Data from: Males in seemingly female-like plumage do not mimic females: UV reflectance reveals temporal cryptic dimorphism in a manakin species exhibiting delayed plumage maturation

Manakins (Pipridae) are neotropical birds that usually exhibit delayed plumage maturation (DPM). Thus, while plumage of most adult male manakins is brightly conspicuous, subadult males and females are basically dull-olive green. Although sexual dichromatism in some bird species may be evident only through UV reflectance, this phenomenon, known as hidden sexual dichromatism, has not been previously studied in manakins to compare subadult males and females. Within this framework, we carried out spectrophotometric analyses in searching for hidden sexual dichromatism in the white-bearded manakin Manacus manacus, through comparison of UV spectra in females and subadult males in green plumage. Our results revealed UV reflectance in both sexes in green plumage. Moreover, we found UV spectral differences in homologous color patches between sexes, particularly at belly. Since the observed differences may allow intraspecific sex recognition of individuals in green plumage, our results do not support the female-mimicry hypothesis to explain delayed plumage maturation in the white-bearded manakin. Although our findings dismiss the female mimicry hypothesis, we cannot state whether these results support the non-mutually exclusive cryptic and status signaling hypotheses. We propose then, that dull coloration of subadult males may serve both as a cryptic trait and to limit the energetic costs of acquiring the adult plumage before sexual maturity. Meanwhile, differential UV color traits between sexes in green plumage may allow adult males to avoid unnecessary energy expenditures in courtship displays in the presence of males near leks, and to selectively focus their the courtship displays on females. In accordance with the signaling status hypothesis, subadult males can be recognized both as males and subordinates and consequently may practice courtship displays without suffering aggressions by adult males. Our results highlight the importance to include a wider range of spectrophotometric information analyses for testing hypotheses regarding delayed plumage maturation.

侏儒鸟科（Pipridae）的侏儒鸟为新热带界鸟类，普遍表现出延迟换羽成熟（delayed plumage maturation, DPM）现象。多数成年雄鸟的羽色艳丽醒目，而亚成体雄鸟与雌鸟的羽色则基本呈暗橄榄绿色。尽管部分鸟类的羽色性二态性仅可通过紫外反射（UV reflectance）显现，这种被称为“隐蔽性羽色二态性”（hidden sexual dichromatism）的现象此前尚未在侏儒鸟类群中针对亚成体雄鸟与雌鸟开展对比研究。基于上述研究背景，我们以白须侏儒鸟（Manacus manacus）为研究对象，通过对比羽色呈橄榄绿色的雌鸟与亚成体雄鸟的紫外光谱，开展分光光度分析（spectrophotometric analyses）以探寻其隐蔽性羽色二态性。研究结果显示，两类个体的橄榄绿色羽衣均存在紫外反射现象；此外，我们还发现两性间同源色斑的紫外光谱存在差异，尤以腹部区域最为显著。鉴于上述差异可帮助橄榄绿色羽衣阶段的个体实现种内性别识别，本研究结果不支持以雌性拟态假说（female-mimicry hypothesis）解释白须侏儒鸟的延迟换羽成熟现象。尽管本研究结论否定了雌性拟态假说，但尚无法确定该结果是否支持非互斥的隐蔽假说（cryptic hypothesis）与地位信号假说（status signaling hypotheses）。据此我们提出，亚成体雄鸟的暗钝羽色可能兼具两项功能：一是作为隐蔽性特征，二是可降低性成熟前获取成年羽衣所需的能量成本。与此同时，两性间橄榄绿色羽衣的紫外色彩差异可帮助成年雄鸟规避在求偶场（lek）遇到其他雄鸟时开展不必要的求偶炫耀，并有针对性地将求偶炫耀指向雌鸟。根据地位信号假说，亚成体雄鸟可同时被识别为雄性与从属个体，因此它们在开展求偶炫耀时不会遭到成年雄鸟的攻击。本研究结果凸显了纳入更广泛的分光光度信息分析，以检验延迟换羽成熟相关假说的重要性。