Hylocichla Research Articles

Nest predation in an anthropogenic landscape

Wood Thrushes (Hylocichla mustelina) are experiencing widespread population declines. Knowing the relative contribution of predator species to overall rates of nest predation of Wood Thrushes, and understanding how the thrushes are affected by temporal and landscape factors, may be important elements in choosing and devising effective management strategies. We used miniature video cameras to identify nest predators of Wood Thrushes in a highly fragmented landscape in Ontario. Eleven species of birds and mammals were recorded as nest predators. Birds accounted for almost twice as many predation events as mammals, and three species – Brown-headed Cowbird (Molothrus ater), Cooper's Hawk (Accipiter cooperii), and raccoon (Procyon lotor) – accounted for the majority. Species such as American Crow (Corvus brachyrynchos), Blue Jay (Cyanocitta cristata), eastern gray squirrel (Sciurus carolinensis), and Common Grackle (Quiscalus quiscula) that are often speculated to be important nest predators in agricultural and suburban landscapes contributed little or nothing to overall predation rates. We tested hypotheses concerning effects of nest stage, time of nesting season, forest size, forest cover, urban housing pressure, and prior predation events at a nest on the probability of nest predation. Our models showed only two of these factors to be significant: prior predation at a nest increased the chance of a subsequent predation event and increasing the measure of urban pressure reduced the chance of a predation event. The many alternate and easy food sources associated with humans might divert the attention of potential predators from nesting birds in urban forests.

Understanding Sex Differences in Parental Effort in a Migratory Songbird: Examining a Sex-Specific Trade-off between Reproduction and Molt

Migratory birds are expected to experience a trade-off between reproductive effort, the timing and pace of molt, and initiation of fall migration. The purpose of this study was to investigate if males and females of a songbird that migrates to the neotropics, the Wood Thrush (Hylocichla mustelina), experience a trade-off between parental care and the timing of molt. We determined the relative contribution of males and females in feeding young, assessed how reproductive effort influenced timing of molt, and tested the prediction that the sex provisioning nestlings at the higher rate should molt later. Males fed significantly more than females throughout the breeding period, and males with higher feeding rates had greater nesting success. Males compensated for females' reduced provisioning rate at late nests, and females initiated molt earlier than males. We found a significant negative relationship between the timing of molt and the number of young fledged per season. Males that began molt earlier than females and late-molting males also increased their pace of molt. For males, the cost of reduced parental care is likely higher than the benefit of earlier molt, but delayed onset of molt is partially mitigated via a faster pace of feather growth.

What the Thrush Said to T. S. Eliot

Although birds and birdsongs have inspired myriad poems for millennia, the thrush has generated a special fascination for English and American poets over the last two centuries. This little-known fact is borne out by a cabal of well-known poets who have written poems in pursuit of the elusive thrush and its ethereal song. In most of these poems, the thrush seems to know something the speaker doesn't, and its song taunts the speaker and reader alike with the possibility of hidden meaning beyond the reach of words. Many examples could be adduced, such as Thomas Hardy's “The Darkling Thrush,” Siegfried Sassoon's “Thrushes”, William Carlos Williams's “To a Wood Thrush”, Robert Frost's “Come In” and others. This fascination did not escape T. S. Eliot, and he dramatically incorporates thrush songs into his two greatest poems, The Waste Land and Four Quartets. These allusions locate Eliot in a conversation between his poetic predecessors and successors, which I would argue has a bearing on both of these poems.

Landscape-based population viability models demonstrate importance of strategic conservation planning for birds

Efforts to conserve regional biodiversity in the face of global climate change, habitat loss and fragmentation will depend on approaches that consider population processes at multiple scales. By combining habitat and demographic modeling, landscape-based population viability models effectively relate small-scale habitat and landscape patterns to regional population viability. We demonstrate the power of landscape-based population viability models to inform conservation planning by using these models to evaluate responses of prairie warbler (Dendroica discolor) and wood thrush (Hylocichla mustelina) populations in the Central Hardwoods Bird Conservation Region to simulated conservation scenarios. We assessed the relative effectiveness of habitat restoration, afforestation, and increased survival and differed placement and levels of effort for implementing those approaches. Population projections of the two species confirmed the potential for large-scale conservation to sustain regional populations. For example, abundances of prairie warblers and wood thrush tripled under afforestation and increased survival scenarios, respectively. Furthermore, responses to conservation actions were driven by interacting local and large-scale population processes such as source–sink interactions and dispersal. Relying on randomly placed habitat conservation was ineffective and potentially counterproductive whereas strategic placements resulted in greater populations and viability of prairie warbler and wood thrush. These models offer a valuable advance in conservation planning because they allow an understanding of the effects of local actions on regional growth, which is necessary for translating regional goals into local actions.

Birds and Land Classes in Young Forested Landscapes

In the Mississippi Coastal Plain of the southeastern United States, we explored relationships among bird species and vegetation types and landscape characteristics at four different scales. We modeled abundance of priority avian species from Breeding Bird Surveys using land class metrics at 0.24, 1, 3, and 5-km extents. Our modeling method was logistic regression and model selection was based on Akaike’s Information Criteria and validation with reserved data. Northern bobwhite (Colinus virginianus), red-headed woodpecker (Melanerpes erythrocephalus), northern parula (Parula americana), Swainson’s warbler (Limnothlypis swainsonii), prairie warbler (Dendroica discolor), hooded warbler (Wilsonia citrina), and brown-headed cowbird (Molothrus ater) had models containing positive area or core area variables. White-eyed vireo (Vireo griseus) and gray catbird (Dumetella carolinensis) had models with a combination of area and edge associations at different scales. Acadian flycatcher (Empidonax virescens), red-bellied woodpecker (Melanerpes carolinus), wood thrush (Hylocichla mustelina), and yellow-breasted chat (Icteria virens) had positive edge density models. Modeling at different scales produced more complete habitat associations for most species and landscape variables were more influential at larger extents than the smallest extent. Although Mississippi is heavily forested, the landscape is unexpectedly fragmented, with small areal extents of vegetation types. Managers should seek to provide large extents of a variety of habitats, including historically representative vegetation types such as low density pine, to support persistence of a complete suite of avian species.

Repeat Tracking of Individual Songbirds Reveals Consistent Migration Timing but Flexibility in Route

Tracking repeat migratory journeys of individual animals is required to assess phenotypic plasticity of individual migration behaviour in space and time. We used light-level geolocators to track the long-distance journeys of migratory songbirds (wood thrush, Hylocichla mustelina), and, for the first time, repeat journeys of individuals. We compare between- and within-individual variation in migration to examine flexibility of timing and route in spring and autumn. Date of departure from wintering sites in Central America, along with sex and age factors, explained most of the variation (71%) in arrival date at North American breeding sites. Spring migration showed high within-individual repeatability in timing, but not in route. In particular, spring departure dates of individuals were highly repeatable, with a mean difference between years of just 3 days. Autumn migration timing and routes were not repeatable. Our results provide novel evidence of low phenotypic plasticity in timing of spring migration, which may limit the ability of individuals to adjust migration schedules in response to climate change.

Local- versus landscape-scale effects on the demography of three forest-breeding songbirds in Ontario, Canada

Reproductive success of songbirds breeding in forest fragments can be influenced by local habitat characteristics and by anthropogenic land uses in the surrounding matrix such as exurban development and agriculture. Effectively managing these songbirds requires an understanding of which spatial scales most strongly influence their demography. We conducted a multiscale study to investigate the relative influence of local vegetation characteristics and landscape composition at two spatial scales (100 and 2000 m) in a predominantly agricultural landscape on songbird demography. Density, pairing success, nest success, and productivity were assessed for Ovenbirds ( Seiurus aurocapilla (L., 1766)), Wood Thrush ( Hylocichla mustelina (J.F. Gmelin, 1789)), and American Robins ( Turdus migratorius L., 1766) in 16 deciduous forest fragments in southeastern Ontario. Demography of Ovenbirds was most strongly associated with local vegetation characteristics, while demography of Wood Thrush and American Robins was most strongly related to landscape composition within a 2000 m buffer. For all three species, cross-scale correlations influenced nest success, although other demographic parameters were less affected. We conclude that relationships between local- and landscape-scale metrics and songbird demography are complex, species-specific, and differ among reproductive parameters, necessitating a multiscale approach to management.

Evaluating the ability of regional models to predict local avian abundance

AbstractSpatial modeling over broad scales can potentially direct conservation efforts to areas with high species‐specific abundances. We examined the performance of regional models for predicting bird abundance at spatial scales typically addressed in conservation planning. Specifically, we used point count data on wood thrush (Hylocichla mustelina) and blue‐winged warbler (Vermivora cyanoptera) from 2 time periods (1995–1998 and 2006–2007) to evaluate the ability of regional models derived via Bayesian hierarchical techniques to predict bird abundance. We developed models for each species within Bird Conservation Region (BCR) 23 in the upper midwestern United States at 800‐ha, 8,000‐ha, and approximately 80,000‐ha scales. We obtained count data from the Breeding Bird Survey and land cover data from the National Land Cover Dataset (1992). We evaluated predictions from the best models, as defined by an information‐theoretic criterion, using point count data collected within an ecological subregion of BCR 23 at 131 count stations in the 1990s and again in 2006–2007. Competing (Deviance Information Criteria <5) blue‐winged warbler models accounted for 67% of the variability and suggested positive associations with forest edge and proportion of forest at the 8,000‐ha scale, and negative associations with forest patch area (800 ha) and wetness (800 ha and 80,000 ha). The regional model performed best for blue‐winged warbler predicted abundances from point counts conducted in Iowa during 1995–1996 (rs = 0.57; P = 0.14), the survey period that most closely aligned with the time period of data used for regional model construction. Wood thrush models exhibited positive correlations with point count data for all survey areas and years combined (rs = 0.58, P ≤ 0.001). In comparison, blue‐winged warbler models performed worse as time increased between the point count surveys and vintage of the model building data (rs = 0.03, P = 0.92 for Iowa and rs = 0.13, P = 0.51 for all areas, 2006–2007), likely related to the ephemeral nature of their preferred early successional habitat. Species abundance and sensitivity to changing habitat conditions seems to be an important factor in determining the predictive ability of regional models. Hierarchical models can be a useful tool for concentrating efforts at the scale of management units and should be one of many tools used by land managers, but we caution that the utility of such models may decrease over time for species preferring relatively ephemeral habitats if model inputs are not updated accordingly. © 2012 The Wildlife Society.

Nest Attendance and Reproductive Success in the Wood Thrush

Abstract. For most bird species, biparental care is expected to play an integral role in offspring survival. Nevertheless, relatively few studies have simultaneously examined male and female investment into nest attendance, the prevalence of nest attendance through the nesting cycle, or the relationship between nest-attendance effort and nesting success. Here, in a monogamous passerine, the Wood Thrush (Hylocichla mustelina), we use radiotracking to examine nest-attendance behaviors of males and females during the laying, incubation, and nestling stages, and the relationships between nest attendance and nesting success. Across nesting stages, males spent between 14–38% of their time <5 m and 21–58% of their time 5–25 m from the nest, and the time males spent near the nest was positively associated with nesting success. During the incubation stage, the amount of time males spent <5 m from the nest depended upon the female's presence on or off of the nest, as males appear to coordinate their nestattendance ...

An examination of stable hydrogen isotope (δD) variation in adult and juvenile feathers from a migratory songbird

Stable hydrogen isotopes (δD) can help predict geographic origin of tissue growth but within-site variation of feather δD (δDf) exists. Multiple hypotheses explain δDf variation: moult timing, physiology, and spatio-temporal differences in source deuterium, but there have been few direct tests of these factors. We assessed δDf variation within a breeding population of Wood Thrush ( Hylocichla mustelina (Gmelin, 1789)), by sampling feathers from hatch-year birds, returning adults (after migration), and to eliminate confounding variables from newly grown adult primary feathers during moult. We evaluated potential mechanisms explaining δDf variation by examining intraindividual variation (different feather types), precipitation δD, prey δD, corticosterone (CORT), and breeding productivity. In addition, we directly compared δDf of newly grown primary feathers to δD blood hematocrit (δDb). We found significant differences in δDf between years and age classes and observed no significant intraindividual variation. δDf and δDb were not significantly correlated. CORT weakly contributed to δDf, but there are other factors influencing δDf. Ten percent of all feather samples had outlying δDf values, and were likely grown away from the breeding grounds. Our results document intrapopulation and intraindividual variation of δDf at a single location and indicated that age class and year-to-year differences contributed to high δDf variance.

Influence of forest structure on density and nest success of mature forest birds in managed landscapes

AbstractManaging for forest wildlife requires attention not only to quantity but quality of forests within the landscape. We examined the extent to which local structural attributes and landscape context of forest stands explained variation in density and reproductive success of mature forest birds across 12 sites in southeast Ohio, USA, 2004–2006. Results suggest that several structural characteristics influenced bird–habitat relationships in our study. Densities of 3 songbird species (i.e., ovenbird [Seiurus aurocapilla], cerulean warbler [Setophaga cerulea], and scarlet tanager [Piranga olivacea]) were positively related to canopy openness, which is usually a function of canopy gaps. Habitat attributes described by ground litter, understory density, and canopy height were positively associated with densities of ground (i.e., worm‐eating warbler [Helmitheros vermivorum]), or shrub nesting species (i.e., Kentucky and hooded warblers [Geothlypis formosaandSetophaga citrina], respectively). Furthermore, the number of small trees likely drove the positive relationship between density of wood thrush (Hylocichla mustelina), a subcanopy nester. After accounting for temporal variability in daily nest survival rates, the odds of nest survival for all species increased 10.5% for every 1% increase in canopy openness and decreased 1.4% for each 5% increase in understory vegetation density. Habitat–nest survival relationships were not apparent at the level of the individual species. Our results suggest that structural attributes produced by increasing habitat heterogeneity may be necessary for conservation of forest bird communities. © 2012 The Wildlife Society.

Evidence of Medullary Bone in Two Species of Thrushes

We used micro-computed tomography to examine if medullary bone was present in Wood Thrush (Hylocichla mustelina) and Veery (Catharus fuscescens), two species of Passeriformes. We scanned bones from males and females collected during spring and fall migration, and the breeding season. Medullary bone was found in the humerus, radius-ulna, and tibiotarsus-fibula of a breeding female Wood Thrush and a breeding female Veery, both of which were ovulatory at necropsy. Two other breeding female Wood Thrush, both post-ovulatory at necropsy, did not have medullary bone. We did not observe medullary bone in females collected during spring or fall migration, nor in any males. Our findings support the presence of medullary bone in breeding female passerines, but future studies with larger, targeted sample sizes are needed to examine the phenology of medullary bone formation and resorption, and to explore the extent of medullary bone's role in eggshell formation in passerines.

Shifts in Dominant Nest Predators along a Rural-to-Urban Landscape Gradient

Abstract. In urban landscapes, predators are often more abundant or diverse than in rural areas, but few studies have examined how the identity of actual nest predators varies with urbanization. From 2007 to 2010, we used time-lapsed video to record activity at nests of the Northern Cardinal (Cardinalis cardinalis), Acadian Flycatcher (Empidonax virescens), Gray Catbird (Dumetella carolinensis), and Wood Thrush (Hylocichla mustelina) in riparian forests in urban and rural landscapes of Ohio, and we examined the extent to which predator identity was predicted by landscape composition. In 99 records of depredation, we identified 21 species of nest predators (17 in rural, 15 in urban). No single species dominated, though the Brown-headed Cowbird (Molothrus ater; 18% of recorded depredations) and northern raccoon (Procyon lotor; 11%) were the most commonly recorded predators. Birds were responsible for 62% of depredations, followed by mammals (36%) and snakes (2%). By category of predator, mesopredators were ...

Gap-crossing by Wood Thrushes (Hylocichla mustelina)in a fragmented landscape

We used radio-telemetry to study the movement patterns of Wood Thrushes ( Hylocichla mustelina (J.F. Gmelin, 1789)) occupying small forest fragments (&lt;5 ha) to examine gap-crossing between fragments and edge use within fragments. We found that 82% (8/11) of males and 33% (2/6) of females made at least one foray off of its resident forest fragment and we documented a total of 26 off-fragment forays (n = 79 h tracking). Males spent, on average, 23.5% of their time off their fragment, while females were gone 12.8% of the time tracked. Most forays were &gt;150 m in distance and foray rate to adjacent fragments declined with increasing gap width. Males on fragments spent more time off their territory (23.5%) and traveled farther (392 m) than males occupying territories within a continuous forest (4.8% and 99 m, respectively). In fragments, 10 out of 17 individuals spent &gt;80% of their time within 20 m of the fragment edge and edge use was significantly more than expected based on the amount of edge available in each fragment. This study adds to the growing evidence for migratory songbirds that during the breeding season, forest fragmentation may increase rather than impede daily movements.

Spring Stopover and Refueling Among Migrant Passerines in the Sierra De Los Tuxtlas, Veracruz, Mexico

The narrowing of the North American continent at the Isthmus of Tehuantepec creates an important geographic bottleneck for songbirds on their northward spring migrations. The Sierra de Los Tuxtlas, in the northwestern portion of the Isthmus, provide an ideal location from which to address questions of resource use and fuel acquisition during migration. We operated mist nets during morning and evening to capture passerines during spring migration in 2003 and 2004. Seven of 13 taxa had significant diurnal increases in body condition (an index of size-adjusted mass): Swainson's Thrush (Catharus ustulatus), Wood Thrush (Hylocichla mustelina), Magnolia Warbler (Dendroica magnolia), Kentucky Warbler (Oporornis formosus), Hooded Warbler (Wilsonia citrina), Worm-eating Warbler (Helmitheros vermivorum), and Ovenbird (Seiurus aurocapilla). All of these species, except Ovenbird, also had a significant increase in fat score. Indigo Buntings (Passerina cyanea) had a significant increase in fat score but not in condition index. A comparison with autumn migration at this site showed overall similarities in percentage of species gaining mass and in the amount gained, but there were seasonal differences within species. There was no relationship between increase in body condition and a mainland versus trans-gulf migratory strategy.

Molting Success of Ixodes scapularis Varies Among Individual Blood Meal Hosts and Species

The blacklegged tick (Ixodes scapularis) is an important vector of emerging human pathogens. It has three blood-feeding stages, as follows: larva, nymph, and adult. Owing to inefficient transovarial transmission, at least for the Lyme disease agent (Borrelia burgdorferi), larval ticks rarely hatch infected, but they can acquire infection during their larval blood meal. Nymphal ticks are primarily responsible for transmitting pathogens to hosts, including humans. The transition from uninfected host-seeking larva to infectious host-seeking nymph is therefore a key aspect of human risk of infection. It can be divided into a series of steps, as follows: finding a host, taking a blood meal, becoming infected, molting, and overwintering. The chance of succeeding in each of these steps may depend on the species identity of the blood meal host. We used a Bayesian method to estimate the molting success of larval I. scapularis collected from four commonly parasitized species of birds and eight commonly parasitized small and mid-sized mammals found in the forests of Dutchess County, New York. We show that molting success varies substantially among host species; white-footed mice, veeries, and gray catbirds support particularly high molting success, whereas ticks feeding on short-tailed shrews, robins, and wood thrushes were less successful. We also show that larval molting success varies substantially between individual blood meal hosts, and that this intraspecific variability is much higher in some species than in others. The causes of both inter- and intraspecific variation in molting success remain to be determined.

Registros adicionales de algunas especies de aves en la cuenca baja del Río Verde, Oaxaca, México

Presento información de cinco especies de aves registradas en la cuenca baja del Río Verde, Oaxaca, en las inmediaciones del Parque Nacional Lagunas de Chacahua. Para Hylocichla mustelina, este es el primer registro en la planicie costera del suroeste de Oaxaca; los registros de Falco femoralis, Aramus guarauna y Peucaea humeralis amplían nuestro conocimiento sobre su distribución en esta parte de Oaxaca, mientras que el de Aramides axillaris es sólo el segundo registro para el estado.

Avian nest success, mammalian nest predator abundance, and invertebrate prey availability in a fragmented landscape

Avian nest success is largely determined by predation, but factors affecting the abundance of potential nest predators are rarely studied. We used an information–theoretic approach to assess relative support for models including invertebrate biomass, mammalian nest predator abundance, and percent cover at nests as explanatory variables for nest success of Ovenbirds ( Seiurus aurocapilla (L., 1766)) and Wood Thrush ( Hylocichla mustelina (J.F. Gmelin, 1789)). We ranked models including local vegetation characteristics and landscape composition at two spatial scales (100 and 2000 m) as explanatory variables for the abundance of mammalian nest predator groups and for prey biomass. The nest success of Ovenbirds was best explained by a positive association with percent cover by forbs and seedlings, whereas a positive relationship with prey biomass best explained the nest success of Wood Thrush. Most mammal genera were associated with landscape composition within 100 m of the study sites, and most were positively associated with housing density. Prey biomass was best explained by a positive association with less intensive agriculture within 2000 m. Implementing silvicultural techniques that preserve important habitat features within fragmented forests, limiting housing density within 100 m, and increasing the amount of less intensive agriculture within 2000 m of forest fragments may improve nest success for forest songbirds.

Extension of landscape-based population viability models to ecoregional scales for conservation planning

Landscape-based population models are potentially valuable tools in facilitating conservation planning and actions at large scales. However, such models have rarely been applied at ecoregional scales. We extended landscape-based population models to ecoregional scales for three species of concern in the Central Hardwoods Bird Conservation Region and compared model projections against long-term trend data from the North American Breeding Bird Survey. We used a spatially-explicit demographic model and structured the regional population into ecological subsections on the basis of habitat, landscape patterns, and demographic rates to assess species viability. Our model projections were within 2% of the Breeding Bird Survey trends over the last 40 years for each species. Wood thrush ( Hylocichla mustelina) populations remained relatively stable over the simulation and worm-eating warbler ( Helmitheros vermivorus) abundance increased throughout most of the time period until reaching carrying capacity. In contrast, the prairie warbler ( Dendroica discolor) population steadily declined by 0.59% annually. The combination of habitat and demographic modeling allowed us to create models that address processes driving these populations at all scales, which is critical to understanding how regional populations respond to landscape processes such as habitat loss and fragmentation. Therefore, because it is spatially explicit and directly addresses population growth and viability, this approach provides a valuable foundation to planning conservation strategies, offering the ability to identify the most salient risks to viability and explore ways to address them.

Comparison of methods for estimating density of forest songbirds from point counts

AbstractNew analytical methods have been promoted for estimating the probability of detection and density of birds from count data but few studies have compared these methods using real data. We compared estimates of detection probability and density from distance and time‐removal models and survey protocols based on 5‐ or 10‐min counts and outer radii of 50 or 100 m. We surveyed singing male Acadian flycatchers (Empidonax virescens), cerulean warblers (Dendroica cerulea), Kentucky warblers (Oporornis formosus), Louisiana waterthrushes (Parkesia motacilla), wood thrushes (Hylocichla mustelina), and worm‐eating warblers (Helmitheros vermivorum) in bottomland and upland forest across 5 states in the Central Hardwoods Bird Conservation Region during the breeding season in 2007 and 2008. Detection probabilities differed between distance and time‐removal models and species detectabilities were affected differently by year, forest type, and state. Density estimates from distance models were generally higher than from time‐removal models, resulting from lower detection probabilities estimated by distance models. We found support for individual heterogeneity (modeled as a finite mixture model) in the time‐removal models and that 50‐m radius counts generated density estimates approximately twice as high as 100‐m radius counts. Users should be aware that in addition to estimating different components of detectability, density estimates derived from distance and time‐removal models can be affected by survey protocol because some count durations and plot radii may better meet model assumptions than others. The choice of a method may not affect the use of estimates for relative comparisons (e.g., when comparing habitats) but could affect conclusions when used to estimate population size. We recommend careful consideration of assumptions when deciding on point‐count protocol and selection of analysis methods. © 2011 The Wildlife Society.