Day and night use of habitats by northern pintails during winter in a primary rice-growing region of Iberia

Loss of natural wetlands is a global phenomenon that has severe consequences for waterbird populations and their associated ecosystem services. Although agroecosystems can reduce the impact of natural habitat loss, drivers of use of such artificial habitats by waterbirds remain poorly understood. Using the cosmopolitan northern pintail Anas acuta as a model species, we monitored home-range and fine-scale resource selection across the agricultural landscape. Individuals were tracked using GPS-GSM transmitters, and a suite of environmental and landscape features were measured throughout the winter seasons. Spatial patterns of habitat use were analysed using generalized linear mixed effect models by integrating field-observations with GPS telemetry. All birds used rice fields as foraging grounds at night and commuted to an adjacent reservoir to roost during daylight. Home-ranges and maximum foraging distances of nocturnally foraging birds increased with decreasing availability of flooded fields, and were positively correlated with moonlight levels. Birds selected flooded rice paddies (water depth range: 9–21 cm) with standing stubble and substrate with pebbles smaller than 0.5 cm in diameter. Density of rice seeds, rice paddy size, and other environmental and landscape features did not emerge as significant predictors. Our findings indicate that nocturnal foraging of northern pintails within rice fields is driven primarily by straw manipulation, water level and substrate pebble size. Thus, the presence of standing stubble in flooded paddies with soft bottoms should be prioritized to improve foraging areas for dabbling ducks. These management procedures in themselves would not increase economic costs or affect rice production and could be applied for dabbling-duck conservation throughout the world.

天然湿地丧失是全球性现象，对水鸟种群及其相关的生态系统服务造成严重影响。尽管农业生态系统（agroecosystems）能够缓解自然栖息地丧失带来的负面影响，但水鸟利用这类人工栖息地的驱动机制仍不甚明晰。本研究以广布性物种针尾鸭（Anas acuta）为模式物种，对农业景观内的家域范围与精细尺度资源选择展开监测。研究对象通过GPS-GSM发射器完成追踪，并于整个冬季期间测定了一系列环境与景观特征。通过整合野外观测数据与GPS遥测数据，采用广义线性混合模型（generalized linear mixed effect models）分析了栖息地利用的空间格局。所有个体均夜间以稻田作为觅食地，日间往返至邻近水库栖息。夜行觅食个体的家域范围与最大觅食距离随淹水稻田可用性降低而扩大，且与月光强度呈正相关。针尾鸭偏好选择水深9～21厘米、留存直立残茬且基质内砾石直径小于0.5厘米的淹水稻田。稻米种子密度、稻田面积及其他环境与景观特征未成为显著的预测因子。本研究结果表明，针尾鸭在稻田内的夜行觅食行为主要受秸秆留存状况、水位及基质砾石尺寸驱动。因此，为改善凫类（dabbling ducks）的觅食栖息地，应优先保留底部松软的淹水稻田中的直立残茬。此类管理措施本身不会增加经济成本，也不会影响水稻生产，可在全球范围内应用于凫类的保护工作。