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.

中文翻译：

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太咸了吗？生长期笑鸥雏鸟的饮食变化

在许多海鸟和水鸟物种中，盐度会给刚孵出的雏鸡带来生理压力，因为它们排泄盐分的能力有限。作为回应，父母可以在成长的第一阶段为雏鸟选择低盐食物。通过使用羽毛的稳定同位素分析，我们确定了笑鸥Leucophaeus atricilla雏鸟的饮食中与生长有关的变化。孵化的同位素测量反映了产卵前母亲的饮食习惯。同时，主要羽毛尖端指示在开始羽毛生长（一个星期大）期间的食物摄入量，主要羽毛基底指示在刚出雏之前的这段时间内父母提供的食物。δ ¹⁵ N和δ ¹³羽毛类型之间的C值表明雏鸟的饮食时空变化。幼雏比起初幼雏（约2％）消耗更多的陆地猎物（象甲虫Sphenophorus sp .；约51％）。但是，在产卵前出雏的雌性和雌性主要消耗海洋猎物（太平洋白对虾凡纳滨对虾和and鱼Anchoa sp。；> 90％）。基极和初级尖端部分具有相似的δ ¹⁵N值，但两个部分都没有孵化那么丰富。这种变化与饮食有关，因为与产卵前的雌性相比，雏鸟的consumption鱼消费比例较低（13.3-14.7％）。在产卵之前，年轻的雏鸡与雏鸟和雌性雏鸡的空间生态位不同，这表明在雏鸡生长期内饮食发生了变化。假设陆地或海洋觅食地区的食物供应在整个雏鸟的生长期（五周）内没有变化，我们的研究结果支持父母在生命的头几天对后代的食物资源选择性，以减轻生理压力由高盐负荷引起。