Revealing the colourful side of birds: spatial distribution of conspicuous plumage colours on the body of Australian birds

In many species of birds, different body parts often display very
different colours. This spatial distribution of coloured plumage patches
may be determined, among other factors, by the balance between being
cryptic to predators, and conspicuous to intended receivers. If this is
the case, ventral and anterior body parts in birds –which are less visible
to predators but more prominent to conspecifics– should present more
conspicuous and sexually dichromatic plumage colours. Here I test these
predictions using reflectance spectrometric measurements of standardised
plumage patches across males and females for nearly an entire avifauna
(Australian landbirds, N = 538 species). My data show that, as predicted,
conspicuous and sexually dichromatic colours are mainly located near the
head, while the plumage of the back is the most cryptic. One clear
exception to this pattern is the conspicuous rump coloration. In many
species, this patch can be concealed by wings, and therefore exposed only
when necessary. In addition, conspicuous rump coloration could deflect or
confuse predators in case of attack. However, there is considerable
variation across species, and this makes position on the body a very poor
predictor of plumage elaboration (R2 < 0.02). Future studies should
try to determine whether differences between species in the distribution
of colours across the plumage are due to variation in ecological factors
(predation risk, habitat, etc.).