Data from: Maternal allocation in eggs when counting on helpers in a cooperatively breeding bird

For cooperatively breeding birds, it has been proposed that breeders should reduce their investment in eggs when they count on helpers, because this can be compensated for by helpers provisioning of nestlings. Data from some species have supported this prediction, but this is not the case in others. It has also been proposed that mothers should not reduce but rather increase investment if the presence of helpers enhances the reproductive value of offspring, a pattern that might also influence egg production as long as helpers are predictable for laying females. Here, we studied maternal expenditure in eggs and clutches in the Iberian magpie, to see whether mothers reduce their expenditure at the egg stage in the presence of helpers. Our results show that investment in clutches varied depending on the year, date in the season and age of the mother, but there were no reductions in maternal expenditure per individual egg when they counted on helpers. On the contrary, a pattern emerged in the opposite direction of more investment in eggs associated with the future presence of helpers at the nestling stage. Our data suggest that the predictability of helpers, along with the type of benefits accrued from the contribution of helpers, may be crucial to understanding the reaction of mothers at egg production.针对合作繁殖鸟类（cooperatively breeding birds），已有假说提出：当亲鸟依赖育雏帮手（helper）时，应降低其产卵投入，因为育雏帮手可通过为雏鸟投喂食物来弥补这部分投入的减少。部分鸟类物种的研究数据支持了这一假说，但其他物种的实验结果并不支持该假说。另有假说提出：若育雏帮手的存在提升了后代的繁殖价值，雌性亲鸟非但不应降低产卵投入，反而应提高投入；只要产卵雌鸟能够预先预判育雏帮手的到来，该模式同样会对产卵过程产生影响。本研究以伊比利亚喜鹊（Iberian magpie）为研究对象，分析其雌性亲鸟的单卵投入与窝卵投入，旨在探究当存在育雏帮手时，亲鸟是否会降低产卵阶段的投入。研究结果显示，窝卵投入会随繁殖年份、繁殖季日期以及雌性亲鸟的年龄发生变化，但当亲鸟依赖育雏帮手时，其单卵投入并未出现降低。与之相反，研究呈现出反向模式：雏鸟阶段未来将有育雏帮手到场的亲鸟，其产卵投入反而更高。本研究数据表明，育雏帮手的可预判性，以及育雏帮手贡献所带来的收益类型，或是理解雌性亲鸟在产卵阶段调控策略的关键所在。