Long-term insights into who benefits from brood reduction

The resource-tracking/facultative brood reduction hypothesis suggests that, under food stress, many altricial birds sacrifice the youngest brood members to enhance the growth and survival of their siblings. Studies examining staggered hatching and food shortage have generally supported this idea, although staggered hatching may serve additional purposes. However, the direct beneficiaries of this selective mortality remain unclear, as most research has overlooked parents and post-fledging outcomes. A life history perspective has rarely been applied to brood reduction. Using a 34-year individual-based dataset on blue-footed booby (Sula nebouxii) reproduction, we investigated whether siblicidal reduction of food-stressed two-chick broods benefits mothers, fathers, or surviving offspring. Results revealed that mothers of reduced broods were ~16% more likely to survive to the next breeding season than mothers of intact broods, indicating a significant maternal benefit. Moreover, cessation of..., Colony monitoring
 Between 1989 and 2023, the contents of all booby nests in two study areas of Isla Isabel, off the Pacific coast of Mexico (21°50’59”N, 105°52’54”W), were monitored every 3 days throughout the first three months of every five-month breeding season and every 6 days subsequently (details in Drummond et al., 1986, 2003). Hatchlings were labelled according to hatching order with coloured leg-wires, then numbered plastic bands, and at 70 days (a proxy of fledging, which can occur as early as 80 days) they were weighed, measured (culmen and ulna), and fitted with alphanumeric steel bands. Sex of breeders was identified by voice (females grunt, males whistle) but sex of chicks was normally unknown until they recruited into the breeding population a few years after fledging. Due to limited natal dispersal in this population (30.5 ± 1.7 m in males and 36.6 ± 1.4 m in females; 𝑥 ± 𝑠𝑒) and lifetime philopatry (Kim et al. 2007), this monitoring captured the development and fl..., ## Long-term insights into who benefits from brood reduction

We have submitted our raw data in five datasets. These datasets include information on known-age adults that either fledged both offspring or experienced brood reduction, and their subsequent survival and reproductive performance.

**PARENTAL_SURVIVAL**
*Variable name and description*
YEAR = Calendar year in which the focal adult either fledged both offspring or experienced brood reduction.
NEST_ID = Unique identifier of the focal adult's nest.
REDUCTION = Brood outcome: 1 = both offspring fledged; 0 = brood reduction occurred.
RING = Identity of the focal adult.
AGE = Age of the focal adult (in years) at the time of fledging both offspring or experiencing brood reduction.
SEX = Sex of the focal adult: 0 = male; 1 = female.
SURVIVAL = Whether the adult survived to the subsequent breeding season: 1 = yes; 0 = no.

**PARENTAL_OUTPUT_SUBSEQUENT_YEAR**
*Variable name and description*
YEAR = Calendar year in which the focal adult ...,

资源追踪/兼性育雏减少假说（resource-tracking/facultative brood reduction hypothesis）指出，在食物短缺压力下，诸多晚成鸟（altricial birds）会牺牲幼雏中最年幼的个体，以提升同胞的生长发育与存活概率。针对异步孵化与食物匮乏的相关研究总体上支持这一观点，尽管异步孵化可能还兼具其他功能。不过，这种选择性死亡的直接获益者仍不明确，因为绝大多数研究都忽略了亲代以及雏鸟离巢后的存活结局。生命史视角极少被应用于育雏减少现象的研究中。

本研究基于一项为期34年的蓝脚鲣鸟（Sula nebouxii）个体繁殖数据集，探究在食物压力下的两雏育雏群中的同胞相杀型育雏减少行为，究竟会使亲鸟母亲、父亲还是存活的幼雏获益。研究结果显示，经历育雏减少的亲鸟母亲，其在下一个繁殖季存活的概率比育雏群完整的亲鸟母亲高出约16%，这表明该行为能为亲代母亲带来显著收益。此外，……的终止，种群监测

**种群监测**
1989年至2023年间，我们在墨西哥太平洋沿岸伊莎贝尔岛（Isla Isabel，坐标21°50′59″N，105°52′54″W）的两个研究区域内，对所有鲣鸟巢穴进行监测：在每五个月繁殖季的前三个月，每3天开展一次监测，后续则每6天开展一次（详细方法参见Drummond等，1986、2003）。研究人员会根据孵化顺序，用彩色脚环标记初孵幼雏，随后更换为带编号的塑料脚环；待幼雏长至70日龄（该日龄可作为离巢的替代指标，而自然离巢最早可发生在80日龄）时，对其称重、测量（喙长与尺骨长度），并安装字母数字组合钢制脚环。繁殖成鸟的性别可通过鸣叫声区分（雌性发出呼噜声，雄性发出哨鸣声），但雏鸟的性别通常要等到其离巢数年后加入繁殖种群时才能确定。由于该种群存在有限的出生扩散（雄性为30.5±1.7米，雌性为36.6±1.4米；均值±标准误）以及终身恋巢性（Kim等，2007），本次监测覆盖了幼雏的发育与离巢……

## 关于育雏减少获益者的长期研究洞察
我们已将原始数据整理为5个数据集并提交。这些数据集包含已知年龄的成鸟相关信息，这些成鸟要么成功抚育两只幼雏离巢，要么经历了育雏减少事件，同时包含它们后续的存活情况与繁殖表现。

**PARENTAL_SURVIVAL**
*变量名称与说明*
YEAR：记录焦点成鸟抚育两只幼雏离巢或经历育雏减少事件的公历年份。
NEST_ID：焦点成鸟巢穴的唯一标识符。
REDUCTION：育雏结局：1=两只幼雏均成功离巢；0=发生育雏减少事件。
RING：焦点成鸟的身份标识环号。
AGE：焦点成鸟在抚育两只幼雏离巢或经历育雏减少事件时的年龄（单位：年）。
SEX：焦点成鸟的性别：0=雄性；1=雌性。
SURVIVAL：成鸟是否存活至下一个繁殖季：1=是；0=否。

**PARENTAL_OUTPUT_SUBSEQUENT_YEAR**
*变量名称与说明*
YEAR：记录焦点成鸟……