Departamento de Ecología Funcional y Evolutiva, Estación Experimental de Zonas Aridas, Almería, Spain.
PLoS One. 2010 May 6;5(5):e10509. doi: 10.1371/journal.pone.0010509.
Nestlings of altricial birds capture parents' attention through conspicuous visual displays, including exposure of their gape coloration which informs parents about their level of need, competitive ability or health; information that parents use for deciding food allocation among their offspring. Thus, because nestlings compete with nest mates for parental care, nestling conspicuousness is expected to increase with level of sibling competition along bird phylogeny.
METHODOLOGY/PRINCIPAL FINDINGS: We test this prediction by jointly using information of brood reduction, clutch size and duration of nestling period as proxies for intensity of sibling competition, and visual models that assess detectability of nestlings by adult birds. As predicted, we found a positive association between nestling conspicuousness and intensity of brood reduction, while clutch size and duration of nestling period did not enter in the best models. Level of brood reduction was positively related with the achromatic component of nestling conspicuousness and body mass was negatively related with the chromatic component.
These associations are in agreement with the hypothesis that sibling competition for parental attention has driven the evolution of visual nestling conspicuousness in a context of parent-offspring communication in altricial birds.
晚成性鸟类的雏鸟通过明显的视觉表现来吸引亲鸟的注意，包括展示张着的嘴巴颜色，这可以向亲鸟传达它们的需求程度、竞争能力或健康状况等信息；亲鸟可以据此决定如何在它们的后代中分配食物。因此，由于雏鸟之间会为了亲鸟的照顾而相互竞争，因此根据鸟类进化史，雏鸟的显眼程度应该会随着兄弟姐妹竞争的程度而增加。
方法/主要发现：我们通过共同使用巢减少、卵大小和雏鸟期持续时间作为兄弟姐妹竞争强度的代理指标，以及评估成年鸟类对雏鸟可见度的视觉模型，来检验这一预测。正如预测的那样，我们发现雏鸟的显眼程度与巢减少的强度之间存在正相关关系，而卵大小和雏鸟期持续时间则没有进入最佳模型。巢减少的程度与雏鸟显眼程度的非彩色成分呈正相关，而体重与颜色成分呈负相关。
这些关联与以下假设一致，即兄弟姐妹之间为了获得亲鸟的关注而竞争，这推动了晚成性鸟类在亲代-后代交流背景下视觉雏鸟显眼程度的进化。
