John C. Withey

Effects of Tagging and Location Error in Wildlife Radiotelemetry Studies

Publisher Summary Important benefits of radio tagging of animals are the accuracy, precision, and completeness of resulting observations. Accurate inference in radiotelemetry depends on unbiased observations. Remotely gathered location estimates differ in precision and accuracy from visual observations. Moreover, behavior is influenced by the act of tagging or tracking. A fundamental assumption in wildlife studies reliant on radiotelemetry is that radio-tagged animals are “moving through the environment, responding to stimuli, and behaving in a manner similar to noninstrumented animals.” This chapter summarizes the effects of transmitters on wildlife, makes recommendations for studying and minimizing effects, and investigates the magnitude and implications of location error resulting from conventional transmitters. It also discusses the importance of conducting site-specific beacon tests to better understand bias and error in specific studies. The chapter encourages all researchers using radiotelemetry to conduct two studies before beginning with the collection of data on actual study subjects. First, the effects of the transmitter and method of transmitter attachment on the study species must be studied. Second, if animal locations are to be estimated remotely, a thorough beacon study in the actual field site under expected field conditions must be conducted. The goal of a beacon study is to produce a spatially explicit map of tracking accuracy for the study area and to quantify the precision and accuracy of the telemetry system.

Lasting recognition of threatening people by wild American crows

While many domestic and laboratory animals recognize familiar humans, such ability in wild animals is only anecdotally known. Here we demonstrate experimentally that a cognitively advanced, social bird, the American crow, Corvus brachyrhynchos, quickly and accurately learns to recognize the face of a dangerous person and continues to do so for at least 2.7 years. We exposed wild crows to a novel ‘dangerous face’ by wearing a unique face mask as we trapped, banded and released 7–15 birds at five sites near Seattle, WA, U.S.A. After trapping, crows consistently used harsh vocalizations to scold and mob people of different sizes, ages, genders and walking gaits who wore the dangerous mask, even when they were in crowds. In contrast, prior to trapping, few crows scolded people who wore the dangerous mask. Furthermore, after trapping, few crows scolded trappers who wore no mask or who wore a mask that had not been worn during trapping. In a fully crossed, balanced experiment in which each site had a unique trapping (dangerous) mask and five neutral masks, crows scolded and mobbed a mask more when it was the dangerous mask at that site than when it was a neutral mask at another site. When simultaneously presented with a person in the dangerous mask and a person in the neutral mask, crows typically ignored the neutral mask and followed and scolded the person wearing the dangerous mask. Risky, aggressive scolding by crows was sensitive to variable costs across study sites; aggression was less where people persecuted crows most. We suggest that conditioned and observational learning of specific threats may allow local bird behaviours to include aversions to individual people.

Economic-based projections of future land use in the conterminous United States under alternative policy scenarios

Land-use change significantly contributes to biodiversity loss, invasive species spread, changes in biogeochemical cycles, and the loss of ecosystem services. Planning for a sustainable future requires a thorough understanding of expected land use at the fine spatial scales relevant for modeling many ecological processes and at dimensions appropriate for regional or national-level policy making. Our goal was to construct and parameterize an econometric model of land-use change to project future land use to the year 2051 at a fine spatial scale across the conterminous United States under several alternative land-use policy scenarios. We parameterized the econometric model of land-use change with the National Resource Inventory (NRI) 1992 and 1997 land-use data for 844 000 sample points. Land-use transitions were estimated for five land-use classes (cropland, pasture, range, forest, and urban). We predicted land-use change under four scenarios: business-as-usual, afforestation, removal of agricultural subsidies, and increased urban rents. Our results for the business-as-usual scenario showed widespread changes in land use, affecting 36% of the land area of the conterminous United States, with large increases in urban land (79%) and forest (7%), and declines in cropland (-16%) and pasture (-13%). Areas with particularly high rates of land-use change included the larger Chicago area, parts of the Pacific Northwest, and the Central Valley of California. However, while land-use change was substantial, differences in results among the four scenarios were relatively minor. The only scenario that was markedly different was the afforestation scenario, which resulted in an increase of forest area that was twice as high as the business-as-usual scenario. Land-use policies can affect trends, but only so much. The basic economic and demographic factors shaping land-use changes in the United States are powerful, and even fairly dramatic policy changes, showed only moderate deviations from the business-as-usual scenario. Given the magnitude of predicted land-use change, any attempts to identify a sustainable future or to predict the effects of climate change will have to take likely land-use changes into account. Econometric models that can simulate land-use change for broad areas with fine resolution are necessary to predict trends in ecosystem service provision and biodiversity persistence.

Climatic and landscape correlates for potential West Nile virus mosquito vectors in the Seattle region

ABSTRACT Climatic and landscape patterns have been associated with both relative mosquito abundance and transmission of mosquitoborne illnesses in many parts of the world, especially warm and tropical climes. To determine if temperature, precipitation, or degree of urbanization were similarly important in the number of potential mosquito vectors for West Nile virus in the moderately temperate climate of western Washington, mosquitoes were collected using CDC carbondioxide/light traps set throughout the Seattle region during the summers of 2003 and 2004. The type and abundance of recovered species were compared to ecological correlates. Temperature and mosquito abundance were positively correlated, while precipitation was not strongly correlated with numbers of mosquitoes. Potential WNV mosquito vectors were most abundant in urban and suburban sites, including sites near communal roosts of American crows (Corvus brachyrhynchos). Exurban sites had the greatest vector species diversity, and Culex pipiens was the most abundant species throughout the region.

DISPERSAL BY JUVENILE AMERICAN CROWS (CORVUS BRACHYRHYNCHOS) INFLUENCES POPULATION DYNAMICS ACROSS A GRADIENT OF URBANIZATION

Abstract American Crow (Corvus brachyrhynchos) populations are increasing across North America, often at high rates in urban areas. A monthly survey of American Crows in the Seattle Christmas Bird Count (CBC) circle suggested that winter counts reflected American Crow abundance at other times of the year, so we used CBC results for American Crows as a measure of population trend. In the Seattle area, local survival and fecundity appear unable to account for exponential population growth. We tested the hypothesis that juvenile dispersal from outlying suburban and exurban areas contributes to growth in the urban population by radiotagging 56 juveniles 5–46 km away from the central business district of Seattle and tracking their movements. Juvenile American Crows’ centers of activity were 0.2–22.2 km away from their natal territory during the first 3–12 months after fledging. An estimated 45% survived one year. Movements of dispersing American Crows varied in their consistency with simulated random-walk paths; the data suggested that, at the population level, American Crows were not drawn into urban areas, though some individuals may have been. Movements of dispersers produced a net influx into the city, because of greater reproductive success outside the city than in it. Simulations of urban population growth that included immigrants and emigrants accounted for most of the observed growth, which indicates the importance of distant suburban and exurban breeding pairs to urban population dynamics. La Dispersión de Juveniles de Corvus brachyrhynchos Influencia la Dinámica Poblacional a lo Largo de un Gradiente de Urbanización

An integrated approach to evaluating urban forest functionality

Despite the fact that forests in urban areas play multiple and often conflicting roles, research and management efforts are typically geared towards a single role or purpose. Urban ecology addresses this multiplicity of function by viewing human and natural systems in urban areas not as separate entities, but as interacting components of an integrated whole. We present an interdisciplinary approach for evaluating the different ways that forests are often valued: economically, socially, and ecologically in residential areas of King County, WA. Economic function is measured as the change in housing prices attributed to location on the gradient, using a hedonic price model. For social function we use a survey to measure (1) residents’ use of parks and forests, and (2) satisfaction with their neighborhoods. We measure ecological function as songbird species richness, using bird survey data. Overlaying the curves of economic, social, and ecological function on the common axis of our urban gradient allows for relationships and tradeoffs to be qualitatively evaluated. Each function responds differently to the gradient. The housing price response is strongest at high and low levels of urbanization, with positive premiums in both areas. Satisfaction with neighborhood attributes decreases with increasing urbanization, while the likelihood of mentioning ‘parks’ as an important element of a resident’s neighborhood increases. Songbird richness peaks in less-developed areas. Evaluating the different functions together is an important step in recognizing and understanding the multiple roles forested areas play.