Findings from the Comparative Psychology Lab

This review studies the historical roots of comparative psychology, linking the work of Charles Darwin to its application in understanding the social dynamics of western lowland gorillas (Gorilla gorilla gorilla) following a key loss within their group. Non-human primates (NHPs) have significantly advanced scientific understanding across disciplines from physiology to behavior. Their capacity for emotional expression and social interaction mirrors human behavior, reinforcing their relevance to comparative psychology and the study of human evolution. Charles Darwin’s pioneering work laid the foundation for comparative psychology by emphasizing the continuity between human and animal behavior (Darwin, 1879). His principles of studying animal emotions and behavior remain central to modern research, as they provide a framework for understanding shared evolutionary origins and their influence on cognition and emotion (Miller et al., 2013). Building on Darwin’s principles, a longitudinal study was conducted at the Gladys Porter Zoo in Brownsville, Texas, to investigate the impact of the silverback Moja’s death on an established group of western lowland gorillas (G. g. gorilla). Using behavioral observation methodology, social interactions, activity patterns, and stress-related behaviors of the members of the group (n = 9) were collected. Qualitative analysis of the behavioral data revealed significant disruptions to group cohesion, with increased solitary behaviors and decreased social affiliation following Moja’s death (James-Aldridge & Martinez, 2014). This research highlights the continued value of comparative psychology in understanding animal behavior and applying these insights to practical challenges. Without these observations, the extent of the disruption to the gorillas’ social structure might have been overlooked, potentially compromising their welfare. This study demonstrates how Darwin’s foundational work continues to inform modern approaches, underscoring the connection between human and animal behavior in comparative psychology.

-Ramiro Gomez, Claudia Martinez, Perry N. Fuchs, and Valerie James-Aldridge

This study investigates behavioral differences by sex and species among three gibbon species housed at the Gladys Porter Zoo in Brownsville, Texas. Over four months, 1570 minutes of behavioral data were collected using focal animal sampling. The subjects included three gibbon pairs (n = 6): Ila and Mateo (Hylobates pileatus), Chrissy and Mel (Hylobates lar), and Aphrodite and Bud (Hylobates muelleri). Descriptive statistics revealed significant sex-based differences within species and distinct species-specific behavioral profiles. Among pileated gibbons, Ila (female) engaged in more locomotion (50.5%) compared to Mateo (male), who exhibited predominantly stationary behavior. In lar gibbons, Chrissy (female) showed the highest levels of affiliative behaviors (64.5%), while Mel (male) spent most of his time stationary. Mueller’s gibbons demonstrated more balanced affiliative behaviors, with Aphrodite (female) and Bud (male) showing similar rates (20.6% and 20.8%, respectively), although Bud displayed slightly more stationary behavior. At the species level, pileated gibbons were the most active, spending 77.4% of their time in locomotion, while lar gibbons demonstrated the highest affiliative behaviors (114.2%). Mueller’s gibbons exhibited a more even distribution of locomotion (52.7%) and affiliative behaviors (41.4%). These behavioral patterns likely reflect species-specific ecological adaptations, environmental conditions, and exhibit design. The findings underscore the importance of tailoring captive care to address the unique needs of different species and sexes, highlighting the role of behavioral monitoring in promoting primate welfare. Future research should explore how factors such as seasonal variations, group dynamics, and targeted enrichment strategies influence these behaviors to optimize captive management practices further. This study provides valuable insights into the behavioral ecology of gibbons and actionable recommendations for enhancing the welfare of captive primates.

-Carolina Morales, Claudia Martinez, Michelle Medina Munoz, Ricardo Ruiz Martinez and Valerie James-Aldridge 

The ongoing construction of the new zip line at GPZ has prompted our team to initiate a focused observation on the pileated gibbons. By collecting data before, during, and after the construction, we aim to comprehensively understand how this significant environmental change may impact the gibbons' behavior and well-being. This study is crucial for several reasons. Firstly, it provides insights into the adaptability of the gibbons to anthropogenic disturbances, helping us better understand their resilience in altered environments. Secondly, the findings will contribute valuable information to the broader literature on the effects of construction activities on primate species, aiding in the development of effective conservation and management strategies. Ultimately, this research serves as a proactive measure to ensure the welfare of the gibbons and informs future decision-making processes related to habitat changes within zoo environments.

-Michelle Medina Munoz, Ricardo Ruiz Martinez and Valerie James-Aldridge 

We examined possible effects of the death of an adult female western lowland gorilla (Gorilla gorilla gorilla) named Martha on the behavior of the remaining six group members, i.e., Martha’s own infant, Kruger; the group’s silverback, Mbundi; and two other adult females, both related to Martha and each with an infant of her own, Penney with infant Sally, Margaret with infant Burchfield. Despite somewhat limited pre-death data due to covid-related issues, descriptive statistics revealed changes in affiliative, anxious, agonistic, and undesirable behaviors. Notably, Kruger, increased initiated affiliative contacts with silverback Mbundi (Pre M=0.46 min per 5-min focal test; Post M=2.16 min) who readily accepted his offspring’s presence. Surprisingly, neither Penney nor Margaret increased their affiliative contacts with Kruger post-death, continuing to focus on their own offspring. Subtle shifts in anxious and agonistic behaviors emerged. Margaret exhibited reduced anxious behaviors (Pre M=0.84 min; Post M=0.05 min) while Burchfield displayed increased agonistic behaviors (Pre M=0.01 min; Post M=0.91 min). Penney, Martha’s full sister, demonstrated an increase in undesirable behaviors (Pre M=0.09 min; Post M=0.24 min), possibly as a result of loss of social support. These findings enhance our understanding of death’s individual impacts on gorilla group dynamics.

-Valerie James-Aldridge, Claudia Martinez, Patricia Scanlan, and Jamie Langbein

Empathy, a pivotal factor in interpersonal connections, explains our capacity to comprehend the needs of others and respond suitably in various scenarios. However, the potential interference of stress with empathetic behavior remains a subject of investigation. To address this, we conducted an experimental study focusing on distress levels and behaviors in female rats subjected to stressful conditions. In our study, four female rats served as subjects, experiencing distress-inducing situations. The experiment involved observing the behaviors of cage mates while one rat endured a rat restrainer, comparing these responses to a pair without restraint. Notably, empathetic behaviors were significantly more frequent during the initial trial, followed by a sharp decline in a subsequent trial. To gauge distress levels, we employed the Rat Grimace Scale, which involves observing and scoring facial expressions and other behaviors that are indicative of pain or discomfort, as both a pre-test and post-test for all subjects. Our results revealed a considerable impact on distress levels in the experimental group, particularly as they endured multiple trials under stressful conditions. These findings underscore a natural expression of empathetic behaviors by the subjects, with a clear correlation between heightened stress and diminished empathetic engagement. Our study suggests that increased stress levels directly impede one's ability to express empathy, leading to reduced engagement with others. In conclusion, this research sheds light on the intricate relationship between stress and empathetic expression. Understanding these dynamics has implications for comprehending the nuanced interplay between psychological states and social interactions, emphasizing the importance of managing stress for fostering empathetic connections.

-Adelyn Garcia and Claudia Martinez 

This research focused on the behavior of Western lowland gorillas, particularly the interaction between adult gorillas and infant gorillas in relation to the visibility of the infants' white tail tufts. The study, conducted at Gladys Porter Zoo in Brownsville, Texas, observed five gorillas, including two adults (Margaret and Mbundi) and three infants (Burchfield, Kruger, and Sally). The researchers found a significant relationship between adult gorilla behavior (discipline and nurture) and the visibility of the infant gorillas' white tail tufts. The data analysis, using a Chi-Square Test, indicated that adult gorillas exhibited varying behaviors based on the visibility of the infants' white tail tufts. The findings suggest that this distinctive infantile characteristic may influence the interaction dynamics between adult and infant gorillas. The implications of this study could contribute to a better understanding of gorilla behavior and inform future research on the subject, particularly in the context of potential risks to infant gorillas with non-visible white tail tufts.

-Dulce Mendoza and Claudia Martinez

In May of 2015, an attempt to introduce a new silverback (adult male) to an established group of six western lowland gorillas (Gorilla gorilla gorilla) housed at Gladys Porter Zoo failed. The introduction process was halted and only protected contact among the gorillas was allowed. On May 1, 2018, another introduction was initiated to three adult females. Twelve months of behavioral data were compared across three time periods and two environments. We predicted that an increase in agonistic and affiliative behaviors would occur while anxious behaviors would decrease. We observed a significant increase in affiliative behavior and a significant decrease in anxious behavior outdoors. Significant decreases in locomotion, manipulation, and stationary behaviors were also observed. In contrast to other reports, levels of agonism were low in all conditions. This second introduction attempt is judged successful. The prolonged period of protected contact and reduced group size may have facilitated group formation.

-Claudia Martinez and Valerie James-Aldridge

A silverback’s role in both captive and wild gorilla groups is to protect and control. In the wild, when a silverback dies, the group members either disperse or transfer to another silverback. However, gorilla groups in captivity cannot do this. The death of a silverback is a rare event, thus only a few studies have looked at captive gorilla group behavior pre- and post-death of the silverback. This study examined the behavior of a family group (n = 9) of western lowland gorillas (Gorilla gorilla gorilla) housed at Gladys Porter Zoo in Brownsville, Texas propelled by the death of the silverback. Behavioral data were collected by means of focal animal sampling for 8 monthsand total observation time was 1744 minutes. Overall, the group’s social behavior decreased from 61.4 % pre-death to 38% post-death, while manipulation decreased from 14.5% to 8.3%, and foraging increased from 6.5% to 10.8% of the total observation time The disruption of the groups’ social behavior is consistent with reports from other institutions, while the increase in foraging behavior is not. These patterns of behavior could indicate higher post-death stress levels within the group.

-Claudia Martinez and Valerie James-Aldridge