Nelson's Sparrow Research Articles

Ecological characteristics explain neutral genetic variation of three coastal sparrow species.

Eco-phylogeographic approaches to comparative population genetic analyses allow for the inclusion of intrinsic influences as drivers of intraspecific genetic structure. This insight into microevolutionary processes, including changes within a species or lineage, provides better mechanistic understanding of species-specific interactions and enables predictions of evolutionary responses to environmental change. In this study, we used single nucleotide polymorphisms (SNPs) identified from reduced representation sequencing to compare neutral population structure, isolation by distance (IBD), genetic diversity and effective population size (Ne) across three closely related and co-distributed saltmarsh sparrow species differing along a specialization gradient-Nelson's (Ammospiza nelsoni subvirgata), saltmarsh (A. caudacuta) and seaside sparrows (A. maritima maritima). Using an eco-phylogeographic lens within a conservation management context, we tested predictions about species' degree of evolutionary history and ecological specialization to tidal marshes, habitat, current distribution and population status on population genetic metrics. Population structure differed among the species consistent with their current distribution and habitat factors, rather than degree of ecological specialization: seaside sparrows were panmictic, saltmarsh sparrows showed hierarchical structure and Nelson's sparrows were differentiated into multiple, genetically distinct populations. Neutral population genetic theory and demographic/evolutionary history predicted patterns of genetic diversity and Ne rather than degree of ecological specialization. Patterns of population variation and evolutionary distinctiveness (Shapely metric) suggest different conservation measures for long-term persistence and evolutionary potential in each species. Our findings contribute to a broader understanding of the complex factors influencing genetic variation, beyond specialist-generalist status and support the role of an eco-phylogeographic approach in population and conservation genetics.

New extralimital breeding records of saltmarsh sparrows (Ammospiza caudacuta) and Nelson's sparrows (Ammospiza nelsoni) and their implications.

Saltmarsh (Ammospiza caudacuta) and Nelson's (A. nelsoni) sparrows are sister taxa that breed in tidal marshes along the coast of the Northeastern United States and Canada. The Saltmarsh Sparrow breeds from mid-coast Maine south to Virginia, while the Acadian Nelson's Sparrow breeds from the Canadian maritime provinces south to northern Massachusetts. Here, we present three extralimital observations of breeding Saltmarsh (n = 2) and Nelson's (n = 1) sparrows. In 2021 and 2022, we observed Saltmarsh Sparrow females attending nests at Mendall Marsh, ME, and Milbridge, ME, respectively, approximately 60 and 110 km beyond the documented northern extent of the Saltmarsh Sparrow breeding range. In 2022, we observed a breeding-condition male Nelson's sparrow singing in the upriver portion of a marsh on Cape Cod, Massachusetts, approximately 115 km beyond the previously documented southern extent of the Nelson's Sparrow breeding range. We confirmed morphological species identification using a panel of microsatellite DNA loci. Due to both the well-documented population declines of these species in the region and the intensity of sampling effort undertaken in recent years, we suggest that these observations likely are not indicative of range expansion. However, they do indicate that these 2 taxa have the capacity to use and successfully reproduce in marshes well beyond their established breeding limits. Our findings provide novel insight into the potential for these taxa to occur and successfully breed outside their documented breeding ranges. Given increased interest in their conservation, these results support the idea that management actions aimed at creating or maintaining nesting habitat across both species ranges could benefit both taxa.

Estimates of breeding season location for 4 mesic prairie bird species wintering along the Gulf Coast

During the last 2 centuries, widespread declines have been observed in migratory species, and these declines have largely been linked to anthropogenic causes. Migrants move across multiple spatiotemporal scales with wide-ranging movements that can cross multiple jurisdictions. Consequently, conservation and management require the incorporation of these wide-ranging movements. However, for many nongame species, basic information on migration and wintering ecology is poorly known. Yellow Rails (Coturnicops noveboracensis), LeConte's Sparrows (Ammospiza leconteii), Nelson's Sparrows (A. nelsoni), and Sedge Wrens (Cistothorus stellaris) represent a diverse avian assemblage that breeds in prairie potholes, boreal forest, and coastal areas of northern and eastern Canada and winters in coastal prairies in the southern United States. We used a stable deuterium isotope (δ2Hf) analysis to assign breeding season locations for individuals captured wintering in the southeastern US. We obtained deuterium values from secondary feathers of birds spending the nonbreeding season from Oklahoma and Texas east to Florida. We found substantial differences in the δ2Hf values of Yellow Rails and Nelson's Sparrows, with birds wintering in Oklahoma and the western Gulf of Mexico having δ2Hf values that were probabilistically assigned to the western half of their breeding range, while birds wintering in Florida were probabilistically assigned to the eastern portion of their breeding range. LeConte's Sparrow breeding season assignments for birds wintering in Texas and Oklahoma overlapped. Sedge Wrens did not exhibit spatial variation in isotope values.

Mercury exposure of tidal marsh songbirds in the northeastern United States and its association with nest survival.

The biogeochemistry of tidal marsh sediments facilitates the transformation of mercury (Hg) into the biologically available form methylmercury (MeHg), resulting in elevated Hg exposures to tidal marsh wildlife. Saltmarsh and Acadian Nelson's sparrows (Ammospiza caudacutua and A. nelsoni subvirgatus, respectively) exclusively inhabit tidal marshes, potentially experiencing elevated risk to Hg exposure, and have experienced range-wide population declines. To characterize spatial and temporal variation of Hg exposure in these species, we sampled total mercury (THg) in blood collected from 9 populations spanning 560 km of coastline, including individuals resampled within and among years. Using concurrent nesting studies, we tested whether THg was correlated with nest survival probabilities, an index of fecundity. Blood THg ranged from 0.074-3.373 µg/g ww across 170 samples from 127 individuals. We detected high spatial variability in Hg exposure, observing differences of more than 45-fold across all individuals and 8-fold in mean blood THg among all study plots, including 4-fold between study plots within 4 km. Intraindividual changes in blood Hg exposure did not vary systematically in time but were considerable, varying by up to 2-fold within and among years. Controlling for both species differences and maximum water level, the dominant driver of fecundity in this system, nest survival probability decreased by 10% across the full range of female blood THg concentrations observed. We conclude that Hg has the potential to impair songbird reproduction, potentially exacerbating known climate-change driven population declines from sea-level rise in saltmarsh and Acadian Nelson's sparrows.

Sperm length divergence as a potential prezygotic barrier in a passerine hybrid zone.

The saltmarsh sparrow Ammospiza caudacuta and Nelson's sparrow A. nelsoni differ in ecological niche, mating behavior, and plumage, but they hybridize where their breeding distributions overlap. In this advanced hybrid zone, past interbreeding and current backcrossing result in substantial genomic introgression in both directions, although few hybrids are currently produced in most locations. However, because both species are nonterritorial and have only brief male–female interactions, it is difficult to determine to what extent assortative mating explains the low frequency of hybrid offspring. Since females often copulate with multiple males, a role of sperm as a postcopulatory prezygotic barrier appears plausible. Here, we show that sperm length differs between the two species in the hybrid zone, with low among‐male variation consistent with strong postcopulatory sexual selection on sperm cells. We hypothesize that divergence in sperm length may constitute a reproductive barrier between species, as sperm length co‐evolves with the size of specialized female sperm storage tubules. Sperm does not appear to act as a postzygotic barrier, as sperm from hybrids was unexceptional.

Wetland water-management may influence mercury bioaccumulation in songbirds and ducks at a mercury hotspot.

Mercury is a persistent, biomagnifying contaminant that can cause negative behavioral, immunological, and reproductive effects in wildlife and human populations. We examined the role of wetland water-management on mercury bioaccumulation in songbirds and ducks at Kellys Slough National Wildlife Refuge Complex, near Grand Forks, North Dakota USA. We assessed mercury concentrations in blood of wetland-foraging songbirds (80 common yellowthroats [Geothlypis trichas] and 14 Nelson's sparrows [Ammospiza nelsoni]) and eggs of upland-nesting ducks (28 gadwall [Mareca strepera], 19 blue-winged teal [Spatula discors], and 13 northern shoveler [S. clypeta]) across four wetland water-management classifications. Nelson's sparrow blood mercury concentrations were elevated (mean: 1.00 µg/g ww; 95% CL: 0.76-1.31) and similar to those reported 6 years previously. Mercury in songbird blood and duck eggs varied among wetland water-management classifications. Songbirds and ducks had 67% and 49% lower mercury concentrations, respectively, when occupying wetlands that were drawn down with water flow compared to individuals occupying isolated-depressional wetlands with no outflow. Additionally, songbirds within impounded and partially drawn-down wetland units with water flow had mercury concentrations that were 26-28% lower, respectively, than individuals within isolated-depressional wetlands with no outflow. Our results confirm that mercury concentrations in songbirds at Kellys Slough continue to be elevated and suggest that water-management could be an important tool for wetland managers to reduce bioaccumulation of mercury in birds.

Divergent selection and drift shape the genomes of two avian sister species spanning a saline-freshwater ecotone.

The role of species divergence due to ecologically based divergent selection—or ecological speciation—in generating and maintaining biodiversity is a central question in evolutionary biology. Comparison of the genomes of phylogenetically related taxa spanning a selective habitat gradient enables discovery of divergent signatures of selection and thereby provides valuable insight into the role of divergent ecological selection in speciation. Tidal marsh ecosystems provide tractable opportunities for studying organisms' adaptations to selective pressures that underlie ecological divergence. Sharp environmental gradients across the saline–freshwater ecotone within tidal marshes present extreme adaptive challenges to terrestrial vertebrates. Here, we sequence 20 whole genomes of two avian sister species endemic to tidal marshes—the saltmarsh sparrow (Ammospiza caudacutus) and Nelson's sparrow (A. nelsoni)—to evaluate the influence of selective and demographic processes in shaping genome‐wide patterns of divergence. Genome‐wide divergence between these two recently diverged sister species was notably high (genome‐wide F ST = 0.32). Against a background of high genome‐wide divergence, regions of elevated divergence were widespread throughout the genome, as opposed to focused within islands of differentiation. These patterns may be the result of genetic drift resulting from past tidal march colonization events in conjunction with divergent selection to different environments. We identified several candidate genes that exhibited elevated divergence between saltmarsh and Nelson's sparrows, including genes linked to osmotic regulation, circadian rhythm, and plumage melanism—all putative candidates linked to adaptation to tidal marsh environments. These findings provide new insights into the roles of divergent selection and genetic drift in generating and maintaining biodiversity.

Evaluating a focal-species approach for tidal marsh bird conservation in the northeastern United States

ABSTRACT Insufficient time and funding remain obstacles to collecting data across broad spatial scales on the fine-scale distribution of multiple species, their life histories, and interactions with other species and the environment. This often necessitates the use of focal species to inform conservation and management decisions. We used the systematic conservation-planning software Marxan to assess quantitatively whether a focal species can aid in conservation and management of tidal marsh birds. Using a metric of relative cost in the region and current protected areas, we identified priority areas for conservation of 5 specialist taxa—Clapper Rail (Rallus crepitans), Eastern Willet (Tringa semipalmata semipalmata), Acadian Nelson's Sparrow (Ammospiza nelsoni subvirgatus), Saltmarsh Sparrow (A. caudacuta), and Seaside Sparrow (A. maritima)—that nest primarily in tidal marshes in the northeastern United States. We compared the spatial prioritization of sites and cost-effectiveness of alternative protectio...

Estimates of tidal‐marsh bird densities using Bayesian networks

ABSTRACTConserving tidal‐marsh bird communities requires strategies to address continuing pressures from human development to the effects of increasing rates of sea‐level rise. Knowing tidal‐marsh bird distributions and population sizes are important for developing these strategies. In the Northeast United States, where estimates of sea‐level rise are 3 times higher than the global average, 5 bird species are tidal‐marsh specialists: clapper rail (Rallus crepitans), willet (Tringa semipalmata), Nelson's sparrow (Ammospiza nelsoni), saltmarsh sparrow (A. caudacuta), and seaside sparrow (A. maritima). We used a regional marsh bird survey to develop Bayesian network models to identify factors that influence patch‐scale species density and to estimate regional population sizes. We modeled species density as a function of habitat covariates at the patch, local, landscape, and regional spatial scales. Densities were most sensitive to patch location and dimension, patch geomorphic setting, indices of human development, and changes in mean sea level. We estimated 110,000 clapper rails (95% CI = 61,000–159,000), 111,000 willets (95% CI = 70,000–152,000), 7,000 Nelson's sparrows (95% CI = 4,000–10,000), 60,000 saltmarsh sparrows (95% CI = 40,000–80,000), and 234,000 seaside sparrows (95% CI = 112,000–356,000) from the United States–Canada border to, and including, the mouth of the Chesapeake Bay, Virginia, USA. Our abundance estimates can be used to identify priority conservation areas at multiple geographic scales and our models help identify key habitat and landscape components for tidal‐marsh restoration and management to benefit tidal‐marsh birds and can be modified for other species. © 2018 The Wildlife Society.

Bidirectional adaptive introgression between two ecologically divergent sparrow species.

Natural hybrid zones can be used to dissect the mechanisms driving key evolutionary processes by allowing us to identify genomic regions important for establishing reproductive isolation and that allow for transfer of adaptive variation. We leverage whole-genome data in a system where two bird species, the saltmarsh (Ammospiza caudacuta) and Nelson's (A. nelsoni) sparrow, hybridize despite their relatively high background genetic differentiation and past ecological divergence. Adaptive introgression is plausible in this system because Nelson's sparrows are recent colonists of saltwater marshes, compared to the specialized saltmarsh sparrow that has a longer history of saltmarsh adaptation. Comparisons among whole-genome sequences of 34 individuals from allopatric and sympatric populations show that ongoing gene flow is shaping the genomic landscape, with allopatric populations exhibiting genome-wide FST estimates close to double of that observed in sympatry. We characterized patterns of introgression across the genome and identify regions that exhibit biased introgression into hybrids from one parental species. These regions offer compelling candidates for genes related to tidal marsh adaptations suggesting that adaptive introgression may be an important consequence of hybridization. These findings highlight the value of considering the landscapes of both genome-wide introgression and divergence when characterizing the evolutionary forces that drive speciation.

The role of divergent mating strategies, reproductive success, and compatibility in maintaining the Saltmarsh–Nelson's sparrow hybrid zone

ABSTRACT Understanding inter- and intra-specific variation in mate compatibility and reproductive success can offer insight into the factors driving sexual selection, behavioral dynamics, and isolating mechanisms across natural populations. This information is particularly relevant when trying to understand the patterns that shape the causes and outcomes of hybridization in natural systems. We evaluated mating patterns and male reproductive success in a hybrid zone between the Saltmarsh (Ammodramus caudacutus) and Nelson's sparrow (A. nelsoni). Specifically, we investigated variation in male reproductive success between pure Saltmarsh and pure Nelson's sparrows and between pure and hybrid males, while testing for assortative vs. random mating. DNA samples were collected from adults (n = 342) and nestlings (n = 348), and paternity analyses and assignment of individuals to pure and hybrid classes were conducted using 11 microsatellite loci. We documented high promiscuity and reproductive skew in Saltmarsh a...

Elevated mercury in blood and feathers of breeding marsh birds along the contaminated lower Penobscot River, Maine, USA

Mercury (Hg) concentrations in the blood and feathers of five species of migratory marsh birds, Nelson's sparrow (Ammodramus nelson subvirgatus), song sparrow (Melospiiza melodia), swamp sparrow (Melospiza geogiana), red-winged blackbird (Agelaius phoeniceus), and Virginia rail (Rallus limicola), breeding in marshes along the lower Penobscot River, Maine, far exceeded reference concentrations, exceeded concentrations associated with reproductive health, and are the highest Hg concentrations reported to date for several species. Blood Hg concentrations in adult Nelson's sparrows were greatest in 2007, at 6.6μg/gww (geometric mean) and in 2012, at 6.5μg/gww and greatest in red-winged blackbirds in 2012, 8.0μg/gww. Mercury in blood increased with residence time on the contaminated marshes at an estimated rate of 0.04 to 0.07μg/gww per day. Feather mercury concentrations in specific primary, secondary and tail feathers (P1, S2, R6) were strongly associated with exposure location at the time of feather formation. Geometric mean Hg concentrations in primary feathers (P1) reached 39.6μg/gfw in 2010 in Nelson's sparrows. The paper documents the dynamic nature of Hg concentrations in avian blood and feathers, an important consideration in contaminant study design, and the increased risk to marsh birds posed by Hg deposition from upstream sources.

Variation in passerine use of burned and hayed planted grasslands

ABSTRACTCreation of grassland communities is a popular approach to conserve grassland‐nesting waterfowl and songbirds. Much uncertainty remains regarding the most appropriate seed mixtures and the type and frequency of management. We conducted line‐transect songbird surveys in grasslands converted from cropland to native and tame grass‐forb mixtures and managed by burning (native only) or haying (native and tame) in Saskatchewan and Manitoba, Canada. Fields were 1–9 years post‐management (YPM). Our objective was to improve our understanding of the effects of management regime (native hayed, native burned and tame hayed fields) and frequency (YPM) on passerine density and occurrence in planted grassland. We found limited support for an effect of management regime on passerine density and occurrence in both provinces. Vesper sparrow (Pooecetes gramineus) occurrence in Saskatchewan was greatest in tame hayed fields, and clay‐colored sparrow (Spizella pallida) density in Manitoba was greater in tame hayed fields than in native burned fields up to 5 YPM. Years post‐management most strongly influenced the occurrence of vesper sparrows in Saskatchewan and sedge wrens (Cistothorus platensis); common yellowthroats (Geothlypis trichas); clay‐colored, Savannah (Passerculus sandwichensis), Le Conte's (Ammodramus leconteii), and Nelson's (A. nelsoni) sparrows; and bobolinks (Dolichonyx oryzivorus) in Manitoba. Five of the 8 species influenced by YPM exhibited a year‐dependent non‐linear response such that they reached their greatest density 4–5 YPM. Our results indicate that the type of stand (native or tame) or management (burning or haying) matters little to the grassland songbird community occupying planted cover fields and that the frequency of management will likely depend upon local environmental conditions in a given region or year. Some form of management of planted grasslands, however, should occur every 4–6 years to maintain habitat for a number of generalist grassland species. © 2017 The Wildlife Society.

Extrinsic and intrinsic factors influence fitness in an avian hybrid zone

The effects of hybridization on evolutionary processes are primarily determined by the differential between hybrid and parental species fitness. Assessing the impacts of hybridization can be challenging, however, as determining the relationship between individual fitness and the extent of introgression in wild populations is difficult. We evaluated the fitness consequences of hybridization for pure and hybrid females in a hybrid zone between two tidal marsh birds, the saltmarsh sparrow (Ammodramus caudacutus), a salt marsh obligate, and Nelson's sparrow (A. nelsoni), which has a broader ecological niche and a much younger evolutionary association with salt marshes. Biotic stressors associated with nesting in tidal environments suggest an important role for differential adaptation in shaping hybrid zone dynamics, with saltmarsh sparrows predicted to be better adapted to nesting in salt marshes. We collected DNA samples from adults (n = 394) and nestlings (n = 431) to determine the extent of introgression using 12 microsatellite loci and tested for the influence of extrinsic (nest placement) and intrinsic (genotype) factors on female reproductive success. We monitored nests (n = 228), collected data on reproductive output, and estimated daily nest survival rates using female genotype and nest characteristics as covariates. To test for reduced survival of hybrid females, we also used capture data to assess the distribution of admixed male and female individuals across age classes. Reproductive success of females varied by genotypic class, but hybrids did not have intermediate success as predicted. Instead, we found that pure Nelson's sparrows had, on average, 33% lower hatching success than any other genotype, whereas F1/F2 hybrids, backcrossed Nelson's sparrows, and backcrossed and pure saltmarsh sparrows all had similar hatching success. We found no effect of genotype or nest placement on daily nest survival probabilities. However, hybrid individuals with a higher proportion of saltmarsh sparrow alleles exhibit nesting behaviours better suited to nesting successfully in tidal marshes. Further, while the proportion of F1/F2 individuals was similar between nestling and adult males, we found that the proportion of F1/F2 individuals was 2.3 times greater in nestling females compared with adult females, indicating reduced survival of F1 females. We conclude that differences in reproductive success among pure and admixed individuals coupled with intrinsic mechanisms (reduced survival in F1 females) shape hybrid zone dynamics in this system.

Population estimates for tidal marsh birds of high conservation concern in the northeastern USA from a design-based survey

ABSTRACT Tidal marsh loss to anthropogenic environmental impacts and climate change, particularly sea level rise, has and will continue to cause declines in tidal marsh bird populations. Distribution patterns of tidal marsh birds are generally known, yet we lack detailed knowledge of local abundance and regional population sizes, which limits our ability to develop effective conservation strategies that will mitigate the impacts of marsh loss. We designed and implemented a probabilistic sampling framework to establish a regional marsh bird monitoring program, and collected baseline information for breeding tidal marsh birds in the northeastern USA (Maine to Virginia). We sampled 1,780 locations in 2011–2012 to provide regional population estimates for 5 tidal marsh–specialist birds. We estimated that there were 151,000 Clapper Rails (Rallus crepitans; 95% CI = 90,000–212,000), 117,000 Willets (Tringa semipalmata; 95% CI = 88,000–146,000), 5,000 Nelson's Sparrows (Ammodramus nelsoni; 95% CI = 1,000–9,000),...

Differential introgression and the maintenance of species boundaries in an advanced generation avian hybrid zone.

BackgroundEvolutionary processes, including selection and differential fitness, shape the introgression of genetic material across a hybrid zone, resulting in the exchange of some genes but not others. Differential introgression of molecular or phenotypic markers can thus provide insight into factors contributing to reproductive isolation. We characterized patterns of genetic variation across a hybrid zone between two tidal marsh birds, Saltmarsh (Ammodramus caudacutus) and Nelson’s (A. nelsoni) sparrows (n = 286), and compared patterns of introgression among multiple genetic markers and phenotypic traits.ResultsGeographic and genomic cline analyses revealed variable patterns of introgression among marker types. Most markers exhibited gradual clines and indicated that introgression exceeds the spatial extent of the previously documented hybrid zone. We found steeper clines, indicating strong selection for loci associated with traits related to tidal marsh adaptations, including for a marker linked to a gene region associated with metabolic functions, including an osmotic regulatory pathway, as well as for a marker related to melanin-based pigmentation, supporting an adaptive role of darker plumage (salt marsh melanism) in tidal marshes. Narrow clines at mitochondrial and sex-linked markers also offer support for Haldane’s rule. We detected patterns of asymmetrical introgression toward A. caudacutus, which may be driven by differences in mating strategy or differences in population density between the two species.ConclusionsOur findings offer insight into the dynamics of a hybrid zone traversing a unique environmental gradient and provide evidence for a role of ecological divergence in the maintenance of pure species boundaries despite ongoing gene flow.Electronic supplementary materialThe online version of this article (doi:10.1186/s12862-016-0635-y) contains supplementary material, which is available to authorized users.

Genotype-environment associations support a mosaic hybrid zone between two tidal marsh birds.

Local environmental features can shape hybrid zone dynamics when hybrids are bounded by ecotones or when patchily distributed habitat types lead to a corresponding mosaic of genotypes. We investigated the role of marsh-level characteristics in shaping a hybrid zone between two recently diverged avian taxa - Saltmarsh (Ammodramus caudacutus) and Nelson's (A.nelsoni) sparrows. These species occupy different niches where allopatric, with caudacutus restricted to coastal marshes and nelsoni found in a broader array of wetland and grassland habitats and co-occur in tidal marshes in sympatry. We determined the influence of habitat types on the distribution of pure and hybrid sparrows and assessed the degree of overlap in the ecological niche of each taxon. To do this, we sampled and genotyped 305 sparrows from 34 marshes across the hybrid zone and from adjacent regions. We used linear regression to test for associations between marsh characteristics and the distribution of pure and admixed sparrows. We found a positive correlation between genotype and environmental variables with a patchy distribution of genotypes and habitats across the hybrid zone. Ecological niche models suggest that the hybrid niche was more similar to that of A.nelsoni and habitat suitability was influenced strongly by distance from coastline. Our results support a mosaic model of hybrid zone maintenance, suggesting a role for local environmental features in shaping the distribution and frequency of pure species and hybrids across space.

Evaluation of autonomous recording units for detecting 3 species of secretive marsh birds

ABSTRACTPopulation status and habitat use of yellow rails (Coturnicops noveboracensis), Nelson's sparrows (Ammodramus nelsoni), and Le Conte's sparrows (A. leconteii) are poorly known, so standardized surveys of these species are needed to inform conservation planning and management. A protocol for monitoring secretive marsh birds exists; however, these species regularly call at night and may be missed during early morning surveys. We tested the effectiveness of autonomous recording units (hereafter, recording units) to survey these species by analyzing recorded vocalizations using bioacoustics software. We deployed 22 recording units at 54 sites in northern Minnesota and eastern North Dakota, USA, and conducted traditional broadcast surveys during May–June, 2010 and 2011. We compared detection probabilities between recording units and standard monitoring protocols using robust‐design occupancy models. On average, recording units detected 0.59 (SE = 0.11) fewer Le Conte's sparrows, 0.76 (SE = 0.15) fewer Nelson's sparrows, and 1.01 (SE = 0.14) fewer yellow rails per survey than were detected using the standard protocol. Detection probabilities using the standard protocol averaged 0.95 (yellow rail; 95% CI = 0.86–0.98), 0.93 (Le Conte's sparrow; 95% CI = 0.78–0.98), and 0.89 (Nelson's sparrow; 95% CI = 0.56–0.98), but averaged 0.71 (yellow rail; 95% CI = 0.56–0.83), 0.61 (Le Conte's sparrow; 95% CI = 0.42–0.78), and 0.51 (Nelson's sparrow; 95% CI = 0.19–0.82) using recording units. Reduced detection by recording units was likely due to the ability of human listeners to identify birds calling at greater distances. Recording units may be effective for surveying nocturnal secretive marsh birds if investigators correct for differential detectability. Reduced detectability may be outweighed by the increased spatial and temporal coverage feasible with recording units. © 2015 The Wildlife Society.

Relationship of phenotypic variation and genetic admixture in the Saltmarsh–Nelson's sparrow hybrid zone

ABSTRACT Hybridization is influential in shaping species' dynamics and has many evolutionary and conservation implications. Identification of hybrid individuals typically relies on morphological data, but the assumption that hybrids express intermediate traits is not always valid, because of complex patterns of introgression and selection. We characterized phenotypic and genotypic variation across a hybrid zone between 2 tidal-marsh birds, the Saltmarsh Sparrow (Ammodramus caudacutus) and Nelson's Sparrow (A. nelsoni) (n = 290), and we sought to identify morphological traits that could be used to classify admixed individuals. Sparrows were sampled from a total of 34 marshes, including 23 sympatric and 11 putatively allopatric marshes. Each individual was scored at 13 plumage traits, and standard morphometric data were collected. We used genotyping analysis at 24 microsatellite loci to categorize individuals into genotypic classes of pure, F1–F2, or backcrossed. Genetic data revealed that 52% of individual...

Development of diagnostic microsatellite markers from whole-genome sequences of Ammodramus sparrows for assessing admixture in a hybrid zone.

Studies of hybridization and introgression and, in particular, the identification of admixed individuals in natural populations benefit from the use of diagnostic genetic markers that reliably differentiate pure species from each other and their hybrid forms. Such diagnostic markers are often infrequent in the genomes of closely related species, and genomewide data facilitate their discovery. We used whole-genome data from Illumina HiSeqS2000 sequencing of two recently diverged (600,000 years) and hybridizing, avian, sister species, the Saltmarsh (Ammodramus caudacutus) and Nelson's (A. nelsoni) Sparrow, to develop a suite of diagnostic markers for high-resolution identification of pure and admixed individuals. We compared the microsatellite repeat regions identified in the genomes of the two species and selected a subset of 37 loci that differed between the species in repeat number. We screened these loci on 12 pure individuals of each species and report on the 34 that successfully amplified. From these, we developed a panel of the 12 most diagnostic loci, which we evaluated on 96 individuals, including individuals from both allopatric populations and sympatric individuals from the hybrid zone. Using simulations, we evaluated the power of the marker panel for accurate assignments of individuals to their appropriate pure species and hybrid genotypic classes (F1, F2, and backcrosses). The markers proved highly informative for species discrimination and had high accuracy for classifying admixed individuals into their genotypic classes. These markers will aid future investigations of introgressive hybridization in this system and aid conservation efforts aimed at monitoring and preserving pure species. Our approach is transferable to other study systems consisting of closely related and incipient species.