Social context affects risk taking by a satellite species in a mixed-species foraging group

Mixed-species flocks of birds form during winter in the easterndeciduous forests of North America. These flocks consist oftwo flock-leading nuclear species, tufted titmouse (Baeolophusbicolor) and Carolina chickadee (Poecile carolinensis), andseveral follower, or satellite, species, including downy woodpecker(Picoides pubescens) and white-breasted nuthatch (Sitta carolinensis).Hypotheses explaining the adaptiveness of participation in suchmixed-species foraging groups have focused on increased foragingsuccess and/or decreased predation risk. We tested the predictionthat if nuthatches join nuclear species to reduce predationrisk, they should be more reluctant to visit an exposed feederin the absence of titmice than in their presence. When the feederwas positioned 16 m from forest cover, latency to visit thefeeder was greater for both male and female nuthatches whentitmice were absent. Removal of titmice had no effect on latencyat 8 m. In the absence of titmice, nuthatches visited the feederless frequently at both distances. These results indicate thatreduced predation risk is a benefit that satellite species gainby flocking with nuclear species.     

Mountain Pine Beetle Presence Affects Nest Patch Choice of Red-Breasted Nuthatches

Abstract: The mountain pine beetle (Dendroctonus ponderosae) outbreak in western Canada poses significant conservation concern; thus, insights into its effects on wildlife habitat are essential. We used generalized linear mixed models to examine the influence of quaking aspen (Populus tremuloides) and mountain pine beetle—infected lodgepole pine (Pinus contortus) on nest patch selection of red-breasted nuthatches (Sitta canadensis) in central British Columbia, Canada. Prior to the outbreak, nuthatches selected nest patches with 64% more suitable nest trees (standing dead aspen, ≥12.5 cm dbh) than available (103 trees/ha vs. 63 trees/ha, respectively), but in outbreak years nuthatches chose nest patches with 37% more beetle-infected pine trees than available (63 trees/ha vs. 46 trees/ha, respectively). Our results suggest that nuthatches select sites that maximize nesting and foraging opportunities and, during food pulses, may trade off higher densities of suitable nest trees for higher densities of foraging trees. (JOURNAL OF WILDLIFE MANAGEMENT 72(3):733–737; 2008)     

Effects of the emerald ash borer invasion on four species of birds

The emerald ash borer (EAB) Agrilus planipennis, first detected in 2002 in the vicinity of Detroit, Michigan, USA, is one of the most recent in a long list of introduced insect pests that have caused serious damage to North American forest trees, in this case ash trees in the genus Fraxinus. We used data from Project FeederWatch, a citizen science program focused on winter bird populations, to quantify the effects of EAB invasion on four species of resident, insectivorous birds known or likely to be EAB predators: three woodpecker species and the white-breasted nuthatch (Sitta canadensis). We compared relative numbers of birds within 50 km of the epicenter of the region where EAB was first detected, an area known to have suffered high ash tree mortality by 2008, to numbers 50–100 km from the epicenter and to control sites within 50 km of five comparable Midwestern cities where damage due to EAB has yet to be severe. We found evidence for significant effects on all four of the species in response to the EAB invasion in the highly impacted region, with red-bellied woodpeckers (Melanerpes carolinus) and white-breasted nuthatches showing numerical increases while downy woodpeckers (Picoides pubescens) and hairy woodpeckers (Picoides villosus) initially declined but exhibited at least temporary increases several years later. Temporal correlation analyses failed to provide support for immigration being a major cause of the elevated numbers in the highly impacted area, and thus these results are consistent with the hypothesis that increases were due to enhanced survival and/or reproduction associated with the EAB invasion within the highly impacted area. Results suggest that the continuing invasion of EAB into new areas is likely to significantly alter avian communities, although not always in ways that will be easy to predict.     

Sexual dimorphism in relation to winter foraging in the white-backed woodpecker ( Dendrocopos leucotos)

Male white-backed woodpeckers (Dendrocopos leucotos) in a 250-km² study area in western Norway are significantly larger than females in bill length and depth, wing and tarsus lengths, and bodyweight. During the winters (October–March 1985–2002), most pairs were observed within their breeding territory where both sexes foraged mainly in grey alder and birch trees, and visited trees of the same tree height and stem width. However, males foraged more frequently on dead trees and on trees broken by storms. Males also used more trees with less bark cover, foraged nearer the ground and used foraging sites of larger diameter. Furthermore, males practised more deep wood-pecking and less bark-pecking than females. Unlike in other sexually dimorphic woodpecker species, the foraging niche breadth in wintering white-backed woodpeckers showed only minor sexual differences, and the sexes overlapped significantly in all parameters examined. Since previous studies in the area have shown that the sexes overlap considerably in use of their territory, it was expected, as found in other size dimorphic woodpeckers, that the larger male would displace the supposedly socially subordinate female to suboptimal feeding sites. In our area, the sexes were rarely seen together, and no sign of aggression between the sexes was observed. Despite the sex-specific differences found in the foraging behaviour of the birds, it is not obvious how the differences should be related to size dimorphism.Communicated by F. Bairlein     

Attributes of trees used by nesting and foraging woodpeckers (Aves: Picidae) in an area with old pollarded Oaks (Quercus spp.) in the Taurus Mountains,Turkey

We used three woodpecker species as umbrella species for old deciduous forests, and analysed their preferences in an area with old pollarded oaks in the Taurus Mountains, Turkey. Using plot inventories, we physically characterised trees utilised for nesting and foraging amongst woodpeckers in general and the Middle Spotted Woodpecker (Leiopicus medius) in particular. Trees more frequently visited by foraging woodpeckers differed from randomly chosen trees by being taller, having a larger circumference, greater bark furrow depth and shorter distance to neighbouring trees. Nesting trees were taller, had a higher proportion of dead wood but a lower surface area of natural cavities. Our results suggest that the woodpeckers in the study area rely upon woodlands containing mature trees, thus have the potential to function as suitable umbrella species’ to highlight the conservation value of oak forest habitats in southern Turkey.     

Short-Term Effects of Fire and Other Fuel Reduction Treatments on Breeding Birds in a Southern Appalachian Upland Hardwood Forest

Abstract: We compared the effects of 3 fuel reduction techniques and a control on breeding birds during 2001-2005 using 50-m point counts. Four experimental units, each >14 ha, were contained within each of 3 replicate blocks at the Green River Game Land, Polk County, North Carolina, USA. Treatments were 1) prescribed burn, 2) mechanical understory reduction (chainsaw-felling of shrubs and small trees), 3) mechanical + burn, and 4) controls. We conducted mechanical treatments in winter 2001-2002 and prescribed burns in spring 2003. Tall shrub cover was substantially reduced in all treatments compared to controls. Tree mortality and canopy openness was highest in the mechanical + burn treatment after burning, likely due to higher fuel loading and hotter burns; tree mortality increased with time. Many bird species did not detectably decrease or increase in response to treatments. Species richness, total bird density, and some species, including indigo buntings (Passerina cyanea) and eastern bluebirds (Sialia sialis), increased in the mechanical + burn treatment after a 1-year to 2-year delay; eastern woodpewees (Contopus virens) increased immediately after treatment. Hooded warblers (Wilsonia citrina), black-and-white warblers (Mniotilta varia), and worm-eating warblers (Helmitheros vermivorus) declined temporarily in some or all treatments, likely in response to understory and (or) leaf litter depth reductions. Densities of most species affected by treatments varied with shrub cover, tree or snag density, or leaf litter depth. High snag availability, open conditions, and a higher density of flying insects in the mechanical + burn treatment likely contributed to increased bird density and species richness. In our study, fuel reduction treatments that left the canopy intact, such as low-intensity prescribed fire or mechanical understory removal, had few detectable effects on breeding birds compared to the mechanical + burn treatment. High-intensity burning with heavy tree-kill, as occurred in our mechanical + burn treatment, can be used as a management tool to increase densities of birds associated with open habitat while retaining many forest and generalist species, but may have short-term adverse effects on some species that are associated with the ground- or shrub-strata for nesting and foraging.     

Seasonal variation in avian auditory evoked responses to tones: a comparative analysis of Carolina chickadees,tufted titmice,and white-breasted nuthatches

We tested for seasonal plasticity of the peripheral auditory system of three North American members of the Sylvioidea: Carolina chickadees (Poecile carolinensis), tufted titmice (Baeolophus bicolor), and white-breasted nuthatches (Sitta carolinensis). We measured three classes of auditory evoked responses (AER) to tone stimuli: sustained receptor/neural responses to pure-tone condensation waveforms, the frequency-following response (FFR), and the earliest peak of the AER to stimulus onset (tone onset response). Seasonal changes were detected in all classes of AERs in chickadees and nuthatches. Seasonal changes in titmice were restricted to the tone onset response. Interestingly, changes detected in chickadees (and to a lesser extent in titmice) were generally in an opposite direction to changes seen in nuthatches, with chickadees exhibiting greater amplitude AER responses in the spring than in winter, and nuthatches exhibiting greater amplitude AER responses in winter than in spring. In addition, the seasonal differences in the sustained responses tended to be broad-band in the chickadees but restricted to a narrower frequency range in nuthatches. In contrast, seasonal differences in the onset response were over a broader frequency range in titmice than in chickadees and nuthatches. We discuss some possible mechanistic and functional explanations for these seasonal changes.     

Landscape Use by Hairy Woodpeckers in Managed Forests of Northwestern Washington

ABSTRACT The hairy woodpecker (Picoides villosus) is a keystone species in forest ecosystems of Washington, USA, providing nesting and roosting cavities for many species of wildlife. Therefore, management practices that promote healthy populations of this bird will help to conserve cavity-nesting communities as a whole. The objective of this study was to determine patterns in forest type and landscape use by hairy woodpeckers, and thus, provide landscape-level recommendations to forest managers. We documented the ranging patterns and habitat use of 23 hairy woodpeckers on the Olympic Peninsula using radiotelemetry and a Geographic Information System analysis. Use patterns of stand age, type, and size, as well as distance-from-edge analyses revealed that the hairy woodpecker is a relative generalist in its use of the managed forest landscape. However, certain features, such as older stands with large trees, were used more heavily by nesting pairs. Hairy woodpeckers used 61–80-year forest stands significantly (P < 0.05) more than expected relative to their availability within the birds' home ranges. We also documented significant underuse of 6–10-year and 11–20-year stands, whereas the birds used 41–60-year stands, >80-year stands, and clear-cuts (< 5 yr) equivalent to their availability. We suggest that hairy woodpeckers select older stands with larger, dying trees for foraging, but also use clear-cuts proportionally due to the residual snags, decaying trees, and remnant dead wood available. Higher use (P < 0.001) by hairy woodpeckers of small forest patches (0–5 ha) and intermediate-sized stands (5–30 ha) than large patches (>30 ha) may be a result of the older, higher-quality habitat available in small stands in the managed forest landscape. We recommend that land managers interested in maintaining healthy managed forest ecosystems with a full complement of cavity-using species in forests of western Washington and northwestern Oregon maintain a landscape mosaic with approximately 45% of the landscape in stands >40 years, and >30% of the landscape in stands >60 years.     

同域分布3种啄木鸟冬季取食的生态位差异

为了掌握黑啄木鸟、三趾啄木鸟和大斑啄木鸟的冬季取食行为特征,特别是三者之间取食生态位的差异,于2016年1月5-13日,在黑龙江省凉水国家级自然保护区以样线法结合样方法对3种啄木鸟的取食生境和取食行为进行了系统调查,收集了15个生境和行为特征变量数据。共布设45条样线,484个对照样方,收集312组啄木鸟取食数据,其中黑啄木鸟73组,三趾啄木鸟97组,大斑啄木鸟142组。多变量回归树和多分类逻辑斯谛分析结果显示,3种啄木鸟在所调查的15项特征上存在显著分异。采用基于利用-可利用方法的Bailey''s方法和双因子方差分析,分别对3种啄木鸟的生境选择和行为特征进行分析,结果显示：黑啄木鸟和三趾啄木鸟偏好在郁闭度较高的原始云、冷杉林中取食,而大斑啄木鸟则随机地在各种林型、生境中取食。黑啄木鸟、三趾啄木鸟多在树干取食,黑啄木鸟更常在倒木上取食,而大斑啄木鸟则多在树冠层取食。黑啄木鸟基本只在主干上凿洞,其他两种特别是大斑啄木鸟则可以在侧枝上取食。与黑啄木鸟和大斑啄木鸟凿洞取食昆虫不同,三趾啄木鸟多通过扒去树皮获得食物。黑啄木鸟的取食树基本为死树,单树取食时间最长,大斑啄木鸟多在活树上取食,单树取食时间最短,经常更换取食树,而三趾啄木鸟的取食树则死活参半,单树取食时间也较长。黑啄木鸟的冬季取食行为节律表现为双峰形,日出后和日落前各有一个活动高峰,其他两种则于白天持续取食。3种啄木鸟取食生境和行为生态位的差异,使它们能够更有效地利用有限的食物资源,共存于同一森林。     

The perils of plasticity: dual resource pulses increase facilitation but destabilize populations of small‐bodied cavity‐nesters

Resource pulses within structured communities can lead to changes in the ecological roles of community members, particularly for species that exhibit plasticity in resource use. The red‐breasted nuthatch Sitta canadensis is a facultative excavating cavity‐nester that forages on seeds and insects, thus exhibits plasticity in both nesting habits and diet. In a long‐term study of cavity‐nesting vertebrates, we used point counts, and nest and vegetation surveys to examine the effects of two resource pulses of mountain pine bark beetle prey Dendroctonus ponderosae and tree cavities via excavator populations, on population densities and cavity reuse of red‐breasted nuthatches, from 1997–2006. We observed a doubling in mean nut‐hatch densities from 0.12 to 0.24 individuals ha^?1 then a collapse later in the decade to 50% below endemic levels (0.06 individuals ha^?1). These regional fluctuations were positively correlated with densities of trees recently infected by bark beetles. Because nuthatches range over large areas in winter, this regional correlation suggests that populations responded to the increase in winter food supply. At the site scale, general linear mixed effects models showed that nuthatch populations increased following years of high densities of downy woodpeckers Picoides pubescens, suggesting that downy woodpeckers were important facilitators, via cavity excavation. Type of nesting cavity used by nuthatches varied during the pulse, such that the use of existing cavities (in lieu of excavation) increased on sites that had harboured downy woodpecker nests in the previous year. We conclude that increased densities of cavity excavators allowed facultative excavators to increase their reuse of cavities, which may have contributed to the dramatic increases in nuthatch populations. However, nuthatch populations collapsed after the boom suggesting that this dual resource pulse may have destabilized populations by enabling densities to reach unsustainable levels. Thus, plasticity in resource use can have serious costs as well as benefits.     

The ecology of mangrove forest birds in Peninsular Malaysia

The density, distribution and feeding ecology of birds of mangrove forests in Selangor on the west coast of Peninsular Malaysia were investigated between February and May 1989. Excluding aerial hunters and wading birds, 47 species were recorded from four mangrove forest sites in Selangor, though undoubtedly some rarer species were missed due to the brevity of the study. The estimated density of birds, using fixed-width transects, ranged from 15 to 26 birds per ha. One quarter of all birds counted belonged to just one species, the Ashy Tailorbird Orthotomus ruficeps. Excluding ground feeders (three species), four foraging guilds were recognized among 17 of the commonest bird species: obligate foliage-foraging insectivores (seven species), bark-foraging insectivores (four), facultative nectar-ivores (five) and aerial hawkers (one). Species within the first and third guilds apparently were partitioned by foraging technique and heights, while those of the second guild (woodpeckers) differed mainly in their selection of plant species. The horizontal distribution of several species corresponded to the zonation of mangroves. Avifaunal differences between sites reflected differences in forest floristics. The greatest number of species occurred at the dry landward edge site, which supported seven bird species not encountered elsewhere in Selangor. This habitat has almost completely disappeared from much of the peninsula owing to land reclamation. Four of the six resident mangrove-specialized bird species in Selangor were regularly recorded at two or more sites, another (Greater Gol-denback Woodpecker Chrysocolaptes lucidus) occurred at only one site and the last (Ruddy Kingfisher Halcyon coromanda) was never recorded. Two species of sunbirds probably play an important role in the pollination of several species of mangroves. The colonization of anthropogenic habitats by many mangrove-dwelling bird species is attributed partly to their generalized foraging niches, which may have evolved in response to regular fluctuations in food availability and the dynamic physiography of mangrove communities.     

Spatial Scale and Shape of Prescribed Fires Influence Use by Wild Turkeys

In recent years, there have been increasing efforts to understand effects of prescribed fire on population dynamics of wild turkeys (Meleagris gallopavo; turkeys) in pine (Pinus spp.) forests. Although distribution of turkeys is not limited to pine forests, these forests provide nesting and brood-rearing habitat throughout the southeastern United States. Previous studies have investigated direct (e.g., nest loss to fire) and indirect (e.g., nest- and brood-site selection) effects of prescribed fire, but little is known about how turkeys are influenced by the spatial scale and shape of prescribed fire. We constructed an individual-based model (IBM) with landscapes of 2 burn unit shapes and 17 spatial scales. We used telemetry data obtained from global positioning system-marked female turkeys to replicate movement behaviors of turkeys within the model. We hypothesized that use of units burned during the current year (<1 yr) would decrease as scale of fires increased, and that shape of burn units would influence use by turkeys. Spatial scale most influenced turkey use; the greatest use was in burned stands of approximately 23 ha in size, whereas least use was associated with burned stands >1,269 ha. At a spatial scale of 23 ha, the daily percent use of rectangular burn units was 7% greater than square-shaped burn units. Likewise, daily percent use of rectangular burn units was 34% greater than square-shaped burn units at a spatial scale of 1,269 ha. When burn units were rectangular-shaped, daily percent use decreased by 48% as the spatial extent of the fires increased from 23 ha to 203 ha. Likewise, when burn units were square-shaped, turkey use decreased by 49% as spatial extent of fires increased from 23 ha to 203 ha. Our findings suggest the importance of managing forested landscapes with prescribed fires not exceeding approximately 200 ha if wild turkeys are a management concern. © 2020 The Wildlife Society.     

Songbirds tradeoff auditory frequency resolution and temporal resolution

Physical tradeoffs may in some cases constrain the evolution of sensory systems. The peripheral auditory system, for example, performs a spectral decomposition of sound that should result in a tradeoff between frequency resolution and temporal resolution. We assessed temporal resolution in three songbird species using auditory brainstem responses to paired click stimuli. Temporal resolution was greater in house sparrows (Passer domesticus) than Carolina chickadees (Poecile carolinensis) and white-breasted nuthatches (Sitta carolinensis), as predicted based on previous observations of broader auditory filters (lower frequency resolution) in house sparrows. Furthermore, within chickadees, individuals with broader auditory filters had greater temporal resolution. In contrast to predictions however, temporal resolution was similar between chickadees and nuthatches despite broader auditory filters in chickadees. These results and the results of a model simulation exploring the effect of broadened auditory filter bandwidth on temporal resolution in the auditory periphery strongly suggest that frequency resolution constrains temporal resolution in songbirds. Furthermore, our results suggest that songbirds have greater temporal resolution than some mammals, in agreement with recent behavioral studies. Species differences in temporal resolution may reflect adaptations for efficient processing of species-specific vocalizations, while individual differences within species may reflect experience-based developmental plasticity or hormonal effects.     

Short-term responses of birds to prescribed fire in fire-suppressed forests of California

Prescribed fire is one tool for restoring fire-suppressed forests, but application of fire during spring coincides with breeding and arrival of migrant birds. We examined effects of low-severity prescribed fires on counts of birds in a managed forest in the Sierra Nevada of California immediately, 1 year, and 3–6 years after fire was applied in spring. Of 26 species analyzed, counts of 3 species increased after fire (Pacific-slope flycatcher [Empidonax difficilis], brown creeper [Certhia americana], and American robin [Turdus migratorius]), and 6 species decreased after fire (Anna's hummingbird [Calypte anna], Hutton's vireo [Vireo huttoni], warbling vireo [Vireo gilvus], golden-crowned kinglet [Regulus satrapa], Nashville warbler [Vermivora ruficapilla], hermit warbler [Dendroica occidentalis]). Black-throated gray warbler (Dendroica nigrescens) increased in the first year following fire but decreased 3–6 years after fire. When grouped into guilds, habitat association and foraging guild best explained responses to fire, with the greatest changes occurring for oak-associated species (negative), riparian-associated species (positive), aerial foragers (positive), and bark foragers (positive). Lastly, when we compared our counts to those collected during the 1910s, changes were consistent with those predicted from fire suppression and species' affinity for burned forests, suggesting that results from contemporary fire studies should be interpreted within an ecological context that includes effects of fire suppression. We found that low-severity prescribed fires applied in spring served to drive the bird community towards pre-suppression conditions. © 2011 The Wildlife Society.     

Interspecific differences in the visual system and scanning behavior of three forest passerines that form heterospecific flocks

Little is known as to how visual systems and visual behaviors vary within guilds in which species share the same micro-habitat types but use different foraging tactics. We studied different dimensions of the visual system and scanning behavior of Carolina chickadees, tufted titmice, and white-breasted nuthatches, which are tree foragers that form heterospecific flocks during the winter. All species had centro-temporally located foveae that project into the frontal part of the lateral visual field. Visual acuity was the highest in nuthatches, intermediate in titmice, and the lowest in chickadees. Chickadees and titmice had relatively wide binocular fields with a high degree of eye movement right above their short bills probably to converge their eyes while searching for food. Nuthatches had narrower binocular fields with a high degree of eye movement below their bills probably to orient the fovea toward the trunk while searching for food. Chickadees and titmice had higher scanning (e.g., head movement) rates than nuthatches probably due to their wider blind areas that limit visual coverage. The visual systems of these three species seem tuned to the visual challenges posed by the different foraging and scanning strategies that facilitate the partitioning of resources within this guild.     

Magellanic woodpecker ( Campephilus magellanicus) abundance and foraging in Tierra del Fuego, Chile

The Magellanic woodpecker (Campephilus magellanicus) is a vulnerable and poorly studied bird in the sub-antarctic deciduous and evergreen beech (Nothofagus) forests of South America. On Tierra del Fuego island (Chile), we compared Magellanic woodpecker abundance and its foraging habitat in two forest types: pure N. pumilio and mixed forests composed by N. pumilio and N. betuloides, including managed and non managed stands. At a regional scale, abundance of woodpeckers was greater in landscapes including both forest types than in pure N. pumilio landscapes. When both forest types occurred together, woodpecker abundance did not differ between them. The number of trees with foraging signs was correlated with Magellanic woodpecker abundance and was also associated with N. betuloides and snag densities, but was not affected by forest management. Occurrence of pecking on foraging trees was greater in mixed Nothofagus than pure N. pumilio stands. Woodpeckers foraged disproportionately more on larger diameter and more decayed trees. Moreover, trees used for foraging were positively correlated with canopy cover and snag density and were negatively correlated with distance to nearby peatlands and beaver ponds. Direct observation revealed that the flying distance between trees was negatively correlated with proportion of trees with foraging signs. Woodpeckers chose trees that were visited before, suggesting a pattern of tree recognition within foraging territories.Communicated by F. Bairlein     

Phenotypic flexibility in passerine birds: Seasonal variation of aerobic enzyme activities in skeletal muscle

Improved winter cold tolerance is widespread among small passerines resident in cold climates and is generally associated with elevated summit metabolic rate (M_sum=maximum thermoregulatory metabolic rate) and improved shivering endurance with increased reliance on lipids as fuel. Elevated M_sum and improved cold tolerance may result from greater metabolic intensity, due to mass-specific increase in oxidative enzyme capacity, or increase in the masses of thermogenic tissues. To examine the mechanisms underlying winter increases in M_sum, we investigated seasonal changes in mass-specific and total activities of the key aerobic enzymes citrate synthase (CS) and β-hydroxyacyl CoA-dehydrogenase (HOAD) in pectoralis, supracoracoideus and mixed leg muscles of three resident passerine species, black-capped chickadee (Poecile atricapillus), house sparrow (Passer domesticus), and white-breasted nuthatch (Sitta carolinensis). Activities of CS were generally higher in winter than in summer muscles for chickadees and house sparrows, but not nuthatches. Mass-specific HOAD activity was significantly elevated in winter relative to summer in all muscles for chickadees, but did not vary significantly with season for sparrows or nuthatches, except for sparrow leg muscle. These results suggest that modulation of substrate flux and cellular aerobic capacity in muscle contribute to seasonal metabolic flexibility in some species and tissues, but such changes play varying roles among small passerines resident in cold climates.     

Demography of Reintroduced Eastern Bluebirds and Brown-Headed Nuthatches

ABSTRACT Species reintroductions are used commonly as a tool for conservation, but rigorous, quantitative assessments of their outcome rarely occur. Such assessments are critical for determining success of the reintroduction and for identifying management actions needed to ensure persistence of reintroduced populations. We collected 9 years of demographic data on populations of brown-headed nuthatches (Sitta pusilla) and Eastern bluebirds (Sialia sialis) reintroduced via translocation into Long Pine Key, Everglades National Park, Florida, USA. Realized population growth of brown-headed nuthatches was positive in the first 3 years after cessation of translocations (λ₂₀₀₂ = 1.15, SE = 0.13; λ₂₀₀₃ = 1.28, SE = 0.12; λ₂₀₀₅ = 1.32, SE = 0.20) but became negative thereafter (λ₂₀₀₆ = 0.67, SE = 0.10; λ₂₀₀₇ = 0.77, SE = 0.13). Realized growth rate for the Eastern bluebird population did not vary among years and indicated either a stable or a slowly declining population (λ = 0.92, SE = 0.04). Reintroductions were a qualified success; they resulted in the re-establishment of populations of both species, but neither population grew to the extent expected and both remained at risk of extinction.     

Traffic noise and responses to a simulated approaching avian predator in mixed-species flocks of chickadees,titmice, and nuthatches

Traffic noise likely reaches a wide range of species and populations throughout the world, but we still know relatively little about how it affects anti-predator behavior of populations. We tested for possible effects of traffic noise on responses to predator acoustic cues in Carolina chickadees (Poecile carolinensis), tufted titmice (Baeolophus bicolor), and white-breasted nuthatches (Sitta carolinensis) near 14 independent feeding stations in eastern Tennessee. We compared anti-predator calling and seed-taking behavior in response to playbacks of predator stimuli (screech owl calls) at sites naturally exposed to traffic noise and at sites that faced relatively little traffic noise. The screech owl call playback was designed to simulate the approach of this dangerous predator to a feeder being used by these small songbirds. We found that chickadees responded consistently to the owl stimuli across different levels of traffic noise. However, titmice, and nuthatches exhibited different behavioral responses to the predator stimulus, suggesting that traffic noise masked these low-frequency predator calls. Overall, chickadees and nuthatches showed the broadest anti-predator behavioral responses in comparison to titmice, corroborating earlier published work with an Indiana population. Finally, populations exposed to traffic noise overall seemed less able to detect predator cues potentially masked by that noise, and future work will need to assess likely seasonal variation in these responses as well as species-level variation in anti-predator responses in mixed-species groups.     

A decade of emerald ash borer effects on regional woodpecker and nuthatch populations

The emerald ash borer (EAB) Agrilus planipennis, first detected in 2002 in the vicinity of Detroit, Michigan, USA, has spread throughout much of eastern and midwestern North America as of 2016, resulting in widespread mortality of ash trees in the genus Fraxinus. We investigated the effects of this newly available, exotic food source on populations of six species of largely resident insectivorous birds, including five species of woodpeckers and white-breasted nuthatch (Sitta canadensis), using North American Breeding Bird Survey data for breeding season estimates and Audubon Christmas Bird Counts for winter season estimates. We found evidence for relatively modest and variable effects of EAB invasion on the populations of these birds during the breeding season, but highly significant numerical increases during the winter that in several cases appeared to be increasing as the EAB invasion has progressed. Our results confirm that the EAB invasion is resulting in increased populations of several insectivorous birds, primarily during the winter. They also suggest that the numerical response of woodpeckers to EAB may be such that avian predation, which represents a significant, and possibly the largest, morality factor affecting some EAB populations, may continue to increase and help control the EAB epidemic as the invasion continues.