Nesting in large aggregations provides several important advantages for colonially breeding birds. However, it also imposes certain costs, associated with facilitated pathogen transmission and social stress. The cost-benefit ratio is not similar for all the birds in a colony and it might be mediated by nest density. To investigate the influence of nest density on cell-mediated immune function and on physiological condition of nestlings, we arranged a cross-fostering experiment in three breeding colonies of black-headed gulls Chroicocephalus ridibundus. First, we exchanged eggs between plots of high and low nest density. Afterwards, we performed phytohaemagglutinin (PHA) skin test and we measured blood haemoglobin concentration in nearly 350 nestlings from experimental (exchanged) and control (non-exchanged) groups. We found that PHA response was lowest in high nest density control group, indicating that depressed immune function of offspring, likely caused by social stress, can be considered as a cost of colonial breeding. Contrastingly, body condition of nestlings was the poorest in low density control group. Nestlings hatched and raised in high nest density plots did not have higher blood haemoglobin concentration in comparison to other study groups. Furthermore, they were affected with depressed cell mediated immune function, which is possibly driven by combined maternal (corticosteroid hormones deposited in yolk) and environmental (elevated social stress) effects. These results indicate that breeders from high nest densities do not benefit by rising offspring in better quality, in terms of immune function and body condition, although, in the light of previous studies, high nest densities are occupied by birds of higher individual quality, than low density areas. Our study provides a novel insight into the mechanisms of density-dependence that govern fitness of colonially nesting birds.

中文翻译：

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半早成群居鸟雏鸟免疫功能和生理状况的密度依赖性：交叉寄养实验


大型聚集地筑巢为群体繁殖的鸟类提供了几个重要的优势。然而，它也带来了一定的成本，与促进病原体传播和社会压力有关。对于一个群体中的所有鸟类来说，成本效益比并不相似，它可能是由巢穴密度调节的。为了探讨巢穴密度对细胞介导的免疫功能和雏鸟生理状况的影响，我们在三个黑头鸥Chroicocephalus rodibundus繁殖群中进行了交叉饲养实验。首先，我们在高巢密度和低巢密度的地块之间交换鸡蛋。随后，我们对实验组（交换组）和对照组（非交换组）的近 350 只雏鸟进行了植物血凝素 (PHA) 皮试，并测量了血液中的血红蛋白浓度。我们发现，高巢密度对照组的 PHA 反应最低，表明可能由社会压力引起的后代免疫功能下降，可以被视为群体繁殖的成本。相比之下，低密度对照组雏鸟的身体状况最差。与其他研究组相比，在高巢密度地块中孵化和饲养的雏鸟的血液血红蛋白浓度并不较高。此外，它们还受到细胞介导的免疫功能下降的影响，这可能是由母体（沉积在卵黄中的皮质类固醇激素）和环境（社会压力升高）共同影响所致。这些结果表明，在免疫功能和身体状况方面，高巢密度的饲养者并不能从质量更好的后代中受益，尽管根据之前的研究，高巢密度被个体质量更高的鸟类所占据。低密度区域。 我们的研究为控制群体筑巢鸟类健康的密度依赖性机制提供了新的见解。