DISSERTATION RESEARCH: Interspecific Competition Increases Cooperative Group Sizes in Brown-headed Nuthatches (Sitta pusilla).

褐头裸毛鹦鹉以家庭群居的形式生活和繁殖。这些家庭群体似乎共同努力，保护巢穴不受其他物种的伤害，这些物种也需要在树上挖洞才能筑巢。由于毛羽是小鸟(10克)，如果它们不合作，它们的巢往往会被更大的物种所取代。这个项目试图了解棕头裸毛鹦鹉对筑巢洞穴的合作防御是否会增加它们为下一代贡献的后代数量。合作繁殖者经常与亲戚合作，因为外部繁殖的机会很少，目前还不清楚这种合作是一种适应性策略，还是鸟类只是在最大限度地利用糟糕的情况。该项目通过测试合作伙伴是否真的比不合作伙伴有更多的后代来解决这些替代方案。因此，该项目可能会揭示合作养殖的潜在新好处，并提供关于棕头毛雀自然历史的信息，褐头毛雀是一种面临全球变暖和城市化双重威胁的物种。该项目已经增加了当地棕头毛雀的种群数量，联合首席调查员将继续参与该物种的保护工作，方法是在农贸市场的摊位上非正式地发言，并鼓励当地人在他们的土地上放置毛羽大小的盒子。这个项目测试了以前未被验证的观点，即种间竞争在棕头毛雀(BHNU，Sitta pusilla)中作为一种重要的群体规模选择力量发挥作用。关键假设是，同等规模的竞争者之间的竞争会影响合作繁殖的好处，并选择更大的群体规模。通过揭示与其他物种的竞争如何在不同的竞争压力下和在不同的群体规模下影响群体成员的包容性适合度，该项目测试了异种竞争是否可以提高BHNUs在群体中的适合度，从而选择增加合作的群体规模。关于合作育种存在的一个传统假说是，生态限制阻碍了独立繁殖，并推动了群体规模的增加，预测随着群体规模的增加，个体的包容性适应度将降低。然而，这个项目的激励假设，即通过在异种防御中的助手效能，适合度随着群体规模的增加而增加，预测了完全相反的模式。遗传亲子关系的确定和包容性适合度的计算，将使这项研究能够区分生态限制和异种防御效益，作为合作育种BHNU群体规模增加的驱动因素。

Brown-headed nuthatches live and breed in family groups. These family groups appear to work together to defend nesting holes from other species that also need holes in trees to nest. Since nuthatches are small birds (10 g), they often lose their nests to larger species if they do not cooperate. This project seeks to understand if cooperative defense of nesting holes by brown-headed nuthatches increases the number of offspring they contribute to the next generation. Cooperative breeders often cooperate with relatives because outside opportunities for breeding are rare, and it is unclear whether this cooperation is an adaptive strategy or whether the birds are simply making the best of a bad situation. This project addresses those alternatives by testing whether cooperating nuthatches actually have more offspring than non-cooperators. This project therefore could uncover a potential new benefit of cooperative breeding, and it also provides information on the natural history of brown-headed nuthatches, a species facing the dual threats of global warming and urbanization. This project has already increased local population sizes of brown-headed nuthatches, and the Co-Principal Investigator will continue to participate in conservation efforts for this species by speaking informally at a farmer's market booth and encouraging locals to place nuthatch-sized boxes out on their property. This project tests the previously untested idea that interspecific competition functions as an important selective force on group size in the Brown-headed nuthatch (BHNU, Sitta pusilla). The key hypothesis is that competition among equally sized competitors influences the benefits of cooperative breeding and selects for larger group sizes. By uncovering how competition with other species impacts inclusive fitness for group members under differing competitive pressures, and at various group sizes, this project tests whether heterospecific competition can increase the fitness of BHNUs in groups, and thus select for increased cooperative group sizes. A traditional hypothesis for the existence of cooperative breeding is that ecological constraints prevent independent breeding and drive increases in group size, predicting that the inclusive fitness of individuals will decrease as group sizes increase. However, the motivating hypothesis of this project, that fitness increases as group size increases through helper efficacy in heterospecific defense, predicts exactly the opposite pattern. Genetic parentage determination, and the calculation of inclusive fitness, will allow this research to distinguish between ecological constraints and heterospecific defense benefits as drivers of increased group size in the cooperatively breeding BHNU.