Landscape-level responses of boreal forest bird communities to anthropogenic and natural disturbance

In an attempt to manage values other than timber production, forestry companies have sought a new paradigm to manage forest resources. Based on the hypothesis that wildlife in the boreal forest has adapted to habitat structures created by natural disturbances, some forest harvests have been modified to approximate patterns left after natural disturbance. Attempts at approximating natural disturbance have included retention of patches of live trees within cutblock boundaries, cutting to natural stand boundaries and application of harvest plans with spatio-temporally aggregated cutblocks (single-pass harvests). Single-pass harvesting is a recent attempt to better approximate natural disturbance in the boreal and has not been evaluated for its potential to sustain wildlife. I therefore contrasted residual patch pattern and composition, as well as landscape-scale avian abundance and composition in 1) single-pass; 2) multi-pass; and 3) salvage logged post-fire harvests, and contrasted these with unsalvaged post-fire sites. Post-fire sites were used to define the Natural Range of Variation (NRV). Seventy-two plots (12 post-fire, 15 post-salvage harvest, 16 single-pass harvest, and 29 multi-pass harvest) were surveyed for avian community composition and abundance one to five years post disturbance. I contrasted the composition of remaining live forest stands at the landscape-scale and in residual patches by pairwise comparison of pre- and post-disturbance composition. At the landscape-scale, non-metric mutlidimensional scaling suggested post-disturbance landscape composition of post-fire and salvage-logged plots was similar to pre-disturbance landscape composition, with a tendency toward greater survival of hardwoods and lower survival of jack pine (Pinus banksiana) or black spruce (Picea mariana). However, harvesting of hardwoods and mixedwood stand types in single and multi-pass harvests led to landscapes with more bog and swamp habitats. Comparison of residual patch composition with pre-disturbance composition was made using blocked multi-response permutation procedures. Post-fire plots (i.e. NRV) had residual patches that were representative of pre-disturbance composition, but with slightly more hardwoods and less black spruce/jack pine than expected by chance. All harvested treatments had similar biases among residuals to those left by fire, except that multi-pass harvests tended to leave less mixedwood habitat than expected. Multi-pass harvests also had less area in residual patches, and patches were smaller, more isolated and less complex in shape. Single-pass harvests had residual patches that were more representative of the size, shape, complexity, and change in composition seen post-fire. Multi-pass harvests only had 14% of the residual patch area in patches at least 5 ha in size, whereas this proportion was higher in fire (83%), salvage-logged areas (42%), and single-pass harvests (57%). Old-growth associated species might only persist in patches 5 ha or larger, and so multi-pass harvesting may have negative consequences for these forest birds.Redundancy analysis indicated that bird communities differed from the NRV in all harvest treatments. However, single-pass harvests provided a slightly better fit to NRV than did multi-pass harvesting. Community similarity was influenced by non-linear responses to area harvested, residual retention, residual composition and pre-disturbance forest composition. An optimization routine was used to select harvest characteristics that would maximize community similarity to NRV. Optimization suggested that community similarity to NRV can be maximized by using single-pass harvests over multi-pass harvests, harvesting 66-88% of of a planning unit, and retaining 5-19% of the harvest area as live residual patches.My results suggest that single-pass harvesting may be ecologically more sustainable than multi-pass harvests. Future studies are required to determine whether both harvesting treatments converge with NRV through time. Greater overlap of salvage-logged avian communities with NRV suggests that experimentation with prescribed fire as a post-harvest treatment may be the best method to bring harvests ecologically closer to NRV, and highlights the need to conserve early post-fire habitats

Estimated Avian Nest Loss Associated with Oil and Gas Exploration and Extraction in the Western Canadian Sedimentary Basin

Annual mortality within bird populations can be attributed to numerous sources; however, the extent to which anthropogenic sources of mortality contribute to avian demography is largely unknown. Quantifying the relative magnitude of human-related avian mortality could inform conservation efforts, particularly if multiple sources of human-related mortality can be contrasted. The unintentional destruction of nests and their contents by industrial activities conducted during the breeding season of resident and migratory birds presumably leads to one such source of human-caused avian mortality. As part of a broader effort to quantify major sources of human-related avian mortality, we estimated the magnitude of nest loss resulting from the terrestrial oil and gas sector in Canada, including: (1) seismic exploration, (2) pipeline right-of-way clearing, (3) well pad clearing, and (4) oil sands mining within the Western Canadian Sedimentary Basin (WCSB). We estimated nest losses as the product of estimated nest densities, the area disturbed annually, and the proportion of annual disturbance presumed to occur during the breeding season. The estimated number of nests disturbed annually by all oil and gas sectors combined ranged between 11,840 - 60,380. Interannual variation in exploration and extraction, and uncertainty in nest densities and the proportion of the disturbances occurring during the breeding season contributed to the variation. Accounting for natural mortality suggests an estimated loss of 10,200 - 41,150 (range) potential recruits into the migratory bird population in a subsequent year. Although nest destruction is only one small component of the potential impacts of the oil and gas industry upon avian populations, these estimates establish a baseline for comparison with other sources of human-caused avian mortality. Models are now needed to compare nest losses against the legacy effects of oil and gas sector habitat disturbances and associated cumulative effects so that mitigation efforts can be prioritized

An Estimate of Nest Loss in Canada Due to Industrial Forestry Operations

Annual loss of nests by industrial (nonwoodlot) forest harvesting in Canada was estimated using two avian point-count data sources: (1) the Boreal Avian Monitoring Project (BAM) dataset for provinces operating in this biome and (2) available data summarized for the major (nonboreal) forest regions of British Columbia. Accounting for uncertainty in the proportion of harvest occurring during the breeding season and in avian nesting densities, our estimate ranges from 616 thousand to 2.09 million nests. Estimates of the impact on numbers of individuals recruited into the adult breeding population were made based on the application of survivorship estimates at various stages of the life cycle. Future improvements to this estimate are expected as better and more extensive avian breeding pair density estimates become available and as provincial forestry statistics become more refined, spatially and temporally. The effect of incidental take due to forestry is not uniform and is disproportionately centered in the southern boreal. Those species whose ranges occur primarily in these regions are most at risk for industrial forestry in general and for incidental take in particular. Refinements to the nest loss estimate for industrial forestry in Canada will be achieved primarily through the provision of more accurate estimates of the area of forest harvested annually during the breeding season stratified by forest type and Bird Conservation Region (BCR). A better understanding of survivorship among life-history stages for forest birds would also allow for better modeling of the effect of nest loss on adult recruitment. Finally, models are needed to project legacy effects of forest harvesting on avian populations that take into account forest succession and accompanying cumulative effects of landscape change

Multi-Isotopic (δ\u3csup\u3e2\u3c/sup\u3eH, δ\u3csup\u3e13\u3c/sup\u3eC, δ\u3csup\u3e15\u3c/sup\u3eN) Tracing of Molt Origin for Red-Winged Blackbirds Associated with Agro-Ecosystems

We analyzed stable-hydrogen (δ2H), carbon (δ13C) and nitrogen (δ15N) isotope ratios in feathers to better understand the molt origin and food habits of Red-winged Blackbirds (Agelaius phoeniceus) near sunflower production in the Upper Midwest and rice production in the Mid-South of the United States. Outer primary feathers were used from 661 after-second-year (ASY) male blackbirds collected in Minnesota, Montana, North Dakota and South Dakota (spring collection), and Arkansas, Louisiana, Mississippi, Missouri and Texas (winter collection). The best-fit model indicated that the combination of feather δ2H, δ13C and δ15N best predicted the state of sample collections and thus supported the use of this approach for tracing molt origins in Red-winged Blackbirds. When considering only birds collected in spring, 56% of birds were classified to their collection state on the basis of δ2H and δ13C alone. We then developed feather isoscapes for δ13C based upon these data and for δ2H based upon continental patterns of δ2H in precipitation. We used 81 birds collected at the ten independent sites for model validation. The spatially-explicit assignment of these 81 birds to the δ2H isoscape resulted in relatively high rates (~77%) of accurate assignment to collection states. We also modeled the spatial extent of C3 (e.g. rice, sunflower) and C4 (corn, millet, sorghum) agricultural crops grown throughout the Upper Midwest and Mid- South United States to predict the relative use of C3- versus C4-based foodwebs among sampled blackbirds. Estimates of C3 inputs to diet ranged from 50% in Arkansas to 27% in Minnesota. As a novel contribution to blackbird conservation and management, we demonstrate how such feather isoscapes can be used to predict the molt origin and interstate movements of migratory blackbirds for subsequent investigations of breeding biology (e.g. sex-specific philopatry), agricultural depredation, feeding ecology, physiology of migration and sensitivity to environmental change

An evaluation of isotopic (d2H) methods to provide estimates of avian breeding and natal dispersal

Natal and breeding dispersal represents an important component of animal demography and metapopulation theory. This phenomenon also has implications for conservation and management because understanding movements of individuals potentially allows the identification of key habitats that may be acting as population sources or sinks. Intrinsic markers such as stable isotope abundance in tissues that can be associated with provenance can provide a coarse but pragmatic solution to understanding such movements. Different methodologies have been proposed to quantify natal and breeding dispersal by using stable isotope analyses of keratinous tissues (hair, feathers), each of them with their own advantages and limitations. Here, we compared results provided by four different methods to estimate dispersal (three already published and one novel) in animals using stable isotope measurements. We used a single large dataset of feather δ2H values from golden-winged warblers (Vermivora chrysoptera) representing five different populations breeding in North America to compare model results. We propose one method as the most adequately supported by data, and we used this method to demonstrate how biological factors explaining dispersal status can be identified and geographical origins of immigrants inferred. Our results point to a generalized methodological approach to using stable isotope data to study immigration and dispersal in birds and other animals

Linking Hydrogen (δ2H) Isotopes in Feathers and Precipitation: Sources of Variance and Consequences for Assignment to Isoscapes

Background: Tracking small migrant organisms worldwide has been hampered by technological and recovery limitations and sampling bias inherent in exogenous markers. Naturally occurring stable isotopes of H (d 2 H) in feathers provide an alternative intrinsic marker of animal origin due to the predictable spatial linkage to underlying hydrologically driven flow of H isotopes into foodwebs. This approach can assess the likelihood that a migrant animal originated from a given location(s) within a continent but requires a robust algorithm linking H isotopes in tissues of interest to an appropriate hydrological isotopic spatio-temporal pattern, such as weighted-annual rainfall. However, a number of factors contribute to or alter expected isotopic patterns in animals. We present results of an extensive investigation into taxonomic and environmental factors influencing feather d 2 H patterns across North America. Principal Findings: Stable isotope data were measured from 544 feathers from 40 species and 140 known locations. For d 2 H, the most parsimonious model explaining 83 % of the isotopic variance was found with amount-weighted growingseason precipitation d 2 H, foraging substrate and migratory strategy. Conclusions/Significance: This extensive H isotopic analysis of known-origin feathers of songbirds in North America and elsewhere reconfirmed the strong coupling between tissue d 2 H and global hydrologic d 2 H patterns, and accounting for variance associated with foraging substrate and migratory strategy, can be used in conservation and research for th

Positive relationships between association strength and phenotypic similarity characterize the assembly of mixed-species bird flocks worldwide

Competition theory predicts that local communities should consist of species that are more dissimilar than expected by chance. We find a strikingly different pattern in a multicontinent data set (55 presence-absence matrices from 24 locations) on the composition of mixed-species bird flocks, which are important sub-units of local bird communities the world over. By using null models and randomization tests followed by meta-analysis, we find the association strengths of species in flocks to be strongly related to similarity in body size and foraging behavior and higher for congeneric compared with noncongeneric species pairs. Given the local spatial scales of our individual analyses, differences in the habitat preferences of species are unlikely to have caused these association patterns; the patterns observed are most likely the outcome of species interactions. Extending group-living and social-information-use theory to a heterospecific context, we discuss potential behavioral mechanisms that lead to positive interactions among similar species in flocks, as well as ways in which competition costs are reduced. Our findings highlight the need to consider positive interactions along with competition when seeking to explain community assembly

Recipient mucosal-associated invariant T cells control GVHD within the colon

Mucosal-associated invariant T (MAIT) cells are a unique innate-like T cell subset that responds to a wide array of bacteria and yeast through recognition of riboflavin metabolites presented by the MHC class I–like molecule MR1. Here, we demonstrate using MR1 tetramers that recipient MAIT cells are present in small but definable numbers in graft-versus-host disease (GVHD) target organs and protect from acute GVHD in the colon following bone marrow transplantation (BMT). Consistent with their preferential juxtaposition to microbial signals in the colon, recipient MAIT cells generate large amounts of IL-17A, promote gastrointestinal tract integrity, and limit the donor alloantigen presentation that in turn drives donor Th1 and Th17 expansion specifically in the colon after BMT. Allogeneic BMT recipients deficient in IL-17A also develop accelerated GVHD, suggesting MAIT cells likely regulate GVHD, at least in part, by the generation of this cytokine. Indeed, analysis of stool microbiota and colon tissue from IL-17A–/– and MR1–/– mice identified analogous shifts in microbiome operational taxonomic units (OTU) and mediators of barrier integrity that appear to represent pathways controlled by similar, IL-17A–dependent mechanisms. Thus, MAIT cells act to control barrier function to attenuate pathogenic T cell responses in the colon and, given their very high frequency in humans, likely represent an important population in clinical BMT

Disease Dynamics and Bird Migration—Linking Mallards Anas platyrhynchos and Subtype Diversity of the Influenza A Virus in Time and Space

The mallard Anas platyrhynchos is a reservoir species for influenza A virus in the northern hemisphere, with particularly high prevalence rates prior to as well as during its prolonged autumn migration. It has been proposed that the virus is brought from the breeding grounds and transmitted to conspecifics during subsequent staging during migration, and so a better understanding of the natal origin of staging ducks is vital to deciphering the dynamics of viral movement pathways. Ottenby is an important stopover site in southeast Sweden almost halfway downstream in the major Northwest European flyway, and is used by millions of waterfowl each year. Here, mallards were captured and sampled for influenza A virus infection, and positive samples were subtyped in order to study possible links to the natal area, which were determined by a novel approach combining banding recovery data and isotopic measurements (δ2H) of feathers grown on breeding grounds. Geographic assignments showed that the core natal areas of studied mallards were in Estonia, southern and central Finland, and northwestern Russia. This study demonstrates a clear temporal succession of latitudes of natal origin during the course of autumn migration. We also demonstrate a corresponding and concomitant shift in virus subtypes. Acknowledging that these two different patterns were based in part upon different data, a likely interpretation worth further testing is that the early arriving birds with more proximate origins have different influenza A subtypes than the more distantly originating late autumn birds. If true, this knowledge would allow novel insight into the origins and transmission of the influenza A virus among migratory hosts previously unavailable through conventional approaches