Effects of nocturnal outdoor enclosure access on space use and sleep-related behaviour in captive giraffes

Abstract

Traditional management of large captive animals in zoos involves keeping them outside enclosures during the day and indoors before dark until the next morning. However, the indoor conditions may be uncomfortable for animals especially during summer because of small space, high temperature and humidity. The present study evaluated the nocturnal space utilization and sleep characteristics of giraffe housed in outdoor enclosures (partially covered with sand or grass) compared to those maintained in indoor enclosures a 5–7 mm2 small stone surface. Specifically, we examined two key aspects: 1) space usage between daytime and night-time for three giraffes, and 2) characteristics of sleep-related behaviour (recumbent posture) in indoor and outdoor enclosures during night-time for four giraffes. The study was conducted at Kyoto City Zoo, Japan over a period of 18 nights in 2020, as well as during daytime hours and an additional 13 nights in 2021. Daytime space usage was assessed through direct observation, whereas night-time observations were made using camera traps and night-vision remote cameras. A modified Spread of Participation Index (mSPI) was employed to analyse space usage. Results indicated that mSPI values did not significantly differ between daytime and night-time for all individuals. Regarding sleep-related behaviour, the older female predominately chose to lie on grass in the outdoor enclosure and remained in the lying position for longer periods compared with the indoor enclosure. We concluded that careful consideration should also be given to individual-level impacts, while housing giraffes outdoors during summer night-time did not negatively affect their behaviours.