SGS-LTER Long-term Monitoring Project: Spotlight Rabbit Count on the Central Plains Experimental Range, Nunn, Colorado, USA 1994-2006, ARS Study Number 98

This data package was produced by researchers
working on the Shortgrass Steppe Long Term
Ecological Research (SGS-LTER) Project,
administered at Colorado State University.
Long-term datasets and background information
(proposals, reports, photographs, etc.) on the
SGS-LTER project are contained in a comprehensive
project collection within the Digital Collections
of Colorado
(http://digitool.library.colostate.edu/R/?func=collections&collection_id=3429).
The data table and associated metadata document,
which is generated in Ecological Metadata
Language, may be available through other
repositories serving the ecological research
community and represent components of the larger
SGS-LTER project collection. Additional information and referenced materials can be found:
http://hdl.handle.net/10217/83448. Rabbits are the most important small-mammal
herbivores in shortgrass steppe, and may
significant influence the physiognomy and
population dynamics of herbaceous plants and woody
shrubs. Rabbits also are the most important prey
of mammalian carnivores such as coyotes and large
raptors such as golden eagles and great horned
owls. Two hares (Lepus californicus, L.
townsendii) and one cottontail rabbit (Sylvilagus
audubonii) occur in shortgrass steppe. In 1994, we
initiated long-term studies to track changes in
relative abundance of rabbits on the Central
Plains Experimental Range (CPER). On four nights
each year (one night each season, usually on new
moon nights in January, April, July, October), we
drove a 32-km route consisting of pasture
two-track and gravel roads on the CPER. This was
the same route as that driven for carnivore scat
counts. Surveys began at twilight. Observers with
two spotlights sat in the back of a 4WD pick-up
driven at <15 mph. We recorded the
perpendicular distance (in m) to each rabbit using
a meter tape or range finder; the direction of the
rabbit relative to the road; and noted if
individuals were solitary or in clusters. We also
recorded any carnivores or other animals seen
during spotlight surveys. Beginning in Spring
1998, we recorded the vegetation type (habitat)
and topographic position of each rabbit seen, as
well as position relative to human features, eg
windmills, cattle guards, on the landscape. We
used the number of rabbits of each species spotted
per km of route as an index of relative abundance.
We used line-transect approaches in DISTANCE to
estimate population densities from perpendicular
distance data.

本数据包由开展短草草原长期生态研究（Shortgrass Steppe Long Term Ecological Research, SGS-LTER）项目的研究人员编制，该项目由科罗拉多州立大学负责管理。
短草草原长期生态研究项目的长期数据集及背景资料（含研究方案、报告、影像资料等）均收录于科罗拉多数字馆藏（Digital Collections of Colorado）的综合项目馆藏中，访问网址为http://digitool.library.colostate.edu/R/?func=collections&collection_id=3429。
本数据集包含的数据表及以生态元数据语言（Ecological Metadata Language）生成的关联元数据文档，可通过服务于生态研究社区的其他馆藏获取，且均属于SGS-LTER项目更大规模馆藏的组成部分。更多相关信息及参考资料可通过以下链接获取：http://hdl.handle.net/10217/83448。
兔类是短草草原中最为关键的小型哺乳类植食动物，可对草本植物与木本灌木的外貌特征及种群动态产生显著影响；同时它们也是郊狼等哺乳类食肉动物，以及金雕、大雕鸮等大型猛禽的主要猎物。短草草原境内共分布有2种野兔（加州兔Lepus californicus、汤森德野兔Lepus townsendii）与1种棉尾兔（奥杜邦棉尾兔Sylvilagus audubonii）。
1994年，研究团队启动长期监测研究，以追踪中央平原实验牧场（Central Plains Experimental Range, CPER）内兔类的相对丰度变化情况。
每年开展4次夜间调查（每季1次，通常选在1月、4月、7月、10月的新月之夜），沿着中央平原实验牧场内总长32公里的路线行进，该路线涵盖牧场两轨便道与碎石公路，与此前用于食肉动物粪便计数的调查路线完全一致。
调查于黄昏时分启动，两名携带探照灯的观测人员坐在时速低于15英里的四轮驱动（4WD）皮卡车厢内，以低速行进。研究人员通过卷尺或测距仪记录每只兔类到观测路线的垂直距离（单位：米）、兔类相对于道路的方位，并记录个体是单独活动还是集群活动。
此外，研究人员还记录了探照灯调查过程中观测到的所有食肉动物及其他动物。1998年春季起，团队额外记录每只观测到的兔类所处的植被类型（生境）、地形位置，以及其与风车、牲畜护栏等人类设施的相对空间位置。
研究以每公里调查路线内观测到的各物种兔类数量作为相对丰度指数，并采用DISTANCE软件中的线路样带法，基于垂直距离数据估算兔类的种群密度。