Secondary transfer of adult mantled howlers (Alouatta palliata) on Hacienda La Pacifica, Costa Rica: 1975-2009.

Natal emigration by male and female mantled howlers (Alouatta palliata), and subsequent immigration into breeding groups, is well documented for the free-ranging population on Hacienda La Pacifica, Costa Rica, but secondary transfer was considered rare (Glander in Int J Primatol 3:415-436, 1992). Population surveys in 1998 and 2006 caused us to question our assumptions and to re-evaluate our long-term data set from a post hoc perspective. We first identified all animals observed or captured as adults in more than one non-natal group anywhere in the population.

Natal emigration by both sexes in the La Pacifica population of mantled howlers: when do some stay?

We have reported previously that all male and female mantled howlers emigrate from natal groups at Hacienda La Pacifica, Costa Rica. In the years since that report, a small number of juveniles have stayed in the natal group without experiencing a solitary phase. Here, we present a post hoc analysis on juvenile emigration in six groups of howlers under observation for varying amounts of time between 1972 and 2005.

Behavior and endocrine concentrations do not distinguish sex in monomorphic juvenile howlers (Alouatta palliata).

Behavioral observations on juvenile mantled howlers are limited by visually undifferentiated genitalia; however, animals can be sexed when they are very young or if they are captured. Behavioral data and fecal samples from juveniles during month-long field studies from 1993 to 1995 were analyzed to determine whether there are developmental differences in behavior or hormone concentrations that can be used to differentiate males from females. The subjects were juveniles of known sex and age from five different social groups on Hacienda La Pacifica, Costa Rica.

Mantled howler population of Hacienda La Pacifica, Costa Rica, between 1991 and 1998: effects of deforestation.

A survey of the mantled howler (Alouatta palliata) population on Hacienda La Pacifica, Guanacaste, Costa Rica, was done in July and August of 1998 to determine population parameters following deforestation due to major canal construction between 1990 and 1994. The survey was carried out in a manner identical to our 1991 survey and consisted of a single pass and two re-surveys of all forested areas of the farm. As canal construction effectively increased fragmentation of the habitat, we predicted decreased population and group size over this time.

Behavioral, immunological, and hormonal responses associated with social change in rhesus monkeys (Macaca mulatta).

Twelve animals to be socially reorganized in a group of 49 animals were compared with ten animals in a socially stable group (n = 51) for reproductive hormones, cortisol concentrations, immune function, and behavioral patterns for a 6 week baseline and 16 week postreorganization period. Cortisol values, mitogen-induced lymphocyte blastogenesis, and rates of behavior reflected social events. Increased cortisols, increased noncontact aggression, and decreased mitogen response were associated with animal introductions.

Population trends of the mantled howler groups of La Pacifica, Guanacaste, Costa Rica.

A complete survey of La Pacifica in Guanacaste Province, Costa Rica was conducted in July 1984 in order to determine whether the howler (Alouatta palliata) population had declined since 1972 as a result of deforestation. During the 6-day survey, 257 howlers were located, representing 16 different social groupings and nine solitary animals. The total number of howlers, the number and location of groups, and the age-sex composition were very similar to a 1972-1976 survey of the same population.

Brief report: Infant-killing and infant disappearance following male takeovers in a group of free-ranging howling monkeys (Alouatta palliata) in Costa Rica.

Events surrounding an infant-killing following a male takeover are described for a group of free-ranging howling monkeys in Costa Rica, and additional evidence is presented for infant disappearances following three previous male takeovers. Infant-killing is best interpreted in this context as a male reproductive strategy, as infant-killing did effectively shorten the interbirth interval, and only infants of high-ranking females died or disappeared following a male takeover. Due to the exclusive access of the dominant male to high-ranking estrous females, an incoming male who had lived as a peripheral male before taking over the group would run little risk of eliminating his own offspring in the course of killing the offspring of high-ranking females.

Adoption of infant howling monkeys (Alouatta palliata).

During 3 years of continuous field observations on mantled howlers (Alouatta palliata Gray) in Costa Rica we observed five infants without mothers in the main study group. Four of these infants solicited care and two were adopted (one permanently, one temporarily) by lactating females. The other two were carried but not adopted.