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

棕头猫以家庭为单位生活和繁殖。这些家族似乎共同保护巢穴免受其他物种的攻击，这些物种也需要在树上筑巢。由于nuchches是小型鸟类（10克），如果它们不合作，它们经常会失去巢穴给更大的物种。该项目旨在了解棕头nuchches对巢洞的合作防御是否会增加它们为下一代贡献的后代数量。合作繁殖者经常与近亲合作，因为外部繁殖的机会很少，这种合作是一种适应策略，还是鸟类只是在糟糕的情况下尽力而为，目前还不清楚。这个项目通过测试合作的nuchats是否真的比不合作的nuchats有更多的后代来解决这些选择。因此，该项目可以揭示合作繁殖的潜在新好处，并且还提供了面临全球变暖和城市化双重威胁的褐头nuchches的自然历史信息。这个项目已经增加了当地褐头猫的数量，联合首席研究员将继续参与保护这一物种的努力，在农贸市场的摊位上进行非正式的演讲，并鼓励当地人在他们的土地上放置褐头猫大小的盒子。该项目验证了先前未经验证的观点，即种间竞争在褐头nutchch的群体规模中起着重要的选择作用（BHNU, Sitta pusilla）。关键的假设是，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。通过揭示在不同的竞争压力和不同的群体规模下，与其他物种的竞争如何影响群体成员的包容性适合度，本项目测试了异种竞争是否可以增加bhnu在群体中的适合度，从而选择增加合作群体规模。关于合作繁殖存在的传统假设是，生态约束阻碍了独立繁殖，推动了群体规模的增加，并预测个体的包容性适合度会随着群体规模的增加而降低。然而，这个项目的激励假设，即适应性随着群体规模的增加而增加，通过异种防御中的帮助者效能，预测了完全相反的模式。遗传亲缘关系的确定和包容性适应度的计算将使本研究能够区分生态约束和异种防御利益作为合作繁殖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.