Vireo Olivaceus Research Articles

Avian haemosporidians of the genera Plasmodium and Haemoproteus from resident and Neotropical migrant birds in Colombia

Avian haemosporidians of the genera Plasmodium and Haemoproteus are a group of widely distributed blood parasites that can negatively affect the fitness of their hosts. Colombia contains the greatest diversity of birds on the planet, but knowledge about the associations between haemosporidian and its avifauna is scarce and fragmented. We collected blood samples from 255 birds (203 residents and 52 neotropical migrants) belonging to 27 families and 108 species. The study was conducted in six localities in the inter-Andean valleys of the Cauca and Magdalena rivers. Parasites of the genera Plasmodium and Haemoproteus were identified in the samples by morphological and molecular analysis of a fragment of the mitochondrial gene cyt b. Among the samples, 9.3% (n = 24) were positive for Plasmodium or Haemoproteus. Co-infection with Plasmodium and Haemoproteus was found in Red-eyed Vireo. Seventeen haemosporidian lineages were identified, five of which were reported for the first time in resident birds (Common Ground Dove, Checker-throated Stipplethroat, Tropical Kingbird, Pale-breasted Thrush, and Ruddy-breasted Seedeater) and one in the Summer Tanager (neotropical migrant). The research results confirm the wide diversity of haemosporidian present in tropical lowlands and the possible role of neotropical migratory birds in dissemination on haemosporidian along their migratory routes.

The composite identity of Muscicapa virens Linnaeus, and a neotype designation for Eastern Wood Pewee Contopus virens (Tyrannidae)

I reviewed the material basis of Muscicapa virens Linnaeus, 1766, long presumed to be the original description of Eastern Wood Pewee Contopus virens (Linnaeus), type species of the genus Contopus Cabanis, 1855, and found it to be an unidentifiable taxonomic composite. Linnaeus' (1766) account was partly based on Brisson's (1760) ‘Gobe-mouche Cendré de la Caroline’, which was based on (1) a non-extant specimen that, as demonstrated herein, was probably a species in the genus Empidonax Cabanis, 1855, and (2) Catesby’s (1731) ‘little brown Fly-catcher’, which was also a taxonomic composite. Linnaeus (1766) also included a novel character in his original description of M. virens—a white supercilium (‘superciliis albis’)—which is lacking in Eastern Wood Pewee, and was probably miscopied from Catesby’s (1731) description of ‘Red-eyed Fly-catcher’ (= Red-eyed Vireo Vireo olivaceus Linnaeus, 1766), which appeared on the same plate as the ‘little brown Fly-catcher’. In light of these ambiguities, after a thorough review of literature and relevant primary sources, I designate a neotype specimen for C. virens (Linnaeus) that stabilises nomenclature in accordance with prevailing use.

The New Mitogenome of Erpornis zantholeuca (Aves: Passeriformes): Sequence, Structure, and Phylogenetic Analyses

White-bellied Erpornis (Erpornis zantholeuca) is a group of birds in the order Passeriformes, but its taxonomic status remains controversial. To understand the phylogenetic position of E. zantholeuca and phylogenetic relations within this family, we sequenced the complete mitochondrial genome of E. zantholeuca, which was 16,902 bp in length, containing 13 protein-coding genes (PCGs), 22 transfer RNA (tRNA) genes, 2 ribosomal RNA (rRNA) genes, and a control region. The nucleotide composition of the whole genome was 30.10% A, 30.48% C, 15.14% G, and 24.28% T and showed an elevated AT content (54.38%). All genes were encoded on the H-strand, with the exceptions of 8 tRNAs (trnQ, trnA, trnN, trnC, trnY, trnS2(UCN), trnP, trnE) and 1 PCG (Mt-ND6). Most PCGs used standard ATN as start codons, and TAN as stop codons. All tRNAs were predicted to form the typical cloverleaf secondary structures. The gene order of E. zantholeuca was consistent with that of Gallus gallus, which was considered to be a plesiomorphic or typical avian gene order. Phylogenetic relationships based on bayesian inference and maximum likelihood methods showed that E. zantholeuca was well supported as the sister group of (Vireo altiloquus + Vireo olivaceus). In addition, Pteruthius melanotis was sister to the other members of Vireonidae.

Fat Stores and Antioxidant Capacity Affect Stopover Decisions in Three of Four Species of Migratory Passerines With Different Migration Strategies: An Experimental Approach

During migratory stopovers, birds must make decisions about when and where to travel and these decisions are likely contingent on their fuel stores, food availability, and antioxidant capacity as well as seasonal changes in key environmental factors. We conducted a field experiment on an offshore stopover site (Block Island, Rhode Island, United States: 41°130N, 71°330W) during autumn migration to test the hypothesis that birds with greater fuel stores and non-enzymatic antioxidant capacity have shorter stopovers than lean birds with low antioxidant capacity, and to determine the extent to which this depends on migration strategy. We used a 2 × 2 factorial field experiment (two levels each of available food and dietary polyphenols) with four species of songbirds kept in captivity for 3–5 days to produce experimental groups with different fuel stores and antioxidant capacity. We attached digital VHF transmitters to assess stopover duration and departure direction using automated telemetry. Non-enzymatic antioxidant capacity increased during refueling for Red-eyed Vireos (Vireo olivaceus) and Blackpoll Warblers (Setophaga striata) fedad libdiets, and forad libfed Hermit Thrushes (Catharus guttatus) supplemented with polyphenols, but not for Yellow-rumped Warblers (Setophaga coronata coronata). Glutathione peroxidase (GPx) decreased during captivity and was influenced by dietary treatment only in Red-eyed Vireos. Oxidative damage decreased during captivity for all species except Yellow-rumped Warblers. Stopover duration was shorter for Vireos and Blackpolls fedad libas compared to those fed maintenance.Ad libfed Hermit Thrushes supplemented with polyphenols had shorter stopovers than those fedad lib, as did thrushes fed at maintenance and supplemented with polyphenols compared with those fed at maintenance alone. There was no influence of condition on stopover duration for Yellow-rumped Warblers. Departure direction was not strongly related to condition, and birds primarily reoriented north when departing Block Island. Thus, fat stores and oxidative status interacted to influence the time passerines spent on stopover, and condition-dependent departure decisions were related to a bird’s migration strategy. Therefore, seasonal variation in macro- and micro-nutrient resources available for refueling at stopover sites can affect body condition and antioxidant capacity and in turn influence the timing and success of migration.

Stopover behavior of Red-eyed Vireos (Vireo olivaceus) during fall migration on the coast of the Yucatan Peninsula

BackgroundFor migrating birds, stopover requires spending time and energy that otherwise could be allocated to flying. Thus, birds optimally refuel their subsequent migratory flight by reducing stopover duration or foraging activity in food-rich environments. In coastal habitats, birds may forego refueling and take short stopovers irrespective of local food availability. Given the paucity of studies exploring how migrants adjust stopover behavior in response to temporal variation in food availability, especially in the Neotropics, we fixed radio tags to 51 Red-eyed Vireos (Vireo olivaceous) over two years at two sites on the coast of Mexico’s Yucatan Peninsula.MethodsWe applied VHF radio tags during the fall of 2016 and 2017, and tracked birds using automatic and manual receiving units. We estimated stopover duration and activity levels (one site only) for between six and fifteen birds, depending on site and year. We measured fruit availability weekly along the net lanes where we captured birds. We used a generalized linear model to estimate the relationships between stopover duration/activity level and fruit density, bird body mass and year. We interpreted relationships for the model with the lowest AICc value.ResultsWe found that approximately half of the birds departed on the same day they were captured. For the birds that stayed longer, we could not discern whether they did so because they were light, or fruit density was high. On the other hand, lighter birds were more active than heavier birds but only in one of the two years.ConclusionsGiven our results, it is unlikely that Red-eyed Vireos refuel along the Yucatan coast. However, they still likely need to recuperate from crossing the Gulf of Mexico, which may necessitate foraging more often if in poor body condition. If the birds then move inland then stopover should be thought of as a large-scale phenomenon, where habitats with different functions may be spread out over a broad landscape.

Multiple sub-repertoires and singing patterns of Red-eyed Vireos (Vireo olivaceus)

Some songbirds produce only one or a few song types, but others sing large repertoires with many different song types. Birds with large repertoires can arrange these songs in a variety of distinct singing patterns that add a layer of complexity to their vocal production. Both large repertoires and singing patterns may communicate important information to conspecific males and females. Previous estimates of repertoire size of Red-eyed Vireos (Vireo olivaceus) range from 39 to 59. These estimates were based on a small number of recorded phrases per individual, and on single recordings of most individuals. I have made lengthy, multiple recordings over periods of days and weeks of 46 Red-eyed Vireos to revisit the question of their repertoire size. Repertoire size estimated for the birds I recorded varied between 17 and 341 phrase types, with a mean of 91. Fourteen birds for which I recorded at least 1,000 phrases had a mean repertoire of 154 phrase types. Previous estimates may have been low by a factor of 2–3 because of limited sampling. Plotting of phrase type vs. phrases sung for each bird showed a variety of singing patterns. Six birds sang a single limited repertoire of 17–47 phrase types. Nineteen birds sang a single repertoire, but new phrases continued to be added as more recordings were made, so these repertoires had no clear size limits. Twenty birds sang multiple groups or sub-repertoires of phrase types at different times, often changing between sub-repertoires during a single continuous bout of singing. Five birds sang frequent repetitions of a small number of phrase types selected from larger repertoires. The mean singing rate of the birds studied climbed from a low of 33 phrases/min at the beginning of the breeding season to a high of 46 phrases/min at the peak, and declined to 34 phrases/ min at the end of the breeding season. My study shows that Red-eyed Vireo repertoires are significantly larger than previously estimated, that singing patterns vary widely among individual birds, and that many birds group phrase types into multiple sub-repertoires, sung at different times.

The Iowa Bird That Inspired Antonín Dvořák's American String Quartet in 1893: Controversy over the Species’ Identity and Why It Matters

Antonín Dvořák composed the String Quartet in F major (op. 96, the ‘American’) in June 1893 while visiting the town of Spillville, Iowa, USA. Based on accounts from Dvořák's secretary Josef Kovařík, portions of the quartet's Scherzo movement were inspired by birdsong Dvořák heard in Spillville. Kovařík's account included both Dvořák's visual description of the bird that inspired him and a transcribed fragment of the birdsong Dvořák reportedly used. In 1954, Clapham identified the bird as a scarlet tanager (Piranga olivacea), based mainly on the visual description. This widely accepted identification was questionable because of the poor match of the tanager's song to musical material in the Scherzo. In 2016, Floyd proposed the red-eyed vireo (Vireo olivaceus) as Dvořák's inspiration, based on song rather than appearance. The vireo's song is clearly identifiable in the Scherzo as well in the birdsong fragment recorded by Kovařík. The mismatch between the visual description and the transcribed song fragment could have occurred when Dvořák heard and recorded the persistent singing of a cryptic red-eyed vireo, but misidentified the song's source when he caught sight of a brightly coloured tanager. Correct identification of the birdsong changes the interpretation of the movement. Previously, birdsong has been considered the source of a short secondary motif. But red-eyed vireo songs are highly variable, and a slight variation of Kovařík's song fragment could be the basis of the main theme of the Scherzo. Therefore, Dvořák may have used American birdsong in the movement considerably more than previously appreciated.

Predicting effects of selection cutting on avian diversity and abundance in shade-tolerant hardwood forests of central Ontario

Emulating natural disturbance (END) patterns to conserve biodiversity is often a goal of forest management but the impact of forest cutting is still controversial. We examined effects on avian assemblages of partially-cut forest stands of 1–10, 11–20 and > 45 years (cut classes) post-harvest differing in the % basal area retained as wildlife species’ habitat in 85 shade-tolerant hardwood stands in Algonquin Park, Ontario. Permutational multivariate analysis of variance indicated significant compositional differences among cut classes, after controlling for year and township (spatial variation in surficial geology and topography), both of which were also significant. Pairwise comparisons indicated significant compositional differences only between young and old stands. The difference in beta diversity (homogenization/differentiation) among cut classes was marginally significant (P = 0.066). Pairwise differences were significant between old versus mid-aged cut classes, marginally significant for young versus old cuts, and non-significant for young versus mid-aged cut classes. Six species and cavity users as a group were more abundant in > 45 years post-harvest stands than in the other two cut classes. Six species had higher abundances in younger cuts than > 45 years post-harvest cuts. Red-eyed vireo (Vireo olivaceus) showed a nonlinear response and was least abundant in 11–20 year cuts. Blackburnian warblers Setophaga fusca, black-throated green warblers S. virens and pileated woodpeckers Dryocopus pileatus increased with the density of supercanopy trees (≥ 60 cm diameter at breast height - dbh) and in the case of pileated woodpeckers more large snags (≥ 40 cm dbh). Brown creeper Certhia americana abundance increased with greater basal area of trees ≥ 25 cm dbh and ovenbird numbers were significantly related to overall basal area. Chestnut-sided warbler S. castanea abundance decreased with an increase in overall basal area and was higher in the 1–10 year cuts and American redstarts S. ruticilla decreased with an increase in basal area. Our modelling suggests that effects of selection cutting systems on the avian community may be reduced as tolerant hardwood stands become regulated and have higher residual basal areas. Current guidelines in Ontario for the retention of large, scattered conifer trees appear to meet the requirements for most, but not all, species; however, guidelines for supercanopy trees are too low. These results indicate that the END paradigm for single-tree selection cutting in tolerant hardwoods may be partially effective but requires modifications, such as retaining higher densities of supercanopy trees that would be beneficial for birds.

Intrinsic Markers Reveal Breeding Origin and Geographically-Structured Migration Timing of Two Songbird Species at a Coastal Stopover Site

AbstractWe used stable hydrogen isotope markers to identify geographic provenance of Blackpoll Warblers (Setophaga striata) and Red-eyed Vireos (Vireo olivaceus) passing through a coastal stopover area in the Gulf of Maine on fall migration, and supplemented δ2 H signatures from feathers with wing length data as an additional proxy for migration origin, since geographic size variation has been documented for this species. We captured migrant blackpolls with putative origins from as close as the Adirondacks, New Brunswick, and northwestern Maine, and potentially as far as Alaska. We captured vireos with putative origins from as close as Maine and Nova Scotia, and potentially as far as British Columbia and Alberta. We found a significant relationship between blackpoll wing length and capture date indicating that birds with longer wings– and thus likely from more western and northern breeding regions – passed through the capture site earlier in the season than more local breeders. In contrast, vireos from more distant breeding latitudes passed through the capture site later in the season. These results demonstrate that mid-coast Maine serves as a catchment area for both Blackpoll Warblers, and Red-eyed Vireos, and provides some evidence that connectivity between breeding areas and stopover sites may be strong for blackpolls; however, additional study linking breeding and stopover sites across the migratory range of both species is necessary to understand more fully how strong connectivity is between breeding and stopover areas for these species.

Partitioning global change: Assessing the relative importance of changes in climate and land cover for changes in avian distribution.

Understanding the relative impact of climate change and land cover change on changes in avian distribution has implications for the future course of avian distributions and appropriate management strategies. Due to the dynamic nature of climate change, our goal was to investigate the processes that shape species distributions, rather than the current distributional patterns. To this end, we analyzed changes in the distribution of Eastern Wood Pewees (Contopus virens) and Red‐eyed Vireos (Vireo olivaceus) from 1997 to 2012 using Breeding Bird Survey data and dynamic correlated‐detection occupancy models. We estimated the local colonization and extinction rates of these species in relation to changes in climate (hours of extreme temperature) and changes in land cover (amount of nesting habitat). We fit six nested models to partition the deviance explained by spatial and temporal components of land cover and climate. We isolated the temporal components of environmental variables because this is the essence of global change. For both species, model fit was significantly improved when we modeled vital rates as a function of spatial variation in climate and land cover. Model fit improved only marginally when we added temporal variation in climate and land cover to the model. Temporal variation in climate explained more deviance than temporal variation in land cover, although both combined only explained 20% (Eastern Wood Pewee) and 6% (Red‐eyed Vireo) of temporal variation in vital rates. Our results showing a significant correlation between initial occupancy and environmental covariates are consistent with biological expectation and previous studies. The weak correlation between vital rates and temporal changes in covariates indicated that we have yet to identify the most relevant components of global change influencing the distributions of these species and, more importantly, that spatially significant covariates are not necessarily driving temporal shifts in avian distributions.

Using automated radio telemetry to quantify activity patterns of songbirds during stopover

ABSTRACT During migration, birds require stopover habitat to rest and refuel before resuming flight. While long-distance migratory flights represent a large energy investment, stopover accounts for roughly two-thirds of a bird's total energy expenditure during migration. Therefore, birds should minimize energy expenditure while also minimizing time and predation risk during stopover. To understand activity during migration, we recorded activity patterns (i.e. fine-scale movements associated with a range of behaviors) of 3 species, Red-eyed Vireo (Vireo olivaceus), Swainson's Thrush (Catharus ustulatus), and Wood Thrush (Hylocichla mustelina), at a stopover site along the northern coast of the Gulf of Mexico during autumn migration using automated radio telemetry. We found Red-eyed Vireos to be the most active and Swainson's Thrushes the least active. For each species, we used boosted regression trees to investigate associations between activity and factors known to influence bird behavior during stopover....

Bayesian state-space models reveal unobserved off-shore nocturnal migration from Motus data

Recent advances in wildlife tracking technology, including the Motus system, have allowed researchers to continuously track small organisms with lightweight radio transmitters over large spatial and temporal ranges. The quantity and format of data generated by the Motus system is unprecedented and requires novel statistical methods. Building from the bsam package in R, we propose new biologically informed Bayesian state-space models for animal movement in JAGS that include informed assumptions about behavior. To apply the models, we employed a localization routine on a Motus data set from migrating Red-eyed Vireos (Vireo olivaceus). This allowed us to apply the new models to estimate unobserved locations and behaviors. Directed migratory flights were detected at night and often over water (e.g. the Bay of Fundy, the Long Island Sound and the New York Bight). Migratory flights were not exclusively nocturnal.

Prolonged stopover and consequences of migratory strategy on local-scale movements within a regional songbird staging area

ABSTRACT Geolocator technology has recently demonstrated that many songbird species exhibit prolonged stopovers during migration that may be analogous to the staging behavior typically attributed to shorebirds. Although staging areas can act as ecological bottlenecks, there is little information on how or why songbirds engage in prolonged stopover and whether this behavior differs among individuals. We used automated radio telemetry along the eastern coastline of North America to compare stopover and migration behavior of Blackpoll Warblers (Setophaga striata) and Red-eyed Vireos (Vireo olivaceus), species that differ markedly in migratory strategy during fall migration. We also tested whether migratory behaviors differed within each species by capture date or breeding origin. Prolonged stopover was more common and longer for Blackpoll Warblers, which suggests that it may be a particularly adaptive behavior for supporting the transatlantic endurance flights they make from the region. Both species made pro...

Occurrence of quiescence in free-ranging migratory songbirds

Quiescence is a period of inactivity that occurs before the onset of migratory activity in nocturnally migrating birds. This behavior has been observed in captive birds in migratory disposition, but its occurrence in free-ranging migratory birds has been documented only anecdotally, and causal factors and function(s), if any, are unknown. In this study, we documented and characterized quiescence in three migratory songbird species (red-eyed vireo [Vireo olivaceus], Swainson’s thrush [Catharus ustulatus], and wood thrush [Hylocichla mustelina]) by measuring movement and proportion of time spent inactive prior to departure from a stopover site during fall migration. Individuals of each species displayed a period of inactivity prior to departure which varied from less than 30 min to over 90 min with red-eyed vireos engaged in the longest, most pronounced quiescence. We also examined how quiescence was related to intrinsic and extrinsic factors known to influence the departure of migrating birds, and found some evidence for an effect of age and departure time but no effect of a migrant’s energetic condition, departure direction, atmospheric conditions around departure, or day of year on quiescence. Our novel application of an automated radiotelemetry system yielded a large amount of data to characterize quiescence in free-ranging migratory birds, and we provide guidance for future studies to tease apart the various causal factors and function(s) of this migratory behavior. Quiescence is a poorly understood period of inactivity observed among captive and free-ranging migratory songbirds prior to the onset of nocturnal activity. Our novel use of automated radiotelemetry revealed quiescence among three intercontinental migratory songbirds. It also enabled us to ask how quiescence might be related to intrinsic and extrinsic factors known to influence the departure of migrating birds, and provided an opportunity to explore possible function(s), if any, of this intriguing behavior.

Fall migratory departure decisions and routes of blackpoll warblers Setophaga striata and red‐eyed vireos Vireo olivaceus at a coastal barrier in the Gulf of Maine

Each year, millions of songbirds concentrate in coastal areas during fall migration. The choices birds make at the coast about stopover habitat use and migratory route can influence both the success of their migratory journey and fitness in subsequent life stages. We made use of a regional‐scale automated radio telemetry array to study stopover and migratory flights and migratory routes of blackpoll warblers Setophaga striata and red‐eyed vireos Vireo olivaceus during fall migration in the Gulf of Maine, USA. We focused on differences between species, sexes, age groups, breeding origins, and time of year. Both species made within‐stopover relocations (i.e. ‘stopover flights’) from the coastal capture site. Stopover flights were primarily oriented inland, and were more frequent for blackpolls (87%) than vireos (44%). By studying migratory behavior at a broad spatial scale, we demonstrated that most blackpolls and vireos took coastal and offshore routes through the Gulf of Maine, despite initially relocating inland from the capture site. Though we captured blackpolls and vireos from a broad breeding range, more than 70% of migratory flights from the capture site were oriented for coastal or offshore travel for both species, suggesting that birds actively chose coastal and offshore routes, and were not simply displaced by wind drift. Later vireos oriented offshore more frequently during migratory flights from the coast, indicating that they may be more inclined towards time‐minimizing overwater flight routes and thus more exposed to coastal and offshore collision hazards than earlier conspecifics.

Avian Malaria, Body Condition, and Blood Parameters In Four Species of Songbirds

ABSTRACT Avian malaria is a common disease in songbirds, caused by protozoa in the genera Plasmodium, Haemoproteus, and Leucocytozoon. These parasites can negatively impact bird health, survival, and reproductive success. Four species of songbirds were sampled for blood parasites during the reproductive season; the American Redstart (Setophaga ruticilla), the Gray Catbird (Dumetella carolinensis), the Cedar Waxwing (Bombycilla cedrorum), and the Red-eyed Vireo (Vireo olivaceus). The study aimed to determine parasite prevalence in these species, as well as to explore a relationship between infection and bird health, measured by body condition and blood parameters. We also tested whether age and sex had an effect on this relationship. Results detected a high parasite prevalence across all species using PCR (94%) but a much lower one using microscopy (37%), suggesting that parasite prevalence is high while parasitemia is low. Red-eyed Vireos were the only species with high prevalence and parasitemia. Parasit...

Variation In Early-Successional Habitat Use Among Independent Juvenile Forest Breeding Birds

ABSTRACT Adults and juveniles of some forest breeding birds shift habitat use during the post breeding season from late to early successional forest. Juveniles of smaller passerine species are difficult to radio-track, and there is limited information on their habitat preferences, especially once they become older and independent. We determined if independent hatch-year birds captured in early-successional habitat remained there for extended periods, or if these habitats were only occupied infrequently during foraging activities. We determined habitat use for Ovenbirds (Seiurus aurocapilla), Worm-eating Warblers (Helmitheros vermivorum) and Red-eyed Vireos (Vireo olivaceus) during the independent post-fledging period in the Missouri Ozarks. We placed radio transmitters on 29 hatch-year birds captured in clearcuts and attempted to relocate them for 24 days in the summer of 2012. All three species had a greater relative probability of use of clearcut forest stands with small trees than older forests. Ovenbi...

Cryptic speciation and gene flow in a migratory songbird Species Complex: Insights from the Red-Eyed Vireo (Vireo olivaceus)

Migratory species that alternate between sympatry and allopatry over the course of an annual cycle are promising subjects for studies seeking to understand the process of speciation in the absence of strict geographic isolation. Here we sought to identify cryptic species and assess rates of gene flow in a clade of neotropical migrant songbirds in which geography and taxonomy are currently out of sync: the Red-Eyed Vireo (V. olivaceus) Species Complex. Phylogenetic, clustering, and statistical species delimitation analyses found that V. olivaceusincludes two non-sister lineages migrating in opposite directions across the equator. Analyses of gene flow identified low levels of introgression between two species pairs, but none between northern and southern olivaceus. We also identified substantial well-supported conflicts between nuclear and mitochondrial topologies. Although the geographic distribution of mito-nuclear discordance is suggestive of hybridization and mitochondrial capture, we found no evidence of introgression in the nuclear genome of populations with discordant mitochondrial gene trees. Our study finds that species boundaries match breeding range and migratory phenology rather than the existing taxonomy in this group, and demonstrates the utility of genomic data in inferring species boundaries in recently diverged clades.

Interspecific Pair-Bonding and Hybridization In Warbling (Vireo gilvus) and Red-Eyed (Vireo olivaceus) Vireos

ABSTRACT We present field observations and genetic evidence of interspecific mate-selection and nesting resulting in successful hybridization between the Warbling Vireo (Vireo gilvus) and the Red-eyed Vireo (V. olivaceus). Two interspecific nesting pairs were found in western North America, each of which produced two fledglings. We examined the DNA of a salvaged fledgling from the nest of a mixed-species pair in Reno, Nevada, using mitochondrial and nuclear DNA analyses. The mitochondrial DNA of this individual indicated a Red-eyed Vireo mother, while its nuclear DNA was heterozygous and consistent with a hybrid origin. Phenotypic traits of the fledglings from the nest of a second mixed-species pair near Juneau, Alaska supported heterospecific parents for those offspring as well. We discuss these findings in the context of reproductive barriers that appear to result in little or no admixture across broad areas of sympatry in these two species.

Multi-scale responses of breeding birds to experimental forest management in Indiana, USA

Forest managers frequently must balance timber production and wildlife conservation goals when choosing management approaches. We studied the response of the breeding bird community to silvicultural treatments at multiple spatial scales over a 10-year period in 60–90year old oak-hickory forests of Indiana, USA. We conducted point count surveys in a 3603-ha study area both before (n=3years) and after (n=6years) application of silvicultural treatments. Bird responses were analyzed at two spatial scales: management units and individual harvests. At the multi-stand management unit scale, treatments were even-aged management, uneven-aged management, and a no-harvest control. We also analyzed the responses of birds at the spatial scale of individual timber harvests (clearcuts, patch cuts, shelterwood harvests, and single-tree selection). Multi-species N-mixture models were used to estimate bird species density and richness at both spatial scales. At the management unit scale, 4 species increased in density following even-aged management (relative to the control), while 1 species (Red-eyed Vireo [Vireo olivaceus]) declined. A larger number of species responded both positively (n=9) and negatively (n=3) to uneven-aged management. Overall richness was significantly greater in the even- and uneven-aged treatments than in the control. At the harvest scale, only the clearcuts and patch cuts resulted in changes in the density of any species, but a larger number of species were impacted and effect sizes were generally larger in these harvests than at the management unit scale. In the clearcuts, 13 species increased in density relative to the no-harvest control, while 5 species declined. A larger number of species were impacted by patch cut harvests (18 species increasing and 6 decreasing). Overall richness was greatest in the clearcut harvests. At both scales, species that increased were generally those associated with early successional habitat, including the Eastern Towhee (Pipilo erythrophthalmus) and Indigo Bunting (Passerina cyanea), while species that declined were typically associated with mature forest habitat (e.g., Red-eyed Vireo [Vireo olivaceus] and Ovenbird [Seiurus aurocapilla]). Harvesting appeared to benefit several species of conservation concern in Indiana, including the Cerulean Warbler (Setophaga cerulea) and Black-and-white Warbler (Mniotilta varia). Both management treatments appear to be good options for simultaneously conserving bird species diversity (particularly of early-successional specialist species) while meeting other forest management goals. However, the impact of the next phases of the shelterwood harvests remains to be evaluated.