Abstract Reproductive phenology (timing) is a heritable trait that confers a range of fitness or survival advantages. Giraffe ( Giraffa spp.) breed year-round; however, some studies have suggested adaptive birth pulses, where demanding stages of reproduction coincide with seasonal increases in resource availability (phenological match). Here we use 3.5 years of demographic data to investigate the sociosexual behaviour and reproductive phenology of Angolan giraffe ( G. g. angolensis ) in the hyper arid northern Namib Desert, Namibia. We show that, in a highly seasonal desert ecosystem, giraffe gave birth to significantly more calves during the wet season. These calves were more likely to survive their first year of life, suggesting that season of birth may convey a fitness advantage. Furthermore, we show a decrease in sexual segregation between dominant (dark) adult males and adult females during the hot-dry season, suggesting a possible hot-dry season conception pulse. Finally, we demonstrate that the strongest correlation between the temporal pattern of births (wet-season pulse) and that of decreased sexual segregation (hot-dry season pulse) was time lagged by 15 months. This time lag corresponds to the period of gestation in giraffe, suggesting that a seasonal reduction in sexual segregation in this population may explain a seasonal birth pulse. These findings add to a sparse literature on the breeding phenology of giraffe, of asynchronously breeding megaherbivores, and of species with a gestation period of greater than 1 year. Results are discussed in terms of the possible environmental drivers of both season of conception and season of birth in this population. Furthermore, we highlight how predicted increases in seasonal instability due to climate change could reduce any putative fitness advantage associated with earlier birth dates. Significance statement To maximize survival, many species align giving birth with periods where food resources are increased. We studied this phenomenon in giraffe, a large mammal that breeds year-round at all latitudes but, in seasonal environments, possibly aligns the most energetically demanding stages of reproduction with resource-rich periods. We demonstrate that in a highly seasonal desert ecosystem, giraffe gave birth to significantly more calves during the wet season. These calves were more likely to survive their first year of life, suggesting that the wet season birth pulse is adaptive. Furthermore, we show that dominant male giraffe are more likely to seek females in the hot-dry season, suggesting a conception pulse that helps to explain the wet season birth pulse. These results advance our understanding of giraffe social and mating behaviours and contribute to a better understanding of breeding phenology in megaherbivores.

中文翻译：

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长颈鹿社会性行为和生殖物候的季节性变化

摘要 生殖物候（时间）是一种可遗传的性状，可赋予一系列健康或生存优势。长颈鹿 (Giraffa spp.) 全年繁殖；然而，一些研究提出了适应性出生脉冲，其中繁殖的苛刻阶段与资源可用性的季节性增加（物候匹配）相吻合。在这里，我们使用 3.5 年的人口统计数据来调查纳米比亚纳米布沙漠北部极度干旱的安哥拉长颈鹿（ G. g. angolensis ）的社会性行为和生殖物候。我们表明，在高度季节性的沙漠生态系统中，长颈鹿在雨季生下了更多的小牛。这些小牛更有可能在生命的第一年存活下来，这表明出生季节可能会带来健康优势。此外，我们显示在干热季节占优势的（深色）成年雄性和成年雌性之间的性别隔离减少，表明可能是干热季节受孕脉冲。最后，我们证明了出生时间模式（湿季脉搏）与性别隔离减少（干热季脉搏）的时间模式之间的最强相关性滞后了 15 个月。这个时间滞后对应于长颈鹿的妊娠期，这表明该种群性别隔离的季节性减少可能解释了季节性出生脉冲。这些发现增加了关于长颈鹿、异步繁殖的大型食草动物和妊娠期超过 1 年的物种的繁殖物候学的稀少文献。结果根据该人群受孕季节和出生季节的可能环境驱动因素进行了讨论。此外，我们强调了由于气候变化导致的季节性不稳定的预测增加如何减少与较早出生日期相关的任何假定的健康优势。意义声明 为了最大限度地提高生存率，许多物种将生育与食物资源增加的时期保持一致。我们在长颈鹿身上研究了这种现象，长颈鹿是一种全年都在所有纬度繁殖的大型哺乳动物，但在季节性环境中，可能会将最需要能量的繁殖阶段与资源丰富的时期保持一致。我们证明，在高度季节性的沙漠生态系统中，长颈鹿在雨季生下了更多的小牛。这些小牛更有可能在生命的第一年存活下来，这表明雨季的出生脉搏是适应性的。此外，我们表明占主导地位的雄性长颈鹿更有可能在干热季节寻找雌性长颈鹿，这表明受孕脉搏有助于解释雨季的出生脉搏。这些结果促进了我们对长颈鹿社交和交配行为的理解，并有助于更好地了解大型食草动物的繁殖物候。