Robert H. Horwich

Geographical distribution of the black howler (Alouatta pigra) in Central America

The geographic range of the black howler,Alouatta pigra in Mexico, Guatemala, and Belize was investigated by travelling through and visiting 65 locations within or close to the expected range. The existence of the species was noted through first hand observations or was documented by talking with residents and knowledgeable people in the area. Observations were made on captive animals as well. All sites and probable sites ofA. pigra were noted to be under 1,300 ft in altitude and in areas with a mean annual temperature above 25°C and a mean annual rainfall over 1,000 mm per year. This area coincides with tropical rain forest areas, including both tropical evergreen and semievergreen rain forests.A. pigra was most plentiful in riverine areas which showed flooding for some part of the year. Two areas of possible sympatry withA. palliata were noted. In all cases, the troop sizes ofA. pigra were extremely small, under ten individuals, and infants could easily be sexed, in contrast toA. palliata which is known to occur in troops of 15–18 and is difficult to sex at an early age. Finally, a very gross method for population estimation from searching time emerged from the study.

Maternal care and infant transfer in two species ofColobus monkeys

Three infantColobus guereza and twoColobus polykomos were observed during their first 3 months, when infant transfer between females was prevalent. Such mother-infant relations as nipple contact, time on the mother, infant returns to the mother, infant resting on the mother, and the mothers retrieval of the infant were recorded. Maternal behaviors and interactions between non-mothers and the infant were also noted. Additionally a description of infant pelage change during this period was described. Inter-relationships of these behaviors were discussed. During early development, non-mothers performed more maternal behaviors and transferred and carried the infant more than its mother. With infant recognition of its mother and increased locomotor abilities after 3–5 weeks, less transfers occurred and the infant spent more time on its mothers nipple. A period of high nipple contact, reminiscent of an infant regressive period, occurred. Male-infant interactions were highest at 4–9 weeks. Finally, the existence of infant transfers in Colobinae and its relationship to “aunt” behavior in Cercopithecinae was discussed. Female motivations during transfers and the possible functions of the behavior were also discussed.

Breeding behaviors in the black howler monkey (Alouatta pigra) of belize

Adulterous breeding between a female howling monkey (Alouatta pigra) of one troop with a male of an adjacent troop occurred despite territorial defense between the two troops. The specific behaviors are described as well as a synopsis of daily events which occurred between the female and two males from adjacent troops. A discussion of how this interaction and the behavior patterns relate to what is known about breeding in howler monkeys and related species follows.

Roaring rhythms in black howler monkeys (Alouatta pigra) of Belize

Roaring was recorded during 15-min intervals for 55 days from April 29 to July 14, 1981 in the area around Bermuda Landing, Belize. Roaring profiles were compiled to represent four three-week periods in which roaring was graphed against the time of day. Rates of roaring were also calculated for three troops. Results indicate a gradual change in the daily profile of roaring from dry to rainy season. The marked bimodality of roaring at dawn and dusk in the dry season changed to a more dampened bimodality with reduced dawn and dusk peaks and more roaring during the midday in the rainy season. This seems related to the decreased hours of sun and the amount of rain during the wet season. Additionally, literature on monkeys with long range vocalizations suggests that bimodal peaks in calling may be more prevalent in species which display territorial defense.

Regressive periods in primate behavioral development with reference to other mammals

Studies on behavioral development in 12 species of monkeys indicate normal fluctuations of high frequency of nipple contact. These periods decrease in intensity as the infant develops and occur at similar times in development in the 12 species. Literature on 11 species of primates and three species of non-primates indicates similar regressions in mother-infant contact, which implies a common genetic basis for the phenomenon.

Development of Behaviors in a Male Spectacled Langur (Presbytis obscurus)

An infant langur,Presbytis obscurus, was observed in a group setting, from birth until 1 year of age. Frequency or duration of 30 behaviors was recorded during 2 hour periods and plotted chronologically. Based on fluctuations and interrelations of these behaviors, age classes were designated. The Maternal Care Period (0–20 days) is characterized by close mother-infant contact, including a great deal of nipple contact and a high frequency of maternal behaviors. The Individuation Period (21–70 days) is typified by maternal restraint and retrieval, and independence and self-oriented behaviors like scratching, mouthing, and locomotory skills. The Socialization Period (71–240 days) is manifested by behavioral fluctuations, involving nipple contact, play, and care by other troop members and coincides with the molt from infant to juvenile pelage. Finally, during the Juvenile Period, the motherinfant distance increases and the mother interacts more with other troop members. Behavioral fluctuations observed in this infant langur are discussed with reference to other primates studied.

Eye Marks in Vertebrates as Aids to Vision

Lines leading forward from the eye may function as aiming sights in many small vertebrates. The chief evidence is the correlation of distribution and positions of eye-lines in various vertebrate groups with predatory feeding habits. Dark patches around the eye may serve to reduce glare in species in bright environments. Facial patterns often have multiple functions.

Species status of the black howler monkey,Alouatta pigra, of Belize

Small troop sizes which averaged 5.23 members per troop and the early descent of male testes inAlouatta pigra show a marked difference fromA. palliata. These differences strengthenSmiths (1970) observations of morphological differences betweenA. pigra andA. palliata.

Socio-maternal behaviors in response to an infant birth inColobus guereza

A number of social behaviors were observed in a captive troop ofColobus guereza on a regular basis for eight months. These included clasping and related behaviors, forward mounts, rear mounts, presents, troop positions during rest periods, infant transfers and attempted transfers, play, and grooming. During the observation period two significant events occurred: a re-introduction of a mother and her juvenile female, and the birth of an infant to a resident female. These events caused an increase in certain adult behaviors indicating a relationship of them with similar behaviors done between mothers and infants. This similarity seemed to indicate the co-evolution of “maternal” behaviors for use in adult social interactions and the phenomenon of infant transfer or sharing. The maternal and socio-maternal behaviors and their infantile precursors are then discussed in relation to the ontogeny of behavioral forms, the ontogeny of motivation in such behaviors, and the idea of infantile regression during development and in adult life.

The whooping display in nilgiri langurs: An example of daily fluctuations superimposed on a general trend

Field data on the whooping display in the Nilgiri langur were recorded in two ways: (1) the number of whoops heard while in the forest during a complete day; (2) the number of whoops heard by each of three troops while under constant observation from dawn to dusk for a total of 18 days. The temporal, visual, and auditory qualities of the display are described. Different methods of graphically representing the daily pattern of the whooping display are then exhibited. One method shows a main bimodal trend in whooping with a main peak in early morning and a smaller peak in the afternoon which is in accordance with other primate species. Secondarily, other ways of representing the data show that the morning peak is actually a series of peaks which decrease in magnitude after the initial peak. Additionally, the total amount of whooping is reduced during clear days and the initial morning peak is affected by the seasonal change in sunrise. The methods of representing data show that the gross trend of whooping is in reality a series of fluctuations which probably have relevance to the general activity as measured by the percent of individuals in the troop observed feeding. As in whooping the feeding activity when observed continuously in one troop for one day is a series of four to seven peaks rather than a bimodal distribution as represented by data of many days lumped together. A similar phenomenon of cycling in ontogenetic data is discussed.