Breeding success and traits of equal and unequal pairs of little penguins (Eudyptula minor) on Phillip Island during 2001-2008

According to life-history theory, individuals optimize their decisions in order to maximize their fitness. This raises a conflict between parents, which need to cooperate to ensure the propagation of their genes but at the same time need to minimize the associated costs. Trading-off between benefits and costs of a reproduction is one of the major forces driving demographic trends and has shaped several different parental care strategies. Using little penguins (Eudyptula minor) as a model, we investigated whether individuals of a pair provide equal parental effort when raising offspring and whether their behavior was consistent over 8 years of contrasting resource availability. Using an automated identification system, we found that 72% of little penguin pairs exhibited unforced (i.e., that did not result from desertion of 1 parent) unequal partnership through the postguard stage. This proportion was lower in favorable years. Although being an equal pair appeared to be a better strategy, it was nonetheless the least often observed. Individuals that contributed less than their partner were not less experienced (measured by age), and gender did not explain differences between partners. Furthermore, birds that contributed little or that contributed a lot tended to be consistent in their level of contribution across years. We suggest that unequal effort during breeding may reflect differences in individual quality, and we encourage future studies on parental care to consider this consistent low and high contributor behavior when investigating differences in pair investment into its offspring. Key words: attendance patterns, individual quality, meal size, parental care, reproductive costs, seabirds.

根据生活史理论（life-history theory），个体通过优化决策以最大化自身适合度（fitness）。这引发了亲代间的冲突：二者本需携手合作以保障基因传递，却又需尽可能降低相关成本。繁殖行为的收益与成本权衡是驱动种群动态演变的核心力量之一，也塑造了多种不同的亲代抚育策略。本研究以小企鹅（Eudyptula minor）为模式生物，探究了配对个体在育幼过程中是否会付出均等的亲代投入，以及它们的行为在8年资源可获得性迥异的周期内是否具有一致性。借助自动化识别系统，我们发现72%的小企鹅配对在育雏后期（postguard stage）呈现出非因一方弃巢导致的非均等合作关系。该比例在资源条件优越的年份更低。尽管均等投入的配对看似更优策略，但其实际观测频率却最低。投入低于配偶的个体，其经验水平（以年龄衡量）并未更低，且性别差异也无法解释配对个体间的投入差距。此外，投入较少或较多的个体，其年度投入水平往往具有稳定性。我们推测，繁殖期间的非均等亲代投入可能反映了个体质量的差异，并呼吁未来的亲代抚育研究在探究配对对子代的投入差异时，纳入这种稳定的低、高投入者行为模式。关键词：出勤模式（attendance patterns）、个体质量（individual quality）、单次喂食量（meal size）、亲代抚育（parental care）、繁殖成本（reproductive costs）、海鸟（seabirds）