RECOVER MAP 3.1.3.13 Trophic Level - Wading Bird Nesting Colony Location, Size, and Timing

A central prediction of the current Everglades restoration plan is that the return to natural flows and hydropatterns will result in large, sustainable breeding wading bird populations; a return to natural timing of nesting; and restoration of nesting in the coastal zone. The timing, location, size, and productivity of wading bird nesting will be monitored over the geographic range of the Everglades ecosystem. Monitoring methods will allow for comparison of historical and current information. The geographic regions monitored will include Florida Bay; mangrove estuaries and ecotone; freshwater marshes of ENP; WCAs 1, 2, and 3; Rotenberger and Holey Land; and BCNP. Nesting of six wading bird species will be monitored: wood stork, white ibis, roseate spoonbill, snowy egret, great egret, and great white heron. These are the species for which the best historical comparisons exist for one or more of the parameters of interest: range of trophic levels, prey sizes, and foraging techniques used (Ogden, 1994; Frederick et al., 1996). Nesting will be monitored between January and late June of each year, with the exception of Florida Bay (November through June). However, there is the possibility that monitoring in the mainland areas will need to be expanded if wood storks begin nesting earlier than January. Evidence of early nesting (eggs or young) is likely to be discovered on January surveys, and timing of surveys will be adjusted accordingly. The timing, location, and size of nesting events will be monitored using systematic aerial surveys followed by ground counts. Established techniques used in the freshwater marsh sections of the study area (Frederick et al., 2001) will be adapted to specific habitats in Big Cypress and the mainland mangrove estuary. Ground counts will focus on the largest colonies of each species based on the analysis of past years, which suggests that 90% of nesting birds are found on average in 3 to 33 colonies depending on the species (Frederick, personal communication). Accuracy in aerial counts of large colonies will be improved through the use of aerial photography followed by later counts of those photos (Frederick et al., in prep.). Florida Bay. Roseate spoonbill and ibis nests in Florida Bay are generally located in dense red mangrove stands and are not generally visible from outside the colony. All islands that were previously reported to have had nesting colonies (Lorenz et al., 2001) will be surveyed monthly during the nesting season, and the number of nests will be counted. While traversing Florida Bay by boat, locations of roseate spoonbill and white ibis activity will be investigated for new nesting sites. The timing of colony surveys late in the incubation period and during mild climatic conditions and the limitation of time in an individual colony to less than one hour whenever possible will minimize impacts of surveys on colonies (Lorenz et al., 2001). Roseate Spoonbill Foraging Location. In order to use nesting effort and nesting success as criteria for ecosystem evaluation, the location of primary foraging grounds must be monitored for each colony group (Lorenz et al., 2001). In order to identify the direction of foraging grounds from nesting colonies, flight line counts similar to those described by Dusi and Dusi (1978) will be made at the two largest colonies in each colony group. Flight line counts will yield an estimate of the proportion of birds using general areas (e.g., eastern, middle, or western mainland sites; mainline keys; etc.). To get more specific foraging locations, individual birds will be followed using a fixed-wing aircraft from their nesting colonies to the first foraging location. Flight line observation and following flights will also greatly aid in identifying new colony sights locations throughout the bay. Refinement of Nest Survey and Counting Methods. Any periodic surveys are likely to lead to underestimates due to asynchronous nesting and the possibility that nests may start and fail in between survey dates. Comparing typical monthly survey schedules with a large sample of known nesting histories of individual nests shows that the monthly survey schedule that has been followed in the central Everglades since 1986 has been associated with a known correction factor, with annual variation in that correction factor of 26% above and below any annual estimate (Frederick et al., in prep.) Therefore, the resulting nesting population estimates are likely to be associated with this level of error. However, estimation of this error rate is based on only 2 – 4 years of information on marked nests, depending on species. The database of individual nest histories will be expanded in order to refine the estimation of error associated with monthly surveys. This involves close monitoring of individual nests at one or more colonies throughout the nesting season in order to measure both duration and seasonal timing of nesting attempts.当前大沼泽地（Everglades）修复计划的核心预测为：恢复自然径流与水文格局，将催生规模庞大且可持续的涉禽（wading bird）繁殖种群；实现筑巢时间的自然回归；并恢复海岸带的筑巢活动。研究团队将在大沼泽地生态系统的全域范围内，监测涉禽筑巢的时间、位置、规模与繁殖成功率，所采用的监测方法可实现历史与当前数据的对比。本次监测覆盖的地理区域包括：佛罗里达湾（Florida Bay）；红树林河口与生态交错带；大沼泽地国家公园（ENP, Everglades National Park）的淡水沼泽；1、2、3号水控制区（WCAs 1,2,3, Water Conservation Areas）；罗滕伯格与霍利兰片区；以及比斯坎国家公园（BCNP, Biscayne National Park）。 本次监测将覆盖6种涉禽：白头鹮鹳（wood stork）、白鹮（white ibis）、玫瑰红琵鹭（roseate spoonbill）、雪鹭（snowy egret）、大白鹭（great egret）以及白颈大蓝鹭（great white heron）。上述物种均具备可供对比的优质历史数据，可用于分析其营养级范围、猎物尺寸与觅食策略等目标参数（Ogden, 1994; Frederick et al., 1996）。筑巢监测的常规时间为每年1月至6月下旬，佛罗里达湾除外，其监测周期为11月至6月。若白头鹮鹳开始在1月前筑巢，则需拓展大陆地区的监测范围。1月的调查中大概率会发现早期筑巢迹象（卵或幼雏），届时将相应调整调查时序。 将通过系统性航空调查（aerial survey）辅以地面计数（ground count）的方式，监测筑巢事件的时间、位置与规模。研究区域淡水沼泽片区已成熟的调查技术（Frederick et al., 2001），将适配到大柏树片区（Big Cypress）与大陆红树林河口的特定生境。地面计数将优先针对各物种的大型筑巢群——过往分析显示，平均而言，90%的涉禽个体集中在3至33个筑巢群中，具体数量因物种而异（Frederick, 私人通讯）。借助航空摄影后对影像开展人工计数的方式，可提升大型筑巢群航空计数的精度（Frederick et al., 待刊）。 佛罗里达湾。佛罗里达湾内的玫瑰红琵鹭与白鹮筑巢点通常位于茂密的红红树林群落中，从巢群外部无法直接观测。所有此前被记录存在筑巢群的岛屿（Lorenz et al., 2001）将在筑巢季每月开展调查，并统计筑巢数量。在乘船穿越佛罗里达湾时，将对发现的玫瑰红琵鹭与白鹮活动区域进行排查，以寻找新的筑巢点。在孵化后期与气候温和时段开展筑巢群调查，并尽可能将单群调查时长控制在1小时以内，可最大限度降低调查对筑巢群的干扰（Lorenz et al., 2001）。 玫瑰红琵鹭觅食地监测。为将筑巢强度与筑巢成功率作为生态系统评估的核心指标，需对每个筑巢群集群的主要觅食地位置开展监测（Lorenz et al., 2001）。为确定筑巢群的觅食方向，将在每个集群组的两个最大筑巢群中开展类似Dusi与Dusi（1978）所述的航线计数。航线计数可估算使用特定区域（如东、中、西大陆栖息地；主群岛链等）的鸟类占比。为获取更精准的觅食位置，将使用固定翼飞机追踪个体鸟类，从其筑巢群飞往首个觅食地的全过程。航线观察与追踪飞行同样有助于识别海湾内的新筑巢点。 筑巢调查与计数方法的优化。由于筑巢异步性以及两次调查期间可能出现筑巢启动后失败的情况，常规周期性调查大概率会低估种群数量。对比1986年以来大沼泽地中部沿用的月度调查方案与大量已知个体筑巢历史的样本数据显示，该月度调查方案存在已知的校正系数，且年度校正系数的波动幅度为年度估算值的±26%（Frederick et al., 待刊）。因此，最终得到的筑巢种群估算值将伴随该水平的误差。不过，该误差率的估算仅基于标记巢穴2至4年的观测数据，且因物种而异。研究团队将扩充个体筑巢历史数据库，以优化月度调查相关误差的估算精度。这需要在整个筑巢季对一个或多个筑巢群的个体巢穴进行密切监测，以测量筑巢尝试的持续时长与季节时间分布。