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.
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. Note the iridescent, purple feathering
covering the entire body of the bird.
||An ASY (adult) male Purple
Martin from the back. Note the iridescent, purple feathering covering
the entire body of the bird.
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. Note 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.
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.
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.
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.
Learn more about how to identify the age and sex of
Purple Martins by their Crissum (undertail coverts)
Printed in Issue 11(4) of
the Purple Martin Update.
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