Behavioral Functions of Vocal Imitation in Parrots

鹦鹉声音模仿的行为功能为什么有些动物会模仿复杂的声音？这个问题在鸣禽中最为常见，它们学习鸣叫主要是为了保卫领地和/或吸引配偶。然而，这些解释可能不适用于鹦鹉，因为鹦鹉已经独立于鸣禽进化出了非凡的模仿能力。那么，鹦鹉为什么会模仿声音呢？Striedter实验室最近的数据表明，鹦鹉的声音学习在配对键的形成中起着重要作用。具体来说，当雌雄虎皮鹦鹉成对放置时，雄虎皮鹦鹉会不断模仿与之配对的雌虎皮鹦鹉的接触叫声，而雌虎皮鹦鹉则保持原来的叫声。这种模仿行为中的性别不对称表明，雄性模仿雌性是为了影响雌性的择偶选择。如果这个假设是正确的，那么有三个预测应该成立：1)性选择应该导致雄性和雌性虎皮鹦鹉在声音学习能力上的不对称。这一假设将通过比较全雄性和全雌性虎皮鹦鹉群体发出共同接触叫声的速度来验证。如果男性在声乐学习方面“更好”，那么男性的发音收敛应该比女性更快。2)男性应该优先模仿他们所追求的女性。这一假设将通过确定雄性学习雌性叫声所需的时间是否与他对雌性的兴趣成反比来验证，这是通过其他众所周知的求爱行为的频率来衡量的。雌性的吸引力将通过在她的心脏上涂漆来控制，成熟的雌性是棕色的，而不成熟的雌性是浅蓝色的。雌性虎皮鹦鹉应该优先与已经学会模仿自己的雄性虎皮鹦鹉交往。这一假设将通过确定雌性是否对已经知道自己的叫声的陌生雄性（因为它们是由另一只与测试雌性分享叫声的雌性指导的）比不知道测试雌性叫声的雄性表现出更多的求爱行为来验证。在一项补充实验中，通过选择性地切断听觉和发声运动系统之间的联系，一些雄性虎皮鹦鹉将被赋予模仿障碍。这些实验可能会对“性选择”和“女性选择”领域产生重大影响，因为大多数先前的研究都集中在女性对显性身体特征的选择上，而不是学习能力。提出的实验也为更机械地分析为什么雄性虎皮鹦鹉模仿雌性的叫声铺平了道路。

Behavioral Functions of Vocal Imitation in ParrotsPI: Georg F. Striedterco-PI: Nancy T. BurleyWhy do some animals imitate complex sounds? This question has most frequently been addressed in songbirds, which learn their songs primarily to defend a territory and/or attract a mate. These explanations may not hold for the parrots, however, because parrots have evolved their remarkable imitative abilities independently of the songbirds. So, why do parrots imitate sounds? Recent data from the Striedter laboratory suggest that parrot vocal learning plays a role in pairbond formation. Specifically, when male and female budgerigars are placed in pairs, the males consistently imitate the contact calls of the females with whom they are paired, while the females retain their original calls. This sexual asymmetry in imitative behavior suggests that males imitate females in order to influence female mate choice. If this hypothesis is correct, then three predictions should hold: 1) Sexual selection should have led to an asymmetry in the vocal learning abilities of male and female budgerigars. This hypothesis will be tested by comparing how quickly all-male and all-female groups of budgerigars develop shared contact calls. If males are "better" at vocal learning, then vocal convergence should occur more quickly among males than among females. 2) Males should preferentially imitate females whom they are courting. This hypothesis will be tested by determining whether the time it takes for a male to learn a female's call is inversely correlated with his interest in this female, as measured by the frequency of other, well-known courtship behaviors. The female's attractiveness will be manipulated by painting her cere, which is brown in mature females but pale blue in immature females. 3) Female budgerigars should associate preferentially with males that have learned to imitate them. This hypothesis will be tested by determining whether females give more courtship displays towards unfamiliar males that already know their call (because they were tutored by another female that shares the test female's call) than towards males that do not yet know the test female's call. In a complementary experiment, some male budgerigars will be rendered imitation-impaired by selectively severing the connection between their auditory and vocal motor systems. The proposed experiments could significantly impact the field of "sexual selection" and "female choice" because most prior studies focused on female choice for overt physical traits - not learning ability. The proposed experiments also pave the way for a more mechanistic analysis of why male budgerigars imitate female calls.