Wood Thrush Hylocichla mustelina occupancy patterns reveal sensitivity to low precipitation on nonbreeding grounds in northern Costa Rica.

Climatic change and anthropogenic disturbances are reshaping animal populations. Habitat loss and extreme climatic events are particularly strong drivers of declines in species that depend on forested areas. For migratory songbirds, climate and the persistence of suitable habitat over time are fundamental to sustaining populations annually. In Neotropical regions, habitat requirements during the nonbreeding season remain poorly understood for many migratory birds. In this study, we examined factors influencing occupancy of the Wood Thrush Hylocichla mustelina, a species that has experienced alarming population declines in recent decades. Specifically, we tested whether forest structure, precipitation, or both explained its occupancy within a large protected area in Costa Rica, the Área de Conservación Guanacaste (ACG). We deployed autonomous recording units in 71 stations within 12 sites for four consecutive days, to detect Wood Thrush vocalizations and estimate its occupancy. The sites spanned dry, wet, and cloud forest along elevational and precipitation gradients in ACG. Sampling occurred from 0500 to 0730 h during two nonbreeding seasons: December 2022–February 2023 and October–November 2023. At each station, we measured forest structure variables (canopy openness, leaf area index, basal area, understory cover, palm abundance) and obtained daily precipitation from meteorological stations. We modelled single season occupancy and found that Wood Thrush was positively associated with precipitation in both seasons, consistent with a preference for wetter conditions within a continuous forest landscape. During the season December–February, its occupancy increased at stations with high basal area in interaction with higher precipitation. The effect of precipitation on Wood Thrush occupancy may reflect greater prey availability in wetter habitats compared to drier locations. As climate change reduces moisture availability, its habitat suitability in nonbreeding grounds could decline. Our findings highlight the importance of wetter habitats within protected areas for Wood Thrush and other migratory and resident forest-dependent bird species on the nonbreeding grounds.气候变化与人为干扰正在重塑全球动物种群结构。依赖森林生境的物种，其种群衰退尤其受到栖息地丧失与极端气候事件的强烈驱动。对于迁徙鸣禽（migratory songbirds）而言，气候条件与适宜生境的长期存续是其年度种群维持的核心基础。在新热带区（Neotropical regions），多数迁徙鸟类的非繁殖季（nonbreeding season）生境需求仍未得到充分解析。 本研究以近几十年来种群数量出现令人担忧的急剧下降的棕林鸫（Wood Thrush，学名*Hylocichla mustelina*）为研究对象，探究影响其生境占用率的驱动因素。具体而言，我们在哥斯达黎加的瓜纳卡斯特保护区（Área de Conservación Guanacaste，ACG）这一大型保护地中，检验森林结构、降水或二者的共同作用能否解释该物种的生境占用格局。 我们在12个样点内的71个监测站连续4天部署自动录音设备（autonomous recording units），以记录棕林鸫的鸣叫声并估算其生境占用率。这些样点横跨瓜纳卡斯特保护区内沿海拔与降水梯度分布的旱林、湿林与云雾林。采样时段为两个非繁殖季的每日5:00至7:30，分别为2022年12月至2023年2月，以及2023年10月至11月。 在每个监测站，我们测定了多项森林结构变量：林冠开度、叶面积指数、胸高断面积、林下盖度与棕榈科植物丰度，并从区域气象站获取每日降水数据。 我们构建单季占用模型（single season occupancy model）开展分析，结果显示棕林鸫在两个非繁殖季均与降水呈显著正相关，这与其在连续森林景观中偏好较湿润生境的结论一致。在2022年12月至2023年2月的非繁殖季，当降水水平较高时，胸高断面积较高的监测站其棕林鸫生境占用率会显著提升。降水对棕林鸫生境占用的影响，可能源于较湿润生境相较于干旱生境具备更高的猎物可获得性。随着气候变化导致区域水分可获得性下降，该物种非繁殖地的生境适宜性或会随之降低。 本研究结果凸显了保护地内的湿润生境对于棕林鸫，以及其他依赖森林的迁徙与留居鸟类非繁殖季生存的关键意义。