Yes, if birds see at wavelengths between 300-400nm (ultraviolet range), it generally means that the objects they see reflect or emit light within that specific wavelength range. The ability of birds to perceive ultraviolet light is due to the presence of specialized photoreceptor cells in their eyes called "UV cones." These cones are sensitive to ultraviolet wavelengths and enable birds to see a broader spectrum of light than humans, whose vision is limited to the visible spectrum of wavelengths (approximately 400-700nm).
In the case of objects that appear differently in the ultraviolet range to birds, it means that these objects reflect or emit ultraviolet light, which can be perceived by birds but not by humans. Certain flowers, feathers, and patterns on the plumage of birds are known to have ultraviolet reflectance or fluorescence, which aids in their communication, mate selection, or foraging. The ultraviolet reflection or emission from these objects provides additional visual information to birds that is not available to humans.