Bark-foraging Birds Research Articles

The importance of tree species identity and trait-based winter foraging ecology of bark-foraging bird species in a large Central European floodplain forest

Beyond preferences for particular species of tree, bark-foraging birds are associated with various tree characteristics such as decay stage, trunk diameter, or bark roughness. Our objectives were to study the winter foraging ecology of different bark-foraging bird species in the highly diverse floodplain forests of Donau-Auen National Park (Austria) by examining the importance of tree species and characteristics. We used 'first-foraging' observations on the great spotted woodpecker (Dendrocopos major), middle spotted woodpecker (Leiopicus medius), Eurasian nuthatch (Sitta europaea), treecreepers (Certhia spp.), great tit (Parus major), Eurasian blue tit (Cyanistes caeruleus), and marsh tit (Poecile palustris). We examined bird-tree relationships with a bird-plant network approach, where we compared traits of trees and their preferences among avian species. The five most important tree species relative to distance-weighted fragmentation were European white elm (Ulmus laevis), pedunculate oak (Quercus robur), common ash (Fraxinus excelsior), and white and black poplar (Populus alba, P. nigra). Avian taxa differed only in the use of tree condition, where woodpeckers used decayed and dead trees more than tits. Most species preferred trees of larger trunk diameter with rougher bark. We suspect that changes in these highly diverse floodplain forest stands will eventually lead to changes in bark-foraging bird assemblages. For the protection of such highly diverse floodplain forests, conservation-based water management practices will be crucial to maintaining a sufficient groundwater table. Our findings also suggest that forest management practices should focus on more diverse commercial forest stands with a critical amount of secondary tree species, a variety of size classes, varying tree conditions, and species with different bark roughness classes.

Arthropod Abundance and Biomass in Response to Pinus taeda L. Trunk Height

The trunks of southeastern pines provide vital habitat for many invertebrates that are, in turn, available as prey for bark-foraging birds. Knowing how these arthropods are distributed vertically on tree trunks is important and may allow for a rapid assessment of prey response to forest management practices. In this study, we used a fast-acting insecticide to sample the arthropods on the lower (0–3 m) and upper (3–9 m) bole sections of nine loblolly pine, Pinus taeda L., trees. We collected over 1,600 arthropods representing 15 orders and 66 families. Ants (Hymenoptera: Formicidae) were the most abundant group collected, and wood cockroaches (Blattodea: Blattellidae) accounted for the greatest overall biomass. Abundance and biomass of arthropods per m2 were greater on the lower trunk, but these values were strongly correlated with those from the upper trunk. Nonmetric multidimensional scaling and permutational multivariate analysis of variance showed that arthropod community composition differed significantly between the two trunk positions. Additionally, indicator species analysis found four flightless taxa to be significantly associated with the lower trunk (Araneae, Zygentoma, Hymenoptera, and Pseudoscorpiones) but none with the higher trunk position. These findings show that bark-dwelling arthropods are generally more abundant near the bases of trees and that there is a strong relationship between abundance and biomass between lower and upper trunk sections. Knockdown insecticides offer an effective tool for rapidly assessing the availability of invertebrate prey for bark-foraging birds.

Niche modeling reveals life history shifts in birds at La Brea over the last twenty millennia

A species presence at a particular site can change over time, resulting in temporally dynamic species pools. Ecological niche models provide estimates of species presence at different time intervals. The avifauna of La Brea includes approximately 120 species dating to approximately 15,000 years ago. Niche models predicted presence at the Last Glacial Maximum for over 90% of 89 landbird species. This confirms that niche modeling produces sensible range estimates at the Last Glacial Maximum. For 97 currently local species that are as yet undocumented at La Brea over 90% were predicted to occur; absence is due to insufficient study, lack of the ecological niche, transient occurrence or a behavioral ability to avoid entrapment. Our 366 niche models provide a prospective checklist of the landbird fauna of La Brea. The models indicate fluidity in life history strategies and a higher proportion of resident birds at the LGM (88% to 60%). We evaluated a subset of 103 species in breeding and winter periods using two climate models (MIROC−ESM, CCSM4) with a variety of differing parameters, finding differences in 5% of the niche models. Niche breadths in bark-foraging birds changed little between the present and LGM, suggesting that greater species diversity at the LGM was due to greater niche availability rather than contractions of niche breadths (i.e., niche partitioning).

Native bark-foraging birds preferentially forage in infected ash (Fraxinus spp.) and prove effective predators of the invasive emerald ash borer (Agrilus planipennis Fairmaire)

Inadvertently introduced into North America in the 1990s, the invasive emerald ash borer (EAB, Agrilus planipennis) has been spreading across the Great Lakes Region resulting in widespread ash tree (Fraxinus spp.) mortality. Native woodpeckers and other bark-foraging insectivores represent one of the few potential natural predators of EAB in the U.S. In this study, we combined observational and destructive tree harvesting approaches to assess bark-foraging bird predation on EAB larvae in a deciduous forest of central Ohio. Results of our observational study show that in an EAB impacted forest, bark-foraging birds forage more heavily on ash trees than non-ash trees, and that they forage preferentially on ash trees that exhibit canopy decline symptoms relative those with healthy canopies. These patterns were further supported by the destructive sampling of 46 ash trees wherein predation by bark-foragers significantly reduced tree-level EAB densities by upwards of 85%. Bark-foraging predation intensity increased with increased EAB infestation levels, with bark-foragers harvesting ∼45% of EAB in trees with thinning canopies compared to ∼22% in ash trees with healthy canopies. Woodpeckers harvest EAB in a density-dependent pattern that could contribute to population control. Despite bark-forager predation, EAB had a high likelihood of successfully emerging from the heavily infested ash trees (∼30% or 35 EAB per m2). Our results suggest that woodpeckers and other bark-foragers may use visual canopy decline, and perhaps other cues, to target ash trees with increased EAB densities. Moreover, our results provide insight into the indirect effects of invasive species on biotic interactions in forest ecosystems highlighting potential shifts in bark-foraging and other bird behaviors in response to a novel forest pest. Bark-foragers respond to EAB infestation and may thus potentially help regulate EAB populations and their spread in a mixed deciduous forest. We suggest that maintaining snags and nesting sites during and after forest pest outbreaks may enhance populations of bark-foraging bird species and, thus, their biological control of pest insects in temperate deciduous forests.

Management, Morphological, and Environmental Factors Influencing Douglas-Fir Bark Furrows in the Oregon Coast Range

Many land managers in the Pacific Northwest have the goal of increasing late-successional forest structures. Despite the documented importance of Douglas-fir tree bark structure in forested ecosystems, little is known about factors influencing bark development and how foresters can manage development. This study investigated the relative importance of tree size, growth, environmental factors, and thinning on Douglas-fir bark furrow characteristics in the Oregon Coast Range. Bark furrow depth, area, and bark roughness were measured for Douglas-fir trees in young heavily thinned and unthinned sites and compared to older reference sites. We tested models for relationships between bark furrow response and thinning, tree diameter, diameter growth, and environmental factors. Separately, we compared bark responses measured on trees used by bark-foraging birds with trees with no observed usage. Tree diameter and diameter growth were the most important variables in predicting bark characteristics in young trees. Measured environmental variables were not strongly related to bark characteristics. Bark furrow characteristics in old trees were influenced by tree diameter and surrounding tree densities. Young trees used by bark foragers did not have different bark characteristics than unused trees. Efforts to enhance Douglas-fir bark characteristics should emphasize retention of larger diameter trees’ growth enhancement.

Microhabitat Selection of Bark-Foraging Birds in Response to Fire and Fire Surrogate Treatments

Abstract We examined the short-term response of the bark-foraging bird community to mechanical thinning, prescribed fire, and thinning/prescribed fire combination treatments designed to reduce fuel loads at study sites throughout the continental United States as part of the national Fire and Fire Surrogate (FFS) project. We modeled the effects of study site, treatment, treatment category, and time since treatment on the foraging encounter rate of four individual species (red-breasted nuthatch [Sitta canadensis], mountain chickadee [Poecile gambeli], hairy woodpecker [Picoides villosus], and brown creeper [Certhia americana]) and assessed the relative importance of several tree and snag characteristics in the selection of foraging trees by these same species. The foraging encounter rate of all four species responded inconsistently across both treatment categories and study sites. Substrate diameter was the strongest and most consistent characteristic positively influencing the selection of foraging habitat structures for all species across all treatment categories. Other influential variables included the presence of bark beetles for red-breasted nuthatches, hairy woodpeckers, and brown creepers in control and burn-only treatment areas and tree species for brown creepers in burn-only and thin-only treatment areas. Although this study did not detect any major negative treatment response by any species, our results suggest that there is substantial variability in the reaction of this particular bird community to fuel reduction treatments and that managers may need to evaluate the effects of these treatments on a site-by-site and species-by-species basis.

Relationship of Coarse Woody Debris to Arthropod Availability for Red-Cockaded Woodpeckers and Other Bark-Foraging Birds on Loblolly Pine Boles

This study determined if short-term removal of coarse woody debris would reduce prey available to red-cockaded woodpeckers (Picoides borealis Vieillot) and other bark-foraging birds at the Savannah River Site in Aiken and Barnwell counties, SC. All coarse woody debris was removed from four 9-ha plots of mature loblolly pine (Pinus taeda L.) in 1997 and again in 1998. We sampled arthropods in coarse woody debris removal and control stands using crawl traps that captured arthropods crawling up tree boles, burlap bands wrapped around trees, and cardboard panels placed on the ground. We captured 27 orders and 172 families of arthropods in crawl traps whereas 20 arthropod orders were observed under burlap bands and cardboard panels. The most abundant insects collected from crawl traps were aphids (Homoptera: Aphididae) and ants (Hymenoptera: Formicidae). The greatest biomass was in the wood cockroaches (Blattaria: Blattellidae), caterpillars (Lepidoptera) in the Family Noctuidae, and adult weevils (Coleoptera: Curculionidae). The most common group observed underneath cardboard panels was Isoptera (termites), and the most common taxon under burlap bands was wood cockroaches. Overall, arthropod abundance and biomass captured in crawl traps was similar in control and removal plots. In contrast, we observed more arthropods under burlap bands (mean ± SE; 3,021.5 ± 348.6, P = 0.03) and cardboard panels (3,537.25 ± 432.4, P = 0.04) in plots with coarse woody debris compared with burlap bands (2325 ± 171.3) and cardboard panels (2439.75 ± 288.9) in plots where coarse woody debris was removed. Regression analyses showed that abundance beneath cardboard panels was positively correlated with abundance beneath burlap bands demonstrating the link between abundance on the ground with that on trees. Our results demonstrate that short-term removal of coarse woody debris from pine forests reduced overall arthropod availability to bark-foraging birds.

Sexual differences in the foraging behaviour of Crested Shrike-tits, Falcunculus frontatus, during winter

Sexual differences in foraging behaviour are common among bark-foraging birds. I compared the foraging behaviour of male and female Crested Shrike-tits, Falcunculus frontatus, a species well known for its bark-tearing habits, at two localities in the Northern Tablelands of New South Wales during winter. At both Wollomombi Falls and Armidale males visited dead branches and large coiled ribbons of bark more than females, while the latter concentrated on leaves, petioles and galls. There were no significant differences between the sexes in foraging heights at Wollomombi Falls but at the Armidale sites, 40 km away, females foraged significantly more at upper levels than males. Males took larger prey than females, but there were no significant sexual differences in the taxonomic composition of prey, with insect larvae comprising half of the diet, and adult beetles and spiders making up much of the remainder. This study provides further evidence of substantial variation in intersexual niche differentiation at both regional and local scales, and suggests that the availability of decorticating bark may be an important determinant of such variation in this species. While sexual dimorphism may partly account for sexual differences in the foraging niche of shrike-tits, it is possible that interference competition for food (via male dominance) and/or cultural transmission of sex-specific behaviour play a role in its maintenance.

Effects of Winter Weather on Horizontal and Vertical Use of Isolated Forest Fragments by Bark-Foraging Birds

We examined how wind and temperature below the thermoneutral zone may reduce the suitability of small, isolated woodlots for permanent resident woodland birds. Carolina Chickadees (Poecile carolinensis) and Tufted Titmice (Baeolophus bicolor) exhibited significantly reduced foraging height in the forest canopy with increasing wind strength. The horizontal area of woodlots frequented by most mixed-species flock members was significantly reduced by the combined effect of wind and temperature. In particular, all mixed-species flock members except female Downy Woodpeckers (Picoides pubescens) were found farther from windward edges of woodlots when wind speeds were higher and temperatures were lower. We conclude that chickadees and titmice may be most affected by abiotic edge effects, both sexes of White-breasted Nuthatch (Sitta carolinensis) and male Downy Woodpeckers intermediately affected, and female Downy Woodpeckers least affected. Our results suggest that effects of wind and temperature may be important to populations of bark-foraging birds inhabiting highly fragmented habitat in the Temperate Zone.

Benefits to satellite members in mixed-species foraging groups: an experimental analysis

Hypotheses proposed to explain the formation of mixed-species foraging groups have focused on both foraging and antipredation benefits. Mixed-species flocks of bark-foraging birds form during the winter in the eastern deciduous forests of North America. These flocks are composed of two parid nuclear species, tufted titmice,Baeolophus bicolor, and either Carolina or black-capped chickadees,Poecile carolinensisorP.atricapillus, and several satellite species including downy woodpeckers,Picoides pubescens, and white-breasted nuthatches,Sitta carolinensis. The parid nuclear species seem to act as flock leaders and are closely followed by the satellite species. To elucidate what advantages downy woodpeckers and white-breasted nuthatches gain by flocking with parids, we removed parids from eight Ohio woodlots isolated by surrounding agricultural fields and compared the woodpeckers and nuthatches in these woodlots to those in eight controls. We tested four predictions generated by group-foraging hypotheses: compared with controls, satellite birds in treatment woodlots should (1) forage more in microclimates that reduce metabolic costs, (2) increase their vigilance, (3) exhibit reduced nutritional condition and (4) exhibit higher mortality rates. As predicted, female downy woodpeckers in treatment woodlots tended to forage in locations that were more sheltered from wind, presumably thereby reducing metabolic costs. Treatment males and females of both species significantly increased their vigilance. Finally, in the absence of parids, male nuthatches showed significantly reduced nutritional condition according to ptilochronology analysis of feathers grown during the experimental manipulation, and tended to exhibit increased mortality

Foraging Behavior of Bark-Foraging Birds in the Sierra Nevada

Data on foraging behavior are often used for examining use of habitat and describing community structure among co-occurring species of birds using the same resource base (e.g., Johnson 1966, Eckhardt 1979, Rusterholz 1981). Differences in tree species, foliage morphology, and bark structure may influence the types of prey taken and the species of bird using the substrate (e.g., Jackson 1979, Holmes and Robinson 1981, Robinson and Holmes 1984). Elucidation of foraging behaviors and tree species preferences is important if we are to determine the role of birds in forest ecosystems, and make informed decisions regarding management of these forests. In this study we describe the use of tree species, foraging modes, and foraging substrates by a group (or guild, sensu Root 1967) of bark-foraging birds breeding in the western Sierra Nevada. A similar study on foliage insectivores was conducted previously near our study area (see Airola and Barrett 1985). The species analyzed, in order of decreasing abundance, were: Red-breasted Nuthatch (Sitta canadensis), Brown Creeper (Certhia americana), Red-breasted Sapsucker (Sphyrapicus ruber), White-headed Woodpecker (Picoides albolarvatus), Hairy Woodpecker (P. villosus), and Pileated Woodpecker (Dryocopus pileatus) (see Morrison et al. 1986). All are typical inhabitants of coniferous forests in the Sierra Nevada (Grinnell and Miller 1944). The Downy Woodpecker (Picoides pubescens) and Northern Flicker (Colaptes auratus) occurred rarely in our study area and are not analyzed herein. STUDY AREA

Competition among Bark-Foraging Birds in Central Illinois: Experimental Evidence

competition in structuring avian communities. Even if niches were arranged randomly with respect to one another, differences would exist. Observational studies can reveal very little about how avian species influence one another except when direct aggressive interactions are observed. Experimental evidence is needed to more fully understand community organization as suggested by Reynoldson and Bellamy (1974), Colwell and Fuentes (1975) and Connell (1975). Thus, observation is useful as a first step to suggest hypotheses, which then need to be tested.