Abstract

Animals balance foraging with other activities, and activity patterns may differ between sexes due to differing physical requirements and reproductive investments. Sex-specific behavioural differences are common in sexually dimorphic mammals, but have received limited research attention in monomorphic mammals where the sexes are similar in body size. Eurasian beavers (Castor fiber) are obligate monogamous and monomorphic mammals and a good model species to study sex-specific differences. As females increase energy expenditure during reproduction, we hypothesized differing seasonal activity budgets, circadian activity rhythms and foraging patterns between male and reproducing female beavers. To test this hypothesis, we equipped adult beavers with VHF transmitters (N=41; 16 female, 25 male) and observed them throughout their active period at night from spring to late summer. Occurrence of their main activities (foraging, travelling and being in lodge) and use of food items (trees/shrubs, aquatic vegetation and herbs/grasses) were modelled to investigate sex-specific seasonal activity budgets and circadian activity rhythms. The sexes did not differ in time spent foraging across the season or night, but during spring, females resided more in the lodge and travelled less. Males and females both foraged on aquatic vegetation during spring, but females used this food source also during late summer, whereas males mostly foraged on trees/shrubs throughout the year. We conclude that seasonal activity budgets and foraging differ subtly between the sexes, which may relate to different energy budgets associated with reproduction and nutritional requirements. Such subtle seasonal behavioural adaptions may be vital for survival and reproduction of monomorphic species.

Significance statement

Activity budgets and foraging patterns of animals are key to their survival and may differ between males and females with different body sizes and physical requirements. In monomorphic species, where males and females have similar body sizes, fewer differences are expected, but may still be pronounced during certain times of the year. We modelled sex-specific seasonal activity budgets and circadian activity rhythms and use of food items in a monomorphic mammal, the Eurasian beaver. By treating season and time of day as a continuous variable rather than modelling differences within distinct predefined periods, we identified subtle sex-specific seasonal trends in activity budgets and use of food items.

中文翻译：

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大小并不代表一切：单态哺乳动物的性别和觅食方式不同

摘要

动物在觅食与其他活动之间保持平衡，并且由于身体需求和生殖投入的不同，性别之间的活动方式也可能有所不同。性别特定的行为差异在性二态性哺乳动物中很常见，但在性别相似的单态性哺乳动物中受到的研究关注有限。欧亚海狸（蓖麻纤维）是专性一夫一妻制和单态哺乳动物，是研究性别特异性差异的良好模式物种。随着雌性繁殖过程中能量消耗的增加，我们假设雄性和繁殖雌性海狸之间有不同的季节性活动预算，昼夜活动节奏和觅食方式。为了验证这一假设，我们为成年海狸配备了VHF发射器（N= 41; 16位女性，25位男性），并在春季至夏末的整个夜间活动期间观察它们。他们主要活动的发生（觅食，旅行和寄宿）和食物的使用（树木/灌木，水生植物和草药/草）被建模以调查特定性别的季节性活动预算和昼夜节律。整个季节或夜晚，男女在觅食上的时间没有差异，但是在春季，雌性在小屋中居住的次数更多，而出游的次数则更少。春季，雄性和雌性均在水生植物上觅食，但雌性在夏末也使用这种食物，而全年中，雄性大多在树木/灌木上觅食。我们得出的结论是，性别之间的季节性活动预算和觅食存在细微差别，这可能与与生殖和营养需求相关的不同能源预算有关。这种微妙的季节性行为适应对于单态物种的生存和繁殖可能至关重要。

重要性声明

动物的活动预算和觅食方式是它们生存的关键，并且在不同体型和体力需求的雄性和雌性之间可能有所不同。在雄性和雌性具有相似体型的单态物种中，预计差异较小，但在一年中的某些时候仍可能明显。我们对特定性别的季节性活动预算和昼夜节律进行了建模，并模拟了单态哺乳动物欧亚海狸中的食物使用。通过将季节和一天中的时间视为连续变量，而不是对不同的预定义时段内的差异进行建模，我们在活动预算和食品使用中确定了细微的性别特定季节趋势。