World Passerine Birds Research Articles

Faster evolution of a premating reproductive barrier is not associated with faster speciation rates in New World passerine birds.

Why are speciation rates so variable across the tree of life? One hypothesis is that this variation is explained by how rapidly reproductive barriers evolve. We tested this hypothesis by conducting a comparative study of the evolution of bird song, a premating barrier to reproduction. Speciation in birds is typically initiated when geographically isolated (allopatric) populations evolve reproductive barriers. We measured the strength of song as a premating barrier between closely related allopatric populations by conducting 2339 field experiments to measure song discrimination for 175 taxon pairs of allopatric or parapatric New World passerine birds, and estimated recent speciation rates from molecular phylogenies. We found evidence that song discrimination is indeed an important reproductive barrier: taxon pairs with high song discrimination in allopatry did not regularly interbreed in parapatry. However, evolutionary rates of song discrimination were not associated with recent speciation rates. Evolutionary rates of song discrimination were also unrelated to latitude or elevation, but species with innate song (suboscines) evolved song discrimination much faster than species with learned song (oscines). We conclude that song is a key premating reproductive barrier in birds, but faster evolution of this reproductive barrier between populations does not consistently result in faster diversification between species.

Development syndromes in New World temperate and tropical songbirds.

We studied avian development in 49 to 153 species of temperate and tropical New World passerine birds to determine how growth rates, and incubation and nestling periods, varied in relation to other life-history traits. We collected growth data and generated unbiased mass and tarsus growth rate estimates (mass n = 92 species, tarsus n = 49 species), and measured incubation period (n = 151) and nestling period (n = 153), which we analyzed with respect to region, egg mass, adult mass, clutch size, parental care type, nest type, daily nest predation rate (DMR), and nest height. We investigated covariation of life-history and natural-history attributes with the four development traits after controlling for phylogeny. Species in our lowland tropical sample grew 20% (incubation period), 25% (mass growth rate), and 26% (tarsus growth rate) more slowly than in our temperate sample. Nestling period did not vary with respect to latitude, which suggests that tropical songbirds fledge in a less well-developed state than temperate species. Suboscine species typically exhibited slower embryonic and post-embryonic growth than oscine passerines regardless of their breeding region. This pattern of slow development in tropical species could reflect phylogenetic effects based on unknown physiological attributes. Time-dependent nest mortality was unrelated to nestling mass growth rate, tarsus growth rate, and incubation period, but was significantly associated with nestling period. This suggests that nest predation, the predominant cause of nest loss in songbirds, does not exert strong selection on physiologically constrained traits, such as embryonic and post-embryonic growth, among our samples of temperate and lowland tropical songbird species. Nestling period, which is evolutionarily more labile than growth rate, was significantly shorter in birds exposed to higher rates of nest loss and nesting at lower heights, among other traits. Differences in life-history variation across latitudes provide insight into how unique ecological characteristics of each region influence physiological processes of passerines, and thus, how they can shape the evolution of life histories. While development traits clearly vary with respect to latitude, trait distributions overlap broadly. Life-history and natural history associations differ for each development trait, which suggests that unique selective pressures or constraints influence the evolution of each trait.

A new blood parasite of leaf warblers: molecular characterization, phylogenetic relationships, description and identification of vectors

BackgroundBlood parasites of the genus Haemoproteus Kruse, 1890 are cosmopolitan, might be responsible for mortality in non-adapted birds, and often kill blood-sucking insects. However, this group remains insufficiently investigated in the wild. This is particularly true for the parasites of leaf warblers of the Phylloscopidae Alström, Ericson, Olsson & Sundberg the common small Old World passerine birds whose haemoproteid parasite diversity and vectors remain poorly studied. This study reports a new species of Haemoproteus parasitizing leaf warblers, its susceptible vector and peculiar phylogenetic relationships with other haemoproteids.MethodsWood warblers (Phylloscopus sibilatrix Bechstein) were caught in Lithuania during spring migration, and blood films were examined microscopically. Laboratory reared Culicoides nubeculosus Meigen were exposed experimentally by allowing them to take blood meals on one individual harbouring mature gametocytes of the new Haemoproteus species (lineage hPHSIB2). To follow sporogonic development, the engorged insects were dissected at intervals. The parasite lineage was distinguished using sequence data, and morphological analysis of blood and sporogonic stages was carried out. Bayesian phylogeny was constructed in order to determine the phylogenetic relationships of the new parasite with other haemoproteids.ResultsHaemoproteus (Parahaemoproteus) homopalloris n. sp. was common in wood warblers sampled after arrival to Europe from their wintering grounds in Africa. The new parasite belongs to a group of avian haemoproteid species with macrogametocytes possessing pale staining cytoplasm. All species of this group clustered together in the phylogenetic analysis, indicating that intensity of the cytoplasm staining is a valuable phylogenetic character. Laboratory-reared biting midges C. nubeculosus readily supported sporogony of new infections. Phylogenetic analysis corroborated vector experiments, placing the new parasite in the clade of Haemoproteus (Parahaemoproteus) parasites transmitted by biting midges.ConclusionsHaemoproteus homopalloris n. sp. is the third haemoproteid, which is described from and is prevalent in wood warblers. Phylogenetic analysis identified a clade containing seven haemoproteids, which are characterised by pale staining of the macrogametocyte cytoplasm and with ookinetes maturing exceptionally rapidly (between 1 to 1.5 h after exposure to air). Both these features may represent valuable phylogenetic characters. Studies targeting mechanisms of sporogonic development of haemoproteids remain uncommon and should be encouraged. Culicoides nubeculosus is an excellent experimental vector of the new parasite species.

Avian migration and the distribution of malaria parasites in New World passerine birds

AbstractAimMigrating birds transport their parasites, often over long distances, but little is known about the transfer of these parasites to resident hosts in either the wintering or breeding ranges of the migratory host populations. We investigated the haemosporidian parasite faunas of migratory and resident birds to determine connections among distant parasite faunas, plausibly brought about by migratory host populations.LocationSamples were obtained, primarily during or shortly after the local breeding season, throughout the Americas, from the United States through the Caribbean Basin and into northern South America.MethodsInfections were identified by PCR and sequencing of parasite DNA in avian blood samples. The analyses were based on c. 4700 infections representing 79 parasite lineages of Plasmodium and Haemoproteus spp. Geographical connections of lineages between regions in the Americas were compared to those in the Euro‐African migration system, where migration distances are longer for many host species and the migrant and resident avifaunas in the wintering areas are phylogenetically more divergent.ResultsHaemosporidian lineages exhibited considerable variation in distribution in the Americas, and patterns of distribution differ markedly between the Americas and the Euro‐African migration system. In particular, few lineages were recovered from resident species in both temperate and tropical latitudes, particularly in the Euro‐African system, in which a large proportion of lineages were restricted to migrants. Parasite lineages in the Euro‐African system exhibited considerable phylogenetic conservatism in their distributions, that is, a tendency of related lineages to exhibit similar geographical distributions. In contrast, clades of parasites in the Americas displayed more geographical diversity, with four of 12 clades exhibiting all four of the distribution types representing the combinations of resident and migrant host species in both temperate and tropical latitudes.Main conclusionsLong‐distance migrants connect communities of avian haemosporidian parasites in breeding and wintering areas with disparate avifaunas and different vector communities. The degree of parasite lineage sharing between migrants and residents in breeding and wintering areas appears to reflect, to a large degree, the taxonomic similarity of migrants to the resident species in both areas.

Historical limits on species co‐occurrence determine variation in clade richness among New World passerine birds

AbstractAimSpecies richness is unevenly distributed among clades, reflecting differences in the extent to which species co‐occur, their rates of geographical turnover and total area occupied. Here, we study richness variation among 10 large clades of New World passerine birds, assessing the dynamics of range expansion and diversification that led to the build‐up of co‐occurring species.LocationNew World.MethodsWe defined co‐occurrence based on the presence in 1°×1° grid cells, an area substantially smaller than the geographical scale of speciation in birds, implying that range expansion is the main mechanism by which species accumulate within grid cells. For each species, we estimated its ‘diversification rate’, a measure of the extent to which it is a member of an actively diversifying lineage. Within each group, we ranked all species by this measure, before dividing them into quartiles.ResultsNeither clade age nor geographical area correlates with overall clade richness, but the maximum number of co‐occurring species does. Within each group, locations supporting large numbers of species in actively diversifying lineages generally differ from those containing many species belonging to more ancient groups. The tropical Andes and Amazon are notable for continuously generating and maintaining species, such that the most species‐rich clades have predominantly radiated in these areas. Based on the timing of their speciation events, we infer that a lack of reproductive isolation may limit the co‐occurrence of species that are members of actively diversifying lineages, but not those that are generally long diverged.Main conclusionsSpatiotemporal differences in the rates of range expansion and diversification are likely set by the capacity of regions to generate and maintain species. This, rather than the rate at which reproductive isolation accrues, area occupied, or time for diversification, appears to be the major factor underlying the disparity in clade richness between New World passerine groups.

Niche-tracking migrants and niche-switching residents: evolution of climatic niches in New World warblers (Parulidae).

Differences in life-history traits between tropical and temperate lineages are often attributed to differences in their climatic niche dynamics. For example, the more frequent appearance of migratory behaviour in temperate-breeding species than in species originally breeding in the tropics is believed to have resulted partly from tropical climatic stability and niche conservatism constraining tropical species from shifting their ranges. However, little is known about the patterns and processes underlying climatic niche evolution in migrant and resident animals. We evaluated the evolution of overlap in climatic niches between seasons and its relationship to migratory behaviour in the Parulidae, a family of New World passerine birds. We used ordination methods to measure seasonal niche overlap and niche breadth of 54 resident and 49 migrant species and used phylogenetic comparative methods to assess patterns of climatic niche evolution. We found that despite travelling thousands of kilometres, migrants tracked climatic conditions across the year to a greater extent than tropical residents. Migrant species had wider niches than resident species, although residents as a group occupied a wider climatic space and niches of migrants and residents overlapped extensively. Neither breeding latitude nor migratory distance explained variation among species in climatic niche overlap between seasons. Our findings support the notion that tropical species have narrower niches than temperate-breeders, but does not necessarily constrain their ability to shift or expand their geographical ranges and become migratory. Overall, the tropics may have been historically less likely to experience the suite of components that generate strong selection pressures for the evolution of migratory behaviour.

Into and out of the tropics: the generation of the latitudinal gradient among New World passerine birds

AbstractAimOne prominent explanation for the latitudinal gradient in biodiversity proposes that its prime cause is the greater age and/or higher origination rates of tropical clades, and the infrequent or delayed dispersal of their component species into temperate regions. An alternative is that species’ carrying capacities vary regionally, which influences rates of time‐averaged diversification via ecological opportunity. We contrast these hypotheses, in order to assess potential historical influences upon the latitudinal gradient of New World passerine birds (order Passeriformes), comparing patterns among the two suborders present (oscines and suboscines), which are known to have had different routes of dispersal across the region.LocationNew World.MethodsWe examine diversity patterns, their abiotic and biotic correlates, and the distributions of phylogenetically old and young species.ResultsStrong latitudinal gradients are present within both oscine and suboscine birds, with maximum diversity towards the equator, but their overall shapes differ. Among the oscines, older lineages are found towards the north, with progressively younger lineages present further south. Regional variation in oscine richness is statistically well explained by a combination of productivity and elevation (R2 = 0.76). In contrast, few suboscine groups have colonized the north, so their current diversity is well correlated with temperature seasonality (R2 = 0.74).Main conclusionsBecause the oscines colonized the Americas from the north, their latitudinal gradient must reflect regional differences in time‐averaged diversification rates, and not the time present within a region. The richness patterns derived from phylogenetic data and the strong predictive power of the normalized difference vegetation index (NDVI) suggest that the radiation of the oscines is consistent with the idea that entry into a new region stimulates a burst of diversification, which is higher and/or continues for longer in areas with greater carrying capacity. Conversely, the suboscine distributions potentially reflect a large historical barrier to dispersal and niche conservatism of climatic tolerances, possibly coupled with competition from the oscines. Although contemporary conditions can explain much of the passerine diversity patterns, history has had an important influence on the taxonomic composition of this gradient.

Going to Extremes: Contrasting Rates of Diversification in a Recent Radiation of New World Passerine Birds

Recent analyses suggest that a few major shifts in diversification rate may be enough to explain most of the disparity in diversity among vertebrate lineages. At least one significant increase in diversification rate appears to have occurred within the birds; however, several nested lineages within birds have been identified as hyperdiverse by different studies. A clade containing the finches and relatives (within the avian order Passeriformes), including a large radiation endemic to the New World that comprises ~8% of all bird species, may be the true driver of this rate increase. Understanding the patterns and processes of diversification of this diverse lineage may go a long way toward explaining the apparently rapid diversification rates of both passerines and of birds as a whole. We present the first multilocus phylogenetic analyses of this endemic New World radiation of finch relatives that include sampling of all recognized genera, a relaxed molecular clock analysis of its divergence history, and an analysis of its broad-scale diversification patterns. These analyses recovered 5 major lineages traditionally recognized as avian families, but identified an additional 10 relatively ancient lineages worthy of recognition at the family level. Time-calibrated diversification analyses suggested that at least 3 of the 15 family-level lineages were significantly species poor given the entire group's background diversification rate, whereas at least one-the tanagers of family Thraupidae-appeared significantly more diverse. Lack of an age-diversity relationship within this clade suggests that, due to rapid initial speciation, it may have experienced density-dependent ecological limits on its overall diversity.

Annual adult survival in several new world passerine birds based on age ratios in museum collections

We estimated annual survival from proportions of first-year and older birds in museum collections of several species of North American and Neotropical passerine birds (Order Passeriformes). The quality of estimates of survival from museum specimens depends on accurate aging, usually based on plumage markers, and unbiased collecting. The advantages of an age-ratio approach are broad temporal and geographic sampling, large sample sizes, reduced bias from adult dispersal, and access to species and areas not readily sampled in mark–recapture studies. Biases in estimated survival due to sex- and age-based biases in collecting are discussed in detail. Survival estimates were higher in tropical compared to temperate populations/species in Pyrocephalus, Icterus, Pheucticus, and Cyanocompsa, but not Catharus. In seven of nine North American species, estimates of survival from museum collections exceeded those obtained in local MAPS mark–recapture studies. Generalizations concerning adult survival rates in natural populations continue to be elusive, but the use of a variety of estimation approaches will enrich the empirical database and strengthen confidence in perceived patterns of life-history traits.

A phylogeny for the Cisticolidae (Aves: Passeriformes) based on nuclear and mitochondrial DNA sequence data, and a re-interpretation of an unique nest-building specialization

Based on some general similarities in feeding adaptations, a large number of Old World passerine birds were in the past lumped in one broad family, the Sylviidae. Recent molecular studies, starting with the DNA–DNA hybridization work by Sibley et al. [Sibley, C.G., Ahlquist, J.E., 1990. Phylogeny and Classification of Birds: A Study in Molecular Evolution, Yale University Press, New Haven, CT], have revealed that this group is in fact a paraphyletic assemblage, mainly in the superfamily Sylvioidea, and within this assemblage a distinct group (the Cisticolidae) can be identified around the genus Cisticola. In this study we try to define natural lineages within it, based on DNA sequence data from 35 ingroup taxa representing 12 putative genera. Both nuclear myoglobin intron II (630 bp in our study) and mitochondrial ND2 (1041 bp) genes were sequenced, and 1671 bp were aligned and subjected to parsimony, maximum likelihood and Bayesian analyses. The results strongly support the monophyly of a cisticolid clade, with the Malagasy warblers Neomixis constituting the deepest branch within the clade. Three major clades receive statistical support, but not all relationships between and within these are well resolved. All species of the genus Bathmocercus belong to the Cisticolidae but in two different clades. The tailorbirds appear also polyphyletic with most species of the genus Orthotomus (but O. cucullatus falling in the outgroup) and the African metopias being in two different clades. Also the genus Apalis is polyphyletic, but all other included genera seem to be confirmed as natural units. Based on these findings we resurrect the genera Scepomycter and Artisornis. Calamonastes is confirmed to be in the Cisticolidae and grouped with Camaroptera. Main basic nest types do not follow the phylogenetic branching, and notably the peculiar “tailorbird” technique of stitching leaves together around the nest is found in different parts of the phylogeny. The basic types of nests seem to be found in particular environments, and the sewing may therefore have evolved in some ancestor of the Cisticolidae and was later lost or modified in some genera or species following the spread of drier habitats from the mid-Miocene.

Understanding avian nest predation: why ornithologists should study snakes

Despite the overriding importance of nest predation for most birds, our understanding of the relationship between birds and their nest predators has been developed largely without reliable information on the identity of the predators. Miniature video cameras placed at nests are changing that situation and in six of eight recent studies of New World passerine birds, snakes were the most important nest predators. Several areas of research stand to gain important insights from understanding more about the snakes that prey on birds' nests. Birds nesting in fragmented habitats often experience increased nest predation. Snakes could be attracted to habitat edges because they are thermally superior habitats, coincidentally increasing predation, or snakes could be attracted directly by greater prey abundance in edges. Birds might reduce predation risk from snakes by nesting in locations inaccessible to snakes or in locations that are thermally inhospitable to snakes, although potentially at some cost to themselves or their young. Nesting birds should also modify their behavior to reduce exposure to visually orienting snakes. Ornithologists incorporating snakes into their ecological or conservation research need to be aware of practical considerations, including sampling difficulties and logistical challenges associated with quantifying snake habitat use.

An analysis of clutch‐size in New World passerine birds

Variation in clutch‐size among New World passerine birds was analysed with respect to four variables: body‐mass, geographic latitude, the frequency of nest predation, and the structure of the nest. Data were analysed separately by averaging traits at three taxonomic levels: species, genus, and subfamily. Allometric scaling with body‐mass did not account for significant variation in clutch‐size regardless of the taxonomic level of analysis. Latitudinal effects on clutch‐size were highly significant at all taxonomic levels. For species building small‐pensile nests and open‐cup nests, nest predation had a significant partial effect on clutch‐size, with latitude held constant. When nest predation and latitude were held constant, clutch‐size was significantly different among species building small‐pensile nests, open‐cup nests, and domed nests. These results suggest that New World passerine clutch‐size is related to at least three variables: latitudinal effects, nest predation, and nest structure.

“Spshing Noise”: Biological Significance of Its Attraction and Nonattraction by Birds

Many New World passerine birds, especially migrants which join mixed flocks of local species in the Neotropics, are attracted to a noise termed "spshing" used by humans to attract birds into view. The noise is effective because it mimics the vocalizations of certain bird species which play a central bonding role in mixed species flocks. Migrants join these flocks to gain local expertise about food sources and/or potential enemies in unfamiliar environments. Old World passerine migrants do not react to "spshing." In Africa, they do not join mixed flocks of local species because of more favorable environmental conditions negating the need to do so. In tropical Asia, many migrants join mixed flocks but the local bonding species give vocalizations unlike those of their counterparts in the Neotropics, and thus not like "spshing."