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Ovenbirds represent a clade of exclusively Neotropical birds that are exceptionally diverse, despite their rather dull, melanin-based plumage. In general, sexes are considered monomorphic in size and colour, but several authors have reported females of some species within this family as being slightly paler than their conspecific counterparts. Our aim was to assess levels of sexual dichromatism in a set of ovenbird species representing a diversity of genera and plumage patterns; Furnarius rufus, Phleocryptes melanops, Synallaxis spixi and Schoeniophylax phryganophilus. For each species, we quantified sexual differences in brightness and colouration among 8–10 different plumage regions through modelling avian perceptual colour-space distances. To best inform our visual modelling parameters, we successfully sequenced the SWS1 gene fragment (associated with short-wavelength, including ultraviolet, visual sensitivity in birds) for one species, P. melanops, and found it possessed an amino acid sequence consistent with the VS-type SWS1 visual system. This provides further evidence supporting the presence of VS-sensitive opsin in ovenbirds. Among all four species, females were consistently brighter than males in at least one plumage patch, but chromatic colour differences between sexes were significant only for the throat patches of Schoeniophylax phryganophilus. Overall, we interpret ovenbirds to exhibit very low levels of sexual dichromatism, manifest mainly by achromatic colour differences.

Visual sensitivity in ultraviolet (UV) light is widespread in the animal kingdom and occurs in all major taxonomic groups, including birds, which possess UV-sensitive photoreceptors and thus perceive UV light and use it in food selection, mate choice, offspring care and egg discrimination. However, no studies have been conducted to elucidate whether birds (aerial predators) could detect nests by UV light reflectance of eggs. In the present study, we performed artificial tree nest experiments in which pairs of pigeon eggs were treated with either a UV-blocker or a control substance before being exposed to nest predators in a tropical forest. The results showed that nest predation increased with duration of exposure, and that blocking UV reflectance of eggs could significantly reduce nest predation on tree nests. This provides experimental evidence for nest predation risk being linked to UV reflectance, and implies that aerial nest predators may detect nests by UV reflectance of eggs.

Tree cavities are usually superabundant, and offer the safest nest sites. However, not all bird species utilize them. One of the reasons could be insufficient illumination in such places. As no visual system can operate in complete darkness, some nest cavities may be too dark to be usable even by cavity nesters, and some species may not have sufficient visual sensitivity to make use of dark cavities. So, presumably, light conditions could constrain both the evolution of the cavity-nesting habit and the selection of the nest site by the cavity-nesting birds. However, due to a paucity of data on light conditions in cavities, these suggestions have not been investigated to date. To provide more information on illumination inside tree cavities, we took measurements inside the nest cavities of Collared Flycatchers Ficedula albicollis breeding in a primeval forest (Białowieża National Park, Poland). Illuminance inside cavities was recorded at daybreak, just after the parents commenced feeding nestlings. We found that only ca. 4 % of incoming light reached the nest level, and birds could adjust light conditions inside cavities by placing their nests closer to smaller entrances. Illuminance at nests (median = 0.05 lx) fell within the mesopic–scotopic range of vertebrate eyes. Measurements performed on a sunny, cloudless midday in a model cavity showed that illuminance strongly decreased with distance from the entrance. Our results indicate cavities are always dark places where colour vision is usually impaired or absent and the “lighting” requirements of cavity nesters can affect their use of tree cavities. We discuss the implications of the findings for understanding the adaptations of cavity nesting in birds.

A nationwide volunteer survey was conducted to investigate the time at which common species of birds arrived at garden feeders in the morning during winter, and over 5,800 participants submitted observations. We examined the relationship between species’ eye size and their time of arrival at feeders, in order to investigate whether the time at which foraging was initiated was constrained by visual capability. There was a negative correlation between eye size and time of arrival at garden feeders across species, and this relationship remained significant when body mass was taken into account. This suggests that the time at which garden birds begin to forage on winter mornings may be limited by their visual capability at low light intensities.