Blue tit colours
The blue tit (Parus caeruleus) has been classified as sexually monochromatic, which means that male and female are the same colour. This classification is based, though, on human colour perception, not on blue tit colour perception.
Like all birds, blue tits can see ultra-violet light and the front of their heads glow brightly under UV light. Researchers have found that it is the males who choose the females with the brightest heads; this is unusual because it is usually the females who do the choosing. Females with bright ultra-violet heads are more successful mothers; they rear more chicks to the point of fledging.
All gallery images taken by DKG in the reserve.
Most birds can’t create pigments other than melanin on their own. The reserve’s blue tits can’t produce the pigment carotene that makes their tummies yellow; it comes from pigments in the green caterpillars they eat. The more caterpillars a blue tit eats, and the brighter its tummy is, the more likely he or she is to attract a mate.