Animal personality is characterized by consistent among-individual differences in behavior across time and contexts and can influence a wide range of ecological and evolutionary processes. Although consistent behavioral differences have been linked to variation in behaviors that create or modify extended phenotypes, their role in shaping the deployment of chemical effectors that induce phenotypic changes in other organisms remains largely unexplored. Venom provides an ideal system for addressing this question because venomous animals can regulate how much venom they deploy, and the quantity delivered can strongly influence the resulting phenotype expressed by the recipient. In this study, we subjected 48 subadult and adult southern Pacific rattlesnakes (Crotalus oreganus helleri) to standardized venom extractions to examine the repeatability of venomous bite characteristics across three trials. All measured bite attributes exhibited significant repeatability, including number of strikes during tubing for restraint, bite occurrence during the extraction, number of venom pulses from the fangs, volume of venom expended, and venom volume per pulse. Larger snakes expended more venom and venom expenditure increased with the number of venom pulses delivered, but consistent among-individual differences persisted in all traits after accounting for these factors. These results indicate that, similar to other defensive traits, venom deployment comprises a repeatable component of the defensive behavior of rattlesnakes. Although repeatability of venom expenditure needs to be tested in additional contexts, our study demonstrates consistent individual differences in the deployment of a chemical effector used to generate an extended phenotype, thus highlighting the importance of consistent behavioral variation in determining how organisms deploy chemical weapons and other bioactive compounds that alter the behavior, physiology, or fitness of other organisms.
Kalyn A. Otzelberger, Teresa Romero, Julia E. Meyers-Manor
The lives of humans and dogs are greatly intertwined, making it crucial to understand how human emotions impact companion animals. While previous work found dogs respond greatly to humans and emotions through different metrics, including heart rate variability (HRV), person-oriented behaviors, a cognitive bias task (CBT), and owner-reported empathy surveys, little work has compared these measures of emotional responsiveness. We examined relationships between the aforementioned measures while dogs were presented with human emotions by their owner and a stranger. We hypothesized that these metrics would highly correlate if all measured empathy-related responses. We found the most person-oriented behaviors for expressions of negative emotions (i.e., crying), followed by positive ones (i.e., laughing), and similar physiological responses to previous research. Survey results suggested that dogs with higher empathy scores showed more person-oriented behaviors while their owner cried and had marginally greater attachment scores. However, dogs did not show any evidence of pessimism based on the emotional state they were exposed to in the CBT. Lastly, dogs who displayed more person-oriented behaviors showed greater physiological stress (i.e., low HRV) when the stranger cried or owner laughed. Our findings suggest that dogs respond to human emotions, which is reflected through physiological measures, and owners can predict their dog’s emotional responsiveness. Additionally, dogs with greater attachment are viewed as more empathetic by their owners, and orient to and interact with humans when they show distress. However, dogs may not feel that emotional state, or the CBT may not be an effective method of evaluating those short-term states.
Rhiannon L. Schultz, Isabella L. K. Clegg, Roberta Salmi
Regurgitation and reingestion (R&R) is a widely observed, yet poorly understood, abnormal ingestive behavior among zoo-housed apes, including gorillas. While frequently characterized as a stereotypical behavior, emerging hypotheses suggest R&R may serve metabolic or self-regulatory functions in response to altered feeding patterns in captivity. In this study, we investigated which patterns of activity and food intake are associated with increased likelihood of R&R events in 21 male western lowland gorillas across five zoological institutions in the United States. Behavioral observations were recorded using focal and instantaneous sampling to generate activity budgets of R&R behavior. R&R was found to be negatively correlated with the time spent feeding and to occur more frequently in the afternoons. Predictive modeling identified high-risk behavioral sequences that may be associated with increased likelihood of R&R. R&R was frequently preceded by travel, feeding, and inactivity, suggesting a potential link to satiety signaling or boredom. Nutrient data were also analyzed to determine whether certain food items were disproportionately associated with the behavior. Commercial primate chow, fruit juice, cabbage, nuts, and carrots were among the foods most likely to be regurgitated and reingested. These results support the hypothesis that both behavioral context and dietary composition contribute to the expression of R&R in captive gorillas. This research may help identify opportunities for refining feeding strategies and enrichment protocols to mitigate the occurrence of R&R in managed care populations.
Elisa Torretta, Laura Giussani, Giulia Rampazi, Olivia Dondina, Monica Di Francesco, Luca Canova, Achaz von Hardenberg
The recent spread of wolves into highly human-modified landscapes in Europe is an important example of large carnivore recovery and illustrates their ability to live in environments very different from those usually considered suitable for the species. This study aimed to evaluate how wolf feeding habits vary over time and across space by comparing diet composition, trophic niche breadth, and key prey consumption between the historical Apennine range and the recently colonized Po Plain in north-western Italy, based on scat samples collected between 2021 and 2025. Results show that wolf diet remained overwhelmingly based on wild prey, with negligible use of anthropogenic resources such as livestock or pets across both sectors. However, marked spatial and temporal differences in wild prey composition were detected, with wild ungulates dominating in the Apennines and medium-sized mammals, particularly coypu, prevailing in the Po Plain. Coypu emerged as a key ecological resource in the newly colonized area, while roe deer remained the main prey in the Apennines, with both species explaining most dietary divergence and showing converging temporal trends. Trophic niche breadth remained relatively narrow in both sectors, although increasing in the Plain over time, indicating progressive dietary adjustment as colonization proceeded. Overall, wolves expanded into a human-dominated landscape without increasing their use of human food sources. Instead, they changed the main prey they rely on, with coypu acting as an important early food resource and this trophic shift reflecting a dynamic process during population establishment.
