Data from: Spatial dynamics of habitat use informs reintroduction efforts in the presence of an invasive predator

1. Islands experience major impacts from introduced species, especially nocturnal predators. The Brown Treesnake (Boiga irregularis) extirpated almost the entire native avifauna on Guam shortly after introduction. Reintroductions from neighboring islands can restore bird communities but will take place in heavily managed units where snake populations can be controlled. Yet reintroductions often proceed without relevant biological information such as nocturnal habitat and space use when nocturnal predators are present. To guide efforts, we studied diurnal and nocturnal habitat and space use by the avian frugivore community on the nearby island of Saipan where the snake is absent. 2. Using radio telemetry and a Bayesian framework, we first compared data typically accessible to resource managers (diurnal home range [DHR] and habitat selection) and which often forms the basis of reintroduction plans. We contrast this with data on nocturnal habitat use that is often not available but relevant when nocturnal predation threat is high. 3. DHR size varied within and among species with Micronesian Starlings (Aplonis opaca) having DHRs at least 45 ha larger than other species. For all species, night roost locations were generally spatially clustered within a DHR and covered a smaller spatial extent. Two species had higher probabilities of roosting outside DHR boundaries but, when outside, roosts were often within 200 m of the DHR boundary. All species selected forested habitats during day and night, with some species choosing native forest over non-native habitat. 4. Synthesis and applications If individuals roosted randomly throughout DHR’s, landscape-level suppression of B. irregularis might be the only viable option for reintroductions of some species. However, individuals of all species showed clustered roosting and high site fidelity. If site fidelity is common, then individuals that roost within fenced areas where snake populations are severely reduced or eliminated will experience high survivorship even if DHRs extend into surrounding unprotected matrix. There was large overlap in habitat selection during day and night indicating managed areas should be composed of native forest with non-native forests of secondary importance. In systems with nocturnal predators, understanding variability in diurnal and nocturnal habitat use could lead to better informed decisions.

1. 外来物种对岛屿生态系统造成显著冲击，尤以夜行性捕食者为甚。棕树蛇（Boiga irregularis）在引入关岛后不久，便几乎彻底清除了当地原生鸟类区系。从邻近岛屿实施鸟类再引入可恢复当地鸟类群落，但此类再引入项目通常会在经过严格管控、可有效控制蛇类种群的区域开展。然而，现有再引入工作往往缺乏关键生物学信息，例如存在夜行性捕食者时，鸟类的夜行栖息地选择与空间利用模式。为指导相关保护实践，我们针对蛇类未入侵的塞班岛开展研究，分析该岛鸟类食果群落的昼夜栖息地与空间利用特征。
2. 本研究借助无线电遥测技术与贝叶斯（Bayesian）框架，首先对比了资源管理者通常可获取的数据——即日间活动家域（diurnal home range, DHR）与栖息地选择——这类数据常作为再引入规划的核心依据；同时将其与另一类通常难以获取，但在夜行性捕食威胁较高时至关重要的夜行栖息地利用数据进行对比分析。
3. 研究结果显示，不同鸟类物种的日间活动家域大小存在种内与种间差异，密克伦椋鸟（Aplonis opaca）的日间活动家域至少比其他物种大45公顷。对于所有研究物种而言，夜间宿巢点通常在日间活动家域内呈空间聚集分布，且覆盖的空间范围更小。其中两个物种有更高概率在日间活动家域边界外宿巢，但即便超出边界，宿巢点通常也距离家域边界不足200米。所有物种在日间与夜间均偏好森林生境，部分物种更倾向于选择原生林而非非原生林。
4. 综合与应用：若鸟类个体在日间活动家域内随机宿巢，那么对棕树蛇进行全域性种群压制或许是部分物种再引入的唯一可行方案。但本研究发现，所有物种的个体均呈现聚集性宿巢行为与较高的栖息地保真度。若栖息地保真度普遍存在，则即便日间活动家域延伸至未受保护的周边生境基质，在蛇类种群被大幅抑制或清除的围栏区域内宿巢的个体仍可获得较高的存活率。研究同时发现，物种在昼夜时段的栖息地选择存在高度重叠，这表明管控区域应以原生林为主，非原生次生林仅作为次要生境。在存在夜行性捕食者的生态系统中，厘清昼夜栖息地利用的变异特征，可为保护决策提供更科学的依据。