Data from: Top-down effects of repatriating bald eagles hinder jointly recovering competitors

1. The recovery of piscivorous birds around the world is touted as one of
the great conservation successes of the 21st century, but for some
species, this success was short-lived. Bald eagles, ospreys, and great
blue herons began repatriating Voyageurs National Park, USA, in the
mid-20th century. However, after 1990, only eagles continued their
recovery, while osprey and heron recovery failed for unknown reasons. 2.
We aimed to evaluate whether top-down effects of bald eagles, and
bottom-up effects of inclement weather, habitat quality, and fish
resources contributed to the failed recovery of ospreys and herons in a
protected area. 3. We quantified the relative influence of top-down and
bottom-up factors on nest colonization, persistence (i.e., nest reuse) and
success for ospreys, and occurrence and size of heronries using 26 years
(1986-2012) of spatially-explicit monitoring data coupled with
multi-response hierarchical models and Bayesian variable selection
approaches. 4. Bald eagles were previously shown to recover faster due to
intensive nest protection and management. Increased numbers of eagles were
associated with a reduction in the numbers of osprey nests, their nesting
success, and heronry size; while higher local densities of nesting eagles
deterred heronries nearby. We found little evidence of bottom-up
limitations on the failed recovery of herons and ospreys. 5. We present a
conservation conundrum: bald eagles are top predators and a flagship
species of conservation that have benefited from intensive protection, but
this likely hindered the recovery of ospreys and herons. Returning top
predators, or rewilding, is widely promoted as a conservation strategy for
top-down ecosystem recovery, but managing top predators in isolation of
jointly recovering species can halt or reverse ecosystem recovery.
Previous studies warn of the potential consequences of ignoring biotic
interactions amongst recovering species, but we go further by quantifying
how these interactions contributed to failed recoveries via impacts on the
nesting demography of jointly recovering species. Multi-species management
is paramount to realizing the ecosystem benefits of top predator recovery.

1. 全球食鱼鸟类（piscivorous birds）的恢复被赞誉为21世纪最伟大的保护成功案例之一，但对部分物种而言，这一成功却转瞬即逝。白头海雕（Bald eagles）、鹗（ospreys）与大蓝鹭（great blue herons）于20世纪中期开始重返美国Voyageurs国家公园。然而，1990年后，仅白头海雕持续恢复，而鹗与大蓝鹭的恢复因未知原因失败。
2. 我们旨在评估白头海雕的自上而下效应（top-down effects），以及恶劣天气、栖息地质量、鱼类资源等自下而上效应（bottom-up effects），是否导致了保护区内鹗与大蓝鹭的恢复失败。
3. 我们利用1986-2012年共26年的空间显式监测数据（spatially-explicit monitoring data），结合多响应分层模型（multi-response hierarchical models）与贝叶斯变量选择方法（Bayesian variable selection approaches），量化了自上而下与自下而上因素对鹗的巢定植（nest colonization）、持续性（即巢复用，nest reuse）及筑巢成功率（nesting success），以及对鹭巢群（heronries）的出现与规模的相对影响。
4. 此前研究表明，白头海雕因强化巢保护与管理而恢复更快。其数量增加与鹗巢数量减少、筑巢成功率下降及鹭巢群规模缩小相关；且局部筑巢白头海雕密度较高时，会驱离附近的鹭巢群。我们未发现自下而上因素限制鹗与大蓝鹭恢复失败的显著证据。
5. 我们提出一个保护困境：白头海雕作为顶级捕食者与保护旗舰物种，受益于强化保护，但这可能阻碍了鹗与大蓝鹭的恢复。引入顶级捕食者（或称再野化，rewilding）被广泛推崇为促进生态系统自上而下恢复的保护策略，但孤立管理顶级捕食者而忽视协同恢复物种，会停滞或逆转生态系统恢复。此前研究已警示忽视恢复物种间生物相互作用（biotic interactions）的潜在后果，而我们进一步量化了这些相互作用如何通过影响协同恢复物种的筑巢种群动态（nesting demography），导致恢复失败。多物种管理（multi-species management）对实现顶级捕食者恢复的生态系统效益至关重要。