DISSERTATION RESEARCH: Effects of Habitat Heterogeneity on Songbird Fecundity in an Experimental Landscape

景观异质性促进了自然生态系统的生物多样性。在北美，高草草原在历史上一直是由火灾和大型食草动物（包括野牛、麋鹿和叉角羚）的选择性放牧相互作用下形成的不同栖息地的马赛克。近几十年来，农业集约化导致管理草原的景观更加均匀，这与北美和欧洲鸣禽数量的广泛减少有关。草原异质性的丧失可能会通过改变食物供应、捕食风险或褐头牛鹂（Molothrus ater）的幼虫寄生率对鸟类产生重大影响。本研究将评估生境异质性对保育鸟小鸟（Spiza americana）运动和存活的影响。该项目将有助于更好地了解管理草原上草原鸣禽的生殖生态，并有助于了解草原管理与生态、鸟类种群和保护之间的关系。这项实地研究将在堪萨斯州东部和俄克拉荷马州的弗林特山生态区进行，那里仍然保留着大片的原生高草草原，但栖息地质量已受到牧场管理不断变化的影响。康扎草原是美国国家科学基金会资助的弗林特山北部长期生态研究（LTER）基地，它提供了一个独特的实验景观，具有不同程度的栖息地异质性，由长期放牧和火灾处理造成。斑烧放牧管理增加了植被结构的异质性，因为在三年轮作计划中，每年只有三分之一的牧场被烧毁，放牧牛的活动不受限制。第四个牧场每年焚烧一次，并在整个季节放牛，这将是一个消极的控制，第五个牧场每年焚烧一次，但不放牧，这将是一个积极的控制。研究人员将在总共60只雏鸟身上安装小型无线电发射器，进行五种实验治疗。雏鸟将在离开巢后的前30天每天重新定位，以确定其运动和生存。该研究将利用野外方法和统计分析来估计羽翼的运动、节肢动物的猎物可用性和羽翼的存活率。了解生物因素如何与巢和雏鸟生存等人口统计学参数相互作用，将有助于理解景观异质性在鸟类生活史策略中的作用。

Landscape heterogeneity promotes higher biodiversity in natural ecosystems. In North America, tallgrass prairie was historically maintained as a mosaic of different habitats by the interaction between fire and selective grazing by large herbivores, including bison, elk and pronghorn. In recent decades, agricultural intensification has led to more homogeneous landscapes in managed grasslands, which has been linked to widespread declines in songbird populations in North America and Europe. A loss of heterogeneity in grasslands could have major consequences for birds by changing food availability, predation risk, or rates of brood parasitism by Brown-headed Cowbirds (Molothrus ater). The proposed field study will estimate the effects of habitat heterogeneity on movements and survival of juvenile Dickcissels (Spiza americana), a songbird of conservation concern. The project will provide a better understanding of the reproductive ecology of grassland songbirds in managed grasslands, and will aid in understanding the relationships among grassland management and ecology, bird populations, and conservation. This field study will be conducted in the Flint Hills ecoregion of eastern Kansas and Oklahoma, where large tracts of native tallgrass prairie still remain, however habitat quality has been impacted by ongoing changes in rangeland management. Konza Prairie is an NSF-funded Long-term Ecological Research (LTER) site in the northern Flint Hills, and provides a unique experimental landscape with different levels of habitat heterogeneity created by long-term grazing and fire treatments. Patch-burn grazing management increases heterogeneity in vegetative structure because only a third of the pasture is burned each year in a three-year rotational scheme, and movements of grazing cattle are unrestricted. A fourth pasture with annual burns and season-long stocking of cattle will be a negative control, and a fifth pasture with annual burns but no grazing will be a positive control. The researchers will attach small radio-transmitters to a total of 60 fledglings, across the five experimental treatments. Fledglings will be re-located daily during the first 30 days after leaving the nest to determine movements and survival. The research will estimate fledgling movements, arthropod prey availability, and fledgling survival using field methods and statistical analyses. Understanding how biotic factors interact with demographic parameters like nest and fledgling survival will help to understand the role of landscape heterogeneity on the life-history strategies of birds.