An important metric for many aspects of species conservation planning and risk assessment is an estimate of total population size. For landbirds breeding in North America, Partners in Flight (PIF) generates global, continental, and regional population size estimates. These estimates are an important component of the PIF species assessment process, but have also been used by others for a range of applications. The PIF population size estimates are primarily calculated using a formula designed to extrapolate bird counts recorded by the North American Breeding Bird Survey (BBS) to regional population estimates. The extrapolation formula includes multiple assumptions and sources of uncertainty, but there were previously no attempts to quantify this uncertainty in the published population size estimates aside from a categorical data quality score. Using a Monte Carlo approach, we propagated the main sources of uncertainty arising from individual components of the model through to the final estimation of landbird population sizes. This approach results in distributions of population size estimates rather than point estimates. We found the width of uncertainty of population size estimates to be generally narrower than the order-of-magnitude distances between the population size score categories PIF uses in the species assessment process, suggesting confidence in the categorical ranking used by PIF. Our approach provides a means to identify species whose uncertainty bounds span more than one categorical rank, which was not previously possible with the data quality scores. Although there is still room for additional improvements to the estimation of avian population sizes and uncertainty, particularly with respect to replacing categorical model components with empirical estimates, our estimates of population size distributions have broader utility to a range of conservation planning and risk assessment activities relying on avian population size estimates.

Species extinctions have defined the global biodiversity crisis, but extinction begins with loss in abundance of individuals that can result in compositional and functional changes of ecosystems. Using multiple and independent monitoring networks, we report population losses across much of the North American avifauna over 48 years, including once-common species and from most biomes. Integration of range-wide population trajectories and size estimates indicates a net loss approaching 3 billion birds, or 29% of 1970 abundance. A continent-wide weather radar network also reveals a similarly steep decline in biomass passage of migrating birds over a recent 10-year period. This loss of bird abundance signals an urgent need to address threats to avert future avifaunal collapse and associated loss of ecosystem integrity, function, and services.

Understanding the susceptibility of highly mobile taxa such as migratory birds to global change requires information on geographic patterns of occurrence across the annual cycle. Neotropical migrants that breed in North America and winter in Central America occur in high concentrations on their non-breeding grounds where they spend the majority of the year and where habitat loss has been associated with population declines. Here, we use eBird data to model weekly patterns of abundance and occurrence for 21 forest passerine species that winter in Central America. We estimate species' distributional dynamics across the annual cycle, which we use to determine how species are currently associated with public protected areas and projected changes in climate and land-use. The effects of global change on the non-breeding grounds is characterized by decreasing precipitation, especially during the summer, and the conversion of forest to cropland, grassland, or peri-urban. The effects of global change on the breeding grounds are characterized by increasing winter precipitation, higher temperatures, and the conversion of forest to peri-urban. During spring and autumn migration, species are projected to encounter higher temperatures, forests that have been converted to peri-urban, and increased precipitation during spring migration. Based on current distributional dynamics, susceptibility to global change is characterized by the loss of forested habitats on the non-breeding grounds, warming temperatures during migration and on the breeding grounds, and declining summer rainfall on the non-breeding grounds. Public protected areas with low and medium protection status are more prevalent on the non-breeding grounds, suggesting that management opportunities currently exist to mitigate near-term non-breeding habitat losses. These efforts would affect more individuals of more species during a longer period of the annual cycle, which may create additional opportunities for species to respond to changes in habitat or phenology that are likely to develop under climate change.

Conservation resources are limited, and prioritizing species based on their relative vulnerability and risk of extinction is a fundamental component of conservation planning. In North America, the conservation consortium Partners in Flight (PIF) has developed and implemented a data-driven species assessment process, at global and regional scales, based on quantitative vulnerability criteria. This species assessment process has formed the biological basis for PIF's continental and regional planning and has informed the ranking and legal listing of bird species for conservation protection by state, provincial, and national agencies in Canada, the U.S., and Mexico. Because of its long time series, extensive geographic and species coverage, standardized survey methods, and prompt availability of results, the North American Breeding Bird Survey (BBS) has been an invaluable source of data, allowing PIF to assign objective vulnerability scores calibrated across more than 460 landbird species. BBS data have been most valuable for assessing long-term population trends (PT score). PIF has also developed methods for estimating population size by extrapolating from BBS abundance indices, allowing the assignment of categorical population size (PS) scores for landbird species. At regional scales, BBS relative abundance indices have allowed PIF to assess the area importance (i.e. stewardship responsibility) of each Bird Conservation Region (BCR) for each species, using measures of both relative density and percent of total population in each BCR. Besides direct applicability to assessment scores, PIF has recently used BBS trend data to create new metrics of conservation urgency (e.g., 'half-life'), as well as for setting population objectives for tracking progress toward meeting conservation goals. Future directions include integrating BBS data with other sources (e.g., eBird) to assess additional species and nonbreeding season measures, working closely with BBS coordinators to expand surveys into Mexico, and providing assessment scores at implementation-relevant scales, such as for migratory bird joint ventures.

Predation by house cats (Felis catus) is one of the largest human-related sources of mortality for wild birds in the United States and elsewhere, and has been implicated in extinctions and population declines of several species. However, relatively little is known about this topic in Canada. The objectives of this study were to provide plausible estimates for the number of birds killed by house cats in Canada, identify information that would help improve those estimates, and identify species potentially vulnerable to population impacts. In total, cats are estimated to kill between 100 and 350 million birds per year in Canada (> 95% of estimates were in this range), with the majority likely to be killed by feral cats. This range of estimates is based on surveys indicating that Canadians own about 8.5 million pet cats, a rough approximation of 1.4 to 4.2 million feral cats, and literature values of predation rates from studies conducted elsewhere. Reliability of the total kill estimate would be improved most by better knowledge of feral cat numbers and diet in Canada, though any data on birds killed by cats in Canada would be helpful. These estimates suggest that 2-7% of birds in southern Canada are killed by cats per year. Even at the low end, predation by house cats is probably the largest human-related source of bird mortality in Canada. Many species of birds are potentially vulnerable to at least local population impacts in southern Canada, by virtue of nesting or feeding on or near ground level, and habitat choices that bring them into contact with human-dominated landscapes where cats are abundant. Because cat predation is likely to remain a primary source of bird mortality in Canada for some time, this issue needs more scientific attention in Canada.

The Rusty Blackbird (Euphagus carolinus), a formerly common breeding species of boreal wetlands, has exhibited the most marked decline of any North American landbird. North American Breeding Bird Survey (BBS) trends in abundance are estimated to be -12.5%/yr over the last 40 years, which is tantamount to a >95% cumulative decline. Trends in abundance calculated from Christmas Bird Counts (CBC) for a similar period indicate a range-wide decline of -5.6%/yr. Qualitative analyses of ornithological accounts suggest the species has been declining for over a century. Several studies document range retraction in the southern boreal forest, whereas limited data suggest that abundance may be more stable in more northerly areas. The major hypotheses for the decline include degradation of boreal habitats from logging and agricultural development, mercury contamination, and wetland desiccation resulting from global warming. Other likely reasons for decline include loss or degradation of wooded wetlands of the southeastern U. S and mortality associated with abatement efforts targeting nuisance blackbirds. In addition, the patchy breeding distribution of this species may inhibit population consolidation, causing local populations to crash when reduced to low levels. Progress in understanding the causes and mechanisms for observed declines has remained limited until recently. Here we present initial attempts to understand the habitat requirements of Rusty Blackbirds and offer specific predictions associated with each of the hypotheses for decline as a way of guiding future research.

Spanning 5.9 million square km, the boreal region of North America stretches from Alaska to Newfoundland, and represents 25% of the earth's remaining intact forests. As one of the largest wilderness areas left on the globe, the boreal forest hosts a diverse and unique avian assemblage that is a valuable component of global biodiversity. We endeavor to quantify its importance to the maintenance of North American bird populations. We used a simple modeling approach to develop an assessment of the conservation value of North America's boreal region for birds and provide one of the first attempts to quantitatively describe the stewardship responsibility of a global-scale ecosystem. Results illustrate that the boreal region is critical to the well-being of many bird species. We found that nearly half (325) of all regularly occurring North American bird species occur regularly within the boreal region and that over 300 species regularly breed there. In at least 96 species, 50% or more of their entire breeding population was estimated to occur within the boreal region. The boreal region of North America represents a unique global conservation asset for birds and other forms of biodiversity that should be protected.

Greenberg, Russell; Demarest, Dean W.; Matsuoka, Steven M.; Mettke-Hofmann, Claudia; Evers, David; Hamel, Paul B.; Luscier, Jason; Powell, Luke L.; Shaw, David; Avery, Michael L.; Hobson, Keith A.; Blancher, Peter J.; and Niven, Daniel K., "Chapter nine: Understanding Declines in Rusty Blackbirds" (2011). USDA National Wildlife Research Center Staff Publications. 1294. https://digitalcommons.unl.edu/icwdm_usdanwrc/1294

An estimated 3-5 billion birds migrate south from the boreal forest ecoregions of Alaska and Canada every fall to winter across the Americas. Many of these boreal forest breeding birds become integrated into winter bird communities in Central and South America and the Caribbean, but their significance and ecological roles are only beginning to be understood. We used existing data sets on distribution and relative abundance to explore both the biogeography of wintering boreal forest migrants and their occurrence and relative abundance within wintering bird communities. We report on (1) the proportion of the wintering populations of boreal migrants estimated to occur within countries and ecological regions; (2) the comparative diversity and abundance of boreal migrants across countries and ecoregions; (3) their occurrence, relative abundance, and diversity within local bird communities; and (4) a survey of the ecological roles of wintering boreal migrants. Species richness, abundance, and density of boreal forest migrants were especially high in Mexico, Central America, and Caribbean countries. Results show that boreal forest migrants of different taxa and from different boreal forest ecoregions and taxonomic groups incorporate themselves into winter bird communities in different regions of Latin America. Our review of the literature demonstrates that boreal forest migrants are commonly the most speciose portion of the migrant community in winter bird communities, that they can numerically dominate the resident bird community, and that they play important ecological roles on their wintering grounds. Consequently, our results support the contention that boreal migrants are significant ecological components of the various communities they inhabit.

Bird population monitoring should be designed to enhance conservation of birds through informing policy decisions and management actions. Many different bird surveys are undertaken in Ontario ranging from province-wide multi-species programs such as the Ontario Breeding Bird Atlas to single-species localized surveys for Species at Risk. Although most surveys provide some useful contributions towards understanding the status of bird populations, there remain significant gaps in both species and geographic coverages, especially in the northern half of the province, and few surveys are sufficient for evaluating the specific effects of current management practices on birds. Enhancing bird monitoring in the province should first involve clearly defining, quantitatively, the information required for management, conservation and decision-making, in the context of an adaptive management cycle, and then identifying the most cost-effective monitoring programs to obtain that information. This can most effectively be implemented through a cooperative effort involving all parties with an interest in bird monitoring data including federal and provincial government agencies, environmental non-government organizations, and industry. Key words: bird population monitoring, evaluation, adaptive management, decision-making

Recent population trends of Ontario’s forest birds were assessed by integrating results across 8 bird surveys to provide an estimate of trend status for all of Ontario, and for 2 forested regions of Ontario separately. Surveys with mid- and longterm trends were relied on most extensively in this assessment. Comparison of the first and second Breeding Bird Atlases was especially important for estimating trends in northern forests, but overall reliability of status assessments in the north was considered poor due to limited coverage and significant potential for bias. Trends of most forest birds were stable or positive at the Ontario-wide scale, with trends at least as positive as forest birds elsewhere in North America, and showing more positive trends overall than birds of agricultural landscapes. Nevertheless, individual species trends ranged from large declines to large increases, and several forest birds have been added to Species at Risk lists largely because of population declines. There were few differences in trend status among forest birds grouped by habitat association or migratory guild, although all 5 aerial insectivore species have declined. Better monitoring coverage of the boreal will be needed if improved reliability of trends is desired in the near future. Key words: Ontario, forest birds, boreal forest, population trend, bird surveys, monitoring reliability

Following the example of the North American Waterfowl Management Plan, deriving numerical population estimates and conservation targets for priority landbird species is considered a desirable, if not necessary, element of the Partners in Flight planning process. Methodology for deriving such estimates remains in its infancy, however, and the use of numerical population targets remains controversial within the conservation and academic communities. By allowing a set of simple assumptions regarding species' detectability, relative abundance data from Breeding Bird Survey (BBS) routes may be extrapolated to derive first approximations of current, total species populations, both rangewide and within Bird Conservation Regions. Preliminary comparisons with independently derived abundance estimates (e.g., Breeding Bird Atlas) suggest that these population estimates are within acceptable limits of accuracy for many species. If restoring populations to early BBS levels (late 1960s) is desirable, trend data may be used to calculate the proportion of a species' population lost during this 35-year period, and an appropriate population target may be set. For example, in the Lower Great lakes/St. Lawrence Plain, BBS data indicate a current (1990-1999) population of about 14,000 Red- headed Woodpeckers (Melanerpes erythrocephalus) and a loss of >50 percent since 1966. A reasonable conservation objective, therefore, may be to double the Red-headed Woodpecker population in this region over some future time period. We encourage the use of numerical population estimates and conservation targets in implementing conservation objectives for priority landbird species, and we encourage further research that leads to refinement of our methodology and our estimates.

Following the example of the North American Waterfowl Management Plan, deriving numerical population estimates and conservation targets for priority landbird species is considered a desirable, if not necessary, element of the Partners in Flight planning process. Methodology for deriving such estimates remains in its infancy, however, and the use of numerical population targets remains controversial within the conservation and academic communities. By allowing a set of simple assumptions regarding species' detectability, relative abundance data from Breeding Bird Survey (BBS) routes may be extrapolated to derive first approximations of current, total species populations, both rangewide and within Bird Conservation Regions. Preliminary comparisons with independently derived abundance estimates (e.g., Breeding Bird Atlas) suggest that these population estimates are within acceptable limits of accuracy for many species. If restoring populations to early BBS levels (late 1960s) is desirable, trend data may be used to calculate the proportion of a species' population lost during this 35-year period, and an appropriate population target may be set. For example, in the Lower Great lakes/St. Lawrence Plain, BBS data indicate a current (1990-1999) population of about 14,000 Redheaded Woodpeckers (Melanerpes erythrocephalus) and a loss of >50 percent since 1966. A reasonable conservation objective, therefore, may be to double the Red-headed Woodpecker population in this region over some future time period. We encourage the use of numerical population estimates and conservation targets in implementing conservation objectives for priority landbird species, and we encourage further research that leads to refinement of our methodology and our estimates.

Waterfowl that eat macroinvertebrates must select among potential nesting or brood-rearing habitats that may vary in food abundance over the season. We compared the reliability of predicting the relative abundance of macroinvertebrates in boreal wetlands using either the number of macroinvertebrates collected at one sampling period, or presence or absence of fish. Wetlands with fish had fewer macroinvertebrates than fishless wetlands in all five sampling periods. Predictions of the relative abundance of invertebrates in a wetland at other sampling periods based on the presence or absence of fish, were equal to or better than predictions based on the actual number of macroinvertebrates collected during one sampling period. These results suggest that fish status of a wetland is a reliable cue to invertebrate abundance in boreal wetlands.

Thirty-one peatlands from two areas of central Ontario were sampled to assess the influence of acid deposition on peatland water chemistry. Factor analysis differentiated peatland water chemistry along three major axes of chemical variation, interpreted as axes of organic concentration, mineral concentration, and deposition influence. Water from the surface mats had a higher organic concentration than water from open pools. Mineral influence in peatland waters was reflected by higher concentrations of Ca, Mg, Na, and silica in fen pools compared to bog pools. The influence of high acid deposition in the Wanapitei study area was indicated by high concentrations of sulphate, Ni, Mn, and Cu, and lower pH compared to an area that has received less acidic deposition (Ranger). Regression analyses indicated that H+ variation in bogs could be largely explained by organic C concentration, but that sulphate concentration was also positively associated with acidity, while Ca was negatively associated with acidity.