Assessing the value of novel habitats to snail kites through foraging behavior and nest survival

Novel ecosystems arise for a variety of reasons, most notably from the introduction of non-native species. To be successful, conservation strategies must both focus on traditional habitats and acknowledge the interplay between novel habitats and species of conservation interest. In the United States, the snail kite (Rostrhamus sociabilis plumbeus) is a federally endangered species whose population in Florida has undergone declines within the past decade. While studying the foraging behavior of breeding snail kites on Lake Tohopekaliga (Lake Toho), we discovered the unexpected use of disturbed ephemeral wetlands adjacent to the lake. These wetlands represent a novel habitat for kites in that they would not have been viable foraging areas prior to the introduction of the exotic island apple snail (Pomacea maculata). The novel wetland areas were highly attractive to kites, likely due to the high snail capture rates in such areas. The survival of kite nests occurring within the novel areas appeared to be similar to that of kite nests occurring in more traditional, nearby areas on Lake Toho. However, whether or not snail kites used novel habitats as nesting areas appeared to be dependent upon water depth and availability of nesting substrate within the novel areas. By examining the differences between snail kite behavior in traditional and novel habitats, we are able to identify some characteristics of novel habitats that may be important in determining the value of novel wetlands to snail kites. More broadly, this study demonstrates the care with which the management and monitoring of novel ecosystems and invasive species should be undertaken, especially when a species of conservation concern is involved.

新型生态系统的形成原因多种多样，其中最突出的原因是外来物种的引入。为达成有效的保护目标，保护策略需同时兼顾传统栖息地，并正视新生栖息地与受保护物种间的相互作用。美国境内的蜗牛鸢（Rostrhamus sociabilis plumbeus）为联邦级濒危物种，其在佛罗里达州的种群在过去十年间持续减少。我们在托霍普卡利加湖（Lake Tohopekaliga，简称托霍湖）开展繁殖期蜗牛鸢觅食行为研究期间，意外发现它们会利用湖泊周边受干扰的临时湿地。这类湿地对于蜗牛鸢而言属于新生栖息地——在外来岛屿苹果螺（Pomacea maculata）被引入之前，此类区域并不具备作为觅食地的可行性。这类新生湿地对蜗牛鸢具有极高的吸引力，究其原因，大概率是此类区域内的螺类捕获率较高。在新生湿地内筑巢的蜗牛鸢，其巢穴存活率与托霍湖周边传统栖息地内的巢穴存活率并无显著差异。不过，蜗牛鸢是否会将新生栖息地作为筑巢场所，似乎取决于新生湿地内的水深与筑巢基质的可获取性。通过对比蜗牛鸢在传统与新生栖息地中的行为差异，我们得以明确部分可用于评估新生湿地对蜗牛鸢价值的关键特征。从更广泛的视角来看，本研究凸显了在开展新生生态系统与入侵物种的管理与监测工作时需保持审慎态度，尤其是当涉及受保护物种时。