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Achromatic plumage variation between and within hybridizing Black‐capped and Mountain chickadees

2021; Association of Field Ornithologists; Volume: 92; Issue: 2 Linguagem: Inglês

10.1111/jofo.12368

1557-9263

Katherine Feldmann, Kathryn C. Grabenstein, Scott A. Taylor,

Wildlife Ecology and Conservation

Feather coloration and patterning are major signals influencing mate choice within and between species. However, most studies of the role of plumage in mate choice have focused on colorful species with obvious sexual dichromatism. To better understand how achromatic plumage might influence hybridization, we quantified plumage variation between and within two achromatic songbirds that occasionally hybridize, Black-capped (Poecile atricapillus) and Mountain (P. gambeli) chickadees. We collected feathers from 43 live birds and photographed 155 prepared museum specimens to measure overall plumage color and the size of the throat and cheek patches. Using principal component analyses and generalized linear mixed models, we characterized plumage patterns within and between Black-capped and Mountain chickadees from Colorado to examine plumage color variation and differences in throat and cheek patch size. We found that Black-capped Chickadees (1) were less achromatic and had brighter plumage with more color contrast than Mountain Chickadees, (2) had smaller throat and cheek patches than Mountain Chickadees, and (3) were not sexually dimorphic. We also found that male Mountain Chickadee museum specimens had brighter plumage with more ultraviolet reflectance than female museum specimens (i.e., they are sexually dimorphic). However, we did not observe sexual dimorphism in live Mountain Chickadees, potentially because we did not sample the supercilium. In contrast to previous studies, we found that Black-capped Chickadees are not sexually dimorphic, potentially because plumage is not used in mating decisions for populations at lower latitudes. Between Black-capped and Mountain chickadees, differences in plumage color and patch sizes may influence hybridization if female Mountain Chickadees prefer the brighter plumage and greater color contrast of male Black-capped Chickadees. Our results will guide future work exploring the role plumage might play in hybridization between Black-capped and Mountain chickadees by informing plumage manipulation experiments investigating the influence of brighter plumage and color contrast in hybridization. Variación acromática del plumaje inter- e intra-híbridos en los carboneros Poecile atricapillus y P. gambeli La coloración y patrones de las plumas son señales mayores que influencian la selección de parejas intra- e interespecíficamente. Sin embargo, la mayoría de los estudios del papel del plumaje en la selección de pareja se han enfocado en especies coloridas con un evidente dicromatismo sexual. Para entender mejor cómo el plumaje acromático podría influenciar la hibridación, cuantificamos la variación del plumaje intra- e inter-específica de dos aves canoras que ocasionalmente se hibridan, los carboneros Poecile atricapillus y P. gambeli. Colectamos plumas de 43 aves vivas y fotografiamos 155 especímenes de museo para medir el color total del plumaje y el tamaño de los parches de garganta y mejillas. Usando un análisis de componentes principales y modelos lineales generalizados mixtos, caracterizamos los patrones del plumaje intra- e inter-específicos de estos carboneros de Colorado para examinar la variación y las diferencias en el tamaño de los parches de garganta y mejillas. Encontramos que P. atricapillus (1) fueron menos acromáticos y tuvieron un plumaje más brillante con más contraste de color que P. gambelli, (2) tenían parches de garganta y mejillas más pequeños que los de P. gambelli y (3) no son sexualmente dimórficos. También descubrimos que los especímenes de museo de machos de P. gambelli tenían un plumaje más brillante con mayor reflectancia ultravioleta que los especímenes de museo de hembras (i.e., son sexualmente dimórficos). Sin embargo, no observamos dimorfismo sexual en P. gambelli vivos, potencialmente porque no muestreamos el supercilium. En contraste con estudios previos, encontramos que P. atricapillus no son sexualmente dimórficos, potencialmente porque su plumaje no se usa en decisiones de apareamiento en poblaciones a latitudes más bajas. Entre P. atricapillus y P. gambelli, las diferencias en color del plumaje y los tamaños de parche podrían influenciar la hibridación si las hembras de P. gambelli prefieren el color más brillante y con mayor contraste de color de los machos de P. atricapillus. Nuestros resultados guiarán trabajo futuro para explorar el papel que el plumaje podría jugar en la hibridación entre estos carboneros, informando experimentos de manipulación de plumaje para investigar la influencia del brillo y el contraste de color del plumaje en la hibridación. Table S1. Repeatability of spectrophotometer measurements—for each wavelength measured using a spectrophotometer, mean and standard deviation for repeated measurements. We measured each patch (i.e., head, throat, cheek and side) for each individual three times. We averaged and computed standard deviation of measurements for each individual and then averaged these values for all individuals for Black–capped and Mountain chickadees. Wavelength1 includes measurements from 300–700 nm. Table S2 Principal component explained variance and loadings for the interspecific, intraspecific Black-capped Chickadee (BCCH) and intraspecific Mountain Chickadee (MOCH) museum specimen models. Columns describing the color variables include Orientation1, Region2, Wavelength3 and Variable4. Orientation1 values include Dorsal (D), Ventral (V) and Lateral (L). Region2 values include Dark (D) and Bright (B). Wavelength3 values include Longwave (LW), Mediumwave (MW), Shortwave (SW), Ultraviolet (UV) and Double-cone (DBL) Reflectance. Variable4 values include Mean (M), Standard Deviation (SD) and Coefficient of Variation (CoV). For entire image variables, Region2 and Wavelength3 describe the variables: Weighted Luminance (Luminance), Weighted RNL Saturation (RNL Sat.), Weighted Luminance Boundary Strength (Lum. BS) and Weighted RNL Saturation Boundary Strength (RNL BS). The value next to the label for each PC indicates the explained variance. Table S3. Comparing interspecific models with and without an interaction between species and sex for the museum specimen and live bird color models. We compared models with and without an interaction using AIC—where models with an interaction were more parsimonious. Entire model results (i.e., models with an interaction) can be found in Tables 2 (museum specimen color) and 4 (live bird color). Table S4. Comparing interspecific models with and without an interaction between species and sex for the museum specimen area model. We compared models with and without an interaction using AIC—where models with an interaction were more parsimonious. Entire model results (i.e., models with an interaction) can be found in Table 3 (museum specimen area). Table S5. Principal component explained variance and loadings for the interspecific, intraspecific Black-capped Chickadee (BCCH), intraspecific Mountain Chickadee (MOCH) and intraspecific Black-capped Chickadee (BCCH) cheek live bird models. Columns describing the color variables include Patch1 and Wavelength2. Patch1 values include Head (H), Throat (T), Cheek (C) and Side (S). Wavelength2 values include 10 nm wavelength ranges from 300–700 nm and overall brightness (bright) for each patch. The value under the label for each PC indicates the explained variance. 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