Pipilo Erythrophthalmus Research Articles

To flock or fight: neurochemical signatures of divergent life histories in sparrows.

Many bird species exhibit dramatic seasonal switches between territoriality and flocking, but whereas neuroendocrine mechanisms of territorial aggression have been extensively studied, those of seasonal flocking are unknown. We collected brains in spring and winter from male field sparrows (Spizella pusilla), which seasonally flock, and male song sparrows (Melospiza melodia), which are territorial year-round in much of their range. Spring collections were preceded by field-based assessments of aggression. Tissue series were immunofluorescently multilabeled for vasotocin, mesotocin (MT), corticotropin-releasing hormone (CRH), vasoactive intestinal polypeptide, tyrosine hydroxylase, and aromatase, and labeling densities were measured in many socially relevant brain areas. Extensive seasonal differences are shared by both species. Many measures correlate significantly with both individual and species differences in aggression, likely reflecting evolved mechanisms that differentiate the less aggressive field sparrow from the more aggressive song sparrow. Winter-specific species differences include a substantial increase of MT and CRH immunoreactivity in the dorsal lateral septum (LS) and medial amygdala of field sparrows but not song sparrows. These species differences likely relate to flocking rather than the suppression of winter aggression in field sparrows, because similar winter differences were found for two other emberizids that are not territorial in winter--dark-eyed juncos (Junco hyemalis), which seasonally flock, and eastern towhees (Pipilo erythropthalmus), which do not flock. MT signaling in the dorsal LS is also associated with year-round species differences in grouping in estrildid finches, suggesting that common mechanisms are targeted during the evolution of different life histories.

A new species of towhee (Aves: Emberizidae: Pipilo) from Quaternary deposits on Bermuda

Abstract Pipilo naufragus, new species, is described from Middle and Late Pleistocene to Holocene cave and pond deposits on the island of Bermuda. It is most similar to the Eastern Towhee P. erythrophthalmus but differs in having a heavier bill, more robust hindlimbs, and reduced wing and pectoral girdle, with the sternum in particular being shorter, wider, and with a much smaller carina. At least one early historical account (1610) contains a description of a large bunting-like bird that almost certainly refers to this species, which would have been exterminated by introduced pigs, rats, and cats following human settlement of Bermuda in 1612.

Fire severity has mixed benefits to breeding bird species in the southern Appalachians

Fire is frequently applied as a management tool on both public and private lands. However, in some ecosystems there is little information about bird species’ responses to these fire programs. In 2004 we measured habitat characteristics and conducted point counts in 12 burned sites and four unburned sites in the Chattahoochee National Forest of northern Georgia. Burns were categorized by severity (low, medium, or high) and time since fire (1–2 or 3–6 years). The basal area of snags, shrub stem density and percent canopy cover were similar among all treatments except high severity. Otherwise, fire severity had limited impacts on measured habitat characteristics. Following fires the densities of early-succession species such as eastern towhee ( Pipilo erythropthalmus) and indigo bunting ( Passerina cyanea) were greatest in areas of higher fire severity. A ground-nesting species (ovenbird [ Seiurus aurocapilla]) was less abundant in burned sites and the density of a shrub nesting species, the hooded warbler ( Setophaga citrine) was greatest in areas that received low severity fires. Scarlet tanager ( Piranga olivacea), tufted titmouse ( Baeolophus bicolor), red-eyed vireo ( Vireo olivaceus), black-throated green warbler ( Setophaga virens), and black-and-white warbler ( Mniotilta varia) had similar densities among all burn severities and showed no relationships with time since fire. Low and medium severity fires provided few benefits for most bird species. When conditions allow for their application, severe fires may be considered as a useful and historically appropriate management tool for some high-priority bird species in the southern Appalachian Mountains.

Nest Survival of Understory Birds in Longleaf Pine Forests Exposed to Fire and Fire-Surrogate Treatments

Longleaf pine (Pinus palustris) forest ecosystems evolved with short-interval, low intensity fires. Fire suppression has reduced or eliminated fire and has caused extensive changes in plant community composition and structure. The National Fire and Fire-Surrogate study was implemented to evaluate effects of alternative habitat treatments, such as herbicide application and mechanical thinning, and to compare them with effects of prescribed fire. We evaluated how treatments influenced the nesting success of birds breeding in 10-ha plots of longleaf pine at Solon Dixon Experimental Forest, Alabama. We measured daily rates of nest mortality for 432 nests of 33 species in unmanipulated (controls), burned, herbicide-treated and burned, thinned, and thinned and burned plots during the three years of our study. Although we accumulated observations of 6,624 days that nests were exposed to possible predation, sample sizes were still too small to permit robust statistical analyses of treatment effects. Data from one (Eastern Towhee, Pipilo erythrophthalmus) of two species with the largest sample sizes suggested that nests in treatment plots experienced higher rates of mortality than did nests in control plots, but sample sizes were still small enough that high estimates of variance prevented strong statistical evaluation. Nest survival for the other common species, Northern Cardinal (Cardinalis cardinalis), showed no such suggestive differences. We present results from all nests of all species for which we found three or more nests so that future researchers can use the data during meta-analyses. We also encourage those designing future similar studies to consider expanding the size of study plots so that at least the most numerous open-cup nesting birds can be found in sufficient numbers for strong statistical analyses. In longleaf pine forests of southern Alabama, we estimate that minimum plot sizes would need to be 50 ha for the two most common species, Eastern Towhee and Northern Cardinal.

Short-Term Effects of Fire and Fire-Surrogate Treatments on Avian Nest Survival: A National-Scale Analysis

We examined the initial response of avian nest success to mechanical thinning, prescribed fire, and thinning/ prescribed fire combination treatments, designed to reduce fuel loads, at study sites throughout the continental USA as part of the National Fire and Fire Surrogate (FFS) Project. We modeled the daily nest survival of ground-, shrub-, tree-, and snag-nesting bird species to test for effects of: (1) overall treatment (2) specific treatment category (i.e., burn, thin, thin/burn); (3) time since treatment; and (4) study site. Of the 7 species examined, only 2 had top models that included effects of the FFS treatments, the remainder had either constant survival rates, or rates that varied only by study site. The Eastern Towhee had top models that included effects of treatment and study site, while the Red-bellied Woodpecker had top models that included effects of treatment category, time since treatment, and study site. All estimates of treatment, treatment category, and study site were statistically weak with confidence intervals including zero. The lack of clear response patterns observed in this study is likely a consequence of the variability inherent across forest types and taxonomic groups we examined. Forest managers should use our results cautiously and also be encouraged to facilitate opportunities for studies of avian nest survival as a function of fire-surrogate treatments that are regional specific, encompass longer time frames and larger spatial scales.

Influence of exurban development on bird species richness and diversity

Exurban development is an accelerating land use trend in the United States with new housing units emerging in formerly closed forests. Conservation practitioners and planners suspect exurban development alters ecological processes and biodiversity to a considerable larger extent than suspected by inhabitants of exurban development areas, but empirical support for this assertion is lacking. To examine the consequences of exurban development, we studied forest bird communities in exurban development and forests located in and around Shenandoah National Park and Massanutten Mountain in northern Virginia, USA. We conducted point-count surveys for birds three times at 106 sample locations from April to July 2006. We recorded 44 species in total; 30 species were present in both exurban development and forests, 9 species were only found in exurban development, and 5 species only in forest. Bird species composition differed significantly between land-use types based on analysis in a multi-response permutation procedure (MRPP; P < 0.01). Relative bird abundance for forest specialist species changed significantly in exurban development versus forest (t test, P < 0.05). Three species, American Robin Turdus migratorius, Northern Cardinal Cardinalis cardinalis, and Common Grackle Quiscalus quiscula were indicators of exurban development. Indicators of forest were Carolina Chickadee Poecile carolinensis, Eastern Towhee Pipilo erythrophthalmus, and Wood Thrush Hylocichla mustelina. Our study demonstrates that exurban development alters bird community composition and relative abundance of forest specialist species.

Highly Variable Acquisition Rates of Ixodes scapularis (Acari: Ixodidae) by Birds on an Atlantic Barrier Island

Acquisition of ticks by bird hosts is a central process in the transmission cycles of many tick-borne zoonoses, but tick recruitment by birds has received little direct study. We documented acquisition of Ixodes scapularis Say on birds at Fire Island, NY, by removing ticks from mist-netted birds, and recording the number of ticks on birds recaptured within 4 d of release. Eight bird species acquired at least 0.8 ticks bird(-1) day(-1) during the seasonal peak for at least one age class of I. scapularis. Gray Catbirds, Eastern Towhees, Common Yellowthroats, and Northern Waterthrushes collectively accounted for 83% of all tick acquisitions; and six individuals apportioned among Black-billed Cuckoo, Gray Catbird, Eastern Towhee, and Common Yellowthroat were simultaneously infested with both larvae and nymphs. Bird species with the highest acquisition rates were generally ground foragers, whereas birds that did not acquire ticks in our samples generally foraged above the ground. Tick acquisition by birds did not differ between deciduous and coniferous forests. Among the 15 bird species with the highest recruitment rates, acquisition of nymphs was not correlated with acquisition of larvae. Tick acquisition rates by individual bird species were not correlated with the reservoir competence of those species for Lyme borreliae. However, birds with high tick acquisition rates can contribute large numbers of infected ticks, and thus help maintain the enzootic cycle, even if their levels of reservoir competence are relatively low.

Misdirected Parental Care by a Male Eastern Towhee at a Wood Thrush Nest

Misdirected parental care, or care directed toward unrelated young, has been recorded for many bird species. The Wood Thrush (Hylocichla mustelina) is not known to practice this behavior or allow other species to attend to its young. We observed a Wood Thrush nest with three Wood Thrush nestlings and one Brown-headed Cowbird (Molothrus ater) nestling being attended by a male Eastern Towhee (Pipilo erythrophthalmus). The towhee fed the young of both species in the nest for at least 5 days and was subsequently observed feeding a Wood Thrush fledgling. The towhee also participated in nest maintenance and defense. The proximate cause of towhee attendance at the Wood Thrush nest remains unknown, but begging calls from the nestlings may have stimulated the behavior.

Divergence in Avian Communities Following Woody Plant Invasions in a Pine Barrens Ecosystem

We compared avian communities and vegetation characteristics in invaded and uninvaded pine barren ecosystems to test whether invasive woody plants were altering native bird communities. We hypothesized that structural changes in vegetation caused by the invasion of fire-intolerant deciduous trees were altering bird communities in the Albany Pine Bush, east central New York State. We recorded bird calls at 55 stations during breeding season to estimate abundances of breeding birds in areas dominated by fire-dependent pine-shrub savanna and areas dominated by invasive hardwoods (black locust, Robinia pseudoacacia, and aspens, Populus tremuloides and P. grandidentata). Vegetation surveys were conducted surrounding each station to quantify woody plant composition and structure. Sites characterized as invaded had more vegetation layers, twice as much closed canopy, and higher tree stem densities in all but the largest (> 25 cm dia) size classes. Forty-seven bird species were recorded; thirty-three at both invaded and uninvaded sites. Grassland/shrubland birds, such as prairie warbler (Dendroica discolor), field sparrow (Spizella pusilla), red-breasted nuthatch (Sitta canadensis), and eastern towhee (Pipilo erythrophthalmus), were twice as frequent and three times as abundant at uninvaded sites. Native bird species characteristic of closed-canopy forest were more frequent and abundant at stations in invaded sites. Multivariate analyses indicate distinct associations of particular birds with unique combinations of vegetation characteristics that differed between invaded and uninvaded points. A campaign of adaptive fire management holds promise to restore critical avian habitat in protected areas of this threatened barrens ecosystem.

SEASONAL FOREST-PATCH USE BY BIRDS IN FRAGMENTED LANDSCAPES OF SOUTH-CENTRAL PENNSYLVANIA

We surveyed birds during breeding, migratory, and wintering seasons in forest patches of two fragmented landscapes in the Valley and Ridge Province of south-central Pennsylvania during 1994–1996. Our objective was to examine presence of species in relation to forest-patch size (<2, 6–20, 40–150, and >1,500 ha) and extent of regional fragmentation. Several species, particularly long-distance migrants (e.g., Eastern Wood-pewee [Contopus virens], Red-eyed Vireo [Vireo olivaceus], Wood Thrush [Hylocichla mustelina], Worm-eating Warbler [Helmitheros vermivorum], and Scarlet Tanager [Piranga olivacea]), were more likely to occur in larger forest patches than in smaller patches during the breeding and spring-migratory seasons. Short-distance migrants (e.g., American Robin [Turdus migratorius], Gray Catbird [Dumetella carolinensis], and Eastern Towhee [Pipilo erythrophthalmus]), responded to fragmentation at a regional scale and were more commonly encountered in the more fragmented landscape, particularly during migratory periods. Species observed during fall migration were not influenced by patch size. The Pileated Woodpecker (Dryocopus pileatus) responded positively to patch size in all seasons, whereas the Song Sparrow (Melospiza melodia) was influenced negatively by patch size in three of four seasons. More research should be conducted at sites during winter and migration to corroborate these results and to examine the role patch size may have in long-term survivorship of migratory birds.

Technical guide to forest wildlife habitat management in New England

Forest wildlife populations and their habitats in New England are products of the land—its condition after centuries of human use and natural processes. Conditions are never static; they are changing continually in response to disturbance and succession. Habitats for all species once were provided continuously by wind, fire, and other disturbances. Native prairies, shrublands, forests opened by burns and blowdowns, and subsequent forest regrowth provided habitats for a diverse New England fauna in a shifting mosaic across the landscape. This is no longer the case. Development of historically open habitats, fire control, and the decline of agriculture have changed the landscape dramatically. Today in much of New England, forests are mature and largely unmanaged. Wildlife species associated with mature forests—fisher and pileated woodpecker, for example—have become common. Species associated with old fields, brushlands, and young forests—field sparrows, eastern towhees, and New England cottontails, among many others—have declined precipitously as their habitats have been developed or have reverted to forest. This volume is a compilation of forest management practices that are now necessary for creating a range of forest habitat conditions to maintain or enhance forest wildlife diversity in the region.

Do the size and landscape context of forest openings influence the abundance and breeding success of shrubland songbirds in southern New England?

Early successional birds have declined in the northeastern United States due to the regeneration of forest on abandoned farm fields and the suppression of natural disturbances that once provided appropriate habitat. These species have become increasingly dependent on early successional habitats generated by such activities as timber harvesting. Recent approaches of timber harvesting, which range from single-tree harvesting to clearcutting, create forest openings of different sizes and configurations embedded in landscapes with different land use patterns. To assess the importance of forest openings created by timber harvesting for shrubland birds, we surveyed birds on 50 m radius plots in 34 harvest sites (0.5–21 ha). We collected data on multi-scaled habitat variables ranging from plot-level vegetation characteristics to land use patterns within 1 km of each study site. We also monitored mating and nesting success of Blue-winged Warblers ( Vermivora pinus) in 10 forest openings. The abundance of most shrubland species was influenced by plot-level habitat variables, such as tree density and vegetation height, rather than shrubland area or the composition of land uses in the surrounding landscape. Only Eastern Towhees ( Pipilo erythrophthalmus) were more frequent in survey plots in larger forest openings. In contrast, neither abundance nor reproductive activity of Blue-winged Warblers was correlated with the size of the forest opening. Their abundance was negatively related to vegetation height, however. Only 54% of the territorial male Blue-winged Warblers in forest openings were mated. We documented relatively low nest success rates of 21.1% during the egg laying and incubation nest stages, but increased success rates during the later stages of nesting. Our results indicate that even small forest openings with low vegetation provide habitat for Blue-winged Warblers and other shrubland birds. The overall reproductive rate of territorial male Blue-winged Warblers in forests openings was low during the 2 years of the study, however. Further studies are needed to assess the long-term value of this type of habitat for sustaining shrubland bird populations.

Associations of Breeding Birds With Fire-Influenced and Riparian-Upland Gradients in a Longleaf Pine Ecosystem

AbstractWe determined the effects of fire history and a riparian-upland gradient on the breeding bird community at Fort Bragg Military Installation in North Carolina, one of the largest remnant areas of the endangered longleaf pine (Pinus palustris) ecosystem. Study sites were classified into two treatments: fire-intense (areas experiencing growing-season burns) and fire-suppressed (areas lacking fires). Within each treatment, bird and vegetation data were recorded at point-count stations positioned at three distances from streamhead pocosins to characterize the riparian-upland habitat gradient: 0, 75, and ≥150 m. Total bird abundance and species richness varied significantly along the riparian-upland gradient, with pocosins contributing greatly to avian biodiversity. Our data revealed strong effects of fire history and riparian-upland gradient on bird species, which we described in terms of breeding-bird assemblages. Members of the open longleaf assemblage (e.g., Red- cockaded Woodpecker [Picoides borealis], Bachman's Sparrow [Aimophila aestivalis]) were most common in fire-intense areas and at upland locations. Members of the fire-suppressed assemblage (e.g., Wood Thrush [Hylocichla mustelina], Ovenbird [Seiurus aurocapilla]) were confined to pocosins in fire-intense areas, but became more abundant in fire-suppressed areas. Members of the pocosin assemblage (e.g., Eastern Towhee [Pipilo erythropthalamus], Common Yellowthroat [Geothlypis trichas]) were largely confined to pocosins and, in some cases, were most abundant in fire-intense pocosins. Fire suppression increased structural diversity of vegetation and promoted one breeding-bird assemblage (fire-suppressed), but at the expense of two others (open longleaf, pocosin). Continued management of Fort Bragg to promote longleaf pine restoration is essential for supporting conservation of the open-longleaf bird assemblage; in addition, it will benefit the pocosin assemblage.Asociaciones de Aves Reproductivas con Áreas Influenciadas por el Fuego y con Gradientes Ribereños-Tierras Altas en un Ecosistema de Pinus palustris

Songbird Use of Regenerating Forest, Glade, and Edge Habitat Types

Population numbers of many bird species associated with early-successional or disturbance-dependent habitat types are declining. We used an information–theoretic approach to evaluate hypotheses concerning factors affecting breeding bird densities in different early-successional habitat types. We studied shrubland bird communities in 3- to 5-year-old regenerating forest (n = 3), glade (n = 3), and forest–pasture edge (n = 3) habitat types in the predominantly forested Missouri Ozarks in 1997–1999. We monitored 8 bird species using spot mapping and total mapping techniques, searched for and monitored nests, and measured vegetation structure within nested circular plots. In evaluating breeding densities in these habitat types, we compared support for a global model with year, habitat type, and a habitat type × year interaction to several reduced models and a null model with only an intercept, and we used model-averaged coefficients to evaluate effect size. We found support for the effects of habitat type on breeding densities of prairie warbler (Dendroica discolor) and yellow-breasted chat (Icteria virens); the effects of habitat type and year on densities of blue-winged warbler (Vermivora pinus), eastern towhee (Pipilo erythrophthalmus), and field sparrow (Spizella pusilla); the effect of year on densities of indigo bunting (Passerina cyanea) and northern cardinal (Cardinalis cardinalis); and no effects on densities of white-eyed vireo (Vireo griseus). The effect size of habitat type on breeding densities varied among species and indicated important species-specific differences in habitat use. Most shrubland bird species used both glades and regenerating forests more than forest–pasture edge sites, and breeding densities of some species were higher in regenerating forests than in glades. For some species, patterns in reproductive success (reported as interval nest success) mirrored observed patterns in breeding densities. However, substantial variation existed among species with respect to patterns in habitat use and nest success. Conservation planning for the persistence of birds requiring early-successional habitat types should consider the ephemeral nature of these areas and the potential contribution from young, regenerating forest.

ASSOCIATIONS OF BREEDING BIRDS WITH FIRE-INFLUENCED AND RIPARIAN-UPLAND GRADIENTS IN A LONGLEAF PINE ECOSYSTEM

We determined the effects of fire history and a riparian-upland gradient on the breeding bird community at Fort Bragg Military Installation in North Carolina, one of the largest remnant areas of the endangered longleaf pine (Pinus palustris) ecosystem. Study sites were classified into two treatments: fire-intense (areas experiencing growing-season burns) and fire-suppressed (areas lacking fires). Within each treatment, bird and vegetation data were recorded at point-count stations positioned at three distances from streamhead pocosins to characterize the riparian-upland habitat gradient: 0, 75, and ≥150 m. Total bird abundance and species richness varied significantly along the riparian-upland gradient, with pocosins contributing greatly to avian biodiversity. Our data revealed strong effects of fire history and riparian-upland gradient on bird species, which we described in terms of breeding-bird assemblages. Members of the open longleaf assemblage (e.g., Red- cockaded Woodpecker [Picoides borealis], Bachman's Sparrow [Aimophila aestivalis]) were most common in fire-intense areas and at upland locations. Members of the fire-suppressed assemblage (e.g., Wood Thrush [Hylocichla mustelina], Ovenbird [Seiurus aurocapilla]) were confined to pocosins in fire-intense areas, but became more abundant in fire-suppressed areas. Members of the pocosin assemblage (e.g., Eastern Towhee [Pipilo erythropthalamus], Common Yellowthroat [Geothlypis trichas]) were largely confined to pocosins and, in some cases, were most abundant in fire-intense pocosins. Fire suppression increased structural diversity of vegetation and promoted one breeding-bird assemblage (fire-suppressed), but at the expense of two others (open longleaf, pocosin). Continued management of Fort Bragg to promote longleaf pine restoration is essential for supporting conservation of the open-longleaf bird assemblage; in addition, it will benefit the pocosin assemblage. Asociaciones de Aves Reproductivas con Áreas Influenciadas por el Fuego y con Gradientes Ribereños-Tierras Altas en un Ecosistema de Pinus palustris

Reservoir Competence of Native North American Birds for the Lyme Disease Spirochete, &lt;I&gt;Borrelia burgdorferi&lt;/I&gt;

Reservoir competence for the Lyme disease spirochete, Borrelia burgdorferi, was tested for six species of native North American birds: American robin, gray catbird, brown thrasher, eastern towhee, song sparrow, and northern cardinal. Wild birds collected by mist netting on Fire Island, NY, were held in a field laboratory in cages over water and locally collected larval ticks were placed on the birds, harvested from the water after engorgement, and tested for infection by direct fluorescentantibody staining after molting to the nymphal stage. American robins were competent reservoirs, infecting 16.1% of larvae applied to wild-caught birds, compared with 0% of control ticks placed on uninfected laboratory mice. Robins that were previously infected in the laboratory by nymphal feeding infected 81.8% of applied larvae. Wild-caught song sparrows infected 4.8% of applied larvae and 21.1% when infected by nymphal feeding. Results suggest moderate levels of reservoir competence for northern cardinals, lower levels for gray catbirds, and little evidence of reservoir competence for eastern towhees or brown thrashers. Lower infection rates in larvae applied to wild-caught birds compared with birds infected in the laboratory suggest that infected birds display temporal variability in infectiousness to larval ticks. Engorged larvae drop from birds abundantly during daylight, so the abundance of these bird species in the peridomestic environment suggests that they might contribute infected ticks to lawns and gardens.

Reservoir Competence of Native North American Birds for the Lyme Disease Spirochete,Borrelia burgdorferi

Reservoir competence for the Lyme disease spirochete, Borrelia burgdorferi, was tested for six species of native North American birds: American robin, gray catbird, brown thrasher, eastern towhee, song sparrow, and northern cardinal. Wild birds collected by mist netting on Fire Island, NY, were held in a field laboratory in cages over water and locally collected larval ticks were placed on the birds, harvested from the water after engorgement, and tested for infection by direct fluorescent-antibody staining after molting to the nymphal stage. American robins were competent reservoirs, infecting 16.1% of larvae applied to wild-caught birds, compared with 0% of control ticks placed on uninfected laboratory mice. Robins that were previously infected in the laboratory by nymphal feeding infected 81.8% of applied larvae. Wild-caught song sparrows infected 4.8% of applied larvae and 21.1% when infected by nymphal feeding. Results suggest moderate levels of reservoir competence for northern cardinals, lower levels for gray catbirds, and little evidence of reservoir competence for eastern towhees or brown thrashers. Lower infection rates in larvae applied to wild-caught birds compared with birds infected in the laboratory suggest that infected birds display temporal variability in infectiousness to larval ticks. Engorged larvae drop from birds abundantly during daylight, so the abundance of these bird species in the peridomestic environment suggests that they might contribute infected ticks to lawns and gardens.

Vocal tract filtering and sound radiation in a songbird

Bird vocalizations resonate as they propagate through a relatively long trachea and radiate out from the oral cavity. Several studies have described the dynamics with which birds actively vary beak gape while singing and it has been hypothesized that birds vary beak gape as a mechanism for varying vocal tract resonances. Nevertheless, few studies have attempted to quantify the effects of beak gape on vocal tract resonances. We replaced eastern towhee, Pipilo erythrophthalmus L., syringes with a small speaker and obtained recordings of frequency sweeps while rotating each subject in a horizontal plane aligned with either the maxilla or mandible. We describe vocal tract resonances as well as how sound radiates as a function of beak gape. Results are inconsistent with the hypothesis that songbirds vary beak gape as a mechanism for 'tracking' fundamental frequencies in vocalizations. Instead, decreases in beak gape seem to attenuate resonances that occur between approximately 4 and 7.5 kHz. We propose that songbirds vary beak gape as a mechanism for excluding and/or concentrating energy within at least two distinct sound frequency channels.

Sound localization in a small passerine bird: discrimination of azimuth as a function of head orientation and sound frequency

Sound localization is critical to communication when signalers are distributed widely in space and when reverberations that accumulate over distance might otherwise degrade temporal patterns in vocalizations. We readdress the accuracy with which a small passerine bird, the eastern towhee, Pipilo erythrophthalmus L., is able to resolve azimuth in the field. We then report results from two-alternative forced-choice (2AFC) experiments in which three of four subjects were able to discriminate an estimated speaker separation angle of approximately 7 degrees . Subjects oriented laterally when discriminating azimuth in the 2AFC task and each subject preferred a different head orientation. Side biases occurred as a function of head orientation and, as a consequence, we conducted a second 2AFC experiment in which subjects were required to discriminate between two closely spaced lights. Subjects oriented similarly in this visual task, however, side biases did not occur as a function of head orientation. Despite side biases in the auditory task, performance generally declined when subjects were played tones with frequencies near approximately 3 kHz.

Long-Term Effects Of Rights-Of-Way Maintenance Via The Wire?Border Zone Method On Bird Nesting Ecology

The long-term nesting ecology of birds was studied during 2002 and 2003 on the State Game Lands (SGL) 33 Research and Demonstration Area, which is located along a 230-kV transmission right-of-way (ROW) of FirstEnergy (Penelec) in the Allegheny Mountain Region, Centre County, Pennsylvania, U.S. The objectives of this study were to compare nest abundance, success, and placement (1) in handcut versus herbicide-treated study sites (units) and (2) in wire versus border zones. In addition, results from this study were compared to those obtained in a previous study conducted in 1991­1992 on the ROW to better understand the long-term effects of vegetation maintenance management on wildlife. Thirty-three and 26 nests of 10 bird species were noted in 2002 and 2003, respectively. The most frequently encountered nests in 1991­1992 and 2002­2003 were those of bird species adapted to early successional habitats, for example, eastern towhee (Pipilo erythrophthalmus), created by the wire­border zone method of vegetation maintenance on the ROW. Thirteen (39%) of 33 nests of all species combined fledged young in 2002 compared to 17 (65%) of 26 nests in 2003. Nesting success in 2003 on the SGL 33 ROW was typical of most studies of bird nesting success in a variety of habitats and was comparable to that recorded in 1991­1992. The low-volume basal unit was more important as nesting habitat than either handcut or mowing plus herbicide units, with nine species nesting in the low-volume basal unit versus only four species in each of the other two units. Thirty-five (59%) of the 59 nests on the ROW were in wire zones, whereas 24 (41%) nests were in border zones. In conclusion, mowing plus herbicide treatment on a ROW may be the best application of the wire­border zone method in terms of resistance to seedling invasion of undesirable trees, cover-type development in the wire zone, and its value as wildlife habitat. Because early successional habitat is becoming less common in the eastern United States and because species dependent on these habitats are showing populations declines, the maintenance of a ROW via the wire­border zone method is extremely valuable to the long-term conservation of early successional bird species.