Data from: Agricultural pastures challenge the attractiveness of natural saltmarsh for a migratory goose

1. Broad-scale land conversions and fertilizer use have dramatically altered the available staging area for herbivorous long-distance migrants. Instead of natural land, these birds rely increasingly on pastures for migratory fuelling and stopover, often conflicting with farming practices. To be able to predict and manage birds’ future habitat use, the relative advantages and disadvantages of natural (e.g. saltmarsh, intertidal) versus anthropogenic staging sites for foraging need to be understood. 2. We compared the migratory staging of brent geese on saltmarsh and pasture sites in spring. Food quality (nitrogen and fibre content), intra-specific antagonistic behaviour, and body weight were quantified at nearby sites in simultaneous seasons. Individuals were tracked with high-resolution GPS and accelerometers to compare timing of migration and time-budgets during fuelling. 3. On pastures, birds rested more and experienced higher ingestion rates, similar or superior food quality and reduced antagonistic interactions than on saltmarsh. 4. Brent geese using fertilized grasslands advanced their fuelling and migration schedules compared to those using saltmarsh. Pasture birds reached heavy weights earlier, departed sooner, and arrived in the Arctic earlier. 5. Intertidal mudflats were frequently visited by saltmarsh birds during the day, and available food there (algae, some seagrass) was of higher quality than terrestrial resources. Availability of intertidal resources was an important factor balancing the otherwise more favourable conditions on pastures relative to saltmarsh. 6. Policy implications: Disadvantages of longer foraging effort, more antagonistic interactions and delayed fuelling schedules on traditional saltmarshes may cause a trend of geese exchanging this traditional niche in favour of pastures, especially in a warming climate that requires advancement of migratory schedules. However, the high quality of intertidal forage allows it to complement terrestrial foraging, potentially removing the incentive for habitat switches to pastures. The relatively high quality of green algae and seagrass, and birds’ remarkable preference for these resources when available, provides a key for managers to create landscapes that can sustain this specialist’s intertidal lifestyle. To keep natural habitats attractive to staging geese with the purpose to prevent conflicts with farming practices, management actions should focus on conservation and restoration of saltmarsh and especially intertidal habitat.

1. 大范围土地转化与化肥使用已极大改变了植食性长距离迁徙鸟类的可用中途停歇地（staging area）。相较于自然生境，这些鸟类愈发依赖牧场开展迁徙补给（migratory fuelling）与中途停留（stopover），这常与农业生产活动产生冲突。为预测并管控鸟类未来的栖息地利用方式，我们需要明确自然生境（例如盐沼（saltmarsh）、潮间带（intertidal））与人为干预中途停歇地在觅食方面的相对优劣。
2. 本研究对比了春季布伦特黑雁（brent geese）在盐沼与牧场的迁徙停歇情况。在同期同区域的站点中，我们量化了食物质量（氮与纤维含量）、种内拮抗行为（intra-specific antagonistic behaviour）以及个体体重。同时通过高分辨率GPS与加速度计（accelerometers）对个体进行追踪，以比较迁徙时机与补给阶段的时间预算（time-budgets）。
3. 相较于盐沼生境，牧场中的鸟类休息时长更长，摄食速率更高，食物质量与之相当甚至更优，且种内争斗更少。
4. 相较于依赖盐沼的个体，使用施肥草地的布伦特黑雁的补给与迁徙日程均有所提前。牧场栖息的个体更早达到适宜迁徙的体重，出发时间更早，并更早抵达北极繁殖地。
5. 盐沼栖息的鸟类日间会频繁造访潮间带泥滩（intertidal mudflats），该处的可利用食物（藻类、部分海草（seagrass））质量高于陆地资源。潮间带资源的可获得性是平衡牧场相较于盐沼更优条件的重要因素。
6. 政策启示（policy implications）：传统盐沼生境中更长的觅食投入、更多的种内冲突以及延后的补给日程，可能促使黑雁放弃传统生态位转而选择牧场，在气候变暖要求迁徙日程提前的背景下这一趋势尤为明显。然而，潮间带觅食资源的高品质使其可与陆地觅食生境形成互补，或可消除鸟类向牧场转移栖息地的动机。绿藻与海草的相对高品质，以及鸟类在资源可获得时对这类生境的显著偏好，为管理者打造可维持该特化物种潮间带生活方式的景观提供了关键思路。为使自然生境对停歇黑雁仍具吸引力，以避免与农业生产产生冲突，管理措施应聚焦于盐沼尤其是潮间带生境的保护与修复。