Annual Molts and Interruption of the Fall Migration for Molting in Lazuli Buntings

The Condor 93:236-250 0 The Cooper OrnithologicalSociety 199 I

ANNUAL MOLTS AND INTERRUPTION OF THE FALL MIGRATION FOR MOLTING IN LAZULI BUNTINGS

BRUCE E. YOUNG Burke Museum and Department of Zoology, NJ-15, Universityof Washington, Seattle, WA 98195

Abstract. Lazuli Buntings,Passerina amoena, interrupt their fall migration in the Amer- ican Southwest to undergo the major portion of their fall molt. Adults molt only limited numbers of body feathers on the breeding groundsbefore migrating to one of two molting “hotspots,” (1) a region bounded by southern Arizona, southwesternNew Mexico, and northern Sonora or (2) southern Baja California. Here they molt the rest of their body feathers and all flight feathers, before continuing on to the winter range in western Mexico. Hatching-year birds undergoa limited prebasicmolt on the breedinggrounds and then stop during migration at one of the same two hotspots to undergo a nearly complete presupplemental molt of all body and most flight feathers. Some individuals of both age classesalso migrate directly to western Mexico to molt on the wintering grounds. A possible cause of the interrupted migration strategyis the combination of dry, food-scarceconditions on the breeding range and locally rainy, food-rich conditions at the molting stopovers from late August through October. After the presupplemental molt, males and females are similar in color to adults in definitive basic plumage. The prealtemate molt is limited to a few head feathersfor all age/ sex classes,with most color change from winter to breeding aspect resulting from wear of buff feather tips which obscurebright male colors during the winter. The definitive prebasic molt takes place August to October, involving replacement of all feathers. This molt is different in timing, location, and extent from that recently reported for two congeners,the Indigo Bunting, P. cyanea,and the Painted Bunting, P. ciris. Key words: Interrupted migration; Lazuli Bunting; Mexico; molt; molt-migration: mu- scumspecimens; Passerina amoena.

INTRODUCTION viously unknown and unexpected patterns are Birds molt both to replace worn feathers and to turning up. For example, Willoughby (1986) dis- change their appearancesin either social signal- covered two complete molts in hatching year ing or predator avoidance contexts. Molt is cost- Cassin’s Sparrow (Aimophila cassinii), and Roh- ly, however, as several studies have shown that wer and Manning (1990) documented that Bul- birds raise their basal metabolism by 946% while lock’s Orioles (Zcterusgalbula bullockit have very in molt (Lustick 1970, Gavrilov 1974, Chilgren different molt and migration schedulesfrom their 1975). Intense molt is thus on a par with repro- eastern counterpart, the Baltimore Oriole (Zcter- duction and migration as a major energetic de- us galbula galbula). mand in the annual cycle (Payne 1972, Walsberg Here I document the sequence, extent, and 1983). Yet despite its importance, molt is much timing of molts in the Lazuli Bunting, Passerina less studied than reproduction and migration. amoena, a migratory, sexually dichromatic pas- For North America, few specieshave been stud- serine of western North America. No quantita- ied in depth, so most of our knowledge of molts tive study of molt in this specieshas ever been comes from older general summaries lacking in undertaken; our knowledge is restricted to a few quantitative data (e.g., Dwight 1900, Forbush comments in Pyle et al. (1987) who largely as- 1924, Dickey and Van Rossem 1938). Especially sume the molt is identical to that of the Indigo lacking are studies of western North American Bunting. My goals for this study were: (1) to de- birds (Rohwer and Manning 1990) where pre- scribe the annual molts; (2) to identify characters that can be used to determine age and sex classes of Lazuli Buntings; (3) to learn where the fall I Received17 September 1990. Final acceptance23 molt occursand to speculateon what factors may January 1991. have led to this pattern; and (4) to compare the

P361 ANNUAL MOLTS OF LAZULI BUNTINGS 237 molt cycle in Lazuli Buntings with the recently for definitions). In each region, I looked for grow- described molts of congeneric Indigo Buntings, ing feathers (i.e., feathers in sheaths) by lifting P. cyunea(Rohwer 1986) and Painted Buntings, featherswith watch-makers forcepsat 5-7 points. P. ciris (Thompson 199 1). I presentevidence that I estimated the percentageof feathersgrowing in some, possibly most, Lazuli Buntings interrupt each region using Rohwer’s (1986) scaleof 0, 10, their fall southward migration to undergo a rapid 30, 50, 70, and 90% of feathers in development. molt, and I show that molt patterns vary mark- In addition, I scored a body region as being in edly among these three congeneric buntings. 100% molt if all featherswere in sheaths.If none or just one feather was in development, I scored METHODS the region as 0%; if two or more (up to 20% of I based this study exclusively on information the total) were in development, I scored the re- gathered from 665 museum specimens. I region as 10% molt. I then calculated a body molt quested loans of Lazuli Bunting specimensfrom score for each specimen as an average of the (1) every North American museum with hold- scoresfor the six regions. In addition, I scored ings of over 10,000 specimens, and (2) smaller feather wear for each body region and for the museums that are located within the range of the individual flight featherson a l-5 scale: 1 = fresh, species(Banks et al. 1973; seeAcknowledgments 5 = extremely worn. I also noted the presenceof for sourcesof specimens and museum abbrevi- feathers in more than one wear class, indicating ations). Since Nearctic passerines generally do they had been grown during different molt epi- not molt while breeding, I requested specimens sodes. that were collected in all months except May and For flight feather molt, I scored each primary June, the usual breeding seasonfor Lazuli Bun- on a O-l .O scale. Old feathers received a 0 score, tings (Jewett et al. 1953, Erickson 1968). How- and growing feathers received positive scores ever, I examined 17 adult male specimens col- based on their lengths: empty follicles received lected in May and housed at the AMNH for buff 0.1; full grown feathers received 1.O; and partly feather tip wear (see below). I use the molt ter- grown feathers received from 0.2 to 0.9 depend- minology proposed by Humphrey and Parkes ing on the fractional growth attained at the time (1959) and the age classterminology used by the of collection. The primary molt score was the Bird Banding Laboratory and modified by Pyle sum of these individual feather scores.For com- et al. (1987). Age class terms used are hatching puting the primary molt scoresof specimens in year (HY), birds that are in their first calendar the presupplemental molt, I summed scoresdis- year and that are in or have completed either tal to and including the fourth primary (P4), the their first prebasic or supplemental molt; second remex at which this molt most commonly ini- year (SY), birds in their secondcalendar year but tiated. I recorded P4 as replaced in those few before the second prebasic molt is so far com- specimens where the molt was initiated at P5. pleted that theseare indistinguishable from older Thus HY specimens could have primary scores birds; after second year (ASY), birds collected from zero to six, and adults, which replace all after their secondprebasic molt; and after hatch- primaries in the fall, from zero to nine. To de- ing year (AHY), all SY and ASY birds. termine the length of time over which flight Scoring molt. To avoid subjective bias, I cov- feathers grow, I followed the regressionmethod ered each specimen label with a piece of paper of Pimm (1976). on which the specimen number was written sev- Early in the study it became apparent that male eral weeks before examination. After scoring, I Lazuli Buntings change from their overall bulfy removed the covers and recorded the date, lo- winter aspectto bright summer blue, cinnamon, cality, and sex from the labels. In general, I fol- and white summer aspect primarily through lowed the methods described by Rohwer (1986) feather tip wear, rather than through an extensive for scoring molt which I briefly outline here, not- prealtemate molt. To document this change in ing departures from this scheme where they oc- males, I scored the percent of feathers with any cur. of their buI& tips remaining in the three dorsal I examined all specimens using a 2 x magni- regions plus the throat region. I averaged these fying lamp lighted with a 60-W incandescentbulb. four scoresto obtain a “percent buff tip” score I scoredbody molt in six regions: throat, breast, for each specimen. I did not score the breast belly, crown, back, and rump (see Rohwer 1986 region since the buff tip color blended in with 238 BRUCE E. YOUNG

TABLE 1. Frequency of HY specimens from the ing juvenal primary coverts (Dwight 1900). The breedinggrounds molting from natal down into juvenal all-brown juvenal coverts are easily distinguish- plumage (N - J), in juvenal plumage (J), in the first able from the blue-edged brown ASY female and prebasic molt (J + B), and having completed the first prebasicmolt (1B) in relation to date. As the first pre- blue-edged dark ASY male coverts. basic molt involves varying numbers of body feathers, There is presently no known external character a specimen having replaced any of its body feathersin that can distinguish sexesof HY Lazuli Buntings this molt is defined as having completed the first basic either on the breeding grounds or in migration molt. (Pyle et al. 1987). Rohwer (1986) suggestedthat rectrix color (flat brown versusbrown with a blue N-J J J-B IB sheen) may be a reliable character for the Indigo 16-30 June : 0 0 Bunting. In examining HY specimens, I discov- l-15 July 1 1 ered that wing bars are either whitish or bully in 16-3 1 July ;I 2 13 10 l-l 5 August 20 8 color. Consequently I scoredthese two characters 16-3 1 August 2 : 10 26 in HY specimensto determine if either could be l-l 5 September 1 6 5 17 used as a reliable sex character. 16-30 September 0 2 1 9 Location and timing of molts. To understand l-l 5 October 0 1 0 1 where and when molt events take place in the Total 23 17 57 72 fall, I divided the breeding and winter rangesinto segments encompassing 5” of latitude. I com- pared monthly profiles of the relative abun- the underlying cinnamon. The white belly feath- dances of specimens taken from these segments ers did not consistently have buff tips after the in relation to the occurrenceof molt to seewhere fall molt, so I did not score these either. Tips of Lazuli Buntings most frequently molt. I com- body feathers also wear in females, but again bined this analysis with the use of mapped spec- these blend well with the overall brown colored imen locations to identify geographic“ hotspots” feathersmaking scoringunreliable. Since the buff of molting activity. tips were not completely gone in all late April Definition of winter and breedingranges. I de- specimens,I examined 17 additional adult males fined the breeding range as that described in the taken in May to form a complete picture of the AOU Checklist (American Ornithologists’ Union loss of these tips. I then plotted the percent buff 1983, p. 674-675): “southern British Columbia, tip score for each specimen with its date of col- southern Alberta, southern Saskatchewan, cen- lection to examine the timing and rate of change tral North Dakota and northeastern South Da- from winter (bull+) to summer (bright blue, cin- kota south to northwestern Baja California, namon, and white) aspect. southern California, southern Nevada, central Species, age, and sex identljication. Several Arizona, central New Mexico and central Tex- specimens arrived misidentified as Lazuli Bun- as, . . . and east to east-central Nebraska, western tings (e.g., Young 1989). These were detected Kansas and western Oklahoma.” The winter using the color and primary length characters range is “southern Arizona and Chihuahua south described by Pyle et al. (1987). to Guerrero and central Veracruz” (American I could determine the appearance of juvenal Ornithologists ’ Union 1983:675). The 1983 AOU feathers by examining juveniles with all flight Checklist erroneously includes southern Baja feathers in sheaths (i.e., individuals having re- California in the winter range. Wilbur (1987: 150) cently fledged).Juvenal body feathersare of low- lists the Lazuli Bunting as a “fairly common er quality than the feathers which replace them spring and fall migrant the length of the penin- in the limited first prebasic molt: they have a sula,” but statesthat “there are no recent winter lower density of vanes along the rachis (seeRoh- recordsfor Baja California.” I therefore consider wer and Manning 1990; Table 1) and adjacent southern Baja California as out of the normal vanes are more loosely attached to each other by winter range, but as a region where some win- the distal barbule hooklets (see Dwight 1900, tering individuals may occur from time to time. Plate IV). Thus I could distinguish juvenal feath- Likewise, southern Arizona harbors very few ers from those grown in the first prebasic molt. wintering Lazuli Buntings (Root 1988). Second year Lazuli Buntings exhibit the pat- Statistical assumptions. Series of specimens tern common to emberizid passerinesin retain- collected by myriad collectors over more than ANNUAL MOLTS OF LAZULI BUNTINGS 239

100 years usually can not be expected to repre- the 58 specimens in this molt (USNM 130489 sent a random or systematic population sample from the Arizona/Mexico border) was found that obeys assumptions of statistical tests. For south of the breeding range. Evidence for early instance, do four subadult male buntings col- onset comes from two molting specimens (SD lected on the same day from the same locality 26875 and SD 26876) collected in late June. The represent one observation or four? Surely they percentageof specimenstaken in this molt reach- may share characteristics unique to their local es a peak by early August and then declines genepool or environmental conditions and would through September (Table 1). This is a leisurely unfairly influence the overall sample if counted molt; the averageof the body molt scoresof spec- individually. On the other hand, if one specimen imens taken in the first prebasic molt was 3.9 (n is in heavy molt and the rest are not, a simple = 56) or about four percent of all body feathers average of the molt scoreswould distort any pic- growing. ture of the intensity of molt in the species.There- In this molt, some but not all juvenal body fore, to avoid flirting with pseudoreplication feathersare replacedby adult-quality basic feath- (sensu Hurlburt 1984) I shied away from using ers. The most obvious color changeoccurs in the inferential statisticsand relied instead on graph- breast where streaky, off-white feathers are re- ical and tabular analyses. I conducted standard placed by buff feathers. Off-white juvenal throat statistical tests (Sokal and Rohlf 1981) where and belly feathers are replaced by first basic chancesof violating assumptions about indepen- feathersof the same color, giving birds a distinct dence of data were minimal (i.e., analyses of a buff breast bar by late summer. Dorsally, brown single age or sex classat a restricted time of year juvenal feathers are replaced by darker brown and geographical location with not more than first basic feathers.Several September specimens one or two specimens per locality per year). in full juvenal plumage were collected south of In addition, collecting effort is often biased by the breeding range in southern Arizona, southern sex or age class, time of year, plumage, molt New Mexico, and northern Sonora (e.g., UCLA stage, or location (e.g., molting specimens may 29302, USNM 235572, UNM 5 199, MNA2890). be underrepresented because they are hard to Since specimens in prebasic molt from these prepare and difficult to collect because of shy- regions are so rare, it is likely that some indi- ness).I assumedthat thesebiases were consistent viduals may molt directly from juvenal to sup- among all collectors. I also assumed that loss of plemental plumage. The molt beginson the breast sheathed feathers during specimen preparation and back and then progressesto the crown, throat, or subsequent handling was inconsequential to and belly. The rump feathersare rarely replaced, my results. Finally, I assumed that no evolution and few individuals replace all juvenal feathers of molt strategy occurred during the time that in any one region. the specimens were collected. Presupplemental molt. At either a migratory stopover or on the wintering grounds, HY birds have another molt that includes all body feathers, RESULTS all rectrices, the outer 4-7 primaries, and the DESCRIF’TION OF MOLTS inner 3-6 secondaries.The only feathers not re- First prebasic molt. HY Lazuli Buntings leave placed are the inner primaries, the outer second- the nest in full juvenal plumage. Examination of aries, and some to all of the primary coverts. “bob-tailed” specimens showed that all body Color change in Lazuli Buntings is from brown feathers were of juvenal quality except for a few juvenal to buff-tipped adult colors in both males feathers on the lower back which were indistin- and females. I call this a presupplemental molt guishable from adult quality feathers. In the 16 for two reasons.First, this molt is in addition to specimens with sheathedjuvenal feathers, these the presumably ancestral fall prebasicand spring back feathers are growing concurrently with the prealtemate molts (following Humphrey and rest. Thus the adult-quality back feathersare un- Parkes 1959). The prebasic molt begins and ends likely to representthe beginning of a first prebasic on the breeding grounds and leaves HY birds molt. with a mix of juvenal and prebasic feathers dis- The first prebasic molt occurson the breeding tinguishable by quality in all body regions except grounds and can begin almost immediately after the lower back and by color in the breast. Then the juvenal feathersare fully grown. Only one of the body feathersare replaced for the secondtime 240 BRUCE E. YOUNG

TABLE 2. Extentof presupplementalwing molt based on featherwear differences in specimenscollected after m completingthe presupplementalmolt but beforebe- q ginning the secondprebasic molt. Sexesare summed as there was no differencein extent of molt between malesand females(Kolmogorov-Smimov two-sample B test,primaries: D = 0.097, NS; secondaries:D = 0.109, NS; Sokaland Rohlf 1981).

Number of Number of 8.i ,,,,,,: ,,,, q, specimens specimens 4 5 6 Primaries showing secondaries showing 0 1 2 3 RplZWd pattern replaced pattern PRIMARY MOLT SCORE

Pl-9 0 Sl-9 0 P2-9 4 S2-9 1 P3-9 35 s3-9 1 P4-9 73 s4-9 4 P5-9 28 s5-9 21 P6-9 0 S6-9 49 P7-9 0 s7-9 55 PS-9 0 S8-9 1 P9 0 s9 0 s q 4c-t.r~ I.,.,. 8. I. 8.84’ 0 1 2 3 4 5 6 7 8 9 PRIMARY MOLT SCORE (or for the first time in the caseofjuvenal feathers FIGURE 1. A) Attempt at estimating duration of not replaced in the first prebasic molt) in this primary replacement in presupplementalmolt. There presupplemental molt. Evidence that all first ba- was no relationship between molt score and date. B) sic and remaining juvenal feathersare lost stems Regression of primary molt score on date for AHY adults. The relationship is described by the equation from (1) the color change in males from brown date = -6.82 + 6.32 (molt score). dorsally and buff-barred off-white ventrally to buff-tipped blue dorsally and buff-tipped blue, cinnamon, and white ventrally in males; (2) the an average molt score of 29.8 (range 1.7-66.7) discovery of three molting specimens (MCZ for the eight specimens in body molt. Primary 16254, DEL 13141, CMNH 126489) with all and secondary development proceedsin typical three feather generations of body plumage which ascendingorder beginning with the third, fourth, are clearly distinguishable by quality, wear, and or fifth primary (Table 2). Secondary develop- color; and (3) the absenceof the first two feather ment appearsto begin with SS, continue with S7 generations in the body plumage of all specimens and S9, and then either stop there or finish with that have completed the presupplemental molt. S5 and S6 (Table 2). As Figure IA shows, I was Second, this second fall molt in Lazuli Bun- unable to estimate the duration of this molt in tings is undoubtedly homologous (sensu Hum- an individual bunting, suggestingthat there is phrey and Parkes 1959) to the presupplemental much between or within-year variation in when molt described in Indigo and Painted Buntings the molt occurs.In 23% of HY and SY specimens (Rohwer 1986, Thompson 1991). In the latter collected with grown supplemental plumage be- two species,most or all of the body feathers are tween 1 November and 30 April (n = 75), one replaced once in the first prebasic molt and then or more (mean 2.1, range 14) of the outermost again in the presupplemental molt. In Lazuli primary coverts had also been replaced with Buntings, the first prebasic molt has been re- adult-like feathers. In 29% of these cases, the duced to a partial body molt, but the presupple- molt was asymmetrical in that different numbers mental molt has remained virtually unchanged of primary coverts were replaced on the right and as a complete body and rectrix molt and partial left wings. remex molt. Prealternatemolt. The change in color from The nine specimens collected in this molt in- winter to breeding aspectcomes about largely by dicate it is completed between late September wear of buff feather tips that exposesunderlying and early November. This molt progressesmuch colored vanes (Fig. 2). The prealtemate molt is more intensely than the first prebasic molt, with reduced to just a few feathers around the auric- ANNUAL MOLTS OF LAZULI BUNTINGS 241

DATE FIGURE 2. Wear of buff contour feather tips after the prebasic molt in AHY males. ulars, eyes, and bill. A slightly more extensive molt can occur in SY males which also replace white throat feathers for buff-tipped blue feathers DEC JAN FEE MAR APR MAY JUN JUL (see below). In all age classes,the new feathers are colored buff-tipped blue in males and brown in females. Becauseof the limited nature of the MONTH molt, the small size of the feathersinvolved, and FIGURE 3. Wear of body feathersafter the prebasic the lack of color change, it was impossible to molt in ASY males and females. For the wear score, 1 = fresh and 5 = extremely worn. Monthly sample know by examining a specimen whether it had sizes indicated. already molted. Thus, I cannot say whether all birds always undergo this molt. Molting birds were collected February through April, and there ers in development (e.g., MOORE 26867). Dur- is some suggestionthat ASY birds begin this molt ing this molt, SY males lose many white throat earlier than SY birds (Table 3). Overall, 17.6% feathers grown in during the presupplemental of the specimenscollected from February through molt, making them appear significantly more April were in molt. I cannot say whether the similar to ASY males by the breeding seasonthan prealtemate molt continues into May as is the in mid-winter. Before the molt (November to case in SY Indigo Buntings (Rohwer 1986) be- March), 64% of 28 specimens had white in the causeI did not examine May specimensfor molt. throat while just 36% of 33 SY males taken in Becauseit is so limited in extent, this molt does July have white throat feathers (G-test of inde- little to stem the gradual increase in feather wear pendence with William’s correction, G,, = that occurs from December through July (Fig. 4.67 14, df = 1, P -C0.05). At this point, SY males 3). differ only in having a duller blue or browner There were no statistically detectable differ- back, brown inner primaries and outer second- ences between age and sex categoriesin the oc- aries, and occasional white feathers in the throat. currence of prealtemate molt (Table 3); however, Dejinitiveprebasicmolt. The prebasicmolt into the most intense prealtemate molt scoresfound definitive plumage involves the replacement of were in SY males, with up to 10% of throat feath- all body and flight feathers.The majority of spec-

TABLE 3. Prealtemate (PA) molt by age, sex class,and date for specimenstaken February through April. The between-classdifferences in molt frequencyare not significant(G-test of independencewith William’s correction, G, = 5.0255, df = 3, P 1 0.1; Sokal and Rohlf 1981).

Age and sex class SY-M SY-F ASY-M ASY-F Total

No. in PA molt 10 0 6 3 19 No. not in PA molt 33 8 49 18 108 Months in which PA molt was found Apr. - Feb.-Apr. Mar. Feb.-Apr. 242 BRUCE E. YOUNG

FIGURE 4. Geographical sequenceof migration and molt events in the fall for Lazuli Buntingsof all ageand sex classes.

imens suggestthat the body molt begins on the males in that (1) definitive back feathers are breeding grounds, is interrupted for migration, brighter blue beneath their huffy tips and (2) chin and then finishes concurrently with the prebasic feathersare almost never white. Females likewise wing and tail molt at a migratory stopover (Fig. change from worn breeding colors to fresh buff- 4). tipped slate blue above and light brown below. In this molt, males change from worn blue to When the body molt begins on the breeding fresh buff-tipped blue dorsally and from worn grounds, replacement occurs in all six regions. blue, cinnamon, and white to buff-tipped blue, The molt intensity is light (Fig. 5B), and feather cinnamon, and white ventrally. Even the wing replacement is everywhere incomplete. Twenty- feathers have buff edges, especially the tertials six percent of the 89 specimensfrom August and (S7-9) and the feathersmaking up the wing bars. the first half of September taken on the breeding The resulting appearance is of overall buff that grounds or in southern Arizona and New Mexico obscures the underlying bright blue and cinna- had some fresh body feathers but were not in mon colors. Adult males differ from subadult active molt (mean percent fresh feathersof those ANNUAL MOLTS OF LAZULI BUNTINGS 243 with new feathers was 26.8). These individuals likely had halted molt for the southward migration which occursat this time of year. The other specimens collected at this time were still in a light molt. As new flight feathers begin growing, the intensity of body molt increases and all remaining worn feathersare replaced.This is there- 60 fore not a presupplemental molt since feathers 1 grown on the breeding ground are not replaced again when the rest of the body and flight feathers grow in. Body feathersofspecimens in fresh basic plumage are in different wear classesindicating they were grown during different molting bouts. The intensity of this part of the body molt is twice that of the breeding ground portion (Fig. JULY AUG SEPT OCT NOV 5B). The primaries and rectricesgrow in the usual ascending manner. In the secondaries,the tertials (S7-9) are replaced first, simultaneous with the first primaries. The rest of the secondaries B follow in ascendingorder beginning with S 1. The 100 rectrices grow in virtually synchronously, the Prebasic Body Mall outer feathers trailing the inner feathers by up to 1 one-third of a grown feather-length. They initiate replacement soon after remigial replacement begins but are completed somewhat before the last primary and secondaryare completed. The body molt is completed concurrently with the flight feather molt. A plot of collection date against molt score showed a significant regression(F,,,, = 53.109, P -c 0.01, r2 = 0.76) and indicates flight feather molt lasts about 57 days (Fig. 1B). Caution is urged in interpreting this result since all sexes, AHY age classes,and locations were JULY AUG SEPT OCT NOV lumped to obtain an adequate sample size. DATE AGE AND SEX IDENTIFICATION FIGURE 5. Molt intensityand featherreplacement I found 21 male specimens collected in either in HY (A) and ASY (B) buntingsduring the fall molts. April or July that had white feathersin the throat. Locationsof the molts are indicatedparenthetically. Numbersrepresent half-month sample sizes. Twenty (95.2%) were secondyear males. The one exception (MCZ 192432) collected in July, had about 10% of its throat feathers white and was 91 males had buff bars). I was less systematic certainly an ASY adult since it had all adult blue- about scoring rectrix color, but am nonetheless edged black remiges and primary coverts. The confident that this also is not reliable. At least throat feathers had not grown in white in the ten of 102 females and nine of 9 1 males were previous molt; instead, it appears that the blue noted with a blue rather than flat brown hue in portions of the feather vanes had completely worn their rectrices. away, exposing the basal white segments of the vanes. TIMING OF MIGRATION AND I found no reliable external character to dis- LOCATION OF FALL MOLTS tinguish sexesin HY birds in juvenal or first basic Figures 5-8 diagram the temporal and geograph- plumage. Males and females were equally likely ic occurrenceof fall migration and molt in Lazuli to have buff versus white or off-white wing bars Buntings. HY birds linger on the breedinggrounds (5 1% of 102 females had buff bars and 49% of until September when they begin to appear in 244 BRUCE E. YOUNG

100

60 2153 40 1161

100

So-1AHY -- SEPTEMBER J I 60

AHY -- OCTOBER

Il.18 ’ ’ HY -- NOVEMBER n-11 AHY - NOVEMBER 80 - 3m 80

60- 60

” 0 c25 25-29 30-34 35-39 40.44 r 44 c25 25-29 3044 35-39 40-44 >44 LATITUDE LATITUDE FIGURE 6. Locationsof HY (left) and AHY (right)specimens before, during, and after the fall molts.Figures above the bars are the number of specimensin flight feathermolt/total number of specimensfor a latitude regionwhere there were 2 one specimenin molt. 30-34” correspondsto the southwesternU.S./northern Sonora regionand ~25” representsboth southernBaja Californiaand westernMexico.

the southwesternU.S./northern Sonora (SWUS/ tember (Fig. 6). Again, some fly to SBC either NS) region. Here they stay into October before directly, or possibly via SWUSNS. All AHY traveling south to the wintering grounds in west- birds then arrive on the wintering grounds by em Mexico (WM). Some also visit southern Baja November. California (SBC); whether they do this in lieu of In HY birds, the first prebasic molt occurs on stopping in SWUS/NS or after stopping there the breeding grounds in June, July, and August cannot be determined. AHY adults depart the (Table 1) and is then followed by a nearly com- breeding grounds sooner than HY birds, arriving plete presupplemental molt in late September, in the SWUS/NS by late August and early Sep- October, and early November (Figs. 5-6). The ANNUAL MOLTS OF LAZULI BUNTINGS 245

All specimens

o HY 1 AHY

FIGURE 7. Locations and age classesof all sDecimensmolting flight feathers; all specimenswere collected between 24 August and 8 November except as noted. presupplemental molt occurs primarily in the molt (the entirety of the first prebasic molt in SWUS/NS and SBC, although two specimens HY, and part ofthe definitive prebasicbody molt (DEL 13 14 1 and DEL 13 142) were in presup- in AHY birds) on the breeding grounds; (2) a plemental molt in Durango, WM (Fig. 7). AHY migration to SWUS/NS or SBC, (3) a continu- birds begin the body molt on the breeding ation of a molt that finishes body feather replace- grounds, then finish the body molt and undergo ment and replaces all flight feathers (i.e., finish the entire flight feather molt in the same SWUSI definitive prebasic molt in AHY birds) or a com- NS and WM regions, but earlier. No AHY spec- plete body molt and a partial flight feather molt imen was found in molt in WM, although two (presupplemental molt in HY birds); and (4) a specimens from this region, an ASY male (KU migration to the wintering grounds in WM. 30164) and a SY female (MOORE 6201), were Evidence for this fall molt-migration sequence found in worn flight and body feathersindicating comes from five observations. First, some body they were likely to molt in this region (Fig. 8). molt clearly occurson the breeding grounds (Fig. Thus there are four stepsto the usual fall migra- 5). Second, Figure 7 showsthat virtually all spec- tion/molt sequence (Fig. 4): (1) a partial body imens in flight feather molt were collected out- 246 BRUCE E. YOUNG

All specimens not 9 molting flight feathers 15Auo-15fW 0 HY, in juvenal or first basic plumage 0 HY, with presupplemental molt complete

q AHY, prebasic body molt not complete, flight feathers worn

. AHY, prebasic body and flight feather molt complete

FIGURE 8. Locations, ageclasses, and plumagesof all specimenscollected 15 Augustto 15 Novembernot in flight feathermolt.

side of the breeding range. This is not due to a (Table 4), indicating that buntings arrive, molt, bias in collecting effort since many specimensnot and then depart the two molting regions. molting flight feathers were taken from the In exception to this schemeof migrating before breeding range during this period (Fig. 8). Third, finishing the fall definitive prebasicmolt, I found many individuals were collected south of the three specimens from the breeding range in ad- breeding grounds in worn plumage (Fig. 8). vanced body and wing molt (Fig. 7) a SY male Fourth, the occurrence of specimens in flight (MVZ 80401), an ASY male (MVZ 80400), and feather molt is skewed to two areas, the SWUS/ an ASY female (UMMZ 75828). These three are NS and SBC (Fig. 7). Specimens from WM were from July whereas all other specimens at this scarce, so I cannot rule this area out as a third stage of the prebasic molt were collected from major site of molting. Finally, the two molting late August through October. I suspect these “hotspots” are out of the normal winter range three failed at breeding and underwent a full molt ANNUAL MOLTS OF LAZULI BUNTINGS 241

TABLE 4. Occurrenceof specimensin all age and sex classesat the major molting regionsbefore, during, and after the major fall molt.

southenl U.S./ kzfy_Fb Date northern Sonora westernMexico n July (beforemolt) 100’ 8 8 I 15 Aug-I 5 Nov (duringmolt) Total 63 20 17 115 Actually molting flight feathers 50 43 7 28 Dee-Mar (aftermolt) 8 6 86 77 *Values representpercentase of total specimenscdected in eachtime period. in lieu of caring for offspring. Several studies graphical areas.Further supporting this resource- show that unsuccessfulbreeders, often yearlings, based explanation is the observation that south- molt earlier than successll breeders(Payne 1972, em Baja California, the second major molting Bancroft and Woolfenden 1982, Rimmer 1988). area for Lazuli Buntings, also receives its rain in the late summer (Wiggins 1980) and likely also DISCUSSION has abundant food at this time. WHY INTERRUPT MIGRATION? A possibledifficulty with this scenario,though, Despite an extensive literature search, I could is that Lazuli Buntings occur in association with find just three additional reports of passerines either riparian habitats or irrigated agricultural interrupting migration to molt: Bullock’s Oriole areas(Erickson 1968). One might not expectthese and Painted Bunting in the SWUS/NS (Rohwer habitats to undergo suchdrastic late summer food and Manning 1990, Thompson 199 1) and Eur- shortages that would cause buntings to leave asian Yellow-breasted Bunting in Asia (Strese- without finishing their molt. Until f%rtherinfor- mann and Stresemann 1966). Among non-pas- mation is available on food abundance in the serines,waterfowl are well-known to take special breeding and molting areas, we cannot be sure molt migrations after breeding, but finding a safe of the basis for the fall molting/migration pattern place to be flightlessduring the molt seemsto be seen in Bullock’s Oriole and Lazuli Bunting. a more important factor than finding food in Nonetheless, three passerineshave now been waterfowl. documented to molt in the southwestern U.S./ Rohwer and Manning (1990) suggestedthat northern Sonora region. Many other speciesare Bullock’s Orioles migrate out of their western known to migrate through these areas as well; North American breeding grounds in the fall to examination of museum specimensof these spe- escape food scarcity brought on by predictable cies collected in the SWUS/NS in September and late summer droughts (see Baldwin 1973). Bul- October may show that even more speciesmolt lock’s Orioles molt in the southwestern U.S./ in this region than are presentlyrecognized. These northern Sonora region where they may be taking yet unidentified speciesand Lazuli Buntings thus advantage of the food flush caused by scattered have a conservation problem akin to shorebirds late summer rains (Shreve and Wiggins 1964, and waterfowl in needing preservation of winter, Ezcurra and Rodrigues 1986, Neilson 1986). breeding, and migratory habitats for complete Likewise, most Painted Buntings from the drier, protection. western portion of their breeding range migrate to the SWUS/NS or Rio Grande valley in the BETWEEN SPECIESCOMPARISONS fall. Here they perform their complete fall molt It is remarkable that the three well-studied and and then resume their migration to their south- presumably closelyrelated Pusserinabuntings are em Mexico wintering grounds(Thompson 199 1). so different in extent and timing of molt relative The factors causing both Bullock’s Orioles and to migration (Table 5). The three speciesdiffer Painted Buntings to interrupt their migration for in extent of the first prebasic molt, timing of the molting are likely to be similar to those acting presupplemental molt relative to migration, col- on Lazuli Buntings since all breed in areas with or change of the presupplemental molt with re- similar climates and all molt in the same geo- spect to adult color, extent of the prealtemate 248 BRUCE E. YOUNG

TABLE 5. A comparison of molt and plumage characters for Painted Bunting, Passerinaciris (Thompson 1991), Indigo Bunting, P. cyanea (Rohwer 1986), and Lazuli Bunting, P. amoena (this study).

Extent of feather Molt Species Time Location’ replacement Color change

First prebasic ciris Jun-Oct BG most body to brighter green cyanea Jun-Oct BG all body to slightly browner amoena Jun-Sep BG some-most body to buff breast bar Presupple- ciris Sep-Nov BG* or migratory all body, P6, 7, or to adult female-like mental stopover 8-P9, S5, 6, or 7s9 cyanea Nov-Dee WG’ all body, P4, 5, 6- M: to scaly blue P9, s7s9 F: no change amoena Sep-Nov migratory stopo- all body, P3, 4, 5- M: to male-like ver or WG P9, S5, 6, 7S9 F: to female-like First prealter- ciris Dee-May WG some to all head, none nate some body cyanea Feb-May WG some to all body M: to male spring blue F: none amoena Apr WG throat, some head M: to male blue F: none Definitive pre- ciris Aug-Nov BG or migratory complete M: to bright male basic stopover F: to female cyanea AugSep BG complete M: to scaly blue F: to female amoena Jul-Oct begin on BG, fin- complete to buff-tipped adult col- ish in migratory OlS stopover or WG Second and ciris Jan-May WG some to all head, subsequent some body prealtemate cyanea Jan-Apr WG all body M: to spring blue F: none amoena Feb-Apr WG few head none

LBG = breeding grounds, WG = wintering grounds. *A few individuals were found to undergo tbis molt on the wintering grounds. ’ A few individuals were found to undergo this molt on the breeding grounds. molt, location of the definitive prebasic molt, buntings by differing in the extent of the preal- and mode of color change from winter to breed- temate molt and in the timing of the prebasic ing aspect. Because the three species are largely molt relative to migration. Furthermore, Roh- allopatric, it is likely that different social, pred- wer and Manning (1990) showed that hybrids atory, and food conditions may have led to the between the two oriole forms can have mal- evolution of the different molt strategies. For these adaptive molt patterns. Emlen et al. (1975) found three species, we have reached the limit of what few Lazuli x Indigo hybrids and speculatedthat museum specimens can tell us. To identify which thesewere at some sort of selectivedisadvantage. are the most important factors influencing molt Assuming that timing relative to migration and evolution, we will need field observation and ex- extent of molt are under genetic control, a mech- perimentation. In light of this study and those anism for strong selection against hybrids of any on other Passerina buntings (Rohwer 1986, two Passerina species(e.g., Sibley and Short 1959, Thompson 199 l), it would be presumptuous to Storer 196 1) may be maladaptive intermediate generalize as Pyle et al. (1987) did about similar molt patterns. molt pattern followed by members of the genus Inspection of Table 5 showsthat the three Pas- except for the names of the molts and the general serina speciesoften display features at different time of year in which they occur. Interestingly, points along several character continua. Passer- Rohwer and Manning (1990) found that the ina amoena often falls at the extremes of the closely related Bullock’s and Baltimore Orioles, character states, having the most reduced preal- presently considered a single species, resemble temate molt, replacing the most primaries in the ANNUAL MOLTS OF LAZULI BUNTINGS 249 presupplemental molt, replacing the fewest vided accessto computer printing facilities. A NSF feathers in the first prebasic and prealternate Graduate Fellowship supported this study. molts, and appearing the most adult-like after LITERATURE CITED the presupplemental molt. Whether this repre- sents a derived or ancestral condition with re- AMERICANORNITHOLOGIS~~ UNION. 1983. Check- spect to the other speciescannot be determined list of North Americanbirds. 6th edition. BALDWIN,J. L. 1973. Climates of the United States. without a good phylogeny of the group. The vari- Natl. Ocean.and AtmosphericAdmin., Washing- ation among Passerina speciesin extent, timing, ton. DC. and geographiclocation (relative to breeding and BANC&,G.T.,ANDG. E. WOOLFENDEN.1982. The wintering ground) of molts would never have molt of ScrubJays and Blue Jaysin Florida. Or- nithol. Monogr.No. 29. AmericanOrnithologists ’ been predicted from their apparent close rela- Union, Washington,DC. tionships. A good molecular phylogeny for the BANKS. R. C.. M. H. CLENCH.AND J. C. BARLOW.1973. entire genusand its closestrelatives might clarifv BLd ccllectionsin the United Statesand Canada. the sequenceof evolutionary changesand strat- Auk 90:136-l 70. egies. Either Painted, Lazuli, and Indigo Bun- CHILGREN,J. D. 1975. Dynamics and bioenergetics of post-nuptial molt in captive White-crowned tings are lessclosely related than earlier work has Sparrows (Zonotrichia leucophrys gambelii). suggestedor many aspects of molting are evo- Ph.D.diss., Washington State Univ., Pullman. lutionarily more labile than conventional wis- DICKEY, D. R., AND A. J. VAN ROSSEM. 1938. The dom has admitted. If the latter is true, then the birdsofE1 Salvador. Field Mus. ofNat. Hist. Publ. Zool. Ser. 23:l-609. genus Passerina holds the potential for being the DU~IGHT,J. 1900. The sequence of plumages and first group of birds for which the direction of moults of the passerinebirds of New York. Ann. change in molt patterns (in a variety of aspects N.Y. Acad. Sci. 13:73-360. of molt) could be deduced from a good phylog- EMLEN, S. T., J. D. RISING, AND W. L. THOMPSON. eny. 1975. A behavioral and morphological study of sympatry in the Indigo and Lazuli Buntingsof the ACKNOWLEDGMENTS Great Plains. Wilson Bull. 87: 145-179. ERICKSON,M. M. 1968. Passerinaamoena (Say), La- I am gratefulto S. Rohwerfor inspirationand guidance zuli Buntina. D. 11l-132. In 0. L. Austin. Jr. led.1. at all stagesof this project.I thank C. Thompsonfor Life histories of North American cardinals, gros: makinghis Master’sthesis available to me. N. Johnson beaks, buntings, towhees, finches, sparrows, and and one anonymousreviewer made many valuable allies. Part One. U.S. Nat. Mus. Bull. 237. commentson thepenultimate draft of thismanuscript. Ezcuaa~, E., ANDV. RODRIGUES.1986. Rainfall pat- I thankthe curators and staffat thefollowing museums terns in Gran Desierto, Sonora, Mexico. J. of Arid for lendingme specimens:Museum of NorthernAri- Environ. 10:13-28. zona (MNA), University of Arizona, Museumof Ver- FORBUSH,E. H. 1924. Birds of Massachusettsand tebrateZoology (MVZ), Moore Laboratoryof Omi- other New England states. Vol II. Massachusetts thology (MOORE), Los Angeles County Museum, Dept. of Agric., Boston. Universityof Californiaat LosAngeles (UCLA), West- GAVRILOV,V. M. 1974. Metabolism of molting birds. em Foundation of Vertebrate Zoology, San Diego Nat- Zool. Zh. 53:1363-1375. Ural Historv Museum (SD).\ ,, California Academv of Sci- HUMPHREY.P. S.. AND K. C. PARKES. 1959. An an- ences, Cowan Vertebrate Museum, Royal Ontario preach’ to the study of molts and plumages. Auk Museum, Denver Museum of Natural History, Pea- 76:1-31. bodv Museum at Yale Universitv. Delaware Museum HURLBURT.S. H. 1984. Pseudorenlicationand the ofNatural History (DEL), Florida StateMuseum, Field design’of ecologicalfield experiments. Ecol. Mon- Museum of Natural History, ChicagoAcademy of Sci- ogr -54:187-2 l-l. ences. Universitv of Kansas Museum of Natural His- JEWET~.S. A.. W. P. TA~OR. W. T. SHAW.AND J. W. tory (KU), Louisiana State University , Museum of &RICH. 1953. Birds of Washingtonstate. Univ. Comparative Zoology (MCZ), University of Michigan of Washington Press, Seattle. Museum of Zooloav (UMMZ). Princeton Museum of LUSTICK.S. 1970. Enerav reauirements of molt in Zoology, Universiiy of New Mexico (UNM), Cornell cowbirds. Auk 87:74%-746: University, American Museum of Natural History NEILSON,R. P. 1986. High-resolution climatic anal- (AMNH), Philadelphia Academy of Natural Sciences, ysis and southwestbiogeography. Science 232:27- CarnegieMuseum of Natural History (CMNH), Texas 34. A&M University, Washington State University, Uni- PAYNE,R. B. 1972. Mechanisms and control of molt, versity of PugetSound, U.S. National Museum ofNat- p. 103-155. In D. S. Famer and J. R. King [eds.], ural History (USNM), University of Washington Burke Avian biology.Vol. II. Academic Press,New York. Museum (UWBM). I especiallythank C. Wood and C. PIMM, S. 1976. Estimation of the duration of bird Spaw of UWBM for assistancehandling the loans and molt. Condor 78:550. providing space to work, and M. LeCroy of AMNH PYLE,P., S. N. G. HOWELL,R. B. YUNICK, AND D. F. for coordinatingmy visits there. E. Kellogg kindly pro- DESANTE. 1987. Identification guide to North 250 BRUCE E. YOUNG

American passerines.Slate Creek Press, Bolinas, STORER,R. W. 1961. A hybrid between the Painted CA. and Varied Buntings. Wilson Bull. 73:209. RAMMER,C. C. 1988. Timing of the definitive pre- STRESEMANN, E., AND V. STRESEMANN.1966. Die basic molt in Yellow Warblers at James Bay, On- Mauser der Vogel. J. Omithol. 107:1445. tario. Condor 90:141-156. THOMPSON,C. W. 1991. The sequenceof molts and Ronwna, S. 1986. A previously unknown plumage plumagesin Painted Buntingsand implications for of first-year Indigo Buntings and theories of de- theories of delayed plumage maturation. Condor laved plumage maturation. Auk 103:28l-292. 93:209-235. Rot&a, S., &J. M ANNING. 1990. Differences in WALSBERG,Cl. E. 1983. Avian ecologicalenergetics, timing and number of molts for Baltimore and p. 16l-220. In D. S. Famer, J. R. King, and K. Bullock’s Orioles: implications to hvbrid fitness C. Parkes [eds.], Avian biology-. VII. Academic and theoriesof delayed plumagematuration. Con- Press, New York. dor 92: 125-140. WIGGINS.I. L. 1980. Flora of Baia California. Stan- ROOT,T. 1988. Atlas of North American winterina ford’univ. Press, Stanford, CA. birds. Univ. of Chicago Press, Chicago. - WILBUR,S. R. 1987. Birds of Baja California. Univ. Stmnvn. F.. ANDI. L. WIGCXNS.1964. Vegetation and of Calif. Press, Berkeley and Los Angeles. flora of the Sonoran Desert. Stanford Univ. Press, WILLOUGHBY,E. J. 1986.- An unusual-sequenceof Stanford, CA. molts and plumages in C&sin’s and Bachman’s SIBLEY,C. G., ANDL. L. SHORT. 1959. Hybridizations Sparrows. Condor 88:461472. in the buntings (Pusserina) of the Great Plains. YOUNG,B. E. 1989. First specimen record of Indigo Auk 76~443-463. Bunting (Passerim cyuneu) in British Columbia. SOKAL,R. R., ANDF. J. ROHLF. 1981. Biometry. 2nd Can. Field-Nat. 103:415. ed. W. H. Freeman and Co.. San Francisco.