Reprinted from: Purple Martin Update 8(1): 15-17
James R. Hill, III
Purple Martin Conservation Association
Each year the Purple Martin Conservation Association hears from bewildered martin landlords who wonder how their colony of "all females and no males" could lay eggs and raise young! Many landlords may find it difficult to sex and age their martins. The Purple Martin, like several other bird species, has "delayed plumage maturation," which means that all members of the population take more than one year to acquire their adult plumage. In martins, it takes two years for both sexes to acquire their adult plumages. Subadults are sexually mature, and typically breed. The landlord with all "females" actually had females and subadult males, which have a female-like plumage.
The subadult plumages of one-year-old male and female Purple Martins are distinct enough that they can be distinguished from each other, and also from the plumages of the adult males and females. Because of this, breeding martins have four, distinct, sex/age classes during the breeding season that an observant martin landlord can identify using plumage differences. These classes are: adult male, adult female, subadult male, and subadult female. (After nestling martins fledge and join the population, there is a fifth distinguishable sex/age class - the juveniles. Juveniles can not be sexed by plumage differences.)
Another system for describing the three age classes of martins is: HY = "hatching year" bird, which is a synonym for juvenile; SY = "second year" bird, a synonym for subadult; and ASY = "after second year" bird, a synonym for adult. Below is a description of these four breeding plumages, plus that of newly-fledged juveniles. The four sex/age classes of Purple Martins are pictured below.
Adult Male: The ASY (i.e., adult) male Purple Martin is entirely glossy purple-black (or steel-blue) and is the easiest of the five sex/age classes to distinguish. They are unmistakable in appearance and give the species its name. Male martins do not acquire this plumage until their 3rd calendar year of life. In other words, a male martin hatched in 1997 will not have the characteristic, all purple-black plumage until the summer of 1999, (e.g. 1997 = 1st calendar year; 1998 = 2nd calendar year; and 1999 = the 3rd calendar year). Male martins molt into this plumage during their second "wintering" stay in Brazil.
|An ASY (adult) male Purple Martin from the front. Not the iridescent, purple feathering covering the entire body of the bird.||An ASY (adult) male Purple Martin from the back. Not the iridescent, purple feathering covering the entire body of the bird.|
Subadult Male: The SY (i.e., subadult) male Purple Martin is often mistaken for a female by the novice landlord. Subadult males differ from females by some subtle plumage differences that can be difficult to see without a good pair of binoculars or spotting scope. First, subadult males have a sprinkling of at least one, but usually many, solid-purple feathers in one or all of the following areas: their chins, throats, breasts, flanks, bellies, or undertail coverts (crissum). The number of these purple feathers is highly variable. Some individuals may only have one purple feather in just one area. Others have so many that they are half-purple on front. The subadult male pictured in Fig. 3 is a particularly dark individual. Many are far more subtly marked. Female martins never have any purple feathering in these areas. Subadult males also have stronger and more extensive purple on their crowns and cheeks than females do. In addition, subadult males have a scattering of isolated purple feathering on their napes (hind neck), backs, and rumps.
|An SY (subadult) male Purple Martin from the front. Not the purple feathers on the chin, throat, breast, flanks, belly, and crissum.||An SY (subadult) male Purple Martin from the front. Note the patchy purple feathers on the crown, cheek, nape, shoulders, back, and rump.|
Subadult Female: In spring and early summer, SY (i.e., subadult) females are easy to distinguish from adult females because of the weak purple to brownish color of their upper surface (i.e., back side) plumage as compared to the much brighter purple of the adult females (see Figs. 6 and 8). As the season advances and the feathers of adult females become worn and sun bleached, it can be more difficult to distinguish these female age classes using back color alone. An alternative method, is to compare the colors of the undertail coverts (compare Figs. 5 and 7). The undertail coverts of adult females are usually quite dusky all over the individual feather vanes. The undertail coverts of subadult females are usually pure white or faintly dusky, with only the central quill a darker color. One caution, there is a lot of variation in crissum color and this field mark should be used in conjunction with back color. And finally, subadult females are also usually slightly lighter on their breasts and bellies than are adult females, which tend to be duskier in these areas.
|An SY (subadult), female Purple Martin. Note how light the crissum (the undertail coverts) is below the perch wire.||An SY (subadult), female Purple Martin. Note how little purple is in the crown and "shoulders," and how brown the back and rump are.|
Adult Female: ASY (i.e., adult) females are far more purple on their crown, nape, "shoulders," back, and rump than are SY females, which tend to be far browner in these areas (see Figs. 6 and 8). In addition, ASY females tend to have slightly (to greatly) darker breasts, bellies, and undertail coverts (i.e., crissums) than do SY females (see Figs. 5 and 7).
|An ASY (adult), female Purple Martin. Note how dark the crissum (the undertail coverts) is below the perch rod.||An ASY (adult), female Purple Martin. Note how much purple feathering there is on the crown, "shoulders," back, and rump.|
Juvenile: The HY (i.e., juvenal) plumage of martins [not shown here] resembles that of the subadult female, but generally has a more washed-out, brownish to watery, blue-green back color than the more strongly-colored, older subadults, plus they have a cleaner, newer-plumaged look to them. The tails of juveniles are shorter and less forked than older birds.
In addition to plumage differences, martins can also be sexed by their sex-specific behaviors. One of the easiest ways to tell all breeding-age males (both adult and subadult) from females, is by their song. Only male martins sing the extremely common song that ends with a rapidly clicking, "krieeek" sound, which they deliver with a conspicuous, thrown-open beak. Another common behavioral difference is that males commonly follow behind their mate as she flies to the ground for nest material, to the eggshell tray for calcium, or to trees for green leaf plucking. This is actually a form of "mate-guarding" and serves to assure that only he fertilizes his mate's eggs. And finally, males frequently chase and pounce on females to copulate with them.
How to Get a Good Look at Your Martins
You can "tame" your martins into allowing closer human approach by regularly spending time standing, sitting, or working about 15 or 20 feet from your housing. The birds will soon accept your presence and eventually will ignore your daily approaches. Then you can use your binoculars or spotting scope to get exceptionally close looks. Once you study the plumages and behaviors of martins close up, you'll find it much easier to distinguish among their various sex/age classes.
Copyright 1998 by Purple Martin Conservation Association. All Rights Reserved.
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