Pattern and Chronology of Prebasic Molt for the Wood Thrush and Its Relation to Reproduction and Migration Departure

Wilson Bull., 110(3), 1998, pp. 384-392

PATTERN AND CHRONOLOGY OF PREBASIC MOLT FOR THE WOOD THRUSH AND ITS RELATION TO REPRODUCTION AND MIGRATION DEPARTURE

J. H. VEGA RIVERA,1,3 W. J. MCSHEA,* J. H. RAPPOLE, AND C. A. HAAS ’

ABSTRACT-Documentation of the schedule and pattern of molt and their relation to reproduction and migration departure are important, but often neglected, areas of knowledge. We radio-tagged Wood Thrushes (Hylocichlu mustelina), and monitored their movements and behavior on the U.S. Marine Corps Base, Quantico, Virginia (38” 40 ’ N, 77” 30 ’ W) from May-Oct. of 1993-1995. The molt period in adults extended from late July to early October. Molt of flight feathers lasted an average of 38 days (n = 17 birds) and there was no significant difference in duration between sexes. In 21 observed and captured individuals, all the rectrices were lost simultaneously or nearly so, and some individuals dropped several primaries over a few days. Extensive molt in Wood Thrushes apparently impaired flight efficiency, and birds at this stage were remarkably cautious and difficult to capture and observe. All breeding individuals were observed molting l-4 days after fledgling independence or last-clutch predation, except for one pair that began molt while still caring for fledglings. Our data indicate that energetics or flight efficiency constraints may dictate a separation of molt and migration. We did not observe Wood Thrushes leaving the Marine Base before completion of flight-feather molt. Departure of individuals with molt in body and head, however, was common. We caution against interpreting the lack of observations or captures of molting individuals on breeding sites as evidence that birds actually have left the area. We argue also that current reports on overlapping of molt and migration based on observations of molting individuals out of the breeding range could be misleading because some individuals may leave the breeding area to molt in other places before starting a true migration. Received 30 June 1997, accepted 18 March 1998.

The Wood Thrush (Hylocichla mustelina) is slow, diurnal migration with frequent feeding one of the most studied avian species in North stops (e.g., hirundinids; Niles 1972). America, and details about its natural history The scarcity of information about timing are relatively well known (Roth et al. 1996 and patterns of molt in Wood Thrushes and and citations therein). Despite this, informa- many other species is not unexpected. During tion about its molt is limited and details on the molt period, birds become secretive and how molt is integrated with reproduction and less likely to be observed or caught, making migration departure are lacking. Separation of documentation of activities during this period reproduction, molt, and migration within the difficult (Ginn and Melville 1983). Because annual cycle is considered an evolutionary individuals of some species move away from strategy to reduce energetic stress (Payne their breeding territory for molting (Nolan 1972, Ginn and Melville 1983) but excep- 1978, Cherry 1985, Rappole and Ballard tions exist. Overlap of reproduction with 1987) following these individuals can be dif- flight- feather and extensive body molt is ap- ficult. Consequently, molt data often come parently common in tropical species (Payne from observations and/or recoveries of indi- 1972, Foster 1974). In temperate regions, its viduals of unknown breeding history or when occurrence has been reported in some species known, these relationships have not yet been that breed at high latitudes where food re- investigated. In recent years there has been an sources are abundant only briefly (Payne increased interest in use of radiotelemetry for 1972). Joint occurrence of molt and migration the study of small birds, mainly because of is less common, except for species with a the improvement in transmitter technology (i.e., smaller size). Transmitters are still relatively expensive and of limited range and life, ’ ’ Virginia Polytechnic Institute and State Univ., Dept. but radiotelemetry-based studies can provide of Fisheries and Wildlife Sciences, Blacksburg, VA information that otherwise would be difficult 24061-0321. to obtain. * Conservation and Research Center, 1550 Remount Rd., Front Royal, VA 22630. The objectives of the study were (1) to pro- 3 Corresponding author; vide information on the patterns and chronol- E-mail: [email protected] ogy of the prebasic molt in the Wood Thrush,

384 Vega Rivera et al. l WOOD THRUSH MOLT 385 and (2) to discuss the interaction between re- receiver (Telonics Communications, Inc.). When a production, molt, and migration departure. birds’ signal could not be found at its previous loca- For the Wood Thrush, a long-distance mi- tion, we searched first along roads using a l-element antenna mounted on the roof of a truck. If loss of con- grant of conservation concern (Hunter 1992) tact lasted more than 4 days, we also performed aerial identification of the schedule of molt and its radiotracking with a Cessna 172 at 350-500 m above relation to reproduction and timing for migra- ground in an area roughly 7 km in radius centered on tion are important for a better understanding a birds’ last known location. We assumed that a bird of its biological cycle. Also, identification on had left the study area if we could not detect its signal during the aerial search. Signal loss also could have how the molt process may modify the behav- been due to transmitter failure, but our experience with ior of individuals and their vulnerability to these transmitters indicates that transmitter failure was predation may be critical to the conservation rare. of this species. For all captured individuals, we recorded the stage (old, missing, in pin, emerging, full grown/new) of STUDY AREA AND METHODS remiges and rectrices and the condition of body molt. Additionally, in 8 of the 18 adults captured in molt, The study was conducted at the U. S. Marine Corps we recorded the length of flight feathers. Primaries, Base in Quantico, Virginia, which is located 56 km which number 10 in Wood Thrushes (10th vestigial, southwest of Washington, D.C. on the eastern edge of not considered), were numbered one to nine distally the Piedmont Plateau physiographic region, along the from the carpal joint. The secondaries were numbered west bank of the Potomac River (Hunt 1967). The Ma- one to nine from the carpal joint inward to the body, rine Base covers an area of 24,364 ha of which 75% including the tertials S7-S9. The six rectrix pairs were is forested. The most common vegetation types in- numbered one to six distally from the center of the cluded American beech (Fagus grandifolia), yellow tail. Molt on four regions of the body was scored using poplar (Liriodendron tulipzfera), oak (Quercus spp.) the terminology of Niles (1972). (47.5% of the forested area); Virginia pine (Pinus vir- We pinpointed locations by approaching each bird ginianus, 16.2%), and Virginia pine/oak (15.2%). until it moved. When possible, we made continuous From May to October 1993-1995, we captured, ra- observations on the birds’ behavior up to 30 minutes dio-tagged, and monitored the movements and behav- after locating it. Specifically, we noted the type of ac- ior of 42 juvenile and 61 adult Wood Thrushes as a tivity (foraging or perching), substrate (ground, bush, part of a larger study on the behavioral ecology and tree), and interactions with conspecifics. Direct obser- habitat use of this species during the breeding and vation of radio-tagged birds allowed us to record if a postbreeding periods (Vega Rivera 1997). During the bird was involved with breeding activities (either in- breeding season, we captured and radio-tagged females cubating, brooding nestlings, or caring for fledglings) and males positively identified as reproducing (i.e., or molting. To obtain data on onset of molt and date those whose nests were found or who were associated of departure from the study area, we relied on radio- with fledglings). Juveniles were captured during the tracking data. Incipient molt was difficult to observe nesting period by locating active nests, and during the from a distance; therefore, for most birds we approx- postfledging period by mist-netting. imated the beginning of the molting period by back- Because some adult birds were killed by predators, dating 15 days from the time we observed the birds in lost their transmitter, or left the study area before ini- heavy molt. We based this approach on the observation tiating molt, this analysis was based on observations that 13-16 days elapsed for four individuals captured of 30 radio-tagged individuals. Five of these birds before they started molting and later captured the first were recaptured when molting. Additionally, we cap- time they were observed in heavy molt. Additionally, tured 13 molting adults for which we did not have for eight birds that changed locality after reproducing, previous data on reproductive activities. Information a similar period elapsed between the day they moved on juvenile molt was obtained from the capture of 23 to the new locality and the first day on which they molting individuals; 21 of these were captured after were observed in heavy molt. they had dispersed. Throughout the paper, individual Wood Thrushes are Adult and fledgling Wood Thrushes were fitted with referred to by a specific letter prefix followed by three radio transmitters attached using a backpack harness numbers. The letter prefix refers to the individuals’ (Rappole and Tipton 1991). Each transmitter weighed age/sex category: M = adult male, F = adult female, 2.1 g (Holohil Systems Ltd., Woodlawn, Ontario, Can- J = juvenile, and U = adult of unknown sex. Values ada) and made up 5-6% of the birds’ body weight presented are means 2 SE. In all statistical tests a when attached. We detected no effect on the behavior probability of 0.1 or less was accepted as significant. of radio-tagged birds as compared with those without All statistical analyses were performed using SAS transmitters. Transmitters had an average life of at least (version 6.03 for PC) software. 120 days, and could be detected at distances of 400- RESULTS 1000 m on the ground, and l-3 km from the air. Radio-tagged birds were located on foot on alternate Most Wood Thrushes arrived at the study days using a 4-element Yagi antenna and a 12-channel area in late April and early May. Nestlings 386 THE WILSON BULLETIN l Vol. 110, No. 3, September 1998 from first and second clutches fledged in late birds. Molt of secondaries, Sl-S6, started May-early June and late July-early August, when replacement of the primaries was al- respectively. For most pairs, timing of clutch- ready underway; shedding of Sl occurred as es subsequent to the first was associated with P5 was out of the pin. Simultaneous replace- the success or failure of previous clutches. ment of two or three secondary feathers was The latest record of an adult attending fledg- observed in three individuals. lings was 14 September, but most adults Twenty-one individuals lost all rectrices at (90%) in the population completed their once. They were observed without tail feath- breeding activities by mid-August. ers or with growing rectrices of the same size. Of 61 adult birds radio tagged during the Shedding of the rectrices occurred shortly af- study, six birds were killed, seven lost their ter P5 was replaced, and finished with the re- transmitters during nesting, and 18 (15 F and placement of P9 or shortly after. 3 M) left the study area after nest failure or Body molt started before that of remiges fledgling independence. Of these, 13 females and rectrices. Two males were captured show- and 1 male left in June and early July, and 2 ing body molt while still possessing all of females and 2 males left in late July-August. their old flight feathers. By the onset of molt Thirty (10 F and 20 M) adults stayed at the in remiges and rectrices, body molt was ex- study area for molting. Of these, 11 (6 F and tensive, and continued at least 13 + 1.4 days 5 M) molted in the same area where they nest- (n = 12) after molt of flight feathers was ter- ed; 4 males moved to deciduous sapling minated or in its final growth stages. We base stands adjacent to their nesting territories and this statement on our observation of adults in 15 (4 F and 11 M) moved 2015 ? 520 m full-new plumage still showing molt on the (range 545-7291 m) from the mature decid- head the day before they left. uous or deciduous-pine forest where they had Molt chronology in adults.-The earliest nested to Virginia pine forest, young decidu- record of a molting adult was of a male cap- ous stands, or forest edges where they molted. tured on 27 July with moderate molt on breast Pattern of molt in adults.-A composite and sides. The earliest and latest records of pattern of molt in adult Wood Thrushes is in- adults observed having completed molt were ferred from 18 captured individuals for which 16 September and 14 October, respectively. we recorded the molt stage. In eight of these For most adults, the molt period extended birds, we measured remiges and rectrices (Fig. from early August to late September (Fig. 2). 1). None of these birds was recaptured, there- Mean date for onset of molt was 10 August fore we lack information on rate of growth. (k2.1 days; females 15 August _‘ 3.4 days, n Loss of Pl marked the beginning of molt = 10; males 7 August 5 2.6 days, n = 17). in remiges. From there, molt proceeded se- Molt of rectrices and remiges lasted 38.4 ? quentially, with P9 the last feather replaced. 0.7 days (n = 17) with no significant differ- Similar size in adjacent growing remiges in ences (t-test, t = -0.90, P > 0.10) between five individuals suggested that replacement of males (38.9 ? 0.8 d; n = 11) and females these feathers may have occurred simulta- (37.5 ? 1.6 d; n = 6) . Complete molt lasted neously or nearly so. In four individuals, molt 52.0 5 1.1 days (n = 21), and was longer (t- of primaries in both wings showed some de- test: t = - 1.80, P < 0.10) in males (53.2 + gree of asymmetry. Molt of secondaries S7- 1.1 days, n = 15) than females (49.2 ? 2.3 S9 (tertials) and Sl-S6 was independent. Re- days; n = 6). Our data suggest that Wood placement of tertials apparently began at the Thrushes that started molting earlier in the same time as that of the inner primaries. The season extended the molt over a longer period order of replacement of tertials varied, and (Pearson correlation: r = -0.83, P < 0.001; was asymmetrical between wings for two n = 21; Fig. 3).

FIG. 1. Molt stage of adult Wood Thrushes captured Aug.-Ott. 1995-1996 in Quantico, Virginia. Dark bars represent old feathers; light-grey bars represent new full-grown and partially growing feathers; narrow-dark bars represent pin feathers. Birds with one wing had symmetrical molt. All birds had heavy feather growth on body. Vega Rivet-a et al. - WOOD THRUSH MOLT 387

M928 M975 Captured24 Aug Captured15 Aug

M527 U624 cCaptured 3 Sep Captured12 Sep

M514 U623 3 Captured2 Sep Captured12 Sep

A U663 M933 x Captured5 Sep Captured12 Sep 388 THE WILSON BULLETIN l Vol. 110, No. 3, September 1998

65 -

F568(94) _I (3)’ (40) r= -0 83, Pc 0 001 F696(95) 1 (36) M552(94) j (38 ’ (50) 60 M933(95)

M930(93) (47)

F991(95) (40 ’ (45) M951(93) (40) r:E.iI F929(93) (41) 2 F556(94) (42) (49) (39) L F603(95) (53) (37) e F509(95) WI -u M907(93) 8 M997(93) (56) (37) 3 M555(94) (50) a

m F516(94) -(I41 3 M928(94) (3)’ (49) (39) F F544(94) w (40) g M583(95) 7 5 M527(94) . (55) IO F9@4(93) (53) July August September M975(95) (56) (69) /^^~ Date for start of molt M514(94) (Jd, (59) F900(94) _ - (32) FIG. 3. Correlation between duration of molt (20 (44) M546(94) - (50) July = day 1) and date of onset of molt in adult Wood M599(95) cw Thrushes (Pearson Correlation Coefficient; r = -0.83, P < 0.001).

we compared the mean distance between con- secutive radiolocations in nesting versus molt- FIG. 2. Molt chronology in adult Wood Thrushes ing sites for 23 birds (114 2 9 m and 67 2 8 breeding in Quantico, Virginia. Numbers above and at m, respectively; Wilcoxon test: Z = 3.13, P the end of the lines indicate the duration (days) of = 0.002) and size of the area used (95% con- flight-feather and complete molt, respectively. A dot- ted line represents a bird staying in the molting area vex polygon, 2.6 L 0.5 ha and 1.4 ? 0.3 ha, after the end of the molt. A circle indicates that the respectively; Z = 1.88, P < 0.1). transmitter fell off the bird. A square indicates that the Overlap between reproduction and molt.- bird was killed. For molting birds for which we obtained breeding data, molt was initiated after reproduction was completed. For these birds, molt Adult behavior during molt.-According to began l-4 days after their young reached in- our observations of radio-tagged adults, heavy dependence or after nest failure. We observed molt seriously impaired maneuverability and only one pair caring for fledglings while molt- ability to sustain flight. We observed five in- ing. This pair was captured when we radio- dividuals that for at least 10 days could barely tagged their three nestlings, on 22 August. fly. For instance, while we tracked a molting The male had general, light body molt. On 6 female, she was observed to hop 1 m up a September, while still caring for one fledgling, branch from which she attempted to fly but the male had lost his rectrices and showed could not. She fell to the ground, and disap- heavy general body molt. It was not until sev- peared, hopping and flapping her wings. Molt- en days later that the fledglings became in- ing adult Wood Thrushes, at least during the dependent. The female attended two of the heaviest molt stage, were very difficult to ob- three fledglings. At the time of capture she serve, and almost impossible to capture in was not molting. On 14 September, while still mist nets. They hid on the ground in the dens- caring for one fledgling, she was in heavy est patches of vegetation where, on occasions, general body molt. Next day the fledgling had we had to approach within 3 m to make them dispersed, and the female was without rectri- move, and ensure that they were alive. These ces. behavioral changes were also evident when Overlap between molt and migration de- Vega Rivera et al. l WOOD THRUSH MOLT 389 parture-Twenty-three of 30 birds that bred individuals for which we had information on and molted at the study area, and for which breeding activities suggest that emancipation we had data, left between 15 September and from parental care by one parent corresponded 14 October. All of these birds had completed to initiation in molt in that parent. This ob- flight feather molt by the time they left. Five servation agrees with published information individuals were known to still have head from studies of other passerine species where molt in progress on the day before they left. known breeding pairs have been identified Prebasic molt in juveniles.-We captured (e.g., Morton and Welton 1973, Sealy 1979, 23 juvenile Wood Thrushes in moderate to Tiainen 1981). heavy general body molt. The earliest date on Behavior during molt.-Flight efficiency in which a juvenile in molt was captured was 27 adult Wood Thrushes was reduced during ex- July. This was an individual with incomplete- tensive molt. Twenty-one birds on which we ly grown rectrices and light molt on the sides. had observations lost all rectrices at once and Nine more juveniles were captured from 9-20 five lost several primaries over a short time. August and 12 from 2-5 September. The last Simultaneous replacement of flight feathers in date on which a molting juvenile was captured waterfowl, resulting in temporary flightless- was 18 September. Juveniles left the study ness, is well known (Jehl 1990). In passerines, area in September and early October, with there are scattered reports that extensive molt 47% leaving in September. may impair or even prevent flight (e.g., Hau- kioja 1971, Verbeek 1973, Rimmer 1988). DISCUSSION Haukioja (1971) suggested that this condition Molt in adults.-The replacement of remi- in passerines is probably more common than ges in Wood Thrushes, including the tertiaries has been estimated from captures or visual ob- which were molted ahead of the other second- servations, but furtive behavior associated aries, was typically passerine (Dwight 1900). with this condition made its detection difficult. Simultaneous molt of rectrices, which oc- Lack of observations or captures of molting curred routinely in our population, is not a individuals on their nesting sites have been common pattern in passerines (Pyle et al. used as justification for the conclusion that 1987). In Wood Thrushes, its occurrence was birds actually have left the nesting area (for previously reported by Weaver (1949). Roth instance Sealy 1979). We caution against this and coworkers (1996) reported 3 adults that interpretation. In this study, if molting birds dropped all rectrices at once. The only other had not been radio-tagged, they would likely member of the Tiudiniae for which data are have passed unnoticed because they were fur- available is Swainsons’ Thrushes (Cutharus tive, silent, and flew very little. Capturing ra- ustulatus; Cherry 1985). Based on calculation dio-tagged molting Wood Thrushes using pas- from recaptured individuals, this species re- sive mist netting was difficult. On several oc- quired 32 days to complete flight-feather molt, casions, we surrounded molting birds with which is close to the measure reported here mist-nets and yet failed to capture them. Only for the Wood Thrush (38 days). active chasing of the birds toward the nets Sex differences in molt.-Our data suggest proved to be effective. that adult male Wood Thrushes commenced Reduced ability to fly may result in in- molt prior to adult females. Average date of creased predation, but during this study only onset of molt in males was eight days earlier two radio-tagged adults were predated while than for females. These results agree with nu- molting, whereas six were predated when they merous reports for other passerine species were nesting. Survival during extensive molt (e.g., Verbeek 1973, Rimmer 1988, Norman can be enhanced by behavioral inconspicu- 1990). In our population, the difference in on- ousness and/or selection of safe areas (Jehl set of molt between the sexes could have been 1990). Both strategies apparently were adopt- influenced by female dispersal. In this study, ed by molting Wood Thrushes; they were se- 15 females, but only 3 males that bred at the cretive and they molted in sites with vegeta- study area, left before molting. Thus, we did tion attributes, such as a dense understory, that not get information on when those females may have enhanced protection (Vega Rivera started molting. Our observations of molting 1997). 390 THE WILSON BULLETIN l Vol. 110, No. 3, September 1998

Relation between reproduction and molt.- parents probably are low. Also, at this time Separation of breeding and molt is considered fledglings are capable of full flight and thus a general strategy that allows these processes they are less vulnerable to predators which to occur with minimal nutritional stress makes parental role in this aspect less critical (Payne 1972, Morton and Welton 1973, Ginn (Vega Rivera 1997). Second, at the study area and Melville 1983; but see King and Murphy the onset of adult molt coincided with a time 1985, Murphy 1996). The initiation of molt when production of fruits and berries was while still caring for fledglings has been re- high. Based on our observations as well as ported for several species (e.g., Rimmer 1988, information in the literature (Martin et al. Norman 1990, Zaias and Breitwisch 1990, 1951, Conway et al. 1994, Roth et al. 1996), Evans Ogden and Stutchbury 1996). In our these resources are commonly eaten by Wood study, all known breeding Wood Thrushes ap- Thrushes in late summer and fall. parently began molt after their young reached Relation between molt and migration.-Si- independence or after nest failure, but two in- multaneous occurrence of flight feather or ex- dividuals were found molting while caring for tensive body molt and migration is considered fledglings. incompatible because of the negative effects It is possible that more Wood Thrushes on flight efficiency and nutritional condition started molting while still taking care of fledg- (Kjellen 1994). Indeed, for most species it is lings, but we lack documentation because of assumed that molt is scheduled so that migrant our inability to detect incipient body molt birds have fully functional flight feathers at without actually capturing the bird. When we the time of migration (Ginn and Melville recorded a bird as molting based on obser- 1983). Based on our observations, we have no vations only, it was the “notable molt” of No- evidence that Wood Thrushes molting at the lan (1978) that we recorded, i.e., a bird with study area left before the replacement of rem- heavy molt on the head or with missing/grow- iges and rectrices was complete. Departure ing flight feathers. None of the birds in this with light body molt was not uncommon. condition, with exception of the two birds There are, however, reports that individuals mentioned, were in the company of fledglings. of some species migrate while molting (e.g., In our radio-tagged population, reproduc- Hyytia and Vikberg 1973, Sealy 1979). We tive effort was apparently extended to a point suggest that many records of birds showing where it did not compromise the timing of flight feather or heavy body molt found out- molt and migration. Reproduction, from build- side the breeding range may represent relo- ing of the nest to fledgling independence, took cation to special molting sites rather than mi- about 51 days. Molt of flight feathers took an gration. Rappole and Ballard (1987) proposed average 38 days. If we consider that 91% of that birds of many species may move to spe- the adults left the study area between 22 Sep- cial molting areas safer from predators and/or tember-10 October, then the latest any pair with better food resources than nesting habi- should have initiated a clutch was 25 June-13 tats. Cherry (1985) captured molting Swain- July. These dates agree with our data. Except sons’ Thrushes 30, 150, and 250 km from the for one pair, which began nest building on 22 closest known breeding areas for the species. July, all breeding pairs initiated their last He concluded that Swainsons’ Thrushes are clutch before 13 July. unlikely to initiate actual southward migratory An overlap between care of fledglings and movement during the middle of molt. In our onset of molt would effectively prolong the study, 18 adults left the study area after nest potential reproductive period for an individual failure or fledgling independence. These birds (Foster 1974, Evans Ogden and Stutchbury were probably not migrating, but were moving 1996). We suggest that Wood Thrushes at- elsewhere to renest or initiate molt. We base tending the last brood of the season may ini- this conclusion on the fact that intensive study tiate molt a few days before fledgling inde- of this species documents that transients do pendence with minimal nutritional stress for not arrive in south Texas until late to mid- two reasons. First, close to independence, September (Rappole and Blacklock 1995) or Wood Thrush fledglings feed mostly by them- in Veracruz, Mexico, until early October selves; therefore their demands for food from (Winker et al. 1990). Vega Rivera et al. l WOOD THRUSH MOLT 391

We propose that birds that left the study nutritional stress in the annual cycles of endo- area relocated some distance from their nest- therms: fact or fiction? Am. Zool. 25:955-964. KJELLBN, N. 1994. Molt in relation to migration in ing sites to specific molting areas. They re- birds-a review. Ornis Svec. 4: l-24. mained for several weeks in these areas while JEHL, R. H. 1990. Aspects of the molt migration. Pp. completing molt and preparing for migration, 102-113 in Bird migration: the physiology and following a time sequence very similar to the ecophysiology (E. Gwwinner, Ed.). Spring-Verlag, birds that remained on the study area. Testing Berlin. of this hypothesis will require additional stud- MARTIN, A. C., H. S. ZIM, AND A. L. NELSON. 195 1. ies. American wildlife and plants: a guide to wildlife food habits. Dover Publications, Inc., New York. ACKNOWLEDGMENTS MORTON, M. L. AND D. E. WELTON. 1973. Postnuptial molt and its relation to reproductive cycle and We thank Dar1 Fletcher and David Condoulis for body weight in Mountain White-crowned Spar- excellent help with field work. We are grateful to the rows (Zonotrichia leucophrys oriantha) in central staff of the Natural Resources Branch at the Quantico Sierra Nevada. Condor 75: 184-189. Corps Marine Base, especially Tim Stamp, for their MURPHY, M. E. 1996. Energetics and nutrition of unconditional support and help during our work at the molt. Pp. 158-198 in Avian energetics and nutri- Quantico Marine Corps Base. J. B. Cruz, R. R. Root, tional ecology (C. Carey, Ed.). Chapman and Hall, and three anonymous reviewers provided comments on New York. the manuscript. This research was supported by the NILES, D. M. 1972. Molt cycles of Purple Martins U.S. Department of Defense, Legacy Program, as a (Progne subis). Condor 74:6 l-7 1. grant to the Smithsonian Institution. NOLAN, V., JR. 1978. 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