Drivers of alloparental provisioning of fledglings in a colonially-breeding bird

Offspring provisioning represents a major reproductive cost. However,
evidence suggests that parents sometimes feed unrelated offspring. Several
hypotheses could explain this puzzling phenomenon. Adults could feed
unrelated offspring that are (1) of close social associates to facilitate
these juveniles’ integration into their social network (resulting in
social inheritance), (2) potential extra-pair offspring, (3) at a similar
developmental stage as their own, (4) coercing feeding by begging, or (5)
less-developed and who’s enhanced survival would benefit the adult or its
own offspring (the group augmentation hypothesis). Colonial breeders are
ideal for investigating the relative importance of these hypotheses
because offspring are often kept in crèches where adults can exhibit
allofeeding. Using automated monitoring of replicated captive zebra finch
(Taeniopygia guttata) colonies, we found that while parents selectively
fed their own offspring, they also consistently fed unrelated offspring
(32.48% of feeding events). Social relationships among adults prior to
breeding did not predict allofeeding, nor was provisioning directed
towards unrelated offspring directed to potential genetic offspring.
Instead, adults preferentially fed less-developed non-offspring, despite
these not begging more frequently than larger ones did. Our study suggests
that allofeeding is consistent with group augmentation, which could be
beneficial through colony maintenance or increased offspring survival.

子代喂养是一项重大的繁殖成本。然而，有证据表明亲代有时会喂养非亲缘后代。若干假说可解释这一令人困惑的现象。成体可能喂养以下类型的非亲缘后代：（1）亲密社会伙伴的后代，以促进这些幼体融入其社交网络（从而实现社会继承）；（2）潜在的婚外后代；（3）与自身后代发育阶段相似的个体；（4）通过乞食强迫喂食的个体；或（5）发育较不成熟且其存活率提高将使成体或其自身后代受益的个体（群体增强假说（group augmentation hypothesis））。集群繁殖者是研究这些假说相对重要性的理想对象，因为后代常被置于育婴群中，成体可在此表现出异亲喂养（allofeeding）行为。通过对重复的圈养斑马雀（Taeniopygia guttata）群体进行自动化监测，我们发现，尽管亲代选择性地喂养自身后代，但它们也持续喂养非亲缘后代（占喂养事件的32.48%）。繁殖前成体间的社会关系无法预测异亲喂养行为，且针对非亲缘后代的喂养也并非指向潜在的遗传后代。相反，成体优先喂养发育较不成熟的非亲缘后代，尽管这些后代的乞食频率并不高于体型较大的个体。我们的研究表明，异亲喂养与群体增强假说一致，这可能通过维持群体或提高后代存活率而带来益处。