Tom Will

The impact of free-ranging domestic cats on wildlife of the United States

Anthropogenic threats, such as collisions with man-made structures, vehicles, poisoning and predation by domestic pets, combine to kill billions of wildlife annually. Free-ranging domestic cats have been introduced globally and have contributed to multiple wildlife extinctions on islands. The magnitude of mortality they cause in mainland areas remains speculative, with large-scale estimates based on non-systematic analyses and little consideration of scientific data. Here we conduct a systematic review and quantitatively estimate mortality caused by cats in the United States. We estimate that free-ranging domestic cats kill 1.4-3.7 billion birds and 6.9-20.7 billion mammals annually. Un-owned cats, as opposed to owned pets, cause the majority of this mortality. Our findings suggest that free-ranging cats cause substantially greater wildlife mortality than previously thought and are likely the single greatest source of anthropogenic mortality for US birds and mammals. Scientifically sound conservation and policy intervention is needed to reduce this impact.

Bird–building collisions in the United States: Estimates of annual mortality and species vulnerability

ABSTRACT Building collisions, and particularly collisions with windows, are a major anthropogenic threat to birds, with rough estimates of between 100 million and 1 billion birds killed annually in the United States. However, no current U.S. estimates are based on systematic analysis of multiple data sources. We reviewed the published literature and acquired unpublished datasets to systematically quantify bird–building collision mortality and species-specific vulnerability. Based on 23 studies, we estimate that between 365 and 988 million birds (median = 599 million) are killed annually by building collisions in the U.S., with roughly 56% of mortality at low-rises, 44% at residences, and <1% at high-rises. Based on >92,000 fatality records, and after controlling for population abundance and range overlap with study sites, we identified several species that are disproportionately vulnerable to collisions at all building types. In addition, several species listed as national Birds of Conservation Concern due to their declining populations were identified to be highly vulnerable to building collisions, including Golden-winged Warbler (Vermivora chrysoptera), Painted Bunting (Passerina ciris), Canada Warbler (Cardellina canadensis), Wood Thrush (Hylocichla mustelina), Kentucky Warbler (Geothlypis formosa), and Worm-eating Warbler (Helmitheros vermivorum). The identification of these five migratory species with geographic ranges limited to eastern and central North America reflects seasonal and regional biases in the currently available building-collision data. Most sampling has occurred during migration and in the eastern U.S. Further research across seasons and in underrepresented regions is needed to reduce this bias. Nonetheless, we provide quantitative evidence to support the conclusion that building collisions are second only to feral and free-ranging pet cats, which are estimated to kill roughly four times as many birds each year, as the largest source of direct human-caused mortality for U.S. birds.

Direct human-caused mortality of birds: improving quantification of magnitude and assessment of population impact.

Hundreds of millions to greater than one billion North American birds are directly killed each year by human stressors, including collisions with man-made structures, predation by feral and pet cats, intentional and accidental poisoning, and pollution. Because these causes of mortality are increasingly abundant and because some result in large bird die-offs, they have received both increased scientific attention and general media coverage. However, quantifying bird mortality remains imprecise and methods to assess whether these losses cause important biological impacts remain underdeveloped. If local mortality studies followed rigorous design and sampling schemes, allowing comparison of data and scaling up of mortality estimates to broad regions, this could lead to improved analyses. Several analytical techniques – including hierarchical and population models – show potential for improving quantification of anthropogenic mortality of birds and inference of population-level effects. Results arising from im...

Refining Estimates of Bird Collision and Electrocution Mortality at Power Lines in the United States

Collisions and electrocutions at power lines are thought to kill large numbers of birds in the United States annually. However, existing estimates of mortality are either speculative (for electrocution) or based on extrapolation of results from one study to all U.S. power lines (for collision). Because national-scale estimates of mortality and comparisons among threats are likely to be used for prioritizing policy and management strategies and for identifying major research needs, these estimates should be based on systematic and transparent assessment of rigorously collected data. We conducted a quantitative review that incorporated data from 14 studies meeting our inclusion criteria to estimate that between 12 and 64 million birds are killed each year at U.S. power lines, with between 8 and 57 million birds killed by collision and between 0.9 and 11.6 million birds killed by electrocution. Sensitivity analyses indicate that the majority of uncertainty in our estimates arises from variation in mortality rates across studies; this variation is due in part to the small sample of rigorously conducted studies that can be used to estimate mortality. Little information is available to quantify species-specific vulnerability to mortality at power lines; the available literature over-represents particular bird groups and habitats, and most studies only sample and present data for one or a few species. Furthermore, additional research is needed to clarify whether, to what degree, and in what regions populations of different bird species are affected by power line-related mortality. Nonetheless, our data-driven analysis suggests that the amount of bird mortality at U.S. power lines is substantial and that conservation management and policy is necessary to reduce this mortality.

Application of Models to Conservation Planning for Terrestrial Birds in North America

Partners in Flight (PIF), a public–private coalition for the conservation of land birds, has developed one of four international bird conservation plans recognized under the auspices of the North American Bird Conservation Initiative (NABCI). Partners in Flight prioritized species most in need of conservation attention and set range-wide population goals for 448 species of terrestrial birds. Partnerships are now tasked with developing spatially explicit estimates of the distribution, and abundance of priority species across large ecoregions and identifying habitat acreages needed to support populations at prescribed levels. The PIF Five Elements process of conservation design identifies five steps needed to implement all bird conservation at the ecoregional scale. Habitat assessment and landscape characterization describe the current amounts of different habitat types and summarize patch characteristics, and landscape configurations that define the ability of a landscape to sustain healthy bird populations and are a valuable first step to describing the planning area before pursuing more complex species-specific models. Spatially linked database models, landscape-scale habitat suitability models, and statistical models are viable alternatives for predicting habitat suitability or bird abundance across large planning areas to help assess conservation opportunities, design landscapes to meet population objectives, and monitor change in habitat suitability or bird numbers over time.

Correction to: Responding to misinformation and criticisms regarding United States cat predation estimates

The article Responding to misinformation and criticisms regarding United States cat predation estimates, written by Scott R. Loss, Tom Will, Travis Longcore, Peter P. Marra was originally published electronically on the publisher’s Internet portal (currently SpringerLink) on 13 July 2018 without open access.

Responding to misinformation and criticisms regarding United States cat predation estimates

Misinformation (or denialism), the disingenuous assertion of information contradicting overwhelming scientific consensus, increasingly poses a challenge for invasion biology. The issue of free-ranging domestic cats (Felis catus) provides an example of this misinformation: overwhelming consensus shows that cats are invasive species that impact wildlife and human health yet free-ranging cat advocates propagate misinformation about such impacts to support policies keeping cats on the landscape. These advocates also attempt to discredit peer-reviewed scientific research on cat impacts, as exemplified by the response to a high-profile paper estimating cats annually kill billions of U.S. birds and mammals (Loss et al. in Nat Commun 4:1396, 2013). Although favorably received by scientific and invasive species management communities, an effort was launched to discredit this paper by criticizing its methods, including a report commissioned by a feral cat advocacy group and a post by a feral cat blogger. These same organizations and individuals have made similar criticisms at scientific conferences and policy roundtables. Given the realized effects of this campaign in influencing invasive species policy, we here respond to these criticisms and show they are characterized by numerous errors and misrepresentations. We conclude that the criticisms are part of the broader campaign to fabricate doubt about outdoor cat impacts and stymie policies favoring removal of cats from the landscape. Because misinformation surrounding cats is emblematic of the broader issue of misinformation and denialism, this response will not only facilitate evidence-based policy for managing cats but also stimulate research and discussion into causes and impacts of misinformation in invasion biology.