Disseration Research: Ecological and Hormonal Bases of Paternal Care in the Chestnut-collared Longspur, Calcarius ornatus

雄性鸟类比其他任何脊椎动物群体的雄性都更多地参与父母的照顾。 因此，鸟类代表了一个非凡的模式，以解开影响照顾年轻的各种因素。当繁殖开始时，雄性经历了睾丸激素（T）的上升，到幼仔孵化时下降。 这种模式可能代表了T水平和父亲关怀表达之间的权衡：实验表明，高水平的T与父亲关怀减少有关，有利于增强性行为。 在栗领长距（CCLO），实验增加T增强性行为蛋孵化前，但令人惊讶的是，不减少照顾雏鸟。 这项研究将测试的假设，这种不寻常的不敏感性T在父母阶段发生，因为男性是雏鸟生存的关键。 通过操纵环境和激素变量，本研究将确定（1）如果男性护理是必不可少的，（2）如果环境驱动男性护理，（3）如果T升高影响CCLO的巢防御。 雄性关怀，虽然在自然界中通常很少见，但在鸟类中却很普遍。 然而，父亲的照顾是由环境因素还是由内部线索驱动的，这是未知的。 本研究将有助于揭示激素和环境线索对父亲关怀表达的相对作用。 确定环境因素的作用，在T和父亲的照顾之间的明显权衡是特别重要的，因为它可以应用到额外的系统中，父亲的照顾是至关重要的生存的年轻。

Male birds participate in parental care more than males of any other vertebrate group. Thus, birds represent an extraordinary model to untangle the various factors that affect care of young. When breeding begins, males experience a rise in the hormone testosterone (T) that declines by the time young hatch. This pattern may represent a trade-off between T levels and expression of paternal care: experimentally, high levels of T are associated with reduced paternal care in favor of enhanced sexual behavior. In chestnut-collared longspurs (CCLO), experimentally increased T enhances sexual behavior before eggs hatch, but surprisingly, does not reduce care of nestlings. This study will test the hypothesis that this unusual insensitivity to T during the parental phase occurs because males are critical for nestling survival. By manipulating environmental and hormonal variables, this study will determine (1) if male care is essential, (2) if the environment drives male care, and (3) if elevated T affects nest defense in CCLO. Male care, though generally rare in nature, is prevalent in birds. Whether paternal care is driven by environmental factors or by internal cues, however, is unknown. This study will help to unravel the relative roles of hormones and environmental cues on the expression of paternal care. Determining the role of environmental factors in the apparent trade-off between T and paternal care is particularly important, because it can be applied to additional systems in which paternal care is critical for survival of young.