While the shimmering colors of the males enchant us in spring, they are much more challenging in fall. Indeed, at this time of year, some of the birds emerging from the boreal forest are yellowish or greenish in color, whether male or female, much to the dismay of many birders.
How can birds have all those colors?
First of all, bird color can be obtained in two ways, either by the presence (or sometimes absence) of pigments, or by the structure of the feathers, which may or may not become iridescent:
– Carotenoids: these pigments are obtained from the birds’ diet and can therefore fluctuate according to the amount of food ingested, the season and the age of the individuals, as in the Cedar Waxwing.
– Melanins: also known to improve feather strength, melanins are present in many handbirds. Melanin can also be associated with pigments, making the color darker or lighter.
– Porphyrins are pigments that are rarer than in some species, and will produce a fluorescent color when exposed to ultraviolet light.
– Iridescent feathers, like those of hummingbirds, are only visible when they face the sun, thanks to their unique structure.
– Non-iridescent feathers, on the other hand, reflect a specific color, such as blue in the Indigo Bunting.
Pictured, a Cape-May Warbler.
Tropical birds are more colorful?
First of all, most warblers winter in Central and South America, where we also find a large number of particularly colorful species. But did you know that tropical birds are more colorful? A recent study by Cooney et al. 2022* showed that tropical birds were on average 30% more colorful than northern hemisphere species. There are many reasons for this, including relatively constant food availability and conditions, as well as food that is often highly colored and therefore rich in pigment.
We generally enjoy observing colorful birds, most of which are males, rather than duller ones. For example, there are 5 times more photos of male Blackburnian Warblers than females on Macaulay Library.
*Cooney, C. R., He, Y., Varley, Z. K., Nouri, L. O., Moody, C. J., Jardine, M. D., … Thomas, G. H. (2022). Latitudinal gradients in avian colourfulness. Nature Ecology & Evolution, 6(5), 622-629. doi:10.1038/s41559-022-01714-1
Pictured, a Blackburnian Warbler.
Why all these colors?
Indeed, for birds, these colors have one or more roles.
– Thanks to the shimmering colors, a male will indirectly convey that he is able to feed well AND escape predators. These are necessary qualities for the female, if she wants her offspring to survive.
– On the other hand, dull colors or colors that enable birds to camouflage themselves in their environment will be particularly interesting if the evolutionary pressure is greater. For example, it’s hard to imagine a Snowy Owl being very successful if it’s bright yellow.
– Colors can also be used when encountering partners or competitors. Hummingbirds, for example, will orient their iridescent feathers towards other individuals under certain conditions.
– Finally, these colors can also be used to attract predators away from the nest or young. You may have already observed the Killdeer, which will pretend to be wounded and expose its colored tail.
Pictured, an Ovenbird.
How to tell them apart
It’s a tough question to answer in just a few sentences, but when trying to identify warblers by sight alone, it’s important to consider several factors.
– Phenology: Birds move at different times, and some species are earlier or later than others. For example, it’s very rare to see a Orange-crowned Warbler in southern Quebec in August, as it’s one of the last warblers to migrate.
– Abundance: If you see several individuals of a species that is generally uncommon or even rare, check that the autumn plumage does not resemble it. The Bay-breasted Warbler is common in Quebec during migration, compared to the Pine Warbler.
– Its contrasts: Without colors, the important thing is to look at finer criteria, but which can appear just as abundant. The Blackburnian Warbler has a brown cheek that stands out well, compared to the Blackpoll Warbler.
– Body parts: This may seem obvious, but paying attention to beak shape, leg color, presence of wing bars, eye circle, etc. can make all the difference.
From left to right, the Blackpoll Warbler (distinguishable by its orange legs), the Blackburnian Warbler (distinguishable by its contrasting brown cheek) and the Bay-breasted Warbler (distinguishable by its strong beak, black legs and, generally, the presence of the bay color on the flanks).
A few tools
It’s the best time of year to start identifying birds in their autumn plumage. Here are a few tools to follow up on the comments above:
– The Warblers Guide: THE most comprehensive guide to distinguishing North American warblers, both visually and aurally, with photos according to the bird’s age.
– The Sibley Guide: Thanks to David Sibley’s superb drawings, it can be easier to distinguish which criteria to look at compared with photos. With the mobile app, you can also compare morphologically similar species.
– The Macaulay Library: an impressive library of photos of birds from all angles at all times of the year, taken by amateur and professional ornithologists.
– Your nearest banding station: What could be better than visiting a banding station and discovering the intricacies of bird plumage in hand, rather than hidden behind a tree leaf?
Pictured, an Orange-crowned Warbler
