Abstract

The black-headed duck (Heteronetta atricapilla) of South America is the only known avian obligate brood parasite with precocial offspring. In Argentina, it relies on two species of coots as primary hosts, which typically reject 35–65% of duck eggs. We show that environmentally driven increases in host egg rejection behavior lead to substantial reductions in the reproductive success of the brood parasite. Episodes of flooding and vegetation loss caused dramatic shifts in host egg-rejection behavior, resulting in rejection (85–95%) of almost all duck eggs. Coots respond to fluctuating water levels by building up their nest, raising their own eggs but leaving duck eggs behind. Coots can apparently recognize parasitic duck eggs, but large-scale rejection is triggered only when hosts must actively make a choice. We use a simple population model to illustrate the unique demographic challenges that black-headed ducks face with their parasitic lifestyle and to explore the potential impact of environmentally induced escalation of egg rejection. Using the best available estimates for key vital rates, we show that obligate parasitism may provide a demographically precarious existence for black-headed ducks, even under benign environmental conditions. Environmentally mediated increases in egg rejection rates by hosts could impact significantly the viability of this enigmatic species of brood parasitic duck. Our results demonstrate that egg rejection rates are not fixed properties of host populations or individuals but are strongly influenced by social and ecological factors. Shifts in these environmental drivers could have important and unforeseen demographic consequences for brood parasites.

中文翻译：

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环境驱动的宿主卵排斥反应的升级加剧了禽卵寄生虫的成功

摘要

黑头鸭（Heteronetta atricapilla）是南美唯一已知的具早熟后代的专性禽类寄生虫。在阿根廷，它依赖于两种老傻瓜作为主要寄主，它们通常拒绝35-65％的鸭卵。我们表明，环境驱动的宿主卵排斥行为的增加导致育雏寄生虫繁殖成功率的大幅降低。洪水和植被的丧失导致宿主拒卵行为发生巨大变化，导致几乎所有鸭卵被拒（85–95％）。老兄通过筑巢，养育自己的卵，但留下鸭卵来应对水位的波动。老兄显然可以识别出寄生鸭蛋，但只有当主人必须主动做出选择时，才会引发大规模拒绝。我们使用简单的种群模型来说明黑头鸭因其寄生生活方式而面临的独特的人口挑战，并探讨环境诱导的拒卵升级导致的潜在影响。使用关键生命率的最佳估计值，我们表明即使在良性环境条件下，专性寄生也可能为黑头鸭提供人口不稳定的生存。宿主在环境中介导的卵排斥率增加可能会严重影响这种神秘物种的育雏寄生鸭的生存能力。我们的结果表明，卵子排斥率不是寄主种群或个体的固定特性，而受社会和生态因素的强烈影响。