Harrier Moltsand PlumagesI welcome any article on molt, aging,and sexing in Birding, I second the cau-tion advised by Jerry Liguori and BrianSullivan in aging male Northern Harri-ers (May/June Birding, pp. 30–35), and Iappreciate the emphasis in this articleon more study based on banded,known-age birds. I’d like to remindbirders that there is a technical literaturedescribing molts and plumages thatusually extends well beyond that illus-trated in field guides.For example, I showed in a pair of

2005 papers that male Northern Harrierscan replace up to 50% of the body feath-ers of the upper parts with grayish feath-ers during the preformative (i.e., postju-

venile) molt (Journal of Raptor Research39:378–385) and that 15% of NorthernHarriers can retain 1–6 secondaries dur-ing their second and later prebasic molts,but that few if any birds retain primaries(Condor 107:823–834). Moreover, in a2006 paper, I showed how the replace-ment sequence of the secondaries in mostlarge birds proceeds distally from s1 ands5 and proximally from the tertials, suchthat a species like the Northern Harrier,with 14–15 secondaries, retains feathersamong s3–s4 and s7–s10 in its second,and often later, prebasic molts (WesternBirds 37:179–185).Further research, based on known

second-cycle and older birds with re-tained feathers representing more than100 specimens of Northern Harriers

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“ I welcome any

article on molt,

aging, and sexing

in Birding.”—Peter Pyle

Discuss the letter writers’ opinions online: aba.org/birding

Birding 13-4_03Letters_Layout 1 8/19/13 2:27 AM Page 10

(summarized in my Identification Guideto North American Birds—Part II, pp.411–414), has led me to conclude thatsecond-cycle (“second-year” in the Bird-ing article) males have a distinctplumage that is reliably distinguishedfrom older (“after second-year” in theBirding article) males in most cases, thatolder males with brown in the plumagemight be third-cycle individuals, andthat paler gray males might be olderthan third or fourth cycle. I also point-ed out (Identification Guide, p. 29) thatolder adult females of most if not all sex-ually dichromatic bird taxa can showmale-like plumage characters, as relatedto hormonal senescence; see also IanOwen and Roger Short’s 1995 paper(Trends in Ecology and Evolution, 10:44–47) and references therein.I see little in Liguori and Sullivan’s ar-

ticle to challenge the technical literatureon plumages in male Northern Harriers,and a misinterpretation of molts andplumages in several of the illustratedbirds weakens my confidence in the ar-ticle’s primary new suggestion, namely,that a substantial proportion of three-year-old and older males may show sig-nificant brown in the plumage.The “classic adult” opposite the title

page has retained s7 on the right wing.It’s hard to say for certain, but this couldbe a juvenal feather, which would indi-cate a second-cycle bird showing moredefinitive-like characters.The four-year-old or older individual

in Fig. 4 with a brown wash to theplumage could be an anomalous male orperhaps an older female (see above), asalso suggested by its broader wings andbulky appearance; females are largerthan males in most hawks.The bird in Fig. 5 may well be a sec-

ond-cycle individual, but I see no re-tained feathers as reported. Rather, dif-ferences in wear among primaries andsecondaries appear to have resulted

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from protracted and/or suspendedmolts; see Joseph Schmutz and SheilaSchmutz’s 1975 Auk paper (92:105–110) and my 2005 Condor paper(107:823–834). Furthermore, the verypale inner primaries and contempora-neously molted secondaries (s1–s2 ands5–s7) make me wonder if this is anolder individual.The three September birds shown in

Figs. 6 and 7 are either still molting ormay have suspended molt for migra-tion, rather than showing retainedfeathers from an arrested molt. As Inoted above, few if any Northern Har-riers retain primaries during incom-plete molts.I accept that it is possible that adult

males show some sort of polymor-phism as older birds. However, I can’tthink of another example amongspecies with delayed plumage matura-tion (gulls, albatrosses, boobies, etc.)in which plumage does not progressthrough early cycles toward a univer-sally definitive plumage state, let aloneshowing sexual dimorphism as well.I do applaud the authors for focusing

on the possibility of retained under-wing coverts and how these might as-sist with reliable age determinations.Because these coverts cannot be viewedon most (round-skin) specimens, weknow very little about variation in theirmolt and coloration. Most blackbirds ofseveral species, despite undergoing oth-erwise complete preformative molts, re-tain a few under-wing coverts—a pat-tern serendipitously discovered byBrooks Meanley in 1966 while examin-ing recently killed blackbirds duringcontrol efforts. This discovery hasproven very reliable in aging thesespecies in the hand. Flamingos can alsoretain under-wing coverts but no otherfeathers during the second and laterprebasic molts, a pattern discoveredonly because color patterns in juvenile

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under-wing coverts are burnt orangewith black tips, very different from thepink coverts of adults. I have been en-couraging bird banders to examine andphotograph the under-wing coverts inother birds reported to have completepreformative molts, among themBushtits, Northern Cardinals, certainsparrows, and meadowlarks, thus farwithout further discovery.

As highlighted by Liguori and Sulli-van, crisp digital imagery may prove avery useful tool for better understand-ing molt and color of under-wingcoverts, not just in Northern Harriersand other raptors, but potentially inpasserines and other birds as well.

—Peter PyleBOLINAS, CALIFORNIA

RESPONSE:We appreciate that Peter Pyle took thetime to read our article, and we’re hap-py to respond to his concerns. Unfortu-nately, Pyle’s comments are speculative,circular, contradictory, or demonstrablyincorrect. Pyle starts out by noting thatseveral of his papers were not cited inour Birding article. While we value hisresearch, the papers cited by Pyle ex-plore general molt sequences of raptors,the findings of which are not disputedin our Birding article. Our main point

was to show the plumage overlap be-tween second-year male vs. older maleNorthern Harriers.

Pyle summarizes his research sug-gesting that second-year males arebrownish above and washed rufous be-low, and that progressively older birdsbecome grayer above and whiter below.We provide examples of gray second-year birds aged definitively by their re-tained juvenile feathers. We know of noreliable way to age third-year or fourth-year male harriers. Male harriers withtwo generations of adult feathers (fron-tispiece and Fig. 7) can only be aged as“after-second-year.”

Pyle indicates that we misinterpretedmolts and plumages in several birds, butwe show below that his interpretationsare incorrect. We also demonstrate the va-lidity of the analysis laid out in our article.

Pyle wonders if the bird in the fron-tispiece could be a second-year individ-ual, but s7 (the 7th secondary) is a re-tained, faded, adult feather showing thesame pattern and the same gray on theinner web as shown by the secondariesadjacent to it, making this bird an after-second-year male. We wish this were asecond-year, as it would provide excel-lent documentation of a grayer variant.

Pyle suggests the bird in Fig. 3 couldbe an older female showing male char-

acters, yet, as stated in the caption, thisis a breeding adult male observed dur-ing the course of several years. There isno evidence that female Northern Harri-ers can show male traits. Adult femaleharriers can show a grayish-brown castto the upper side of the remiges (i.e., theprimaries and secondaries); see p. 35 inLiguori’s Hawks From Every Angle(Princeton University Press). However,they are not known to resemble males inother ways. If the bird in Fig. 3 were a fe-male, there would be no way to distin-guish males and females by plumage.Identifying this bird as a female based onits “broad wings” or “size” is faulty. Shapeand size characters are notoriously diffi-cult to assess with accuracy from a singlephoto. For example, the male on p. 31 ofour Birding article also appears stocky.

Pyle questions the age of the bird inFig. 5 and comments that he can’t seethe retained juvenile feathers as report-ed. The retained juvenile feathers shownin Figs. 4 and 5 are elucidated in thephoto captions. The bird in Fig. 4 ex-hibits brown retained under-wingcoverts; this is easily seen in the insetfigure. The bird in Fig. 5 has retained ju-venile primaries, secondaries, and bodyfeathers, with p7–p10 (the 7th–10thprimaries) showing boldly banded tipsinstead of the solid black tips of adults.

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Pyle also comments about the status ofmolt in the September birds (Figs. 6–7),yet we make no assumption that molt isin progress or arrested. We only point outthat the retained juvenile flight feathersin Fig. 6 age these birds conclusively assecond-year individuals. The bird in Fig.7 is aged as an after-second-year individ-ual because it has two generations ofadult feathers.Our article affirms that most harriers

do not retain remiges between molts, andPyle agrees; see his 2005 paper in theJournal of Raptor Research. This is why ourstudy was arduous and has taken so long(for example, the bird in Fig. 4 was pho-tographed in 1996).Pyle notes that adult males might ex-

hibit polymorphism, and we provide evi-dence in our Birding article for that phe-nomenon. But he questions whetherspecies that take several years to becomeadults can show variation once they reachtheir definitive plumage state. There isvariation in the definitive plumages of sev-eral raptor species, as shown previously byLiguori for Ferruginous, Swainson’s, andRed-tailed hawks and Golden Eagles.Plumage variation in adult male harriers isno greater than that displayed in the up-per-wing mottling and tail bands on Gold-en Eagles, the bibs on Ospreys, the un-derside barring of accipiters, the overallcolors and patterns of adult male Rough-legged Hawks, and especially the colorsand patterns of the tails of adult Harlan’s[Red-tailed] Hawks. (For more on the tailsof Harlan’s Hawks, see Bill Clark’s articlein Birding, January 2009 pp. 30–36.)Pyle closes by pointing out the difficul-

ty of studying under-wing covert molt pat-terns using round-skin specimens. Basedon our study of live birds over many years,we know that juvenile harrier under-wingcoverts are brown and are the last feathersto be replaced, and that adult male under-wing coverts are white or rufous-spotted.Under-wing coverts are frequently re-tained in larger raptors, such as goshawks,eagles, and large falcons. We agree that

specimens are valuable, but on specimensit is often difficult to examine such char-acters as eye color, the under-wing coverts,and the spread wings and tail. Our studyof live birds has helped us substantiatemany characters over the years.One final note. In a 2013 article in British

Birds (106:145–158), Jean François Blancand coauthors showed that plumages ofadult Marsh Harriers (Circus aeruginosus)are highly variable and do not follow the“logical” progression assumed in past liter-ature. In this study of marked birds overmany years, some males never achieved thegray plumage of “typical” males, remainingfemale-like throughout their lives; someprogressed toward a grayer adult plumageover time; and others showed no change af-ter the second prebasic molt. Here is theirparticularly telling conclusion:

Brown males are not just immature birdswith delayed plumage maturity, whichmight seem logical given the similarity oftheir plumage to younger age classes (andfemales). Instead, these brown males rep-resent a distinct morph, a permanent “fe-male-like” plumage that is currentlyknown in only one other bird species, theRuff Calidris pugnax (Jukema andPiersma 2006). However, the situation isnot quite that simple, since our study pop-ulation does not consist of just brown andclassic gray male morphs. In fact, thesetwo types account for <20% of breedingmales, with the remaining 80% exhibitinga wide variety of intermediate plumages.

We maintain that more study is need-ed to determine if a plumage progressionoccurs in Northern Harrier, but we havealso shown that conventional assump-tions about “brown” male Northern Har-riers are erroneous. Adult male NorthernHarriers show plumage variation frombrownish to pearl gray (and with varyingamounts of rufous underneath), and ag-ing such birds based on plumage traitsalone is meretricious.

—Jerry Liguori and Brian Sullivan

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