Cerulean Warbler Research Articles

A comparison of avian communities and habitat characteristics in floodplain forests associated with valley plugs and unchannelized streams

AbstractChannelization of streams associated with floodplain forested wetlands has occurred extensively throughout the world and specifically in the southeastern United States. Channelization of fluvial systems alters the hydrologic and sedimentation processes that sustain these systems. In western Tennessee, channelization and past land‐use practices have caused drastic geomorphic and hydrologic changes, resulting in altered habitat conditions that may affect avian communities. The objective of this study was to determine if there were differences in avian communities utilizing floodplain forests along unchannelized streams compared to channelized streams with valley plugs, areas where sediment has completely filled the channel. During point count surveys, 58 bird species were observed at unchannelized sites and 60 species were observed at valley plug sites. Species associated with baldcypress‐tupelo (Taxodium‐Nyssa) swamps (e.g. Great Egret (Ardea albus) and Black‐crowned Night Heron (Nycticorax nycticorax)) and mature hardwood forests with open midstories (e.g. Eastern Wood‐Pewee (Contopus virens), Yellow‐throated Vireo (Vireo flavifrons), Cerulean Warbler (Dendroica cerulea) and Scarlet Tanager (Piranga olivacea)) were either only found at unchannelized sites or were more abundant at unchannelized sites. Conversely, species associated with open and early successional habitats (e.g. Tree Swallow (Tachycineta bicolor), Northern Mockingbird (Mimus polyglottos) and Blue Grosbeak (Passerina caerulea)) were either only found at valley plug sites or were more abundant at valley plug sites. Results of habitat modelling suggest that the habitat characteristics of floodplain forests at unchannelized sites are more suitable for Neotropical migrant bird species of conservation concern in the region than at valley plug sites. This study, in combination with previous research, demonstrates the ecological impacts of valley plugs span across abiotic and biotic processes and tropic levels. Copyright © 2010 John Wiley & Sons, Ltd.

Use of Fecundity Measured Directly Throughout the Breeding Season to Test a Source-Sink Demographic Model

Populations of landbirds (bird species that occupy terrestrial habitats for most of their life cycle) are declining throughout North America (north of Mexico) and Europe, yet little is known about how demography is driving this trend. A recent model of 5 geographically separated populations of Cerulean Warblers (Dendroica cerulea) that was based on within-season sampling of nest survival and fledgling success shows that all populations are sinks (annual reproduction is consistently less than annual adult mortality). I tested this indirect model by directly measuring fecundity (number of female fledglings/female) during the breeding season for 2 years in a Cerulean Warbler population occupying a mature forest in southwestern Michigan (U.S.A.) I determined territories of male birds on the basis of male plumage characters and phases of the nesting cycle (2007) and on uniquely color-banded males (2008). I transferred locations of identified males to topographic maps. I counted all fledglings in territories from May to July each year. The model I tested may apply only to single-brooded species; therefore, I searched the literature to estimate the percentage of single-brooded species in North America. The breeding season of Cerulean Warblers was short- nearly all nests were initiated from mid-May to late June. Nest predation and brood parasitism were primary and rare causes of nest failure, respectively. Significantly fewer Cerulean Warblers fledged from parasitized than from nonparasitized nests. Fledgling survival required to maintain the population size was well above previously published values for Neotropical migrants. Single-brooded species comprise 62% of North American breeding bird species for which the number of broods per year is known; I believe my results may apply to these species. The consistency between identification of populations as sources or sinks on the basis of either model estimates or direct measurements suggests that a demographic model relying on within-season sampling of fecundity is adequate to determine population status of single-brooded avian populations. In addition, on the basis of results of previous studies, annual adult survival rate of the Cerulean Warbler is typical of parulid warblers that are not declining. Thus, low fecundity, here determined with different quantitative methods, can drive status of landbird species with high-observed survival.

Taxonomic recommendations for British birds: seventh report

Taxonomic recommendations for British birds: seventh report

Comparison of statistical and theoretical habitat models for conservation planning: the benefit of ensemble prediction

Selection of a modeling approach is an important step in the conservation planning process, but little guidance is available. We compared two statistical and three theoretical habitat modeling approaches representing those currently being used for avian conservation planning at landscape and regional scales: hierarchical spatial count (HSC), classification and regression tree (CRT), habitat suitability index (HSI), forest structure database (FS), and habitat association database (HA). We focused our comparison on models for five priority forest-breeding species in the Central Hardwoods Bird Conservation Region: Acadian Flycatcher, Cerulean Warbler, Prairie Warbler, Red-headed Woodpecker, and Worm-eating Warbler. Lacking complete knowledge on the distribution and abundance of each species with which we could illuminate differences between approaches and provide strong grounds for recommending one approach over another, we used two approaches to compare models: rank correlations among model outputs and comparison of spatial correspondence. In general, rank correlations were significantly positive among models for each species, indicating general agreement among the models. Worm-eating Warblers had the highest pairwise correlations, all of which were significant (P < 0.05). Red-headed Woodpeckers had the lowest agreement among models, suggesting greater uncertainty in the relative conservation value of areas within the region. We assessed model uncertainty by mapping the spatial congruence in priorities (i.e., top ranks) resulting from each model for each species and calculating the coefficient of variation across model ranks for each location. This allowed identification of areas more likely to be good targets of conservation effort for a species, those areas that were least likely, and those in between where uncertainty is higher and thus conservation action incorporates more risk. Based on our results, models developed independently for the same purpose (conservation planning for a particular species in a particular geography) yield different answers and thus different conservation strategies. We assert that using only one habitat model (even if validated) as the foundation of a conservation plan is risky. Using multiple models (i.e., ensemble prediction) can reduce uncertainty and increase efficacy of conservation action when models corroborate one another and increase understanding of the system when they do not.

Avian Community and Microhabitat Associations of Cerulean Warblers in Alabama

Abstract Cerulean Warblers (Dendroica cerulea) have experienced one of the highest population declines of any neotropical-Nearctic migratory species in North America. We performed point counts and habitat assessments in areas used and unused by Cerulean Warblers in northern Alabama during the 2005 and 2006 breeding seasons to examine their avian associations and identify microhabitat features that best explained their occurrence. We detected on average ∼50 Cerulean Warbler males (total) in three disjunct populations during each breeding season. Areas used by Cerulean Warblers were characterized by avian communities with significantly higher species richness, diversity, and abundance compared to areas where they were not detected. Correspondence analysis related Cerulean Warblers to inhabitants of riparian, bottomland deciduous forests (e.g., Kentucky Warbler [Oporornis formosus], Acadian Flycatcher [Empidonax virescens], and Northern Parula [Parula americana]) and two edge specialists (Blue-winged Warbler...

Role of topography, canopy structure, and floristics in nest-site selection and nesting success of canopy songbirds

Although oaks ( Quercus spp.) have historically dominated many forests in eastern North America, forest composition is changing due to anthropogenic impacts on disturbance regimes. Silvicultural practices, such as partial harvesting, are one component of management to promote oak regeneration. From 2007 to 2009 our research examined nest-site selection and nesting success for a guild of five canopy songbirds in upland mixed-oak forests in southeastern Ohio, USA. We monitored >700 nests across three state forests in both open canopy shelterwood stands harvested to approximately 50% stocking, and closed-canopy mature second-growth. Habitat attributes, including topography, canopy structure, and floristics, were measured at nest sites and random plots ⩽100 m from nests representing microhabitat available within the territory. Canopy songbirds selected specific topographic microclimates: Eastern Wood-pewees ( Contopus virens) nested on xeric ridgetops, Blue-gray Gnatcachers ( Polioptila caerulea) favored valleys, and Cerulean Warblers ( Dendroica cerulea) preferred productive northeast-facing slopes. Nest sites differed among species in terms of concealment, nest support, topographic position on the slope, and basal area of trees >38 cm dbh. Four of the five focal species selected Quercus alba as the nest substrate more than twice as much as available, and three species avoided Quercus rubra. Daily survival rates of nests were negatively associated with basal area of red oak species (both Quercus velutina and Q. rubra) for several species individually and across the canopy-nesting guild. Additional factors related to success included time of season for Eastern Wood-pewees, nest age for Cerulean Warblers, and concealment and size of the support branch for Scarlet Tanagers ( Piranga olivacea). In the long-term management for oak regeneration could benefit canopy songbirds, but our results indicate that white oaks, especially Q. alba, may be preferable to red oak species.

Conspecific Egg Destruction by a Female Cerulean Warbler

Abstract Conspecific egg destruction is an adaptive behavior that has typically evolved in multi-brooded, polygynous, or colonial avian species, and can be difficult to observe. We describe the first case of egg destruction in the Parulidae, which consists of mostly single-brooded and socially monogamous species. In this case, a female Cerulean Warbler (Dendroica cerulea) destroyed 5-day old eggs at a conspecific's nest. This act was likely committed to secure a breeding opportunity with a high quality male or to decrease local competition for resources. There is also the possibility this behavior may have been pathological and not adaptive.

Migratory bird use of shade coffee: the role of structural and floristic features

Shade coffee plantations support high numbers of Neotropical migratory birds, but relatively little is known about the structural and floristic attributes used by individual species. From 2005 to 2007, we studied the relationship between habitat characteristics and Neotropical migratory birds in shade coffee plantations in the Venezuelan Andes. Our results indicate that density of migrants was significantly related to both structural and floristic attributes of coffee farms. Specifically, upper canopy foragers were positively associated with number of large trees (>38 cm dbh), tree canopy height, and understory vegetation density. Low canopy and ground foragers were positively associated with numbers of small (8–23 cm dbh) and medium (23–38 cm dbh) trees and increased shade cover. Moreover, certain tree species, especially Inga spp., Erythrina spp. and Acnistus arborescens, were important components of habitat for those species that forage in the canopy. For example, our detailed foraging observations showed that Inga trees were used in greater proportion than available throughout plantations by Cerulean Warblers (Dendroica cerulea), a species of high conservation concern. Overall, our research suggests that suitability of coffee plantations for migratory birds may be improved by managing for particular structural and floristic characteristics of plantations.

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.

Cerulean Warbler Occurrence and Habitat use in Oklahoma

Dendroica cerulea (Cerulean Warbler) is a migrant songbird that has declined rangewide in recent decades. We surveyed 150 sites in 2006–2007 to determine if this species still occupied its former breeding range in Oklahoma. We located Cerulean Warblers at 5 sites and confirmed breeding on north slopes of two heavily forested ridges in the Ouachita Mountains. We did not encounter Cerulean Warblers in any bottomland hardwoods, despite the former widespread distribution and abundance of the species in such habitats. While habitat loss and degradation may limit occurrence of Cerulean Warbler in some areas, the pattern of decline for this species at the edge of its range in Oklahoma is also consistent with abandonment of peripheral range as the range-wide population declines.

Effects of Stop-Level Habitat Change on Cerulean Warbler Detections Along Breeding Bird Survey Routes in the Central Appalachians

We examined the effects of habitat change on Cerulean Warbler (Dendroica cerulea) populations at stops along Breeding Bird Survey (BBS) routes in the central Appalachians. We used aerial photographs to compare early (1967/1971), middle (1982/1985), and late (2000/2003) periods and compared 1992 and 2001 National Land Cover Data (NLCD). Mean Cerulean Warbler detections per stop decreased at 68 BBS stops between the early (0.05) and middle (0.01) time periods and their distribution became more restricted (15 vs. 3% of stops), but the amount of deciduous/mixed forest increased. Mean detections at 240 stops decreased from the middle (0.09) to the late (0.06) time periods, but the deciduous/mixed forest land cover and fragmentation metrics did not change. The amounts of deciduous/mixed forest, core forest area, and edge density in the NLCD analysis decreased from 1992 to 2001, whereas the amount of non-forest land cover increased. The number of Cerulean Warbler detections did not change (1992 = 0.08, 2001 = 0.10; P = 0.11). The lack of concordance between Cerulean Warbler detections and broad habitat features suggests that smaller, microhabitat features may be most important in affecting Cerulean Warbler breeding habitat suitability.

Interspecific Song Imitation by a Cerulean Warbler

We report a male Cerulean Warbler (Dendroica cerulea) singing a highly accurate version of another species' song (Hooded Warbler; Wilsonia citrina), as well as a typical Cerulean Warbler song. We performed playback experiments to examine the manner in which this bird used, and responded to, the different songs. He responded aggressively (wing flicks and garbled song), and with his Cerulean Warbler song, to recorded versions of two different types of Cerulean Warbler songs, including a type that he was not observed singing. He did not respond in any manner to playback of Hooded Warbler song.

Birds, Lower Sangay National Park, Morona-Santiago, Ecuador

Sangay National Park is located at the mid-eastern Andean foothills of the Cordillera Oriental of Ecuador. We present a preliminary avifauna inventory corresponding to the lower zone of the Sangay National Park (SNP). One-hundred and twenty-seven bird species belonging to 39 families were recorded, including noteworthy records that represent range extensions for four species, Phaetornis hispidus (Gould 1846) (White-bearded Hermit), Ramphastos ambiguus Swainson 1823 (Black-mandibled Toucan), Phylloscartes orbitalis (Cabanis 1873) (Spectacled Bristle Tyrant), and Microcerculus bambla (Boddaert 1783) (Wing-banded Wren). We also obtained information on threatened species such as Aburria aburri (Lesson 1828) (Wattled Guan), Phlogophilus hemileucurus Gould 1860 (Ecuadorian Piedtail), and Dendroica cerulea (Wilson 1810) (Cerulean Warbler) and reproductive data on one species, Patagioenas speciosa (Gmelin 1789) (Scaled Pigeon). To our knowledge this is a first ornithological survey carried out at this specific site of the SNP.

River-Based Surveys for Assessing Riparian Bird Populations: Cerulean Warbler as a Test Case

Birds concentrated in riparian habitats are poorly sampled by traditional survey methods because of the difficulties associated with accessing these habitats. Our objectives were to test the effectiveness of river-based surveys to determine the status, distribution, and relative abundance for riparian bird species in Missouri and northern Arkansas, with special emphasis on Dendroica cerulea (Cerulean Warbler). Our canoe-based surveys revealed an average of 2.3 and 0.8 singing male Cerulean Warblers/river km along the Current River (128 river km surveyed), MO, and the Buffalo National River (96 river km), AR. Nonparametric estimates for repeated surveys of the same river stretches indicate that 69–79% of singing male Cerulean Warblers were detected. However, the bias associated with the estimate methodology and independent song rate data suggest those are conservative estimates. In comparison with land-based point-counts, this river-based protocol offers a quick and efficient assessment of Cerulean Warblers in riparian areas.

Habitat Selection by Cerulean Warblers in Eastern Kentucky

Abstract We examined habitat characteristics associated with Cerulean Warblers (Dendroica cerulea) in breeding areas on the Cumberland Plateau in eastern Kentucky. Cerulean Warbler distribution was examined in 2004 within a large forest stand and no differences were found between occupied and unoccupied areas. We examined differences between preferred song perches and random points in 2005, and identified three potentially important predictors of Cerulean Warbler habitat: large diameter trees, east-facing aspect, and high shrub cover. Cerulean Warbler habitat selection on the Cumberland Plateau appears to be similar to other well-studied portions of the breeding range. Conservation and management efforts directed toward establishing and protecting large tracts of mature forest, especially those on east-facing slopes, should be a reasonable approach to managing Cerulean Warbler populations in this area.

Migratory songbird use of shade coffee in the Venezuelan Andes with implications for conservation of cerulean warbler

Although previous studies have demonstrated high use of shade coffee plantations by Neotropical migratory birds, we still have a poor understanding of the suitability of shade coffee plantations as habitat on the wintering grounds. We studied density, body condition, and survivorship of Neotropical migrants, with emphasis on cerulean warbler ( Dendroica cerulea), in primary forest and shade coffee plantations in Venezuela. We worked in three primary forest sites and three shade coffee plantations on the western slope of the Cordillera de Mérida of the Andes Mountains. At each site, we surveyed migrants with distance-based line transects and mist-netted and banded migrants during November–February 2005/06 and 2006/07. In addition, we estimated apparent monthly survival for cerulean warbler based on 29 color-banded individuals. Densities of migrants were 3–14× higher in shade coffee plantations than primary forest sites, even after accounting for differences in detectability. Apparent monthly survival of cerulean warblers was estimated at 97% and overwinter persistence was similarly high. In addition, cerulean warblers demonstrated high between-season fidelity, with 65% of the birds banded the first year being resighted during the second year. Interestingly, immature birds returned at nearly half the rate as did adults. Banding data indicated that body condition increased significantly as the season progressed for cerulean warblers, Tennessee warblers ( Vermivora peregrina), and American redstarts ( Setophaga ruticilla). Collectively, these data provide evidence that shade coffee plantations offer high quality wintering habitat for Neotropical migrants, including cerulean warblers.

Song Rates, Mating Status, and Territory Size of Cerulean Warblers in Missouri Ozark Riparian Forest

Abstract We assessed song rates among male Cerulean Warblers (Dendroica cerulea) in Ozark riparian forest in southeastern Missouri to characterize song rate variation and estimate how many males may be missed during censuses. Average (± SD) songs per 5-min intervals for continuous 4-hr observation periods varied from 3.1 ± 4.8 (mated males) to 36.0 ± 18.7 (unmated males; n = 24 males). Unmated males averaged twice the number of songs per 5-min periods than mated males. Considerable song rate variation existed even among mated males. Song rates slightly declined over the 4-hr observation period. Song rate differences between Cerulean Warblers in Ontario and southeastern Missouri suggest caution when making assumptions about breeding status based on auditory surveys. Average male Cerulean Warbler territory size (n = 20) was 0.9 ± 0.1 ha with 27 of 31 males having at least one abutting conspecific territory. All males (n = 24) were silent for 32.7 ± 21.5 and 21.8 ± 17.4% of the 5-min and 10-min periods, resp...

Vocalization Attributes of Cerulean Warbler Song and Pairing Status

Cerulean Warblers (Dendroica cerulea) were recorded throughout the 2005–2006 breeding seasons in southern Indiana; 18 song variables were measured and compared between paired and unpaired males. The best logistic regression model for predicting pairing status included song rates and minimum frequency measures of the second section of a male Cerulean Warbler song. Unpaired males had higher song rates and higher minimum frequencies. On average, unpaired males (n = 12) sang 7.4 songs/min while paired males sang 6.4 songs/min (n = 19). Average minimum frequency was 4.0 kHz for an unpaired male and 3.5 kHz for a paired male counterpart. Female and fledgling call notes were recorded during the latter part of both breeding seasons, and quantitatively analyzed. Female chip notes (n = 4 females) had a frequency range of 4.4–8.0 kHz. Two behaviors positively identified during these vocalizations included foraging and response to a mate. Average frequency range of fledgling begging notes (n = 4 fledglings) was 5.9–7.8 kHz. Begging was the only behavior identified with these particular vocalizations. These analyses offer further understanding of intraspecific call functions and repertoire in this species.

Think globally, manage locally: The importance of steady-state forest features for a declining songbird

Changes in historical forest composition and structure may have cascading effects throughout the forest community. Perhaps nowhere is there a better example of current forests that carry a legacy from their past than in eastern North America. The Cerulean Warbler ( Dendroica cerulea), a declining Neotropical migratory bird of high conservation concern, is one excellent example of a species that seems to be sensitive to both landscape configuration and subtle features of eastern forests of North America. We used the Cerulean Warbler as a model species to demonstrate how an appreciation of fine-scale structural attributes of forests may improve our ability to conserve late-successional forest species. To do this we evaluated the extent to which multiscale habitat features were associated with density, spatial distribution, and nesting success of Cerulean Warblers in 12 mature forest sites in southeast Ohio, 2004–2006. Results suggest that adjacency of regenerating clear-cuts did not influence density or nesting success of Cerulean Warblers in adjacent mature forest. Instead, variation in demographic parameters was best explained by local habitat features. Density and nesting success were positively associated with canopy openness, numbers of large-diameter trees, and number of grapevines—all of which are typical of heterogeneous steady-state phase forests. Thus, improved management for Cerulean Warblers may require creating features (e.g., large canopy gaps) that mimic old-growth forests. Although fragmentation and habitat loss remain important contributors to population declines of many mature forest species, our work provides evidence that subtle changes in forest structure, particularly to features associated with old forests, warrant additional attention from the conservation community.

The saga of migratory birds

The saga of migratory birds