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，已有研究提出：当繁殖亲鸟预期会获得育幼帮手（helper）协助时，亲鸟应降低对卵的投入，因为帮手的育雏投喂行为可弥补这部分投入的减少。部分物种的研究数据支持这一假说，但另有物种并未呈现该规律。另有假说提出：若帮手的存在能提升后代的繁殖价值，那么雌性亲鸟非但不应降低，反而应增加对卵的投入；只要产卵雌性可预期帮手的到来，该模式同样会影响卵的产出。本研究以伊比利亚喜鹊（Iberian magpie）为研究对象，探究雌性亲鸟在有帮手存在时，是否会降低卵阶段的繁殖投入。研究结果显示：窝卵投入会因年份、繁殖季日期以及雌性亲鸟的年龄而有所差异，但当亲鸟预期有帮手协助时，其单枚卵的投入并未出现降低。反之，我们观察到相反的模式：当雏鸟阶段未来会有帮手协助时，亲鸟的卵投入反而更高。本研究数据表明，帮手的可预测性以及帮手贡献所带来的收益类型，或是理解亲鸟在产卵阶段繁殖投入响应的关键因素。