Least Tern Range - CWHR B234 [ds1507]

CWHR species range datasets represent the maximum current geographic extent of each species within California. Ranges were originally delineated at a scale of 1:5,000,000 by species-level experts more than 30 years ago and have gradually been revised at a scale of 1:1,000,000. Species occurrence data are used in defining species ranges, but range polygons may extend beyond the limits of extant occurrence data for a particular species. When drawing range boundaries, CDFW seeks to err on the side of commission rather than omission. This means that CDFW may include areas within a range based on expert knowledge or other available information, despite an absence of confirmed occurrences, which may be due to a lack of survey effort. The degree to which a range polygon is extended beyond occurrence data will vary among species, depending upon each species’ vagility, dispersal patterns, and other ecological and life history factors. The boundary line of a range polygon is drawn with consideration of these factors and is aligned with standardized boundaries including watersheds (NHD), ecoregions (USDA), or other ecologically meaningful delineations such as elevation contour lines. While CWHR ranges are meant to represent the current range, once an area has been designated as part of a species’ range in CWHR, it will remain part of the range even if there have been no documented occurrences within recent decades. An area is not removed from the range polygon unless experts indicate that it has not been occupied for a number of years after repeated surveys or is deemed no longer suitable and unlikely to be recolonized. It is important to note that range polygons typically contain areas in which a species is not expected to be found due to the patchy configuration of suitable habitat within a species’ range. In this regard, range polygons are coarse generalizations of where a species may be found. This data is available for download from the CDFW website: https://www.wildlife.ca.gov/Data/CWHR. The following data sources were collated for the purposes of range mapping and species habitat modeling by RADMAP. Each focal taxon’s location data was extracted (when applicable) from the following list of sources. BIOS datasets are bracketed with their “ds” numbers and can be located on CDFW’s BIOS viewer: https://wildlife.ca.gov/Data/BIOS. California Natural Diversity Database, Terrestrial Species Monitoring [ds2826], North American Bat Monitoring Data Portal, VertNet, Breeding Bird Survey, Wildlife Insights, eBird, iNaturalist, other available CDFW or partner data.CWHR物种分布数据集展示了加利福尼亚州内各物种当前的最大地理分布范围。该分布范围最初由物种专家以1:500万比例尺于30余年前划定，后续逐步以1:100万比例尺进行修订。 物种出现数据被用于界定物种分布范围，但分布范围多边形可能会超出某一特定物种现存出现数据的边界。在绘制分布边界时，加利福尼亚州鱼类与野生动物部（CDFW）倾向于采用宁多勿漏的原则：即便某一区域暂无确认的物种出现记录（这往往源于调查工作的缺失），CDFW仍可基于专家知识或其他可用信息将其纳入物种分布范围。 分布范围多边形超出出现数据的程度因物种而异，取决于各物种的移动能力、扩散模式以及其他生态与生活史特征。分布范围多边形的边界线在绘制时会综合考量上述因素，并与标准化边界对齐，包括水文流域（NHD）、生态区（USDA）或其他具有生态意义的划分方式，例如海拔等高线。 尽管CWHR分布范围旨在表征物种当前的分布范围，但一旦某一区域被纳入CWHR的物种分布范围，即便近数十年内无该物种的记录，该区域仍会保留在分布范围内。除非专家指出某区域经多次调查后多年未被占据，或被认定不再适宜物种生存且不太可能再次被殖民，否则该区域不会从分布范围多边形中移除。 需要注意的是，由于物种分布范围内的适宜栖息地呈斑块状分布，分布范围多边形通常会包含一些理论上不会有该物种出现的区域。就此而言，分布范围多边形是对物种可能分布区域的粗略概括。 该数据集可从CDFW官网下载：https://www.wildlife.ca.gov/Data/CWHR。 以下数据源由RADMAP为分布范围制图与物种栖息地建模工作整理。每个目标类群的位置数据（如适用）均从以下来源提取。BIOS数据集（BIOS datasets）以其‘ds’编号标注，可通过CDFW的BIOS查看器访问：https://wildlife.ca.gov/Data/BIOS。包括：加利福尼亚自然多样性数据库、陆地物种监测[ds2826]、北美蝙蝠监测数据门户、VertNet、繁殖鸟类调查、Wildlife Insights、eBird、iNaturalist，以及其他可用的CDFW或合作方数据。