Forest Restoration Treatment Effects on the Nesting Success of Western Bluebirds (Sialia mexicana)

We examined the effects of presettlement forest restoration treatments on the nesting success of Western Bluebirds in ponderosa pine forests of northwestern Arizona, U.S.A. From 1998 to 2001 we monitored 97 active Western Bluebird nests, 41 in current‐condition untreated forest and 56 in restoration‐treated forest. We found no effect of restoration treatments on clutch size and little effect on the number of nestlings per nest. However, in treated forest stands number of fledglings per nest averaged 1.6 times greater, and probability of a nest surviving to successfully fledge at least one young was up to 4.2 times greater than in untreated forest. Probability of a nest succeeding averaged 0.39 ± 0.11 (SE) and 0.75 ± 0.06 from 1999 to 2001 in untreated and treated forests, respectively. In addition, in treated forest, average number of nests infested with the blowfly parasite Protocalliphora sialia was up to 4.3 times greater, and number of parasites per fledgling was up to 10.7 times greater than in untreated forest. Overall, the data suggest that in treated forest Western Bluebirds have a higher probability of successfully fledging young, but they are at greater risk of parasitic infestations, of which the ultimate effects on post‐fledging survival are unknown.     

Avian Density and Nest Survival on the San Pedro River: Importance of Vegetation Type and Hydrologic Regime

Abstract: Lowland riparian vegetation in the southwestern United States is critically important for maintaining a high richness and density of breeding birds. Further investigation is needed within riparian corridors, however, to evaluate the relative importance of vegetation type and hydrologic regime for avian density and nest survival as targets for regional conservation or restoration efforts. We estimated the densities of 40 bird species and for species grouped on the basis of nest height and dependence on surface water in gallery cottonwood–willow (Populus spp.–Salix spp.) forests, saltcedar (Tamarix spp.) shrub lands, and terrace vegetation types along a gradient in the hydrologic regime of the San Pedro River, Arizona, USA. We also assessed nest survival for shrub-nesting insectivores and herbivores. Canopy-nesting birds as a group and 14 individual bird species reached their greatest densities in cottonwood forests regardless of the hydrologic regime. Water-dependent birds as a group reached their highest density in both intermittent- and perennial-flow cottonwood stands, but certain species occurred almost exclusively in perennial-flow sites. Two shrub-nesting species and the brown-headed cowbird (Molothrus ater) were most abundant in saltcedar shrub lands, and the brown-headed cowbird was most abundant in saltcedar stands with intermittent flows. Mesquite (Prosopis spp.) and big sacaton (Sporobolus wrightii) grassland each maintained the highest densities of certain species within ≥1 hydrologic regime. Shrub-nesting insectivores had the greatest nest survival in cottonwood, including Arizona Bell's vireo (Vireo bellii arizonae), and also had lower proportions of nests parasitized and preyed upon, although 95% confidence intervals among vegetation types overlapped. Nest survival for both shrub-nesting insectivores and herbivores was lowest in intermittent-flow saltcedar, although, again, confidence intervals overlapped. Nest survival was lower in parasitized than nonparasitized nests in mesquite and across vegetation types for Arizona Bell's vireo and in cottonwood for Abert's towhee (Pipilo aberti). Riparian management that maintains heterogeneous riparian vegetation types, including floodplain vegetation comprising cottonwood–willow gallery riparian forests with some stretches of perennial flow, are important for maintaining the high diversity and abundance of breeding birds on the San Pedro River and probably across the region. Cottonwood stands also appear to maintain highest nest survival for some shrub-nesting birds.     

Effects of Wildlife Forestry on Abundance of Breeding Birds in Bottomland Hardwood Forests of Louisiana

ABSTRACT Effects of silvicultural activities on birds are of increasing interest because of documented national declines in breeding bird populations for some species and the potential that these declines are in part due to changes in forest habitat. Silviculturally induced disturbances have been advocated as a means to achieve suitable forest conditions for priority wildlife species in bottomland hardwood forests. We evaluated how silvicultural activities on conservation lands in bottomland hardwood forests of Louisiana, USA, influenced species-specific densities of breeding birds. Our data were from independent studies, which used standardized point-count surveys for breeding birds in 124 bottomland hardwood forest stands on 12 management areas. We used Program DISTANCE 5.0, Release 2.0 (Thomas et al. 2006) to estimate density for 43 species with >50 detections. For 36 of those species we compared density estimates among harvest regimes (individual selection, group selection, extensive harvest, and no harvest). We observed 10 species with similar densities in those harvest regimes compared with densities in stands not harvested. However, we observed 10 species that were negatively impacted by harvest with greater densities in stands not harvested, 9 species with greater densities in individual selection stands, 4 species with greater densities in group selection stands, and 4 species with greater densities in stands receiving an extensive harvest (e.g., >40% canopy removal). Differences in intensity of harvest influenced densities of breeding birds. Moreover, community-wide avian conservation values of stands subjected to individual and group selection, and stands not harvested, were similar to each other and greater than that of stands subjected to extensive harvest that removed >40% canopy cover. These results have implications for managers estimating breeding bird populations, in addition to predicting changes in bird communities as a result of prescribed and future forest management practices.     

Richness and Density of Birds in Timber <Emphasis Type="Italic">Nothofagus pumilio</Emphasis> Forests and their Unproductive Associated Environments

Research on forest management impact focuses mainly on timber stands, and leaves out the unproductive forest environments. These stands are spatially mixed with timber forests. The objective was to evaluate richness and density of birds in timber Nothofagus pumilio forests and their unproductive associated environments, and discuss forest management implications. These stands showed significant differences in their forest structure, which generate a great variety of ecological environments. A total of 1881 individuals belonging to 30 bird species were observed during the sampling, in spring and summer seasons. These species were mainly migratory and insectivores, Passeriforms being the most important group. From 12 to 17 birds/ha were found, which varied with the forest environments and seasons. Timber stands of Nothofagus pumilio support a low number of bird species. Most of them are opportunistic and a few prefer these woods over other forested or afforested areas. Low bird density and richness characterize these austral forests, which share their diversity with a high variety of ecosystems along Patagonia. Timber N. pumilio forests has a marginal value for bird species conservation, considering its richness, density and the percentage of this forest in the total forested landscape of Tierra del Fuego (Argentina).     

Consequences of Fragmentation of Tropical Moist Forest for Birds and Their Role in Predation of Herbivorous Insects

The consequences of habitat alteration on the role of understory insectivorous birds as predators of herbivorous insects in tropical forests are poorly understood. To examine whether fragmentation may affect the top–down controls of herbivory, we compared the number of species, individuals, and the community structure of insectivorous birds between fragments and continuous tropical moist forest in Mexico. We also registered insect herbivore abundances and conducted a larvae predation experiment to evaluate the potential role of insectivorous birds as predators of herbivorous insects. We recorded 63 bird species from 22 families, 43 percent of which were insectivorous birds. Species richness, abundance, and diversity of the avian community were higher in continuous forest compared with forest fragments. For insectivorous birds in particular, there was low similarity in avian insectivore communities between forest types, and forest fragments had more heavily dominated communities of avian insectivores. During the dry season, forest fragments presented significantly higher predation rates on artificial caterpillars, and lower abundance of herbivorous Lepidoptera larvae, compared with continuous forest. Furthermore, there was a significant negative correlation between artificial caterpillar predation rate and larval Lepidoptera abundance, with higher rates of predation in sample sites of low Lepidoptera abundance. Hence, the potentially greater light in the dry season combined with a more dominated avian insectivore community in forest fragments may facilitate increased predation by avian insectivores, resulting in a decline in abundance of larval Lepidoptera, with implications for the process of insect‐driven herbivory in forest fragments.     

Influence of Post‐Clearing Treatment on the Recovery of Herbaceous Plant Communities in Amazonian Secondary Forests

Secondary forests are an increasingly common feature in tropical landscapes worldwide and understanding their regeneration is necessary to design effective restoration strategies. It has previously been shown that the woody species community in secondary forests can follow different successional pathways according to the nature of past human activities in the area, yet little is known about patterns of herbaceous species diversity in secondary forests with different histories of land use. We compared the diversity and abundance of herbaceous plant communities in two types of Central Amazonian secondary forests—those regenerating on pastures created by felling and burning trees and those where trees were felled only. We also tested if plant density and species richness in secondary forests are related to proximity to primary forest. In comparison with primary forest sites, forests regenerating on non‐burned habitats had lower herbaceous plant density and species richness than those on burned ones. However, species composition and abundance in non‐burned stands were more similar to those of primary forest, whereas several secondary forest specialist species were found in burned stands. In both non‐burned and burned forests, distance from the forest edge was not related to herbaceous density and species richness. Overall, our results suggest that the natural regeneration of herbaceous species in secondary tropical forests is dependent on a site's post‐clearing treatment. We recommend evaluating the land history of a site prior to developing and implementing a restoration strategy, as this will influence the biological template on which restoration efforts are overlaid.     

Spatiotemporal variation in avian diversity and the short-term effects of typhoons in tropical reef-karst forests on Taiwan

The diversity and spatiotemporal variation of avifauna in different settings of tropical coral reef-karst forests on the Hengchun Peninsula, Taiwan, were examined. The short-term effects on bird assemblages following two typhoons that severely impacted Hengchun were investigated. Line-transect census recorded 46 species of birds, dominated by forest-associated gleaning insectivores or omnivores, and 13% of the endemics of Taiwan. Prior to the typhoons, the continuous-canopy forest was close to the open forest setting in species evenness, but the species heterogeneity was lower and more variable. The continuous-canopy and open forests differed in overall avian composition, whereas two continuous-canopy forest settings were similar in composition. Typhoons did not significantly lower the mean numbers of either species or birds, nor affect the pattern of their spatial distribution in the forest settings. However, they did increase similarities in the species composition between the open and continuous-canopy settings, and caused a decrease in the similarity between forest edges and interiors. Overall, typhoons affected species composition more in the continuous-canopy forests than in the open setting, and more in interiors than in forest edges. This pattern corresponded to an increase in the species heterogeneity and species evenness in the forest interiors, indicating movements of birds from the edge toward the interior. Among different functional groups, gleaning omnivores tended to retain a pattern of higher abundance in the open forest setting than in the continuous-canopy forests, whereas the abundances of gleaning insectivores and cavity-nesting frugivores tended to decline in the latter or both settings.     

Vertical stratification of an avian community in New Guinean tropical rainforest

Vertical stratification of avian communities has been studied in both temperate and tropical forests; however, the majority of studies used ground-based methods. In this study we used ground-to-canopy mist nets to collect detailed data on vertical bird distribution in primary rain forest in Wanang Conservation Area in Papua New Guinea (Madang Province). In total 850 birds from 86 species were caught. Bird abundance was highest in the canopy followed by the understory and lowest in the midstory. Overall bird diversity increased towards the canopy zone. Insectivorous birds represented the most abundant and species-rich trophic guild and their abundances decreased from the ground to canopy. The highest diversity of frugivorous and omnivorous birds was confined to higher vertical strata. Insectivorous birds did not show any pattern of diversity along the vertical gradient. Further, insectivores preferred strata with thick vegetation, while abundance and diversity of frugivores increased with decreasing foliage density. Our ground-to-canopy (0–27 m) mist netting, when compared to standard ground mist netting (0–3 m), greatly improved bird diversity assessment and revealed interesting patterns of avian community stratification along vertical forest strata.     

Connectivity with primary forest determines the value of secondary tropical forests for bird conservation

Species extinctions caused by the destruction and degradation of tropical primary forest may be at least partially mitigated by the expansion of regenerating secondary forest. However, the conservation value of secondary forest remains controversial, and potentially underestimated, since most previous studies have focused on young, single‐aged, or isolated stands. Here, we use point‐count surveys to compare tropical forest bird communities in 20–120‐year‐old secondary forest with primary forest stands in central Panama, with varying connectivity between secondary forest sites and extensive primary forest. We found that species richness and other metrics of ecological diversity, as well as the combined population density of all birds, reached a peak in younger (20‐year‐old) secondary forests and appeared to decline in older secondary forest stands. This counter‐intuitive result can be explained by the greater connectivity between younger secondary forests and extensive primary forests at our study site, compared with older secondary forests that are either (a) more isolated or (b) connected to primary forests that are themselves small and isolated. Our results suggest that connectivity with extensive primary forest is a more important determinant of avian species richness and community structure than forest age, and highlight the vital contribution secondary forests can make in conserving tropical bird diversity, so long as extensive primary habitats are adjacent and spatially connected.Abstract in Spanish is available with online material.     

Reproductive success of Tree Pipits Anthus trivialis in relation to habitat selection in conifer plantations

Aspects of the reproductive success of Tree Pipits Anthus trivialis were examined in relation to broad‐scale habitat and nest‐site selection in Thetford Forest, a coniferous plantation forest in eastern England. Three habitat classes were defined corresponding to previously reported densities of Tree Pipits: clearfell and recently planted stands (habitat class A: low density), stands 2–5 years old (B: high density) and stands 6 years or older (C: low density). The preference for 2–5‐year‐old stands indicated by higher densities was supported by the timing of territory settlement. Tree Pipits also showed distinct preferences for nest‐site characteristics that were relatively consistent across habitat classes and throughout the breeding season. At the ‘habitat scale’, results were consistent with the predictions of the ideal despotic distribution model. First clutches were laid significantly earlier in the preferred habitat class B. Overall nesting success (i.e. the proportion of nests producing fledglings), but not clutch size, also varied between habitats, being greater in habitat classes B and C than in habitat class A. The variation in overall nesting success between habitats was primarily driven by low nest survival rates during the laying/incubation period in clearfell and recently planted stands. Nest survival rates during the nestling period were lower in the preferred 2–5‐year‐old (and older) stands and declined over the course of the study. Preferences for nest‐site characteristics (at least for those that were measured) provided no apparent benefit to nest survival rates. Overall nesting success thus appeared to be determined at the habitat scale, perhaps because the broad differences in cover between habitats affected the likelihood of nest predation (the main cause of nest failure). It is suggested that the very low nesting success experienced by Tree Pipits in clearfell and new stands may be one factor in the species’ relative avoidance of this habitat and preference for 2–5‐year‐old stands.     

Rapid colonization of a Hawaiian restoration forest by a diverse avian community

Deforestation of tropical forests has led to widespread loss and extirpation of forest bird species around the world, including the Hawaiian Islands which have experienced a dramatic loss of forests over the last 200–800 years. Given the important role birds play in forest ecosystem functions via seed dispersal and pollination, a bird community's response to forest restoration is an important measure of the success of such conservation actions. We evaluated the bird response to reforestation at an important bird sanctuary, Hakalau Forest National Wildlife Refuge, Hawai′i Island, using 26 years of bird count data. We show that most species from within the diverse avian community increased significantly, but species colonized the restoration forest at different rates. Distance from intact forest and time since restoration were both important predictors of colonization rate, interacting such that for most species it took more time to colonize areas farther from the intact forest. In addition, both forest cover and understory diversity helped to explain bird densities, but the effect varied among species, suggesting that different habitat requirements may help drive variation in colonization rates. This article provides the first detailed evaluation of how a diverse community of birds has responded to one of the largest, ongoing reforestation projects in Hawai′i.     

Response of Grassland Birds in Sand Shinnery Oak Communities Restored Using Tebuthiuron and Grazing in Eastern New Mexico

Sand shinnery oak (Quercus havardii) communities are a unique component of grassland bird habitat in eastern New Mexico and have been impacted by human activities for decades. These communities are frequently managed with livestock grazing and herbicide application for shrub control, strategies that potentially can be used to restore the historical shrub–grass composition of this plant community. During spring migration and the breeding seasons of 2004 and 2005, we compared density and community structure of grassland bird species among four combinations of tebuthiuron application and grazing treatments that were being evaluated for restoration of shinnery oak communities. We performed biweekly point transects on sixteen 65‐ha study plots in these communities. Density of all avian species combined did not differ between grazed and ungrazed plots. Tebuthiuron‐treated plots had a 40% higher average density for combined species than untreated plots. There was a 41% higher average density of all species during spring 2005 than 2004, but density was similar during the breeding season of both years. These trends were predominantly influenced by densities of migratory Cassin’s Sparrow (Aimophila cassinii), which were greater in tebuthiuron‐treated plots in both years. Densities of resident Meadowlarks (Sturnella spp.) exhibited little response to tebuthiuron or grazing treatments. Avian species richness, evenness, and diversity were only minimally affected by the tebuthiuron and grazing treatments. This study occurred over a period of highly variable precipitation, so future assessments, spanning longer wet–dry cycles and maturing plant communities, may be necessary to completely determine avian response to these restoration efforts.     

Landscape and Vegetation Effects on Avian Reproduction on Bottomland Forest Restorations

ABSTRACT Forest restoration has been undertaken on >200,000 ha of agricultural land in the Mississippi Alluvial Valley, USA, during the past few decades. Decisions on where and how to restore bottomland forests are complex and dependent upon landowner objectives, but for conservation of silvicolous (forest-dwelling) birds, ecologists have espoused restoration through planting a diverse mix of densely spaced seedlings that includes fast-growing species. Application of this planting strategy on agricultural tracts that are adjacent to extant forest or within landscapes that are predominately forested has been advocated to increase forest area and enhance forested landscapes, thereby benefiting area-sensitive, silvicolous birds. We measured support for these hypothesized benefits through assessments of densities of breeding birds and reproductive success of 9 species on 36 bottomland forest restoration sites. Densities of thamnic (shrub-scrub dwelling) and silvicolous birds, such as yellow-breasted chat (Icteria virens), indigo bunting (Passerina cyanea), and white-eyed vireo (Vireo griseus) were positively associated with 1) taller trees, 2) greater stem densities, and 3) a greater proportion of forest within the landscape, whereas densities of birds associated with grasslands, such as dickcissel (Spiza americana) and red-winged blackbird (Agelaius phoeniceus), were negatively associated with these variables. Vegetation structure, habitat edge, and temporal effects had greater influence on nest success than did landscape effects. Taller trees, increased density of woody stems, greater vegetation density, and more forest within the landscape were often associated with greater nest success. Nest success of grassland birds was positively related to distance from forest edge but, for thamnic birds, success was greater near edges. Moreover, nest success and estimated fecundity of thamnic species suggested their populations are self-sustaining on forest restoration sites, whereas these sites are likely population sinks for grassland and open-woodland species. We recommend restoration strategies that promote rapid development of dense forest stands within largely forested landscapes to recruit breeding populations of thamnic and silvicolous birds that have reproductive success sufficient to sustain their populations.     

Bird Response to Prescribed Silvicultural Treatments in Bottomland Hardwood Forests

ABSTRACT Silvicultural treatments prescribed to enhance wildlife habitat by promoting structural heterogeneity via retention of large live trees, snags, and coarse woody debris has been termed wildlife-forestry. Wildlife-forestry has been advocated for management of bottomland hardwood forests on public conservation lands within the Mississippi Alluvial Valley, USA. On Tensas River National Wildlife Refuge in northeast Louisiana, we used distance sampling during 6 visits to 138 point locations to estimate avian densities within stands subjected to variable-retention harvests, within a 13-year chronosequence, and untreated control stands. Densities of 9 species, including 6 species of conservation concern, were greater in treated stands than on untreated stands. Five species responded negatively to treatments and had greater densities in untreated control stands. Based on conservation concern scores established by Partners in Flight and annual detections of each of 30 species, treated stands afforded greater community-wide bird conservation than did untreated stands. For most species, maximum treatment response was between 5 years and 8 years posttreatment with duration of treatment effect <13 years. Therefore, habitat conditions on treated stands should be reevaluated at circa 15-year intervals and, if warranted, additional silvicultural treatment prescribed to rejuvenate habitat conditions.     

Birds,Cattle, and Bracken Ferns: Bird Community Responses to a Neotropical Landscape Shaped by Cattle Grazing Activities

Large areas of tropical moist forests have been converted to cattle pastures, generating complex landscapes where different habitats are represented by small patches with an uneven spatial distribution. Here, we describe how bird communities respond to the different elements present in a livestock landscape that was originally dominated by tropical moist forest. We surveyed six habitats: open pastures, pastures with shrubs, early‐ and middle‐secondary forests, mature forest, and pastures invaded by bracken ferns (Pteridium aquilinum). Bird diversity was high in secondary and mature forests, and low in fern‐invaded sites and open pastures. Fern‐dominated sites had the lowest bird species richness, and trophic guild diversity of all habitats. Habitat structure affected both bird species richness and densities in similar ways. Tree species richness was the habitat attribute that had a bigger positive effect on bird species richness. Bird community structure varied among sampled habitats, separating habitats in two major groups (forests and pastures). Our data indicate that bracken fern‐invaded pastures were the worst habitat condition for avian communities. To increase bird diversity, we recommend to eliminate or manage bracken fern and to increase shrub and tree cover in open pastures to provide food resources and shelter for birds. Finally, we encourage the maintenance of secondary and mature forest remnants as a strategy to conserve resident birds within a landscape dominated by livestock activities.     

Microhabitat associations of terrestrial insectivorous birds in Amazonian rainforest and second‐growth forests

ABSTRACT Across the Neotropics, small‐bodied terrestrial insectivores are sensitive to forest fragmentation and are largely absent from second‐growth forests. Despite their sensitivity to forest structure, the microhabitat relationships of these birds have not been quantified. From July 1994 to January 1995 in central Amazonia, we characterized habitat at sites where nine species of terrestrial insectivores were observed foraging, as well as at randomly selected sites in continuous forest and two types of 10–15‐yr‐old second‐growth forest common in Amazonia (Vismia‐ and Cecropia‐dominated). We used factor analysis to find suites of correlated variables. From each factor, we selected a representative variable that was relatively easy to measure. We used Bayesian analysis to estimate means and standard deviations of these variables for each species and for each type of habitat. All nine focal species were associated with ranges of microhabitat variables, such as leaf litter depth and tree densities, often absent in second‐growth forests. At least in the early stages of regeneration, neither type of second‐growth forest provides suitable structure for the terrestrial insectivores in our study. The large leaves of Cecropia trees that make up the thick leaf litter may preclude the use of Cecropia‐dominated second growth by our focal species, many of which manipulate leaves when foraging. The leaf litter in Vismia‐dominated second growth was also thicker than sites used for foraging by our focal species. In addition, Vismia‐dominated growth had more small trees and small nonwoody vegetation, perhaps impeding movement by terrestrial birds. In continuous forest, our focal species foraged in microhabitats with characteristics that generally overlapped those of randomly selected sites. Thus, our results are consistent with the hypothesis that microhabitat differences make second‐growth forests unsuitable for our focal species.     

Do Collared Peccaries Negatively Impact Understory Insectivorous Rain Forest Birds Indirectly Via Lianas and Vines?

Tropical rain forest understory insectivorous birds are declining, even in large forest reserves, yet the mechanisms remain unclear. Abundant large mammals can reshape forest structure, which degrades foraging microhabitat. We used six sites in Nicaragua, Costa Rica, and Panama with varying collared peccary (Pecari tajacu) density to test three linked hypotheses: (1) locally declining understory insectivores forage preferentially in liana tangles; (2) vine and liana density, cover, and frequency of dense tangles are lower in the presence of abundant collared peccaries; and consequently (3) abundant collared peccaries are associated with reduced understory insectivorous bird abundance. Three insectivores that declined at La Selva preferentially foraged in liana tangles: Checker‐throated Antwren (Epinecrophylla fulviventris), Dot‐winged Antwren (Microrhopias quixensis), and Ruddy‐tailed Flycatcher (Terenotriccus erythrurus). Vine density, liana cover, liana tangle frequency, and forest cover were lower in the presence of collared peccaries relative to experimental mammal exclosures, with the greatest differences at La Selva Biological Station, Costa Rica. Across sites, five of seven vine and liana measures showed negative, curvilinear relationships with peccary densities. Vine and liana measures peaked at sites with intermediate peccary density, and were low at La Selva. Structural equation models suggest negative indirect effects of the collared peccaries on focal bird densities, mediated by vine and liana density, cover, or tangle frequency. Forest area and rainfall affected both lianas and birds, but collared peccaries also contributed to the reduced abundance of understory insectivores. Indirect effects such as that suggested here may occur even in large, protected forest reserves where large mammal communities are changing.     

Forest Stand Characteristics Altered by Restoration Affect Western Bluebird Habitat Quality

Forest managers are setting Ponderosa pine (Pinus ponderosa) forests in the southwestern United States on a trajectory toward a restored ecosystem by reducing tree densities and managing with prescribed fire. The process of restoration dramatically alters forest stands, and the effects of these changes on wildlife remain unclear. Our research evaluated which aspects of habitat alteration from restoration treatments may be affecting the habitat quality of Western Bluebird (Sialia mexicana), an insectivorous songbird whose populations are declining. Habitat loss resulting from fire‐suppression activities may be partially responsible for their population declines; thus, the bluebird is a good representative species for assessing how the reconstruction of presuppression forest conditions can affect wildlife. We measured habitat variables at 63 successful and 19 unsuccessful Western Bluebird nests in 1999–2001 and 2003. We compared habitat models that represented bluebird biology and habitat changes from restoration. Two models of nest success that included (1) an increased herbaceous and bare ground cover and (2) increased Gambel oak (Quercus gambelii) densities and reduced Ponderosa pine densities were most supported by the data. Increased herbaceous ground cover and Gambel oak density likely represent improved invertebrate assemblages and thus improved forage abundance for nesting bluebirds. Lower Ponderosa pine densities may provide bluebirds with open perches from which to hunt and thereby improve the availability of invertebrates as a food source. We also provide a landscape‐scale example of changes to bluebird habitat quality from treatments, which we recommend as a useful tool in restoration planning.     

Succession of bird communities in young temperate rainforests following thinning

We repeated bird and vegetation surveys in 1991–1992 and 2005–2006 among young managed stands and old-growth forests in southeast Alaska to evaluate whether pre-commercial thinning of managed stands influenced the bird community. We compared decadal changes in bird densities and forest vegetation among 3 stand types: managed stands originating from clearcuts 35 years ago that were left untreated (unthinned), managed stands thinned at uniform spacing (thinned), and old growth with no prior timber harvest. We did not detect differences in decadal trends in avian densities between thinned and unthinned stands for 15 of 16 common bird species using a repeated-measures design. Thinning did not result in greater recruitment of overstory-nesting species as predicted. This was likely because of 1) similar increases in tree heights ( = 9–10 m) and canopy cover ( = 29–43%) between unthinned and thinned stands across decades and 2) the relatively young successional stage of these stands, which had only begun to recruit medium and large size conifers (dbh ≥ 36 cm). Decadal trends in densities of most (88%) understory-nesting bird species did not differ between thinned and unthinned stands. Shrub cover decreased by 22% and 31% across decades in thinned and unthinned stands, respectively. Bird community composition in managed stands reflected the general decadal changes in forest vegetation with a shift in dominance from understory species in the early 1990s (80–85% of total bird density) to an equal abundance of understory (45–54%) and overstory species in the mid-2000s. The latter was more similar to old-growth stands, which were dominated by overstory species (67–71%). Overstory-nesting birds in old growth increased in density by 49% across decades. Densities of cavity-nesting species remained unchanged in managed stands and less than densities in old growth across decades, possibly because of a lack of large trees and snags for nest sites. Overall, thinning of clearcut stands, the primary silvicultural system in the region, had few measurable benefits to birds nearly 20 years after treatment. Monitoring over the 70–100-year harvest rotation may be necessary to fully test whether thinning accelerates succession of bird communities in clearcut stands. However, partial harvests that retain large trees and snags should also be explored as alternatives to better maintain late-succession avifauna throughout the harvest rotation in southeast Alaska. © 2012 The Wildlife Society.