Abstract The interaction of internal clocks and environmental conditions determines the daily behavioural rhythm of an animal. Due to the strong influence of light, these circadian rhythms oscillate in mammals over a cycle length of about 24 h, equivalent to the daily light-dark cycle. The relation between activity and rest within this cycle is species-specific and age dependent. Since strong deviations from existing rhythms can harm health seriously, the observation of animal behaviour using activity budgets is a common tool to assess welfare. This study therefore investigated the nightly activity budget of 63 giraffe (Giraffa camelopardalis) from 13 EAZA institutions. The nightly behaviour was recorded and analysed in the winter seasons 2015–2018 over an observation period from 17:00 to 7:00 h for 10–14 nights, using infrared sensitive cameras. To analyse rest-activity rhythms of three age classes of giraffe during the dark phase of the night, linear mixed models were applied. Our results show that activity increases with increasing age of giraffe. Differences between age classes were further found for the time spent on rapid eye movement (REM) sleep, with juvenile and sub-adult giraffe spending more time in this specific state than adults. Analyses of behavioural rhythmicity indicated a rest-activity cycle length of about four hours, with age determining the rhythmic curve. Overall, this large-scale study confirms a strong age effect for both the nocturnal activity budget and the rest-activity rhythm in giraffe. The results of this study provide an important contribution to the continuous improvement of husbandry and management for zoo housed giraffe.

中文翻译：

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在黑暗中发光：长颈鹿的年龄和光线塑造夜间活动和睡眠行为

摘要 内部生物钟和环境条件的相互作用决定了动物的日常行为节律。由于光的强烈影响，哺乳动物的这些昼夜节律在大约 24 小时的周期长度内振荡，相当于每天的明暗周期。这个周期内的活动和休息之间的关系是物种特异性和年龄依赖性的。由于与现有节奏的强烈偏差会严重损害健康，因此使用活动预算观察动物行为是评估福利的常用工具。因此，本研究调查了来自 13 个 EAZA 机构的 63 只长颈鹿 (Giraffa camelopardalis) 的夜间活动预算。在 2015-2018 年冬季，使用红外敏感相机在 17:00 至 7:00 小时的观察期内记录和分析了 10-14 晚的夜间行为。为了分析三个年龄段的长颈鹿在夜晚的黑暗阶段的休息活动节律，应用了线性混合模型。我们的结果表明，活动随着长颈鹿年龄的增加而增加。在快速眼动 (REM) 睡眠上花费的时间进一步发现了年龄组之间的差异，幼年和亚成年长颈鹿在这种特定状态下花费的时间比成人多。行为节律性分析表明，休息-活动周期长度约为 4 小时，年龄决定节律曲线。总体而言，这项大规模研究证实了长颈鹿夜间活动预算和休息活动节奏的强烈年龄效应。本研究的结果为动物园饲养长颈鹿的饲养和管理的不断改进提供了重要的贡献。