Canada Warbler Research Articles

Over-winter ecology and relative density of Canada Warbler Cardellina canadensis in Colombia: the basis for defining conservation priorities for a sharply declining long-distance migrant

SummaryThe Canada Warbler Cardellina canadensis is a steeply declining Neotropical migratory bird and > 50% of its non-breeding range is within the Colombian Andes. Despite being an abundant migrant in Andean forests, the species’ elevational distribution and non-breeding ecology have yet to be studied, thereby precluding the design of effective conservation actions. During four non-breeding periods (2012–2016), we surveyed Colombia’s three Andean ranges, carrying out passive 5-minute point counts between 700 and 3,150 m asl in five habitats (mature forest, secondary growth, forest edges/riparian forest, shade coffee, sun coffee), recording the perpendicular distance, sex, foraging height, and association with mixed species flocks of Canada Warbler. Habitat variables were recorded at each point. Based on 819 passive point counts, Canada Warblers occupied elevations between 750 and 2,300 m, being more abundant between 1,000 and 2,200 m. Relative densities were higher in mature forest compared to shade coffee and secondary forest, and accordingly abundance increased with canopy height. There was no evidence for a difference in elevation or habitat use by males and females. Within forests, birds foraged at mid-levels, 5–15 m above the ground, and the probability of Canada Warblers occurring in mixed species flocks increased with elevation. Models of variation in relative density throughout the Eastern Andes showed a positive relation with cloud cover and above-ground forest biomass, implying a preference for humid, forested regions. Of the areas in the Eastern Andes with high predicted relative density, ∼ 14% overlapped with protected areas and we identify priority areas where protective measures could benefit the conservation status of the species. For maximum effectiveness, conservation actions should focus on protecting forest fragments and initiating reforestation projects at mid-elevations (1,000–2,200 m), as well as supporting agroforestry practices in humid regions of the Colombian Andes.

Characterizing spatio-temporal variation in survival and recruitment with integrated population models

ABSTRACT Efforts to understand population dynamics and identify high-quality habitat require information about spatial variation in demographic parameters. However, estimating demographic parameters typically requires labor-intensive capture–recapture methods that are difficult to implement over large spatial extents. Spatially explicit integrated population models (IPMs) provide a solution by accommodating spatial capture–recapture (SCR) data collected at a small number of sites with survey data that may be collected over a much larger extent. We extended the spatial IPM framework to include a spatio-temporal point process model for recruitment, and we applied the model to 4 yr of SCR and distance-sampling data on Canada Warblers (Cardellina canadensis) near the southern extent of the species' breeding range in North Carolina, USA, where climate change is predicted to cause population declines and distributional shifts toward higher elevations. To characterize spatial variation in demographic parameters ...

Cross-scale effects of spruce budworm outbreaks on boreal warblers in eastern Canada.

Insect outbreaks are major natural disturbance events that affect communities of forest birds, either directly by affecting the food supply or indirectly by changing the vegetation composition of forest canopies. An examination of correlations between measures of bird and insect abundance across different spatial scales and over varying time lag effects may provide insight into underlying mechanisms. We developed a hierarchical Bayesian model to assess correlations between counts of eight warbler species from the Breeding Bird Survey in eastern Canada, 1966 to 2009, with the presence of spruce budworm (Choristoneura fumiferana Clem.) at immediate local scales and time‐lagged regional scales, as measured by extent of defoliation on host tree species. Budworm‐associated species Cape May warbler (Setophaga tigrina), bay‐breasted warbler (Setophaga castanea), and Tennessee warbler (Oreothlypis peregrina) responded strongly and positively to both local and regional effects. In contrast, non‐budworm‐associated species, Blackburnian warbler (Setophaga fusca), magnolia warbler (Setophaga magnolia), Canada warbler (Cardellina canadensis), black‐throated blue warbler (Setophaga caerulescens), and black‐throated green warbler (Setophaga virens), only responded to regional effects in a manner that varied across eastern Canada. The complex responses by forest birds to insect outbreaks involve both increased numerical responses to food supply and to longer term responses to changes in forest structure and composition. These effects can vary across spatial scales and be captured in hierarchical population models, which can serve to disentangle common trends from data when examining drivers of population dynamics like forest management or climate change.

The Andean Cock-of-the-rock (Rupicola peruvianus) is a frugivorous bird predator

Cotingas are considered essentially frugivorous, but a few records suggest they might include small vertebrates in their diet, mainly during the breeding season. In March 2015, we recorded a young male of an Andean Cock-of-the-rock (Rupicola peruvianus) chasing and eating an adult Canada Warbler (Cardellina canadensis) in Santa Maria, Boyacá (Colombia). The next day, we observed another adult male chasing a Swainson's Thrush (Catharus ustulatus), but we were unable to observe the end of the chase. Observations of hunting small vertebrates suggest this species may be omnivorous, not only during the breeding season but throughout its annual cycle. These may be rare cases, but notably both events involved migratory species that may not recognize these colorful birds as possible predators because they are not exposed to cotingas in the temperate zone. Predation on adult birds is difficult to observe in the wild, but this information is essential to better understand the life histories of birds and the different selection pressures acting on them.

Drivers of demographic decline across the annual cycle of a threatened migratory bird

Migratory species are rapidly declining but we rarely know which periods of the annual cycle are limiting for most species. This knowledge is needed to effectively allocate conservation resources to the periods of the annual cycle that best promote species recovery. We examined demographic trends and response to human footprint for Canada warblers (Cardellina canadensis), a threatened Neotropical migrant, using range-wide data (1993–2016) from the Monitoring Avian Productivity and Survivorship (MAPS) program on the breeding grounds. Declines in abundance were steepest in the eastern breeding region, followed by the western region. Breeding productivity did not decline in any region. In contrast, we observed declining recruitment in all regions, low apparent survival in the east and west, and a decline in apparent survival in the east. Abundance declined with increasing disturbance around MAPS stations. Between 1993 and 2009, the human footprint index on the breeding range increased by 0.11% in contrast to a 14% increase on the wintering range. Landscape-scale disturbance on the breeding grounds may influence abundance in some regions; however, the observed trends in demography and footprint suggests limitation during the non-breeding period as the likely driver of overall declines, particularly for eastern populations.

Extra-pair paternity in a long-distance migratory songbird beyond neighbors’ borders and across male age classes

Roughly 90% of socially monogamous bird species exhibit some degree of extra-pair paternity (EPP), although the extent and the underlying mechanisms vary among species. We analyzed spatial and demographic patterns of EPP over a 6 year period (2005–2010) as part of a long-term population study of Canada Warblers (Cardellina canadensis (L., 1766)). We identified 12 microsatellite loci used to assess paternity for 185 nestlings from 61 nests. Extra-pair young (EPY) accounted for 41.6% of all nestlings and 57.4% of nests contained at least one EPY. Fewer than half of EPY were sired by males who shared territorial boundaries, and some males sired young in nests 1 km from their territory. The age of social males did not differ from males who cuckolded them. The majority (83%) of EPY were sired by males in older age classes (2+ years old), while <17% were sired by 1 year olds. Of the young sired by older males, 58.5% were sired by males 3–7 years old. Males that sired more EPY sired fewer within-pair young (WPY); those without EPY sired more WPY suggesting a possible fitness trade-off between these two strategies. Our findings suggest multiple age-based strategies within a single breeding population, as well as potential strategy shifts to maximize lifetime fitness as they age.

Canada Warbler (Cardellina canadensis): novel molecular markers and a preliminary analysis of genetic diversity and structure

Ferrari, B. A., B. M. Shamblin, R. B. Chandler, H. R. Tumas, S. Hache, L. Reitsma, and C. J. Nairn. 2018. Canada Warbler (Cardellina canadensis): novel molecular markers and a preliminary analysis of genetic diversity and structure. Avian Conservation and Ecology 13(1):8. https://doi.org/10.5751/ACE-01176-130108

Forestry and conspecifics influence Canada Warbler (Cardellina canadensis) habitat use and reproductive activity in boreal Alberta, Canada

ABSTRACT The Canada Warbler (Cardellina canadensis) is a threatened species in Canada due to an annual decline of ∼3% over the last 50 yr. Some studies suggest that Canada Warblers prefer old-growth forest and that forestry practices may reduce suitable habitat, while other research indicates that the species will also use harvested areas. Differences in scale between habitat use studies and behavioral phenomena such as conspecific attraction may explain this discrepancy. We examined how Canada Warblers responded to forestry and conspecifics in Alberta, Canada. We used point counts, burst sampling, and behavioral observations to determine how the density, home range placement (second-order habitat use), within-home-range space use (third-order habitat use), and probability of pairing and fledging young of male Canada Warblers were influenced by postharvest conditions (i.e. amount, age [≤ 30 yr postharvest], and retention of unharvested fragments) and conspecifics. Male density was 86% lower in postharvest...

Single‐visit dynamic occupancy models: an approach to account for imperfect detection with Atlas data

Summary Atlas data provide biodiversity information at a relatively fine spatial grain over a broad spatial extent and, increasingly, at multiple points in time, which make them invaluable for understanding processes that affect species distributions over time. The effect of survey effort on species detection has long been appreciated and Atlases typically include survey standards and records of effort, but challenges remain in analysing Atlas data that have not been collected using a repeated sampling protocol designed to correct for imperfect detection. We developed a single‐visit dynamic occupancy model to quantify the effects of climatic and land‐use drivers on local species extinction and colonization while accounting for imperfect detection using repeat Atlas data. We evaluated model stability using data simulated under alternative scenarios and, ultimately, applied the model to empirical data for Canada warbler Cardellina canadensis, a wide‐spread species exhibiting a long‐term population decline. At sample sizes that are realistic for many Atlases (n = 1000–10 000 independent survey blocks), our models produced unbiased estimates of detection, occupancy, colonization and extinction parameters. Slope estimates for explanatory covariates were somewhat less stable than overall occupancy, colonization and extinction rates, with covariate effects being sensitive to the total number of, and relationships among, explanatory variables. In comparison to other analyses of Canada warbler distributions that indicated minor changes over time, our approach identified a widespread decline in occupancy probability across New York, consistent with the broader population trend, particularly in the areas where it was initially more likely to occur. Synthesis and applications. A single‐visit dynamic occupancy model is a novel method for analysing common, ecologically valuable datasets, such as Atlases, that lack repeated sampling necessary to correct for imperfect detection using alternative multi‐season occupancy modelling approaches. As a result, using this method can improve understanding of species distributions and factors that shape them over time, thereby providing more accurate information to guide conservation and management.

Fall migration and breeding origins of Canada Warblers moving through northern Colombia

Canada Warblers (Cardellina canadensis) are long-distance Neotropical migrants, but little is known about their migratory behavior and ecology. We examined the fall migration of Canada Warblers at two sites, Darien and the Sierra Nevada de Santa Marta, in northern Colombia from 2011 to 2015 using constant-effort mist-netting. Our objectives were to determine: 1) breeding origins and connectivity patterns, 2) migratory pathways, 3) the phenology of migration, 4) possible differences in movements between ages and sexes, 5) their body condition when arriving in Colombia, and 6) evidence of stopover and refueling. Stable hydrogen isotopes (δ2Hf) in flight feathers were analyzed to estimate breeding origins of captured Canada Warblers in North America. The δ2Hf values revealed that most Canada Warblers captured in the Darien likely originated from the central and northeastern regions of their breeding range. The capture of all but one of 162 Canada Warblers in the Darien also indicates a migration route through Central American rather than across the Caribbean Sea. Most captured birds were hatch-year birds (91% vs. 9% after hatch-year birds), and we captured more females (67%) than males (33%). Canada Warblers migrated through the Darien from 20 September to early November, with most arriving in mid-October. Most (89%) individuals arrived with low fuel reserves. These results combined with estimated flight ranges revealed that 46% of the individuals captured in the Darien likely needed to refuel to continue migrating, whereas 31% could continue 50 to 200 km beyond our capture site. However, no individuals were recaptured so stopover duration could not be determined. Canada Warblers may adopt a strategy of 1-d stopovers and short flights or, alternatively, the Darien may represent low-quality habitat and birds quickly left our study site in search of suitable habitat. Further study is needed to determine the possible importance of other (montane) habitats for Canada Warblers in the Darien region to prioritize conservation actions.

Topography of the Andes Mountains shapes the wintering distribution of a migratory bird

AbstractAimIn birds, patterns of migratory connectivity are influenced by landscape structure experienced throughout the annual cycle. Assessing how landscape patterns drive the movements and distributions of migratory species is important for understanding the evolution of migration and determining conservation priorities. We determined migratory connectivity in the Canada Warbler (Cardellina canadensis), a declining Neotropical migratory bird, and evaluated the degree to which the Andean mountains influence winter population distribution in this montane forest specialist.LocationSeven study regions across the Western, Central, and Eastern Andes of Colombia.MethodsWe inferred breeding and natal origins of Canada Warblers overwintering in Colombia by analysing stable hydrogen isotope values (δ2H) in feathers and assigning wintering populations to breeding origins using an established feather δ2H isoscape for North America.ResultsWe found strong evidence for parallel migration between breeding and wintering sites, giving rise to moderately strong migratory connectivity between breeding and wintering regions. The model best explaining population distribution in the Colombian Andes implied that populations were most similar within basins or valleys. Such segregation is notable, given that basins are separated by less than 300 km on the wintering grounds, while breeding populations may be separated by more than 3000 km from east to west.Main conclusionsOur results suggest that the high spine of each Andean cordillera acts to shape the winter distribution of individuals from different breeding populations. To our knowledge, this is the first demonstration that the topography of the Andean mountains can act to shape the winter distribution of populations of a migratory bird. The strength of migratory connectivity found in Canada Warblers may inhibit evolutionary responses to environmental change, and the more rapid population declines recorded in some eastern breeding populations may be related to habitat loss and local environmental conditions in the Eastern Andes, where individuals from these populations were more likely to overwinter.

Patterns of change in body condition in wintering Neotropical-Nearctic migratory birds in shaded plantations in the Andes

Despite the widely accepted idea that shaded plantations are valuable habitats for Neotropical migrants in disturbed landscapes, little empirical evidence is available in relation to the quality of this habitat for Neotropical-Nearctic migratory birds in the Andes. We evaluated the suitability of shaded plantations for overwintering Neotropical-Nearctic migratory birds by examining diurnal and seasonal variation in body condition of migrants in these agroforests in the Andes. During October to April 2008–2009 and 2009–2010, we mist-netted eight species of Neotropical-Nearctic migrants in shaded plantations in the Colombian Andes. Body condition improved throughout the day for Cerulean Warbler (Setophaga cerulea), Blackburnian Warbler (Setophaga fusca), Tennessee Warbler (Leiothlypis peregrina), and especially Canada Warbler (Cardellina canadensis). Similarly, body condition improved across the season for Tennessee Warbler, Rose-breasted Grosbeak (Pheucticus ludovicianus), and Summer Tanager (Piranga rubra). Our results provided additional evidence that several common Neotropical migrants, including species of conservation concern such as Cerulean Warbler and Canada Warbler, may improve their body condition in shaded plantations. However, about half of the species assessed in this study did not show any significant improvement in their body condition (e.g. Red-eyed Vireo). Furthermore, on average, species were in poor condition (i.e. body condition scores were negative) in these coffee farms. Thus, the extent to which this agricultural system represents high quality habitat should be looked with caution. Overall, our data contribute novel information on daily patterns of body condition improvement for several common migratory birds in Andean shaded plantations.

Influence of landscape, habitat, and species co-occurrence on occupancy dynamics of Canada Warblers

ABSTRACT The Canada Warbler (Cardellina canadensis) is a species of high conservation importance because of its low overall density and long-term widespread population declines on the breeding grounds. Results of previous research on the species suggest that its breeding habitat preferences vary across its range. However, the underlying processes associated with habitat use are unknown. Using a 20 yr dataset, we developed occupancy models for Canada Warblers to determine the influence of habitat characteristics (e.g., understory vegetation, canopy cover), landscape context (e.g., edge, forest patch size), and species co-occurrence on occupancy, colonization, and local extinction parameters. Our results show that multiple habitats are used by Canada Warblers on the breeding grounds; common variables associated with large-scale, long-term occupancy dynamics are forest age, landscape composition at the 100 m and 500 m scales, and mean patch size. Overall, Canada Warblers were nearly twice as persistent in ma...

Estimating the spatial scales of landscape effects on abundance

Spatial variation in abundance is influenced by local- and landscape-level environmental variables, but modeling landscape effects is challenging because the spatial scales of the relationships are unknown. Current approaches involve buffering survey locations with polygons of various sizes and using model selection to identify the best scale. The buffering approach does not acknowledge that the influence of surrounding landscape features should diminish with distance, and it does not yield an estimate of the unknown scale parameters. The purpose of this paper is to present an approach that allows for statistical inference about the scales at which landscape variables affect abundance. Our method uses smoothing kernels to average landscape variables around focal sites and uses maximum likelihood to estimate the scale parameters of the kernels and the effects of the smoothed variables on abundance. We assessed model performance using a simulation study and an avian point count dataset. The simulation study demonstrated that estimators are unbiased and produce correct confidence interval coverage except in the rare case in which there is little spatial autocorrelation in the landscape variable. Canada warbler abundance was more highly correlated with site-level measures of NDVI than landscape-level NDVI, but the reverse was true for elevation. Canada warbler abundance was highest when elevation in the surrounding landscape, defined by an estimated Gaussian kernel, was between 1300 and 1400 m. Our method provides a rigorous way of formally estimating the scales at which landscape variables affect abundance, and it can be embedded within most classes of statistical models.

Repertoire structure, song sharing, reproductive success, and territory tenure in a population of Canada Warblers (Cardellina canadensis) in central New Hampshire

Sexual selection for larger repertoires and the social advantages of sharing songs with territorial neighbours are two forces that may drive the evolution of complex song repertoires in songbirds. To evaluate the influence of these two selective pressures on repertoire evolution in a species with a complex repertoire, we examined repertoire structure, song sharing, reproductive success, and territory tenure in a Canada Warbler (Cardellina canadensis (L., 1766)) population in New Hampshire. Over two breeding seasons, we recorded 63 singing males, classified their song repertoires, quantified male song sharing, and determined male reproductive success and territory tenure. Male Canada Warblers had complex repertoires averaging 12 phrases (particular sequences of song elements) and 55 variants (songs composed of particular sequences of phrases). Song sharing decreased significantly with distance between territories, all of which were <1.75 km apart. Network analysis revealed clusters of male neighbours with high variant sharing, which was significantly associated with longer territory tenure. Overall pairing and fledging success were high, but were not related to repertoire size or song sharing. Our results suggest that song sharing aids in male territory acquisition and defence, and that females may therefore select mates based on their ability to retain a high-quality territory.

Regional habitat needs of a nationally listed species, Canada Warbler (Cardellina canadensis), in Alberta, Canada

Regional habitat needs of a nationally listed species, Canada Warbler (Cardellina canadensis), in Alberta, Canada

Factors driving territory size and breeding success in a threatened migratory songbird, the Canada Warbler

Factors driving territory size and breeding success in a threatened migratory songbird, the Canada Warbler

Avian communities of managed and wilderness hemiboreal forests

We compared breeding bird communities of hemiboreal forests in multiple-use managed forests and relatively unmanaged wilderness forests in northern Minnesota. A total of 240 point-count locations, 120 in each of the managed and wilderness areas, were sampled three times across ten paired transects in 2010 and 2011. Transects were paired near lotic systems that cross each management type, with half of the points adjacent to (100m) or distant (400m) from the riparian corridor. Total number of individuals and species richness detected per count were higher within the unmanaged forest (F1,9=9.76, p=0.01; F1,9=11.17, p<0.01) and forest adjacent to the riparian corridor (F1,9=28.30, p<0.001; F1,9=42.12, p<0.001). These results were negatively correlated with increased area of regenerating forests (mainly from logging) within the managed forest and positively correlated with tree species richness and overstory height of forest stands within the wilderness forest. Of 35 species analyzed individually, Black-capped Chickadee (Poecile atricapillus), Brown Creeper (Certhia americana), Canada Warbler (Cardellina canadensis), Golden-crowned Kinglet (Regulus satrapa), Least Flycatcher (Empidonax minimus), Red-breasted Nuthatch (Sitta canadensis), Winter Wren (Troglodytes hiemalis), and Yellow-bellied Flycatcher (Empidonax flaviventris) were more common in the wilderness forest. Only the Mourning Warbler (Geothlypis philadelphia) and Chipping Sparrow (Spizella passerina) were more common in the managed forest. Species associated with mature or mixed forests tended to be found in the wilderness area at higher densities, but most species associated with early-successional habitats did not differ between the managed and wilderness landscapes. Results suggest that forests with natural disturbance and succession regimes provide habitat for a higher density and richness of bird species. Responses by breeding birds were similar in both management types regarding distance from riparian areas. To adequately provide for effective conservation of the avian community, forested regions should include wilderness forests.

Bird–building collisions in the United States: Estimates of annual mortality and species vulnerability

Abstract Building collisions, and particularly collisions with windows, are a major anthropogenic threat to birds, with rough estimates of between 100 million and 1 billion birds killed annually in the United States. However, no current U.S. estimates are based on systematic analysis of multiple data sources. We reviewed the published literature and acquired unpublished datasets to systematically quantify bird–building collision mortality and species-specific vulnerability. Based on 23 studies, we estimate that between 365 and 988 million birds (median = 599 million) are killed annually by building collisions in the U.S., with roughly 56% of mortality at low-rises, 44% at residences, and &amp;lt;1% at high-rises. Based on &amp;gt;92,000 fatality records, and after controlling for population abundance and range overlap with study sites, we identified several species that are disproportionately vulnerable to collisions at all building types. In addition, several species listed as national Birds of Conservation Concern due to their declining populations were identified to be highly vulnerable to building collisions, including Golden-winged Warbler (Vermivora chrysoptera), Painted Bunting (Passerina ciris), Canada Warbler (Cardellina canadensis), Wood Thrush (Hylocichla mustelina), Kentucky Warbler (Geothlypis formosa), and Worm-eating Warbler (Helmitheros vermivorum). The identification of these five migratory species with geographic ranges limited to eastern and central North America reflects seasonal and regional biases in the currently available building-collision data. Most sampling has occurred during migration and in the eastern U.S. Further research across seasons and in underrepresented regions is needed to reduce this bias. Nonetheless, we provide quantitative evidence to support the conclusion that building collisions are second only to feral and free-ranging pet cats, which are estimated to kill roughly four times as many birds each year, as the largest source of direct human-caused mortality for U.S. birds.

Two song categories in the Canada Warbler (Cardellina canadensis)

ABSTRACT. North American wood-warbler species (Parulidae) studied to date have song systems of one or two categories. Those with two categories use them in different temporal and behavioral contexts, which suggests similar functions across species. We conducted the first detailed analysis of the vocal behavior of a species in the genus Cardellina, the Canada Warbler (C. canadensis). We found that males had two performance-encoded song categories, Mode I and Mode II, and used them in contexts similar to those in which parulids of the genera Vermivora, Mniotilta, and Setophaga use their song categories. Males sang Mode I more often during the day, when unpaired, during early nesting, and when alone or near a female. Males sang Mode II at dawn, after pairing, during the postfledging period, and when near another male. In Mode I, males sang more stereotyped songs more slowly and regularly. In Mode II, males sang more variable songs rapidly, with a more variable rhythm, and chipped frequently between songs. Al...