In most bird species, even those whose adults are gaudy and colorful, the juveniles are inconspicuous and dull. That seems reasonable, for much bird coloration is sexually selected (males are colorful, females less so), and although being colorful might attract predators, it attracts even more females of your species. But chicks aren’t at the stage of choosing mates and so avoiding predators trumps sexual selection.
But there are a few exceptions, and two remarkable ones are described in a new paper in the Wilson Journal of Ornithology by Fernando Mendonça D’Horta et al. (full text behind paywall). These are two species of birds in the family Laniisominae that are found in Amazonia. In this case, the adults are far less conspicuous than the juveniles, which are bright orange-red with dappling and, in one case, long crests. The two species appear to be each other’s closest relatives (“sister species”), and so the bright juvenile coloration probably did not evolve independently in each.
Here’s the juvenile of one species, Laniocera hypopyrra. This single specimen was collected in 2002.
A remarkable feature of the crest is the feathers in which there are distal extensions, composed by up to six orange filaments 15 to 22 mm long, possessing white distal and proximal portions (Frontispiece, Fig. 1). The crest, including these filaments, reaches 40 to 48 mm. The same structure is exhibited by some of the dorsal feathers.
Here’s the second species, Laniisoma elegans, for which the authors collected the first juvenile known of the subspecies L. elegans elegans.
Apparently the dichromatism of adult and juveniles in L. elegans was known before, as it’s depicted in this plate from 1880.
Of course, one wonders immediately what the difference in color means, especially since it reverses the common pattern of cryptic chick/showy adult. Earlier workers had suggested that the chicks “had evolved to appear like moss covered by fruits,” but it doesn’t look that mossy and fruity to me.
The authors suggest instead that the chick is warningly colored (i.e., “aposematic”) because it is somehow toxic or distasteful to predators, or, alternatively, that the chick mimics some toxic and unpalatable species that predators have learned to avoid (i.e., the chick is a “Batesian mimic”). Of these two, the latter possibility seems more likely to me, for if the chick is distasteful and avoided by predators, why shouldn’t the adult also keep that pattern? Also, if the chick gets its distastefulness from its diet, well, the parents feed it, and could also have that diet. (Of course, the chick could endogenously manufacture a toxin, but why wouldn’t the adult do that, too, and keep the color?)
It is possible, of course, that the chick’s smaller size plays a role in its resemblance to some other toxic model. In truth, we simply have no idea what’s going on here.
Lest you think that birds can’t be toxic and aposematically colored, there’s at least one example, and it was discovered by Jack Dumbacher, a graduate student in our department. Jack found that the hooded pitohui of New Guinea (Pitohui dichrous), which is black and orange, has a neurotoxin in its skin and feathers. (Jack discovered this when his hands became numb and tingly when handling the bird.) The pitohui may acquire its toxin from eating beetles that contain the poison.
Here’s a hooded pitohui (photo from the NIF blog):
D’Horta, F. M., G. M. Kirwan, and D. Buzzetti. 2012. Gaudy juvenile plumages of Cinereous Mourner (Laniocera hypopyrra) and Brazilian Laniisoma (Laniisoma elegans). Wilson J. Ornithology 123:429-435. DOI: http://dx.doi.org/10.1676/11-213.1