Ronald P. Larkin

Ecological impacts of wind energy development on bats: questions, research needs, and hypotheses

At a time of growing concern over the rising costs and long-term environmental impacts of the use of fossil fuels and nuclear energy, wind energy has become an increasingly important sector of the electrical power industry, largely because it has been promoted as being emission-free and is supported by government subsidies and tax credits. However, large numbers of bats are killed at utility-scale wind energy facilities, especially along forested ridgetops in the eastern United States. These fatalities raise important concerns about cumulative impacts of proposed wind energy development on bat populations. This paper summarizes evidence of bat fatalities at wind energy facilities in the US, makes projections of cumulative fatalities of bats in the Mid-Atlantic Highlands, identifies research needs, and proposes hypotheses to better inform researchers, developers, decision makers, and other stakeholders, and to help minimize adverse effects of wind energy development.

Assessing Impacts of Wind-Energy Development on Nocturnally Active Birds and Bats: A Guidance Document

Abstract Our purpose is to provide researchers, consultants, decision-makers, and other stakeholders with guidance to methods and metrics for investigating nocturnally active birds and bats in relation to utility-scale wind-energy development. The primary objectives of such studies are to 1) assess potential impacts on resident and migratory species, 2) quantify fatality rates on resident and migratory populations, 3) determine the causes of bird and bat fatalities, and 4) develop, assess, and implement methods for reducing risks to bird and bat populations and their habitats. We describe methods and tools and their uses, discuss limitations, assumptions, and data interpretation, present case studies and examples, and offer suggestions for improving studies on nocturnally active birds and bats in relation to wind-energy development. We suggest best practices for research and monitoring studies using selected methods and metrics, but this is not intended as cookbook. We caution that each proposed and executed study will be different, and that decisions about which methods and metrics to use will depend upon several considerations, including study objectives, expected and realized risks to bird and bat populations, as well as budgetary and logistical considerations. Developed to complement and extend the existing National Wind Coordinating Committee document “Methods and Metrics for Assessing Impacts of Wind Energy Facilities on Wildlife” (Anderson et al. 1999), we provide information that stakeholders can use to aid in evaluating potential and actual impacts of wind power development on nocturnally active birds and bats. We hope that decision-makers will find these guidelines helpful as they assemble information needed to support the permitting process, and that the public will use this guidance document as they participate in the permitting processes. We further hope that the wind industry will find valuable guidance from this document when 1) complying with data requirements as a part of the permitting process, 2) evaluating sites for potential development, 3) assessing impacts of operational wind-energy facilities, and 4) mitigating local and cumulative impacts on nocturnally active birds and bats.

Flight speeds observed with radar, a correction: slow “birds” are insects

SummaryBased upon new data and re-analysis of previous data, some results concerning migration of “birds” at night are now attributed to insects. In particular, slowly flying radar targets over land (Larkin and Thompson 1980) and, by analogy, over the ocean (Larkin et al. 1979) are shown to lack wing beat patterns of birds and the appearance of birds when viewed with a radar-controlled high-power telescope and spotlamp. The insect targets overlap with birds in the amount of radar echo returned, are abundant in warmer months, and fly even in March and November in temperate North America. Other previous results are largely substantiated; however, a previous report (Larkin 1980) that migrating birds can detect the wind direction over the ocean is not substantiated.

Partly cloudy with a chance of migration: Weather, radars, and aeroecology

Aeroecology is an emerging scientific discipline that integrates atmospheric science, Earth science, geography, ecology, computer science, computational biology, and engineering to further the understanding of biological patterns and processes. The unifying concept underlying this new transdisciplinary field of study is a focus on the planetary boundary layer and lower free atmosphere (i.e., the aerosphere), and the diversity of airborne organisms that inhabit and depend on the aerosphere for their existence. Here, we focus on the role of radars and radar networks in aeroecological studies. Radar systems scanning the atmosphere are primarily used to monitor weather conditions and track the location and movements of aircraft. However, radar echoes regularly contain signals from other sources, such as airborne birds, bats, and arthropods. We briefly discuss how radar observations can be and have been used to study a variety of airborne organisms and examine some of the many potential benefits likely to aris...

Nocturnal flight calls of Dickcissels and Doppler radar echoes over south Texas in spring

Abstract Recording flight calls of migrating birds with one or more microphones provides information on identity of some birds aloft over each microphone and on the time course of their migration, or at least their calling. Doppler surveillance radar observations, on the other hand, provide information on the numbers and sizes of flying animals aloft over a wide area and on speeds, directions of travel, and height in favorable circumstances. Comparison of calls of Dickcissels (Spiza americana) from sound recording stations across south Texas in spring with images from the KBRO NEXRAD (WSR-88D) radar operated by the National Weather Service showed a surprising correspondence between the two kinds of data, both temporally over the course of a night and geographically across about 115 km. Highly significant correlations between call rates and radar reflectivity were obtained for seven sound recording stations but not for two other stations that were too distant for the radar to receive echoes from birds migrating at the normal heights for passerines.

Radar Observations of Bird Migration over the Western North Atlantic Ocean

Summary1.During two fall migration seasons, a large number of flying targets were tracked by a radar mounted on an oceanographic research vessel. Obervations were made in September and October in a region extending from the New England coast to the area south and east of Bermuda (Figs. 1 and 3). Accurate local wind measurements were made at short intervals during the observations.2.Evidence was obtained that many of the targets were birds engaging in migration between coastal North America and the neotropics. Such birds often appeared in discrete ‘waves’ associated with cold fronts passing the North American coast. Distant from land, long periods occurred between ‘waves’ when no targets were observed.3.Other targets, which were probably also migrating birds, flew in directions which were difficult to explain, or flew at speeds relative to the air which were lower than seem consistent with the energetic requirements of long-range flight. Extrapolations of the possible flight paths of such birds (Figs. 8–10) suggested that birds, even some of those flying at the higher speeds, may take several days in attempting to cross the Western North Atlantic.4.Birds appeared to fly at higher altitudes during the day than at night, perhaps to allow temperature regulation without evaporative water loss.5.The results are discussed in relation to previous laboratory measurements of caloric expenditures and flight speeds of birds in wind tunnels, possible use of structure in the atmosphere by small migrants, and the selection pressures which might play a role in the phenomenon of long migrations over water.

Insects Observed Using Dual-Polarization Radar

Abstract Two radars of different characteristics were used on a clear night in early summer to investigate the nature of the clear air echoes. It is deduced that most of the echoes on this evening were due to insects rather than atmospheric turbulence or birds 1) by the magnitude of differential reflectivity; 2) by the lack of characteristic bird wing beat signature; 3) by the inability to recognize birds using a collimated spotlight; 4) by the strength of the signal return; and 5) by the migration schedules of birds in central Illinois. The CHILL radar measured differential reflectivity, and showed that, at low levels, the insects were flying with a common heading. At higher levels, the differential reflectivity showed no preferential heading of the insects, but was still greater than for atmospheric turbulence. It is proposed that differential reflectivity provides a means of differentiating between echoes due to atmospheric turbulence and insects.

Evidence for widely dispersed birds migrating together at night

Lore and indirect evidence from previous studies suggest that nocturnally migrating vertebrates (perhaps bats but mostly birds) sometimes fly widely dispersed from each other, but in flocks. The observations include stationary and scanning radars, recordings of flight calls, and watching the moon with telescopes. Direct observations of such flocks have been lacking. This article presents data from novel tracking of nocturnal aggregations of radar targets. Statistical analysis of straight, detailed flight paths supported the hypothesis that vertebrates, almost certainly birds, flying within about 200-300 m of each other fly parallel (in the same direction at the same speed) more often than do vertebrates flying farther apart. This inference was strengthened by comparisons with a partial control for wind and for small-scale atmospheric structure: namely, small nocturnal arthropods tracked by the identical method did not fly parallel. Radar data also indicated that birds flying together may have similar wing beats, suggesting taxonomic similarity between birds flying parallel. Possible functions include not only mutual benefits on the ground during migratory stopover (habitat use, avoidance of predators, and social feeding) but also in-flight sharing of information about orientation.

Transoceanic bird migration: Evidence for detection of wind direction

SummaryFurther analysis of radar tracks of migrating birds over the Atlantic Ocean (Larkin et al., 1979) indicates that birds sometimes fly at lower air speeds when winds are in the direction of flight than in crosswinds or head winds. The birds are able to estimate wind direction over open ocean by a mechanism which is presently open to speculation.

Wingbeat frequency of two Catharus thrushes during nocturnal migration

Radio transmitters emitting continuous signals were mounted on Swainsoffs Thrushes (Catharus ustulatus) and Veerys (C.fuscescens) during two spring migration seasons. Wingbeats modulated the continuous signals, and signal-processing techniques permitted examination of wingbeat frequency (WBF) during nocturnal migration. Distinct takeoff and cruising-flight phases were evident in both species. As birds climbed during the takeoff phase (which usually lasted about 15 min), WBF typically declined exponentially by at least 4 Hz. Median cruising WBF from seven flights varied from 9.2 to 10.9 Hz, values similar to those calculated from published equations predicting WBF based on flight mechanics. Cruis- ing WBF typically varied slowly and irregularly throughout all flights by about 1 Hz. During takeoff and cruising flights, all birds flapped continuously, showing no evidence of the flap- coasting pattern common in passerine migrants previously studied with other techniques such as radar. All five birds exhibited departure times, course directions, and flight distances typical for migrating thrushes. Received 23 May 1997, accepted 11 November 1997.