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Research suggests that two newly discovered exon 3 insertions in the nuclear proto-oncogene c-myc may be responsible for shared common ancestry between the New World oscines Cardinalinae, Emberizinae, Icteridae, Parulidae and Thraupinae. These groups possess three amino acids inserted at the 991 position within the chicken sequence.

We examined patterns of variation in skeletal morphometrics (29 characters), allozymes (34 loci), mitochondrial DNA (mtDNA) restriction sites (n = 74) and fragments (n = 395), and mtDNA sequences (1,739 bp from cytochrome b, ND2, ND6, and the control region) among all species of Toxostoma. The phenetic pattern of variation in skeletal morphometrics generally matched traditional taxonomic groupings (based on plumage patterns) with the exceptions of T. redivivum, which because of its large size clusters outside of its proper evolutionary group (lecontei), and T. occelatum, which did not cluster with T. curvirostre. Skull characters contributed highly to species discrimination, suggesting that unique feeding adaptations arose in different species groups. Although genetic variation was detected at isozyme loci (average heterozygosity = 3.6%), these data yielded little phylogenetic resolution. Similarly, mtDNA restriction sites were relatively uninformative; hence, phylogenetic conclusions were based on sequence data. Phylogenetic analyses confirmed the monophyly of these traditionally recognized assemblages: rufum group (T. rufum, T. longirostre, and T. guttatum ), lecontei group (T. lecontei, T. crissale, and T. redivivum ), and cinereum group (T. bendirei and T. cinereum). The cinereum and lecontei groups appear to be sister lineages. Monophyly of the curvirostre group (which also includes T. occelatum) was not confirmed. Sequence data suggest that T. occelatum and T. curvirostre, which differ by 7.7% sequence divergence, are probably most closely related to the rufum group. Toxostoma rufum and T. longirostre have similar external appearances and differ by 5.0%. Toxostoma guttatum is restricted to Cozumel Island and often is considered a subspecies of T. tongirostre; it differs by more than 5% from the other two members of the rufum group and is a distinct species constituting the basal member of this group. The phenotypically distinctive T. bendirei and T. cinereum differ in sequence divergence by only 1.6%. Overall, mtDNA distances computed from coding genes (mean 8.5%) exceeded distances computed from the control region (mean 7.6%), contrary to expectation. Because neither allozymes nor mtDNA could unambiguously resolve the placement of T. occelatum and T. curvirostre, a scenario involving contemporaneous speciation is suggested. Application of a molecular clock suggested that most speciation occurred in the late Pliocene or early Pleistocene.

We estimated genetic differentiation between morphologically distinct tidal marsh populations of Swamp Sparrows (Melospiza georgiana nigrescens) and the more widespread inland populations (M. g. georgiana and M. g. ericrypta). The tidal marsh populations are consistently grayer with more extensive black markings (particularly in the crown), and their bills are larger These differences are variously shared with other species of salt marsh birds and small mammals. We analyzed mitochondrial DNA sequences (5[prime] end of control region, COII/ t-lys/ATPase8, and ND2) of Swamp Sparrows and found low levels of genetic variation and no evidence of geographic structure. These results suggest a rapid and recent geographic expansion of Swamp Sparrows from restricted Pleistocene populations. Morphological differentiation has occurred without long-term genetic isolation, suggesting that selection on the divergent traits is intense. The grayer and more melanistic plumage is probably cryptic coloration for foraging on tidal mud, which tends to be grayish as a result of the formation of iron sulfides, rather than iron oxides, under anaerobic conditions.

We amplified and sequenced a 711 base-pair (bp) fragment of mtDNA at the cytochrome-b locus to reexamine relationships within and among species of Sphyrapicus and representatives of two other woodpecker genera (Melanerpes, Colaptes). Sequences were obtained from 10 individuals of 5 taxa: Red-breasted Sapsucker (S. ruber daggetti), n = 2; Red-naped Sapsucker (S. nuchalis), n = 2; hybrid of S. ruber daggetti x S. nuchalis, n = 1; Yellow-bellied Sapsucker (S. varius varius), n = 2; Williamson's Sapsucker (S. thyroideus thyroideus), n = 2; and Red-bellied Woodpecker (M. carolinus), n = 1. The Melanerpes sequence and a comparable published sequence of Andean Flicker (C. rupicola) were used as outgroups. Levels of mtDNA sequence divergence ranged from 0.0 to 0.6% within species and 0.1 to 10.2% among species of Sphyrapicus, and from 12.5 to 14.5% between members of Sphyrapicus and the two outgroup species. One region of sequence (78 bp) was identified as being especially conserved. Branching topologies based on this study corroborated results from a previous analysis of relationships in Sphyrapicus using allozymes: the phenotypically dissimilar species ruber and nuchalis are most closely related; varius, which is very similar in appearance to nuchalis, branches off next; and thyroideus, the most divergent member of the quartet from the standpoint of plumage pattern and degree of sexual dimorphism, is strongly differentiated genetically. Pairwise mtDNA distances within Sphyrapicus showed a strong curvilinear relationship with allozyme distances (r = 0.996). The monophyly of Sphyrapicus is reaffirmed, with S. thyroideus closer to the ancestral species. Members of Sphyrapicus are more similar to Melanerpes than to Colaptes based on their mtDNA. Prior hypotheses regarding the evolutionary history of sapsuckers in North America are discussed. Despite the near genetic identity of ruber and nuchalis based on both allozymes and mtDNA sequences, and their tendency for limited hybridization in sympatry, an earlier study of mating preference supports the biologic-species status of these taxa.

We review recent developments in the debate over species concepts, exploring differences between the biological species concept (BSC) and the phylogenetic species concept (PSC). Three principal flaws in the BSC are reviewed: (1) the occurrence of paraphyletic or nonhistorical groups; (2) the misrepresention of the significance of hybridization among differentiated taxa; and (3) the logical difficulty in handling allopatric populations. Simple cline theory shows that likely times to fusion for hybridizing taxa exceed the average duration of most species in the fossil record. We address criticisms of PSCs (of which there are several), including the application of phylogenetic methods to populations, and whether species can be monophyletic. We suggest that the evolutionary species concept and the PSC might be more similar than generally appreciated. Empirical studies of variation in the Brown Towhee (Pipilo fuscus) complex and Fox Sparrow (Passerella iliaca) reveal that the BSC and PSC can lead to different species limits. Reasons are given for why the PSC is the preferred concept for comparative biology, phylogenetic inference, historical biogeography, estimation of bio-diversity, hybrid-zone analysis, conservation biology, and speciation analysis. Despite problems associated with all species concepts, we think that a concept consistent with the PSC should replace 'biological' species concepts.

Recently, we acquired DNA of two rare species of heron, the Neotropical Zigzag Heron (Zebrilus undulatus) and the African White-crested Bittern (Tigriornis leucolophus). To estimate their phylogenetic relationships to other herons, we compared these species with representatives of the major heron clades using DNA-DNA hybridization. Even though the Zigzag Heron resembles a tiger-heron in its barred plumage and forest habitat, it is most closely related to bitterns. The White-crested Bittern is monophyletic with the New World tiger-herons (Tigrisoma) and, thus, is better termed the White-crested Tiger-Heron. These findings accord well with phylogenetic analyses based on osteology. The remaining uncertainties in higher-level heron phylogeny are principally: (1) the position and composition of some enigmatic genera (e.g. Gorsachius, Agamia, Pilherodius, and Ardeola); and (2) the identification of the basal heron lineage, which appears to be either tiger-herons or the Boat-billed Heron (Cochlearius).

The Humboldt, Magellanic, Jackass and Galapagos Penguins belong to the species Spheniscus. An allozyme phylogeny study was conducted to determine the phylogenetic relations between these penguins. The resulting phenetic and cladistic trees consistently showed the closest relationship between the Jackass and the Magellanic penguins. Two major clades were revealed, and molecular clock calibration suggests that they diverged about 500,000 mya in the mid-Pleistocene. The Jackass and the Magellanic penguins appeared in the late Pleistocene.

The fragmentary effects of Pleistocene glacial activity have been implicated in speciation among avifauna endemic to the Central Plains of North America. The prairiegrouse complex (genus Tympanuchus), distributed throughout the central United States and Canada, contains three sister taxa believed to have originated from the expansion of late Pleistocene refugial populations. We assayed mitochondrial-DNA (mtDNA) restriction-site and allozyme variation in prairie grouse obtained from localities throughout their current range in North America to examine the nature and timing of events promoting differentiation in Tympanuchus. The genetic data were not consistent with Pleistocene isolation of sufficient duration to allow a taxonomically or geographically structured pattern of genetic variation to emerge. No clear genetic differences among species were observed. Allozymes could not distinguish populations belonging to different species and frequencies were generally similar across taxa. The mtDNA differentiation was characterized by a predominant haplotype shared by all taxa; the remainder (15) were generally infrequent and closely related to the prevalent (and presumably ancestral) haplotype. The presence of unique mtDNA haplotypes within species and absence of certain allozyme alleles from particular taxa implied a degree of isolation and restrictions to gene flow. However, the mtDNA haplotypes did not sort phylogenetically, which suggests recent common ancestry of the lineages and may explain the lack of congruence between genetic variation and species designations. Despite the absence of quantitative genetic differentiation, considerable morphological and behavioral differences are apparent among the putative species. Adult male plumage, vocalization structures, and courtship behaviors form the basis for taxonomic divisions among prairie grouse, but, considering their close association with reproduction, such characters may be subject to sexual selection and may evolve rapidly relative to mtDNA or allozymes. Received 27 January 1993, accepted 19 August 1993.

Mitochondrial-DNA (mtDNA) polymorphisms were studied in the Oilbird (Steatornis caripensis). Twelve closely related (P = 0.06 to 0.35%) mtDNA haplotypes were found in Oilbird colonies studied in northeastern and northwestern Venezuela. Eleven of the mtDNA clones are related to the ancestral one by one or two mutational steps. Female-mediated gene flow is high (Nm > 1) among the colonies studied. As a consequence of the high female-mediated gene flow, no phylogeographic structuring among the mtDNA composite haplotypes was observed. Evidence from mtDNA analysis suggests that Oilbird populations in Venezuela have gone through a bottleneck. Results also seem to indicate that the annual postbreeding migrations of Oilbirds from the Guacharo Cave to the caves in the Mata de Mango area involve mostly the breeding adults, whereas juveniles disperse from the Guacharo Cave to the Mata de Mango cave system for longer periods. Received 3 August 1993, accepted 15 November 1993.

We studied relationships among species of the Neotropical flycatcher genus Leptopogon (Tyrannidae), which have modern-day distributions that include a lowland-tropical-zone member, an upper-tropical-zone member, and two subtropical-zone members. Along the eastern slope of the eastern Andes, species inhabiting the different elevational zones occur parapatrically to one another. Both allozymes and restriction-fragment-length polymorphisms of mitochondrial DNA suggest the same phylogenetic hypothesis: the lowland-tropical-zone species (L. amaurocephalus) is the basal member of the clade, and the upper-tropical-zone species (L. superciliaris) is the sister taxon of the two subtropical-zone species, L. taczanowskii and L. rufipectus. These data are consistent with diversification into successively higher-elevation habitats in the Andes. The biochemical data also suggest that this genus is substantially differentiated from the genera near it in traditional classifications (Mionectes, Phyllomyias, Lophotriccus). Received 6 August 1992, accepted 31 December 1992.

It has been suggested that the distribution of forest and nonforest birds in subtropical South America is the result of forest expansion along the Bermejo and Pilcomayo rivers during the Quaternary. However, this conclusion has a number of flaws, namely, lack of paleoecological support, use of questionable assumptions, problems with habitat classification and the questionable authenticity of a secondary contact zone in the central Chaco.

Multilocus protein electrophoresis of tissue samples from Mediterranean Alectoris revealed their evolutionary development. Calculated genetic distances demonstrated the species diversity among Barbary Partridge (A. barabara) and Chukar (A. chukar) while establishing the consaguinity of Rock Partridge (A. graeca) and Red-legged Partridge (A. rufa). These observations indicate the slow evolution of Alectoris species and their independence from one another.

The Suiriri Flycatcher (Suiriri suiriri) of South America is represented by three distinct forms occurring in parapatry: (1) S. s. suiriri to the southwest in the Chaco/Pampas; (2) S. s. affinis located centrally in the Cerrado/southern Amazonia; and (3) S. s. bahiae to the northeast in the Caatinga. On the basis of an analysis of 366 specimens of S. suiriri, I found meager evidence for long-distance migration, little support for Bergmann's rule, and more support for Gloger's rule. I postulate that an ancestral population of S. suiriri split into three isolated populations, with the central population differentiating most rapidly into affinis, thus explaining the leapfrog pattern of greater similarity between peripheral suiriri and bahiae. After secondary contact, affinis freely hybridized with nominate suiriri in a hybrid zone to the southwest, where specimens demonstrate morphometric intermediacy and increased plumage variability; the rarity of parental phenotypes within the hybrid zone suggests that the two forms are conspecific according to the biological species concept. In the northeast, affinis may have hybridized with a remnant population of suiriri, possibly represented by poorly known bahiae. The intermediate size and increased plumage variability of bahiae resemble that of suiriri x affinis hybrids, supporting a hypothesis of hybrid origin for bahiae, but alternative hypotheses cannot be ruled out. This hypothesis of differentiation is supported by the concordant patterns of disjunction among several pairs of sister taxa of bird species that occur in the Chaco and Caatinga, with no intervening populations in the Cerrado, implying a shared historical process of vicariance. Genetic and behavioral studies are needed to elucidate further the status and history of differentiation within S. suiriri. Received 31 January 2000, accepted 13 December 2000.

We studied the relationships between bill and hindlimb morphology and foraging behavior in 17 species of shorebirds within a phylogenetic framework. The results show that the evolutionary change in bill length is related to the evolutionary change in foraging strategies from visual hunting to tactile hunting. We also found evolutionary relationships between an increase in bill length and both plunging and sweeping foraging movements, and a decrease in bill length and 'routing' behavior. No relationships were found between hindlimb morphology and movement pattern (continuous hunting species vs. pause-travel species). Examining the evolutionary rate of change in bill and hindlimb structures shows that the family Scolopacidae and the subfamily Recurvirostrinae evolved more rapidly than the species of Charadriinae. Results from our ecomorphological and evolutionary analysis support the hypothesis by Zweers and co-workers on the evolution of feeding mechanisms in shorebirds.

New World blackbirds (Icteridae) have long served as model systems for studies of avian ecology, evolution, and behavior. However, this work has been conducted in the absence of a strong phylogenetic hypothesis for the group. We sequenced 890 base pairs (bp) of the mitochondrial cytochrome-b gene for 28 of the 29 icterid genera and subgenera recognized by Blake (1968). We found strong evidence of five lineages of blackbirds: grackles and allies; caciques and oropendolas; orioles; meadowlarks and allies; and a monotypic cup-nesting cacique lineage. However, we found little support for any further structure among these five lineages and no strong evidence supporting icterid monophyly. Our results set the stage for forthcoming work on relationships within lineages and for higher-level studies that address blackbird monophyly and relationships among lineages.

Molecular data and variation in syringeal morphology were used to infer a phylogeny for the family Falconidae and to address three issues currently of interest in systematics: (1) the treatment of multiple data sets in phylogenetic analysis, (2) a priori analysis and differential weighting of molecular data, and (3) the reliability of molecular versus morphological data in phylogenetic analysis. Problems in recovering phylogenetic signal caused by rapidly changing sites in the molecular data were not solved by combining data sets. Differentially weighting saturated partitions of the sequence data, prior to phylogenetic analysis, provided a phylogeny congruent with morphological analysis. Molecular data provide substantially more informative characters than morphological data. However, morphological data provide a higher proportion of unreversed synapomorphies. A reclassification of the family based on the phylogeny results in two subfamilies: (1) the Herpetotherinae, (forest-falcons [Micrastur] and Laughing Falcon [Herpetotheres cachinnans]); and (2) the Falconinae, which includes the tribes Falconini (Spot-winged Falconet [Spiziapteryx circumcinctus], pygmy-falcons [Polihierax], falconers [Microhierax], and the genus Falco) and Caracarini (caracaras). The phylogeny also indicates that two genera, Daptrius and Polihierax, are polyphyletic, and these two are split. Finally, a biogeographic hypothesis derived from the phylogeny implies that the origin and early diversification of the family occurred in South America.

The order Trogoniformes currently is divided into six genera: Apaloderma, Pharomachrus, Euptilotis, Priotelus, Trogon, and Harpactes. For this study, the question of intergeneric relationships was addressed based on mitochondrial cytochrome b and 12S ribosomal RNA genes. Maximum parsimony analyses confirmed the monophyly of currently accepted genera. A monophyletic clade encompassing the New World genera was the sister group to the Asian genus Harpactes. The sister group of these clades, in turn, was the African genus Apaloderma. Within the New World clade, the sister taxon of the genus Trogon was a clade formed by the Eared Trogon (Euptilotis neoxenus) and the Quetzals (Pharomachrus spp.). The most basal genus within the New World clade was Priotelus. These results suggest an Old World (Africa/Eurasia) origin for trogons, with the New World representing a secondary area of diversification. Patterns in plumage coloration concurred with relationships inferred from the molecular data. A hypothesis for the evolution of iridescent structures in trogon feathers suggests an increase in the complexity of these structures in the youngest lineages.

We explored the evolution of geographic distributions in archipelagos by comparing mitochondrial DNA (mtDNA) sequences and morphometric characters within and among conspecific populations of Adelaide's Warbler (Dendroica adelaidae), Plumbeous Warbler (D. plumbea), and Olive-capped Warbler (D. pityophila). Phylogenetic reconstructions were based upon 1,455 nucleotides of protein-coding mtDNA sequence from 53 individual warblers; morphological analyses employed three external measurements from a larger number of museum specimens. Of the three taxa studied, Adelaide's Warbler occupied the broadest and most fragmented geographical distribution and exhibited the greatest interpopulation differentiation in both mtDNA and morphology. Phylogenetic analyses demonstrated that the three Adelaide's Warbler populations are each reciprocally monophyletic with the Puerto Rican lineage basal to sister clades on Barbuda and St. Lucia. Genetic distances among these populations were comparable with those between some continental species. In contrast to the mtDNA pattern, the Puerto Rican and Barbudan Adelaide's Warbler populations were most similar in morphometry. We observed considerably less mtDNA and morphometric differentiation among populations of the two species with more restricted and less fragmented distributions, the Plumbeous Warbler of Dominica and Guadeloupe and the Olive-capped Warbler of the Bahamas and Cuba. High levels of molecular and morphological differentiation among the geographically disjunct Adelaide's Warbler populations and low differentiation in the two species with less fragmented ranges suggest that range disjunctions indicate the long-term evolutionary independence of geographically isolated island populations.