Behavior and safety in the use of canopy bridges by howler monkeys in an experimental environment

Abstract

Urban sprawl advances over forested areas and threatens arboreal species, which often use roads, power lines, and rooftops to move, resulting in roadkill, electrocution, and dog attacks. One measure to mitigate these risks is the installation of canopy bridges, which connect vegetation fragments and provide safe passages for animals. This study evaluated the use of three canopy bridge designs by brown howler monkeys (Alouatta guariba) and black-and-gold howler monkeys (Alouatta caraya) in captivity at the Sapucaia do Sul Zoo. The designs included a ladder rope bridge with PVC pipes, a fire hose bridge, and a braided rope bridge. We recorded primate behavior in relation to the canopy bridges using scan sampling, focal sampling, and ad libitum observations. After 30 days of observation, 270 hours of primate behavior were recorded, with 8.58 % of these behaviors related to bridge use, totaling 476 complete crossings. The analysis revealed that howler monkeys used the bridges primarily for locomotion and play. The type of activity was associated with bridge design for brown howler monkeys, as they used the ladder bridge more for feeding and the fire hose bridge for resting. In contrast, black-and-gold howler monkeys did not exhibit such an association but preferred the braided rope bridge and the fire hose bridge. Both species demonstrated good adaptation to the bridges, using a quadrupedal posture for locomotion, maintaining a good balance and making few missteps. Crossing time did not vary much between bridge designs for either species, but there was a trend of increasing speed over time. Our results indicate that all bridge designs were used by howler monkeys, demonstrating good adaptation and safety. The bridges proved to be valuable tools for both environmental enrichment and facilitating howler monkey locomotion in captivity.