Data from: Too salty for you? Changes of diet in the laughing gull nestlings during the growing period

In many seabird and waterbird species, salinity can impose physiological stress on recently hatched chicks because they have a limited capacity to excrete salt loads. In response, parents can select low-salt food for their nestlings in the first stage of their growth. We determined the growth-related variation in the diet of laughing gull Leucophaeus atricilla nestlings by using stable isotope analysis of feathers. Isotopic measurement of hatchling down reflects the mother's diet before laying eggs. At the same time, the primary feather tip indicates the food intake during the initiation of feather growth (one week of age), and the primary feather base indicates the food provided by parents during the period immediately before fledging. δ15N and δ13C values among the feather types showed a spatiotemporal shift in the nestlings’ diet. Younger chicks consumed more terrestrial prey sources (weevil beetles Sphenophorus sp.; ~51%) than chicks at fledging (~2%). However, fledging chicks and females before egg-laying consumed mostly marine prey sources (Pacific white shrimp Litopenaeus vannamei and anchovy Anchoa sp.; > 90%). The base and primary tip portions had similar δ15N values, but both sections were less enriched than the hatchling down. This change was diet-related, as the nestlings showed a lower percentage of anchovy consumption (13.3 – 14.7%) compared to females before egg-laying (30.4%). Younger chicks had a different spatial niche than fledglings and females before egg-laying, indicating a diet shift through the chick growth period. Assuming that the availability of food in the terrestrial or marine foraging areas did not vary through the nestlings’ growth period (five weeks), our findings support food resource selectivity by parents for their offspring during the first days of life, to reduce the physiological stress caused by high salt loads.

在众多海鸟和水鸟（seabird and waterbird）类群中，盐度会对刚破壳的雏鸟引发生理应激，因其排泄盐分负荷的能力有限。为应对这一问题，亲鸟可在雏鸟生长初期为其投喂低盐食物。本研究通过对羽毛开展稳定同位素分析（stable isotope analysis），探究了笑鸥（Laughing Gull, Leucophaeus atricilla）雏鸟的食谱随生长的变化规律。雏鸟绒羽（hatchling down）的同位素检测结果可反映雌鸟产卵前的食谱；与此同时，初级飞羽尖端（primary feather tip）对应雏鸟羽毛生长启动阶段（约1周龄）的食物摄入情况，而初级飞羽基部（primary feather base）则代表离巢前亲鸟投喂的食物类型。不同羽毛部位的δ¹⁵N与δ¹³C比值显示，雏鸟的食谱存在时空偏移（spatiotemporal shift）。相较于离巢阶段的雏鸟（占比约2%），日龄更小的雏鸟会摄入更多陆生猎物——主要为象鼻虫属（Sphenophorus sp.）象鼻虫，占比约51%。但离巢雏鸟与产卵前雌鸟的食谱则以海洋猎物为主，包括凡纳滨对虾（Pacific white shrimp, Litopenaeus vannamei）与鳀属（Anchoa sp.）鳀鱼，占比均超过90%。初级飞羽基部与尖端的δ¹⁵N比值相近，但二者的同位素富集程度均低于雏鸟绒羽。这一变化与食谱结构相关：相较于产卵前雌鸟（鳀鱼摄入占比30.4%），雏鸟的鳀鱼摄入占比更低（13.3%~14.7%）。日龄更小的雏鸟拥有与离巢雏鸟及产卵前雌鸟不同的空间生态位（spatial niche），表明雏鸟生长期间食谱会发生转变。假设在雏鸟5周的生长周期内，陆生或海洋觅食区的食物可获得性未发生变化，那么本研究结果支持：亲鸟会在雏鸟生命最初几日选择性投喂食物，以降低高盐负荷引发的生理应激。