Molt and Plumage Lab

This week's lab in Ornithology examined plumage and molt patterns in birds. I took a ton of pictures and hope I can convey a few basic concepts.

Let's start by examining the four types of molt cycle. These aren't your "breeding/nonbreeding" or "summer/winter" plumages. It is more complex than that, but I'll try to keep it simple for both your and my own sake. It is easy to get confused.

First, the basics: molt is a replacement of feathers that produces a plumage. A bird changes plumages only through a molt (this will become important later). The vast majority of birds exhibit one yearly molt that is a complete replacement (body and flight feathers). This is called the prebasic molt and produces a basic plumage. Some birds undergo an additional molt per year (almost always only a partial molt) that is called a prealternate molt producing alternate plumage. These two cycles are the two most familiar molt strategies, called quite appropriate, simple basic and simple alternate strategies. Molts occur in cycles, defined by each year's prebasic molt. Basic strategies have one molt per cycle. Alternate strategies have the extra prealternate molt every cycle.

Got that? This is where it gets complicated. Some birds of both basic and alternate strategies add an extra molt during a bird's first cycle. The first cycle follows a bird's first prebasic molt: the molt from downy chick plumage to its first 'real' feathers. This plumage is termed both juvenile and, more appropriately and less confusingly, first basic plumage. If the bird molts again before its next prebasic molt (the molt that will produce second basic plumage), or in alternate strategies if the bird molts twice before the second prebasic molt, this is termed the preformative molt producing the formative plumage. This plumage only exists in the first cycle. The names for these modified strategies, because they add a level of complexity on to the two simple systems, are named: complex basic and complex alternate strategies.

Unless you have already mastered molt terminology (which I assure you not even the TA's in this class have yet, myself included), your head is probably spinning by now. Here are some figures from Howell et al. (2003) to help visualize these four strategies (click to view large):


Howell et al.'s figure demonstrates all of these concepts: the two strategy types of basic and alternate, the complexity of added formative plumages, and the alignment of molt cycles by the prebasic molt.

Now for some examples of the molt strategies outlined above. We'll start with simple basic. This strategy, despite being the simplest, is only used by a few groups of birds. These include pelagics (Procellariiformes) and hawks and falcons (Falconiformes) as well as a few other scattered groups. The example we pulled from the museum was Cooper's Hawk (Accipiter cooperii: Accipitridae):


The bird on the left is a fledgling. This bird is molting (the 1st prebasic molt) from its downy coat into 1st basic (juvenile) plumage. The center bird is an example of 1st basic plumage. Cooper's Hawks retain this "immature plumage" for the first cycle, before molting into "adult plumage" in the 2nd prebasic molt. This "adult plumage" on the right (I am using plumage in parentheses for everything but the specific plumages of molt systems to avoid confusion) is maintained for the rest of the birds life without variation. Each further cycle has one molt and one plumage. Once a bird has reached this adult stage where further cycles do not change in appearance, the molts are referred to as definitive. Thus, the right bird would be referred to as having a definitive basic plumage.

Now let's look at the simple alternate strategy. Recall that this strategy has an additional prealternate molt for each cycle. This molt is a partial replacement of feathers and is often the molt that produces "breeding plumage". Here are three examples:

Loons (Gavia: Gaviidae). The simple alternate strategy is displayed here. From left to right: 1st basic (juvenile), definitive alternate, definitive basic. A quick check of Sibley shows he illustrates both 'juvenile' and '1st summer' birds. These are not different plumages separated by a molt, these are one plumage, the 1st basic. The difference between the two is wear.


Another example of the simple alternate strategy are ducks such as these Blue-winged Teal (Anas discors: Anatidae). Both birds above are males. The bird on the left is the alternate plumage, the bird on the right is an eclipse (basic) male. The basic plumage in ducks is distinguished from regular basic by the name 'eclipse' because of its timing - this plumage and molt is for a short period during the summer when males become flightless (they molt all flight feathers simultaneously) and can use a more camouflaged plumage for hiding away.

Alright, that sums up the simple strategies. Let's get complex. Here is an example of complex basic strategy:

Good ol' Cedar Waxwings (Bombycilla cedrorum: Bombycillidae) demonstrate the extra Formative plumage inserted between 1st Basic and 2nd Basic. On the left is the 1st Basic plumage, recognized by the streaks. On the right is Definitive Basic, the adult plumage that is molted once a year. In the middle is Formative - much like Definitive, but duller and lacking any waxy wingtips. This plumage is referred to in Sibley as "1st Year".

How about complex alternate strategy? I give you two examples to ponder.

Scarlet Tanager (Piranga olivacea: Cardinalidae). This is the most complicated molt yet. From left to right we have: a bird in 1st Prebasic Molt, Formative, Definitive Alternate, Prebasic Molt, Definitive Basic (all male specimens), and a Definitive Alternate female. The extra Formative plumage inserted in the first cycle resembles female plumages and may well be indistinguishable (specimens are sexed by gonads when they are skinned). Note that the male formative differs from later male Definitive Basic plumages by the lack of black wings.


Laughing Gull (Larus atricilla: Laridae). We were actually able to piece together almost a full series from the CUMV collections. From left to right: downy chick, 1st Basic, Formative, 1st Alternate, Definitive Basic, Definitive Alternate. The only distinctive plumage missing is 2nd Basic (2nd Winter in Sibley). I believe 2nd Alternate and beyond are Definitive plumages.

WHEW! That about covers the 4 molt strategies. But I'm not done. There is more...

Did you know there are birds out there that show very distinct seasonal "plumages" that result not from molt, but from feather wear? This process of wear creates two distinct aspects of one plumage. Three examples follow:

European Starling (Sturnus vulgaris: Sturnidae). This species has a basic molt strategy. Above are three males showing the progression from "nonbreeding" to "breeding" plumage. The bird on the left is a fresh basic plumage bird. The second and third individuals show the progression of wear that occurs over the winter to get the distinct 'plumage' we see in the early spring. This occurs along with the bare parts getting brighter, especially the yellow bill, but that is not part of plumage. All of these birds are still the same plumage: basic. On to more interesting species...


Snow Bunting (Plectrophenax nivalis: Emberizidae (for now)). Above you can see the same progression of fresh, winter male on the left to "fresh" (but worn) breeding male on the right.


Bobolink (Dolichonyx oryzivorous: Icteridae): Same progression as the above two examples, except with one addition on the left: a bird in prebasic molt. Compare with the bird in the middle of wear between the two aspects, middle right.

There is just one final detail on molt for today. Take a look at these spread wings. Can you tell which feathers are old, which are fresh, and which direction molt is proceeding?


The first example above is Northern (Eastern (Yellow-shafted)) Flicker (Colaptes auratus: Picidae). The left wing is in molt, the right is not. The outer primaries are very worn: look how brown and washed out they are compared to the relatively fresh primaries on the right wing. This wing is a very good demonstration of primary molt: it is beginning at the primary/secondary divide and progressing outwards.

The second example is Pileated Woodpecker (Dryocopus pileatus: Picidae). While there is no comparison to judge feather wear, this wing also demonstrates the outward progression of primary molt. Secondaries progress inward from the same starting point.

The rest of the lab consisted of examples of a little bit of polymorphism and aberrant plumage, as well as a bunch of really interesting specialized plumage and feather structures. Now that all the intellectual heavy lifting is done, kick back and relax.

Polymorphism - Some birds, in particular herons (Ardeidae) and raptors (Accipitridae) display marked plumage polymorphism. These are color morphs where a plumage abnormality such as melanism (dark morph), leucism (white morph), or erythrism (red morph) birds become a significant percentage of the population rather than just individual aberrations. These are usually defined as polymorphic if the different morphs are largely sympatric, and not attributed to geography, gender, or age. A great example of this is the Eastern Screech-Owl (Megascops asio: Strigidae) with red and gray morphs coexisting broadly across their range. Mon@rch has a good post describing them, with more lifelike pictures than I present here:


Leucism - Leucism is defined as any reduction or incomplete lack of pigment. This includes aberrations know as 'piebald' or 'partial albino', which is a misnomer. Leucism is actually a different type of genetic mutation from albinism, and it is incorrect to refer to leucistic birds as partial albinos. Anyways, check out this really fascinating Blue Jay (Cyanocitta cristata: Corvidae) that I found in the collections. It is lacking the majority of pigment, but retains blue coloration in the flight feathers because this structural, not pigment-derived. The intensity of the blue depends on the angle viewed. View the feather from underneath and it is not visible at all.


Diet-induced erythrism - this is a fairly well known example in Cedar Waxwings (Bombycilla cedrorum: Bombycillidae). Pigments ingested from eating too much fruit from certain Honeysuckles causes red pigments to overlay the yellow tail tips, creating orange. This specimen displayed appears to have grown in a single new feather in a honeysuckle-free environment, providing a nice contrast between the normal yellow and the aberrant orange.


Unknown plumage aberration - I'm not sure what to call this one. While sorting through trays and trays of Scarlet Tanager (Piranga olivacea: Cardinalidae)...


I came across this individual:

It is a perfect example of the aberrant tanager depicted in the Sibley Guide: orange instead of scarlet, with an orange wing bar. Too cool! I do wonder if this is in fact the bird that Sibley illustrated.

Iridescence - this is just too cool! Here's a single hummingbird example, the Fiery Topaz (Topaza pyra: Trochilidae) bottom and top views.


Here's a bird that makes me think I'm birding the wrong hemisphere: African Emerald Cuckoo (Chrysococcyx cupreus: Cuculidae):


Mechanical sound production - This bird, the Club-winged Manakin (Machaeropterus deliciosus: Pipridae) has a crazy feather modification discovered by Cornell's own Kim Bostwick. One modified secondary forms a hollow resonating chamber with ridges. Another modified secondary is bent and serves as a pick. The bird beats its wings extremely rapidly (100x a sec) over its back, where the pick rubs back and forth over the ridges with each beat. The resulting sound is strange and highly unique in the bird world. It is quite similar to the sonation produced by crickets and other insects. The modified secondaries are barely visible in this round skin and we didn't have a flat wing available for display. See Kim's site for more information and video of this neat feather modification.


Elaborate ornamentation - Total free-for-all of wild and wacky bird ornamentation. I love sexual selection!

Crowned Pigeon (Goura: Columbidae)

Magnificent Bird-of-Paradise (Cicinnurus magnificus: Paradisaeidae)

Black Sicklebill (Epimachus fastuosus: Paradisaeidae)

Resplendent Quetzal (Pharomachrus mocinno: Trogonidae)

Black Crowned Crane (Balearica pavonina : Gruidae)

Sunbittern (Eurypyga helias: Eurypygidae): look at the amazing detail on each primary.

Check out amazing photos of the following two Cuckoos here.

Red-crested Malkoha (Phaenicophaeus superciliosus: Cuculidae)

Scale-feathered Malkoha (Phaenicophaeus cumingi: Cuculidae)

There aren't many birds in the world that exhibit the same wonderful powder-blue color as do Chlorophonias (Chlorophonia: Fringillidae). And that's on top of their already lovely green-and-yellow plumage:


I could fill pages and pages with examples such as these! But for now, this is all. Look for more in the future!

References:

Howell, Steve NG. 2003. Understanding Molt: Part I. Birding. Oct. 2003.

Howell, Steve NG. 2003. Understanding Molt: Part II. Birding. Dec. 2003.

Howell, Steve NG, Chris Corben, Peter Pyle, and Danny I Rogers. 2003. The first basic problem: a review of molt and plumage homologies. The Condor. 105:635-653.