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Species limits in the genus Plectrophenax have been difficult to assess. McKay's Buntings (Plectrophenax hyperboreus) are very similar both morphologically and behaviorally to Snow Buntings (P. nivalis). However, their breeding ranges are allopatric, and there is limited evidence of gene flow. The juvenal plumage of McKay's Buntings has never been described as different from that of Snow Buntings. Comparison of a series of McKay's Buntings in juvenal plumage with a series of Snow Buntings in juvenal plumage showed clear differences between the two forms. We used color spectrophotometry to quantify the differences between the two taxa in two areas of the body that appeared to be consistently different, the throat and back. The relative magnitude of the difference between McKay's and Snow buntings was greater than homologous differences between two subspecies of Snow Bunting (P. n. nivalis and P. n. townsendi). Four out of six variables were significantly different between McKay's and Snow buntings, whereas none of the variables were significantly different between the two subspecies of Snow Bunting. Bonferroni corrected t-tests of sexual dimorphism and regression of the variables against year of collection showed that these factors were not associated with these differences. Discriminant analysis accurately separated 100% of the specimens into their respective groups. These differences are notable given the evolutionarily conservative nature of juvenal plumage. Our results support continued recognition of McKay's Bunting as a species and reconfirm the use of juvenal plumage to help determine species limits. Received 7 December 2005, accepted 25 July 2006. Key words: discriminant analysis, juvenal plumage, Plectrophenax, reflectance spectrophotometry, species limits. Los limites entre especies del genero Plectrophenax han sido dificiles de establecer. Plectrophenax hyperboreus es muy similar en morfologia y comportamienento a P. nivalis. Sin embargo, sus rangos de cria son alopatricos y la evidencia de flujo genetico es limitada. El plumaje juvenil de P. hyperboreus nunca ha sido descrito como diferente del de P. nivalis. Una comparacion de series de especimenes de P. hyperboreus y P. nivalis en plumaje juvenil mostro claramente que existen diferencias entre las dos formas. Utilizamos espectrofotometria de color para cuantificar las diferencias entre los dos taxones en dos regiones del cuerpo que parecian diferir consistentemente, la garganta y la espalda. La magnitud relativa de la diferencia entre P. hyperboreus y P. nivalis fue mayor que la de diferencias homologas observadas entre dos subespecies de P. nivalis (P. n. nivalis y P. n. townsendi). Cuatro de seis variables fueron significativamente diferentes entre P. hyperboreus y P. nivalis, mientras que ninguna de las variables fue significativamente diferente entre las dos subespecies de P. nivalis. Pruebas de t corregidas mediante Bonferroni para evaluar dimorfismo sexual y analisis de regresion de las variables contra el ano de coleccion, mostraron que esos factores no estan asociados con las diferencias. Analisis discriminantes separaron el 100% de los especimenes con exactitud en sus grupos respectivos. Estas diferencias son notables dada la naturaleza evolutivamente conservada del plumaje juvenil. Nuestros resultados apoyan el reconocimiento continuado de P. hyperboreus como una especie, y reconfirman el uso del plumaje juvenil para ayudar a determinar los limites entre especies.

Asian-origin avian influenza (AI) viruses are spread in part by migratory birds. In Alaska, diverse avian hosts from Asia and the Americas overlap in a region of intercontinental avifaunal mixing. [...]

The effects of seasonal migration on evolutionary change within lineages is poorly understood, in terms of both differentiation (cladogenesis) and specialization (anagenesis). Regarding differentiation, two contradictory hypotheses exist: Seasonal migration counters differentiation; or it can stimulate differentiation by exposing lineages to new environments. Regarding specialization, the morphological consequences of a migratory life history have not been well explored. We examined these issues by reconstructing morphological and molecular phylogenies of the genus Catharus (Turdidae), a group of forest-dwelling, New World thrushes traditionally considered to include a small 'species flock' of Nearctic-Neotropic migrants. DNA sequence data (2,920-3,027 base pairs) do not support traditional taxonomy, and morphological characters conflicted with these data. Results suggest that long-distance seasonal migration arose independently four times in Catharus sensu lato (including Hylocichla mustelina). Correlated morphological evolution occurred among several characters in these lineages, and these shared traits may stem from ecological conditions in Nearctic forests. Key words: Catharus, convergent evolution, ecological adaptation, molecular systematics, Nearctic-Neotropic migration, parallel evolution, species flocks, thrushes. Los efectos de la migracion estacional sobre el cambio evolutivo de los linajes son poco conocidos en terminos tanto de la diferenciacion (cladogenesis) como de la especializacion (anagenesis). Con respecto a la diferenciacion, existen dos hipotesis contradictorias: que la migracion estacional imposibilita la diferenciacion, o que esta puede estimular la diferenciacion al exponer a los linajes a ambientes nuevos. Con respecto a la especializacion, las consecuencias morfologicas de la historia de vida migratoria no han sido bien exploradas. Examinamos estos aspectos reconstruyendo filogenias morfologicas y moleculares del genero Catharus (Turdidae), un grupo de zorzales del nuevo mundo que tradicionalmente se ha considerado que contiene una pequefia 'bandada de especies' de migrantes neartico-neotropicales. Los datos de secuencias de ADN (2,920-3,027 pares de bases) no apoyan la taxonomia tradicional, y los caracteres morfologicos se encuentran en conflicto con estos datos. Los resultados sugieren que la migracion estacional que involucra grandes distancias surgio independientemente cuatro veces en Catharus sensu lato (incluyendo a Hylocichla mustelina). En estos linajes, sucedio evolucion correlacionada entre varios caracteres morfologicos. Estos rasgos compartidos podrian aparecer como consecuencia de las condiciones ecologicas de los bosques del Neartico.

Population genetic variation in Mallards (Arias platyrhynchos; n = 152) from Western Russia, North Asia, the Aleutian Islands, and mainland Alaska was investigated using 667 base pairs of the 5'-end of the mitochondrial DNA (mtDNA) control region. DNA sequencing revealed two clades that correspond to Avise et al.'s (1990) group A and B mtDNA haplotypes. Group A haplotypes (80.3%) were widespread in all localities from Western Russia to Alaska. Group B haplotypes (19.7%), by contrast, were found primarily in mainland Alaska, where they occurred at high frequency (77.4%), but they also occurred at low frequencies (declining east to west) in the Aleutian Islands (11.8%) and the Primorye region of North Asia (4.4%). Group B haplotypes were not observed in Western Russia or elsewhere in North Asia outside Primorye. Consequently, Mallards exhibited substantial genetic structure between Old World and New World ([[PHI].sub.ST] = 0.4112-0.4956) but possessed little genetic structure within the Old World continental area ([[PHI].sub.ST] = 0.0018). Nonetheless, when only group A haplotypes were included in the analysis, Mallards from the Aleutian Islands differed (albeit with low levels of divergence) from each of the other three sampled regions in the Old World and New World ([[PHI].sub.ST] = 0.0728-0.1461, P < 0.05). Mallards inhabit the Aleutian Islands year-round, so these insular populations may be isolated from Asian and North American populations that occur in the Aleutian Islands only during migration. Overall weak phylogeographic structure and low genetic differentiation within Asia, and between Asia and North America when only group A haplotypes were evaluated, is probably explained by large long-term population sizes and significant intra-continental dispersal. The coexistence and nonrandom distribution of two divergent mtDNA haplotype lineages in Alaska, the Aleutian Islands, and the Primorye region of North Asia, but not in Western Russia or elsewhere in North Asia, is consistent with historical and contemporary hybridization and incomplete sorting of A and B mtDNA haplotype lineages in Mallards and closely related species inhabiting the Old World and New World. Key words: Anas platyrhynchos, hybridization, incomplete lineage sorting, Mallard, paraphyly.

We studied fat stores in passerine migrants at a high-latitude site in Fairbanks, Alaska (64[degrees]50'N, 147[degrees]50'W). We examined fat-deposition strategies during the final (spring) and initial (autumn) stages of long-distance migration, 1992-1998, to (1) improve understanding of geographic fat-deposition patterns by adding a high-latitude perspective; (2) determine whether there are age-related differences in fat-deposition strategies in autumn; and (3) test the 'spring fatter' hypothesis of seasonal fat-deposition, which suggests that migrants should carry more fat in spring when they near their breeding areas than in autumn when they depart. Our analyses examined factors affecting daily fat scores during migration and compared between-season differences in fat stores among a total of 18,685 individuals of 16 migrant species. In autumn, adults had higher visible subcutaneous fat scores than immatures in 11 of 16 species. However, in all but two species, those differences were attributable to the effects of overnight low temperature, day length, and time of day, rather than age, probably because of later departures by adults. Fat scores were higher in autumn than in spring in 6 of 16 species, and body-condition indices were higher in autumn in 5 of 16 species. Only one species showed higher fat scores in spring, but that difference was not reflected in a seasonal comparison of body-condition indices. No species arrived with high fat loads in spring, and generally low fat levels in autumn suggest that high-latitude passerine migrants in North America are paying most of the energetic costs of long-distance migration with resources obtained en route to their wintering grounds. Among passerine migrants near these high-latitude breeding grounds, seasonal fat-deposition strategies appear to be responding to energetic needs at the level of daily maintenance, rather than to hypothesized insurance needs in spring or to the forthcoming needs of a long-distance migration in autumn. Received 16 October 2003, accepted 10 November 2004. Key words: birds, energetics, migration, Nearctic-Neotropic migrants, stopover ecology, subarctic stopover sites.

Research has been conducted on the genetic population structure. The method of approximating Weir and Cockerham's theta, the genetic population structure unbiased estimator, is described via the use of the biased estimators and the results indicate that the estimation algorithm is useful for both model populations and real-world avian populations.

The distribution of autumn migrants among Neotropical wooded habitats was examined using mist nets in a rainforest region of southern Mexico. Capture distributions and local movements from north and South (as reflected by net captures) were examined in 17 species. All species showed significant nonrandom distributions. Captures from the north were not more frequent than expected by chance. Local diurnal movements, therefore, do not reflect the known latitudinal movements occurring in these species, which makes it unlikely that local habitat use is simply the result of directional wandering. Although 65% of captured individuals were first-year birds having no previous experience with tropical rainforest, capture distributions suggested species-specific selectivity to a rather high degree. Also, in the 10 species with adequate sample sizes, distributions between early- and later-day captures tended to be remarkably constant. Habitat selection in these species may be largely endogenous. Received 30 Nov. 1993, accepted 25 Sept. 1994., Habitat selection in birds has long been an important area of study (see Hilden 1965, Cody 1985). The postbreeding, pre-wintering movements of migrant species brings a different aspect to this [...]

Understanding how gene flow affects population divergence and speciation remains challenging. Differentiating one evolutionary process from another can be difficult because multiple processes can produce similar patterns, and more than one process can occur simultaneously. Although simple population models produce predictable results, how these processes balance in taxa with patchy distributions and complicated natural histories is less certain. These types of populations might be highly connected through migration (gene flow), but can experience stronger effects of genetic drift and inbreeding, or localized selection. Although different signals can be difficult to separate, the application of high-throughput sequence data can provide the resolution necessary to distinguish many of these processes. We present whole-genome sequence data for an avian species group with an alpine and arctic tundra distribution to examine the role that different population genetic processes have played in their evolutionary history. Rosy-finches inhabit high elevation mountaintop sky islands and high-latitude island and continental tundra. They exhibit extensive plumage variation coupled with low levels of genetic variation. Additionally, the number of species within the complex is debated, making them excellent for studying the forces involved in the process of diversification, as well as an important species group in which to investigate species boundaries. Total genomic variation suggests a broadly continuous pattern of allele frequency changes across the mainland taxa of this group in North America. However, phylogenomic analyses recover multiple distinct, well supported, groups that coincide with previously described morphological variation and current species-level taxonomy. Tests of introgression using D-statistics and approximate Bayesian computation reveal significant levels of introgression between multiple North American taxa. These results provide insight into the balance between divergent and homogenizing population genetic processes and highlight remaining challenges in interpreting conflict between different types of analytical approaches with whole-genome sequence data. [ABBA-BABA; approximate Bayesian computation; gene flow; phylogenomics; speciation; whole-genome sequencing.] [ABSTRACT FROM AUTHOR]