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Flight Feather Molt of Turkey Vultures

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Flight Feather Molt of Turkey Vultures The Wilson Journal of Ornithology 122(2):354–360, 2010 FLIGHT FEATHER MOLT OF TURKEY VULTURES ROBERT M. CHANDLER,1,6 PETER PYLE,2,3 MAUREEN E. FLANNERY,3 DOUGLAS J. LONG,3,4 AND STEVEN G. HOWELL3,5 ABSTRACT.—We document the molt sequence of flight feathers in Turkey Vultures (Cathartes aura) based on studies of captive and wild birds, and examination of museum specimens. We found an unusual pattern of primary replacement, which appears to be a modified form of Staffelmauser, or stepwise wing molt. A Staffelmauser-like strategy for replacement of the secondaries is also described. These patterns of feather replacement appear to be adaptations to maintain flying performance while replacing all primaries and most secondaries during each molt. To what extent molt patterns in Turkey Vultures reflect convergent adaptation for flight, rather than ancestral characters useful for phylogenetic studies, remains unknown. Received 15 June 2009. Accepted 12 January 2010. Maintaining optimal flight performance is may not reflect that of wild birds (cf. Pyle 2005). essential for Turkey Vultures (Cathartes aura), a Snyder et al. (1987) based their molt study of species adapted for long-term soaring (Rosser and California Condors (Gymnogyps californianus)on George 1986, Tucker 1987). This species locates photographs of wild birds in flight. Bloom and its primary diet of carrion by detecting odor Clark (2001) used banding records with some plumes while aloft, and spends most daylight recaptures to study the molt of the Golden Eagle hours searching for food (Owre and Northington (Aquila chrysaetos), but sample sizes of known 1961, Stager 1964). It is a migratory species that individual birds are low in these studies. Ideally, a can travel hundreds or thousands of kilometers complete understanding of molt strategies would seasonally between southern wintering and north- be based on the study of wild birds, captive ern breeding areas (Stewart 1977, Kirk and individuals, and specimens; we present such an Houston 1995, Bildstein and Zalles 2001). analysis of molt in Turkey Vultures. Little is known about the molt of Turkey Vultures despite its widespread distribution and METHODS abundance (Kirk and Mossman 1998). Identifying A. M. Rea began collecting molt sequence data and understanding molt processes in birds can be on Turkey Vultures in 1972 as part of a larger accomplished in several ways. Miller (1941), study on the phylogenetic relationship of New Stresemann (1963), and Pyle (2005) used data World vultures (Rea 1983). Chandler joined the from museum study skins of raptors to make their project in 1978, collecting feathers from three basic molt sequence hypotheses. Analyzing molt adult individuals held captive at the San Diego patterns from study skins can be difficult and may Natural History Museum (SDNHM) in San Diego, not represent the progression of a single individ- California, USA and studying molt year-round on ual, and sample sizes of large birds are typically several others. Flannery and Long tabulated molt too low to undertake comprehensive analyses. data on five vultures (4 adults and 1first year bird) Houston (1975) observed flight feather replace- between 2002 and 2004, which were held captive ment in both captive and wild individuals of Old by the California Academy of Sciences (CAS) in World vultures (Gyps), but molt in captive birds San Francisco, California. The extended study period of captive individuals allows calculation of 1 Department of Biological and Environmental Sciences, feather replacement rates both within and between Georgia College and State University, Milledgeville, GA individuals to establish ranges of variation. Pyle 31061, USA. 2 Institute for Bird Populations, P. O. Box 1346, Point and Howell visually examined hundreds of Reyes Station, CA 94956, USA. vultures in the field, and Pyle and Flannery 3 Department of Ornithology and Mammalogy, California examined molt in over 20 museum specimens. Academy of Sciences, 55 Music Concourse Drive, San We classified ages of Turkey Vultures using Francisco, CA 94118, USA. head and bill coloration (Henckel 1981), and 4 Department of Natural Sciences, Oakland Museum of known history for captive individuals. Age coding California, 1000 Oak Street, Oakland, CA 94607, USA. 5 PRBO Conservation Science, 3820 Cypress Drive #11, of birds follows Pyle (1997): HY (hatching or first Petaluma, CA 94954, USA. calendar year), SY (second calendar year), TY 6 Corresponding author; e-mail: [email protected] (third calendar year), and ASY (at least third 354 The Wilson Journal of Ornithology wils-122-02-17.3d 10/3/10 11:26:37 354 Cust # 09-094 Chandler et al. N TURKEY VULTURE MOLT 355 calendar year). Chandler collected data from two representing the number of the primary that was captive (SDNHM) ASYs during 1972–1980 and a growing on the observation date. Individuals third ASY during 1979–1980. Flannery and Long with two primaries being replaced simultaneous- collected data from four captive ASYs (3 males ly from different parts of the wing (e.g., an inner and 1 female known to be ages 7+ to 25+ years) and an outer primary) were scored twice in the and a female received as an HY, housed at CAS data set. Secondary molt patterns also were during 2002–2004. The ASYs were from Okla- scored when visible. We analyzed the data using homa, Pennsylvania, and Texas; the HY, received atwo-tailedt-test with JMP Version 5.1 with down still present on the head and the statistical software (SAS Institute 2002) to majority of the beak still dark, was from examine whether or not there was a difference Tennessee and arrived in December 2001. All in mean dates of molt between captive and wild eight individuals were kept in outdoor pens, birds. ensuring they were acclimated to the natural local More than 20 specimens at CAS, Museum of photoperiod and climate. Vertebrate Zoology (MVZ), SDNHM, and the Primaries, secondaries, and rectrices for the National Museum of Natural History (USNM) vultures studied by Chandler (SDNHM) were were examined. Primaries and secondaries were painted with a dot and slash code to identify the scored in the same manner as captive birds, and specific feather (a dot 5 1 and a slash 5 5), and replacement sequences were inferred based on with a year-specific color for each individual for wear clines reflecting protracted molts (Pyle each year of study. The aviary was checked 2005). several times daily for dropped feathers, which were labeled and dated. Wings were examined RESULTS visually for the individuals at CAS, and dropped Primaries.—All data indicate the 10 primaries feathers were examined to tabulate wing molt of a Turkey Vulture molt sequentially from the data. Primaries and secondaries on each healthy innermost primary (P1) to the outermost primary wing of each individual were scored as old, (P10). This process started for the SY at CAS in missing, in pin, growing, or new. The percentage late January with P1 and was completed in late of feather length grown was recorded for each July with P10 (Fig. 1). This SY then replaced P1– growing feather. Data were collected weekly P3 for a second time within the year in during the first year of the study and biweekly or September–November (Fig. 1). The following monthly in subsequent years. Drop dates for each year, as a TY, this individual continued the primary on each bird were estimated by calcu- sequence where it had suspended the year before, lating primary-specific growth rates and obtain- replacing P4–P10 in order between early March ing mean, back-calculated dates for each feather. and early August, and replacing P1–P3 in August– Feathers not dropped that year were designated as September (Fig. 1). The captive ASYs at both being retained in both studies. locations replaced P5–P10 in March–September Pyle and Howell recorded data from 1998 to and replaced P1–P2 in July–August (Fig. 1). This 2006 on wing molt from Turkey Vultures in the pattern averaged later than the drop dates recorded field. Binoculars were used to score primaries as for the younger bird as an SY and a TY. missing, growing, new, or old. Molt was Replacement of P3 and P4 in ASYs was more assumed if the same primary was missing or variable (Fig. 1). growing on both wings simultaneously; individ- Based on the above results, data on P1–P4 from uals with a missing or growing primary on only birds in the field were partitioned as either one wing were not included in the data set. Data molting in August–November or in January– were collected year-round and, although most March (Fig. 2). The remaining primaries, P5– data were obtained from central California, at P10 had sequential mean dates of molt, beginning least 10 birds each from Maryland, Indiana, in April–May (P5) and finishing in September– Mexico, and El Salvador were scored. Vultures October (P10). This pattern was similar to that observed with dark heads and bills, and no recorded for captive birds of all ages (Fig. 2). primary molt in June-December were classified Mean dates of molt for P1–P4 and P7–P8 were not as HYs and not included in the data set. Analysis significantly different between captive and wild was based on date of observation and progres- birds. However, mean drop dates were signifi- sion of molt, including either no molt, or a score cantly earlier (2-tailed t-test, P , 0.01) in captive The Wilson Journal of Ornithology wils-122-02-17.3d 10/3/10 11:26:37 355 Cust # 09-094 356 THE WILSON JOURNAL OF ORNITHOLOGY N Vol. 122, No. 2, June 2010 FIG. 1. Calculated feather drop date by month for Turkey Vultures. Data collected from Turkey Vultures held captive at the California Academy of Sciences.
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