Gorilla Moms 3 - Maternal Behaviors

The first captive birth of a western lowland gorilla occurred at the end of 1956 at the Columbus Zoo. After this infant and several other infant gorillas were not cared for by their mothers, zoos became understandably concerned about gorilla maternal competence. Many gorilla infants were routinely pulled for hand-rearing. Although more and more female gorillas are successfully raising their infants now, there are still unsuccessful mothers.

Two proposed reasons for this lack of maternal competence are that the mother was captive-born and/or the mother herself was not raised by her own mother. It has also been suggested that an important variable is that the mother be raised in a social setting where she can observe other females raising their infants and perhaps even practice mothering. In addition, it is a potential cause for concern if a gorilla female is primiparous and her maternal skills are thus unknown.

Subjects:

Here I compare the maternal behaviors, including proximity to their infants, of three captive gorilla females, each with different rearing and reproductive histories. Two of the females were housed at the Denver Zoo. JoRayK had been raised by her mother and had successfully raised 5 previous offspring. She was 28.5 years old at the birth of her daughter Jabali (see photo). Rapunzel was nursery-reared and later was housed with a group that included a mother and her infant. She had one previous offspring who was nursery-reared. Rapunzel was 21 years old when her second daughter Tinga was born. The third female, Asha, was housed at Cheyenne Mountain Zoo where she had been human-reared next to other gorillas. She was 14 years old when her first offspring, daughter Tumani, was born.

JoRayK was housed with one adult male (Jim) and two adult females (Bassa and Angel). Rapunzel’s social group consisted of one adult male (Kelly) and one other adult female (Evelyn). Asha was housed with one adult male (Rafiki) and three adult females (Roxie, Juju, and Kwisha).

Data Collection:

Data were collected in two phases: after the infant was born (Phase 1), then at 7-8 months when the infant had become more independent and was no longer always in physical contact with its mother (Phase 2). The focal animal instantaneous sampling method was used. Data were recorded in 15-minute intervals, with a data point noted every 30 seconds. Although all behaviors were recorded, behaviors other than maternal behaviors here are lumped into “Other.” Here are the active maternal behaviors that were recorded:

 All 3 Females:  Hold (support infant's weight) 

                            Hold+Other (other = non-maternal behavior, e.g. eating) 

                            Pat, rub 

                            Reposition      

                            Groom, inspect 

                            Gaze, watch 

                            Touch 

                            Play 

JoRayK & Asha:  Restrain

                             Take away object

Rapunzel only:  Push away

Asha only:  Rock

                     Reprimand (not captured in data)

Interactions that were not active on the part of the mother, e.g. the infant sitting in her lap or climbing on her, were not included. Also, nursing was not included for two reasons:  it is an active behavior of the infant; it was often not possible to see if nursing was taking place. 

Two types of mother-infant interactions were included in Other rather than Maternal. JoRayK plucked hair from Jabali. JoRayK and Asha both placed their infants dorsally on the ground, sat ventrally on the infant and thrusted. 

Proximity to infant was also recorded simultaneously with each data point, using the following measurements: Touch = in physical contact; Arm = within one female gorilla’s arm length, but not touching; Close = between one and two arm lengths; and Far = beyond two arm lengths. 

Visibility:  There were no substantial visibility problems with JoRayK and Rapunzel. However, during Phase 2 of data collection Asha spent some time in two areas of the exhibit where she was not visible - the far back of the yard, inside a den between the two indoor exhibits. These data points are included in “Other” unless she was not visible for more than half of the data collection period, in which case that data set was not used.