The two main pigment types in bird feathers are the red, orange, and yellow carotenoids and the black, gray, and brown melanins. Reports conflict, however, regarding the potential for melanins to produce yellow colors or for carotenoids to produce brown plumages. We used high-performance liquid chromatography to analyze carotenoids and melanins present in the yellow and brown feathers of five avian species: Eastern Bluebirds (Sialia sialis), Barn Swallows (Hirundo rustica), King Penguins (Aptenodytes patagonicus), Macaroni Penguins (Eudyptes chrysolophus), and neonatal chickens (Gallus domesticus). In none of these species did we detect carotenoid pigments in feathers. Although carotenoids are reportedly contained in the ventral plumage of European Barn Swallows (Hirundo rustica rustica), we instead found high concentrations of both eumelanins and phaeomelanins in North American Barn Swallows (H. r. erythrogaster). We believe we have detected a new form of plumage pigment that gives penguin and domestic- chick feathers their yellow appearance. No Puedes Juzgar un Pigmento por su Color: Contenido de Carotenoide y Melanina de Plumas Amarillas y Marrones en Golondrinas, Azulejos, Pingüinos y Gallinas Domésticas Resumen. Los dos tipos principales de pigmentos que las aves incorporan en sus plumas son carotenoides, para desarrollar plumajes rojo, naranja o amarillo, y melaninas, para adquirir coloración negra, marrón, gris o tonalidades color tierra. Sin embargo, existe información conflictiva sobre la potencial coloración de plumas amarillas basadas en melanina y la presencia de caroteniodes en el plumaje marrón de ciertas especies. En este estudio, usamos cromatografía líquida de alto rendimiento para analizar los tipos y cantidades de carotenoides y melaninas presentes en las plumas amarillas y marrones de cinco especies de aves: el azulejo Sialia sialis y la golondrina Hirundo rustica, los pingüinos Aptenodytes patagonicus y Eudyptes chrysolophus y el plumón natal amarillo de la gallina doméstica Gallus domesticus. En ninguna de estas especies detectamos pigmentos carotenoides en las plumas. A pesar de que los carotenoides han sido encontrados en el plumaje ventral de la golondrina Hirundo rustica rustica, nosotros en cambio encontramos altas concentraciones de eumelaninas y feomelaninas en H. r. erythrogaster y en azulejos que variaron entre individuos y regiones de plumaje. Creemos que hemos detectado una nueva forma de pigmento de plumaje que le da a las plumas de pingüinos y pollos domésticos su apariencia amarilla.

Several hypotheses have been proposed to explain cyclic fluctuations in abundance of some small mammal populations. These hypotheses have been controversial, however, and there is no consensus among biologists as to why population cycles occur. In a demographically based model, we tested the potential influence of phase-specific changes in life history traits (age at maturity, fertility, juvenile survival and adult survival) on population cycles. Our demographic model considers, and is logically consistent with, the empirical pattern of population characteristics during a cycle. The essence of the model is that phase-specific changes in age at maturity, abetted secondarily by changes in juvenile survival, result in cyclic fluctuations in population size. Changes in adult survival and fertility may playa minor role, but they are neither necessary nor sufficient by themselves to generate population cycles. Phasespecific changes in age at maturity might be related to primary changes in the quality of the ecological and social environment that permit particularly high densities.

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Considerable controversy surrounds the importance of inbreeding in natural populations. The rate of natural inbreeding and the influences of behavioral mechanisms that serve to promote or minimize inbreeding (e.g., philopatry vs. dispersal) are poorly understood. We studied inbreeding and social structuring of a population of black-tailed prairie dogs (Cynomys ludovicianus) to assess the influence of dispersal and mating behavior on patterns of genetic variation. We examined 15 years of data on prairie dogs, including survival and reproduction, social behavior, pedigrees, and allozyme alleles. Pedigrees revealed mean inbreeding coefficients (F) of 1-2%. A breeding-group model that incorporated details of prairie dog behavior and demography was used to estimate values of fixation indices (F-statistics). Model predictions were consistent with the minimization of inbreeding within breeding groups ("coteries," asymptotic F = -0.18) and random mating within the subpopulation ("colony," asymptotic F = 0.00). Estimates from pedigrees (mean F = -0.23, mean F = 0.00) and allozyme data (mean F = -0.21, mean F = -0.01) were consistent with predictions of the model. The breeding-group model, pedigrees, and allozyme data showed remarkably congruent results, and indicated strong genetic structuring within the colony (F = 0.16, 0.19, and 0.17, respectively). We concluded that although inbreeding occurred in the colony, the rate of inbreeding was strongly minimized at the level of breeding groups, but not at the subpopulation level. The behavioral mechanisms most important to the minimization of inbreeding appeared to be patterns of male-biased dispersal of both subadults and adults, associated with strong philopatry of females. Incest avoidance also occurred, associated with recognition of close kin via direct social learning within the breeding groups.