitch compared to a grunt (Moynihan, 1964). The pitch of this call
usually first rises then falls (Moynihan, 1964). This call is emitted by infants and young juveniles
(Moynihan, 1964). This call is uttered when an individual is distressed, for example when it separated from
its parent (Moynihan, 1964).
high trill: This call sounds like three to four squeaks emitted in rapid succession (Moynihan,
1964). This call rises and falls in pitch with the first two notes rising and the last two notes falling in pitch
(Moynihan, 1964). This call may be interpreted as components of squeaks or a discontinuous series
of squeaks (Moynihan, 1964). This call is emitted by infants and young juveniles (Moynihan,
1964). This call is produced in response to distress with an alarm or escape component (Moynihan,
Moynihan (1964) made an interesting comment regarding infant vocal patterns:
"It is interesting that the vocal patterns uttered by infants
who want to attract or join their
parents are similar to those
of adults who want to attract or copulate with their mates.
might suggest that the sexual tendencies
of adults develop from the infantile tendency to keep in
contact with parents."
urine-wash: This is when an individual will deposit urine on its hands and then rub the
hands on a branch or other substrate. This is used to communicate sexual attraction.
social sniffing: This is when one individual will approach another, stick its neck out, and smells the
other individual (Moynihan, 1964). The duration of each sniffing bout lasts for a few seconds, and the
individual being sniffed will remain motionless while this occurs (Moynihan, 1964). The individuals start
out nose-to-nose before a sniffing bout will occur, then individual who will sniff will bring its head as close
to other as possible (Moynihan, 1964). The most common places which are sniffed are the armpit and/or the
perineal region (Moynihan, 1964). The individual being sniffed will sometimes respond by sniffing, and
two individuals may occasionally sniff each other's perineal region simultaneously (Moynihan, 1964). This
behavior is done when two individuals meet each other for the first time, thus this functions as part of a
greeting ceremony (Moynihan, 1964). Individuals who have just met each other may repeat social
sniffing for the first few hours after first introduction (Moynihan, 1964). This behavior is also seen
before copulation amongst mates (Moynihan, 1964).
back-arch: This is when an individual will raise the dorsal part of the body while in a
quadrupedal stance, with all four limbs held straight (Moynihan, 1964). Sometimes an individual will have
the hands free, in a standing position with the knees slightly bent and the palms facing outward, when
performing this behavior (Moynihan, 1964). This display is used to communicate aggression.
swaying: This is when an individual will move its body back and forth, from side to side in a
smooth, regular, moderately rapid, wide arch (Moynihan, 1964). The head of the individual is either facing
straight forward while moving or turns the head to the right when moving to the right and turning the head
to the left when moving to the left (Moynihan, 1964). This behavior may have gruff-grunts or
gulps occurring at the beginning or the ending of a bout (Moynihan, 1964). An individual will do
this with the hands clasping or free from a branch (Moynihan, 1964). This is done in response to the
presence of a predator or a potential predator (Moynihan, 1964). This behavioral pattern is often followed
by overt escape (Moynihan, 1964). An individual might do this to let the potential predator know that they
have been detected, thus discouraging the predator (Moynihan, 1964). An individual can save energy that
would be used for escaping by doing this because the predator would not waste time chasing after the
individual because it knows it has been detected (Moynihan, 1964).
rubbing: This is when an individual will flex their legs, press their perineal region against a
substrate, and start rubbing the region against the substrate with rapid side-to-side motions (Moynihan,
1964). Individuals tend have favorite sites where to perform this behavior (Moynihan, 1964). This behavior
is done between males and females and in the context of hostile or copulatory patterns (Moynihan, 1964).
This behavior is done more by females than by males (Moynihan, 1964). Males tend to be slightly dominate
over females, and in an instance where a female was dominant over a male, the male performed
rubbing during an encounter with her (Moynihan, 1964). This suggests that perhaps this behavior is
a submissive display.
rejection bite: This is done by the mother to the infant after suckling or when the infant tries to
establish contact after the first week; also done by the male more after the first 8 weeks (Dixson and
Fleming, 1981). The mother will bite the tail, hands or feet of the infant, signaling it to move away (Dixson
and Fleming, 1981). The infant will often squeal after being bitten (Dixson and Fleming, 1981). The mother
does this in higher frequency than the male up to the first 8 weeks of an infants life (Dixson and Fleming,
social grooming: This behavior is only associated with copulation in this species (Moynihan, 1964).
This is where one individual will use the hands and the teeth to remove dead hairs, dead skin, and small
arthropods from hair of another (Moynihan, 1964). The hands are used to separate the hair so that the teeth
may be used to get at the base of the hair (Moynihan, 1964). The most common places groomed are the
sides, back, crown, and back of the head (Moynihan, 1964). Social sniffing usually occurs before a
grooming bout will occur (Moynihan, 1964). This behavior occurs before and after both successful and
unsuccessful copulation attempts (Moynihan, 1964).
Spix's owl monkey most often gives birth to a single offspring, although twins have been recorded. The interbirth interval for this species is one year. The birth season for this species is from November to January (Aquino et al., 1990). Copulation attempts tend to be brief and rapid, with the male and female first quietly
approaching each other (Moynihan, 1964). Then the male performs social sniffing, and the female
may social sniff while the male is doing the same to her (Moynihan, 1964). Mating is done dorso-
ventrally, with the male inserting his penis under the female's tail, with female moving the tail slightly
(Moynihan, 1964). The male usually makes 3 to 4 pelvic thrusts, with ejaculation occurring on the last
thrust (Moynihan, 1964).
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