Bird Use of Imperial Valley Crops [ds427]

Agriculture crops in the Imperial Valley of California provide valuable habitat for many resident and migratory birds and are a very important component of the Salton Sea Ecosystem (Patten et. al. 2003), but detailed information regarding avian species use, distribution and abundance is lacking. In 2006 the California Department of Fish and Game, the Salton Sea Authority, and the USGS initiated a monthly survey of birds using Imperial Valley agriculture fields to provide information regarding avian species composition and use. Driving transects were originally delineated on a map as one continuous transect projected to cover a good representation of a subset of the entire Imperial Valley agriculture area. The original transect included mostly highways with heavy traffic and high speeds. It was decided for safety reasons that slower speed limits and lighter traffic areas would be more suitable to this type of survey. The result is two transects of roughly the same distance. The west transect is west of Highway 111, beginning at the junction of Highway 111 and Sinclair Road and ending on Harris Road and Butters Road. The east transect is east of Highway 111, beginning at the junction of Highway 111 and Sinclair Road. and ending on Harris Road and Butters Road. See map for details http://nrm.dfg.ca.gov/FileHandler.ashx?DocumentID=4964 . Surveys began 30 minutes after sunrise on the west transect. The east transect was completed on the next consecutive day commencing at 30 minutes after sunrise. Driving speed was limited to 25 miles per hour where possible. When available, the survey was conducted with a driver and an observer. Many times the driver was alone and made all of the observations. As the vehicle followed the transect, fields on either side of the road were scanned for birds. When birds were observed in a field the vehicle was stopped and a GPS location was taken using a Magellan Sport Trac Topo. All bird species were counted using Steiner Merlin 10 x 42 binoculars and/or Nikon Fieldscope ED 20x45 zoom. Passerines were excluded from counts. Bird numbers were estimated by first counting all members of a species within one view of the binoculars or the spotting scope. This was done three to five times and an average number per optic view determined. The average value was then multiplied by the number of optic views required to cover the concentration of birds at that site. The resulting number was recorded as the estimated number of birds present. All members of a species present at an observation site were totaled to provide an estimated number of that species present at that site. Crop information, time of observation, and notes about the condition of the field were recorded for the field in which birds were detected The maximum distance birds were observed varied based on weather, angle of the sun with respect to the observer, or distance to the edge of the field birds were observed in. As a general estimate of mean maximum distance I used 400M. This distance is based on a visual estimate of the distance from a road to the far edge of a field in the Imperial Valley. Many fields had late stage crops that were tall and dense and subsequently could not be accurately surveyed from a vehicle. No effort was used to count and remove these crops from the survey area. If birds were observed flying out of or into these late stage crops information was recorded on only the birds seen in flight.加利福尼亚州帝国谷的农业耕地为众多留鸟与候鸟提供了宝贵栖息地，同时也是索尔顿海生态系统（Salton Sea Ecosystem）的重要组成部分（Patten等人，2003），但目前仍缺乏关于鸟类物种栖息地利用、分布与种群丰度的详细资料。 2006年，加利福尼亚州鱼类与狩猎局（California Department of Fish and Game）、索尔顿海管理局（Salton Sea Authority）以及美国地质调查局（USGS）启动了一项针对帝国谷农业耕地的月度鸟类调查，以获取鸟类物种组成与利用情况的相关数据。 研究人员最初在地图上划定了一条连续的行车样线（transect），旨在覆盖帝国谷农业区域中具有代表性的部分地块。但该初始样线大多途经交通繁忙、车速较高的公路，出于安全考量，最终确定选择车速更低、交通更平缓的区域开展调查会更为适配。 最终形成两条总长度相近的样线：西样线位于111号公路以西，起点为111号公路与辛克莱路交汇处，终点为哈里斯路与巴特斯路；东样线位于111号公路以东，起点同样为111号公路与辛克莱路交汇处，终点为哈里斯路与巴特斯路。详细路线请参见地图：http://nrm.dfg.ca.gov/FileHandler.ashx?DocumentID=4964。 西样线的调查于日出后30分钟启动，东样线则于次日同一时间（日出后30分钟）依次开展。 行车速度尽可能控制在25英里/小时。调查优先配备驾驶员与观测员两名工作人员，但多数情况下仅驾驶员一人兼任观测工作，独立完成所有观测任务。 车辆沿样线行驶时，需对道路两侧的农田开展鸟类扫描观测。若在某块农田中发现鸟类，则立即停车并使用麦哲伦Sport Trac Topo手持GPS（Magellan Sport Trac Topo）记录点位坐标。 所有鸟类物种均通过视得乐Merlin 10×42双筒望远镜（Steiner Merlin 10 x 42 binoculars）和/或尼康Fieldscope ED 20×45变焦观鸟镜（Nikon Fieldscope ED 20x45 zoom）进行计数，且本次调查排除鸣禽（Passerines）的统计。 鸟类种群数量的估算流程如下：首先统计单次观测视野内可见的某一物种个体数，重复该步骤3至5次并计算单次视野的平均个体数；随后将该平均值乘以覆盖该区域内鸟类聚集群所需的观测视野总数，所得结果即为该点位该物种的估算个体数。最终将某一观测点位的所有物种个体数汇总，即可得到该点位各物种的总估算数量。 对于发现鸟类的农田，需同步记录其作物类型、观测时间以及农田生长状况等备注信息。 鸟类观测的最大距离受天气状况、观测者与太阳的夹角，以及观测农田的边缘距离等因素影响。本研究将平均最大观测距离估算为400米，该数值基于帝国谷农田从公路至田块远端的视觉距离测算得出。 部分农田的作物处于生长后期阶段，植株高大茂密，无法通过车辆完成精准调查，因此未将此类农田从调查区域中剔除。若观测到鸟类飞入或飞出此类后期作物农田，则仅记录飞行中的鸟类个体。