V. Alistair Drake

What Is Migration

ABSTRACT We outline a general scheme for migration that applies across taxa, incorporates the several varieties of migration, and includes all levels of biological organization, from genes to populations. The scheme links the environment, pathways, traits, and genes, and highlights the selective forces that shape and maintain migratory adaptation. We endorse an individual-based behavioral definition of migration that allows an objective distinction between migration and other forms of movement. We recognize migration as an adaptation to resources that fluctuate spatiotemporally either seasonally or less predictably, and note that it is often preemptive. Migration plays a central role in the spatial dynamics of mobile populations, and is largely distinct in both form and function from the within-population mixing arising from postnatal dispersal and from the interpatch movements characteristic of metapopulations. We call for more interaction between biologists studying different taxa and different forms of movement, and between behaviorists and population ecologists.

Recent insights from radar studies of insect flight

Radar has been used to study insects in flight for over 40 years and has helped to establish the ubiquity of several migration phenomena: dawn, morning, and dusk takeoffs; approximate downwind transport; concentration at wind convergences; layers in stable nighttime atmospheres; and nocturnal common orientation. Two novel radar designs introduced in the late 1990s have significantly enhanced observing capabilities. Radar-based research now encompasses foraging as well as migration and is increasingly focused on flight behavior and the environmental cues influencing it. Migrant moths have been shown to employ sophisticated orientation and height-selection strategies that maximize displacements in seasonally appropriate directions; they appear to have an internal compass and to respond to turbulence features in the airflow. Tracks of foraging insects demonstrate compensation for wind drift and use of optimal search paths to locate resources. Further improvements to observing capabilities, and employment in operational as well as research roles, appear feasible.

Recognition and characterization of migratory movements of Australian plague locusts, Chortoicetes terminifera, with an insect monitoring radar

Abstract Two special purpose insect-detecting radar units have operated in inland eastern Australia, in the region where nocturnal migratory movements of Australian plague locusts Chortoicetes terminifera occur, for over 10 years. The fully automatic radars detect individual insects as they fly directly overhead and “interrogate” them to obtain information about their characters (size, shape, and wing beating) and trajectory (speed, direction, and orientation). The character data allow locusts to be distinguished from most other migrant species. A locust index, calculated from the total count of locust-like targets for a night, provides a simple indication of migration intensity. For nights of heavy migration, the variation of numbers, directions, and speeds with both height and time can be examined. Emigration and immigration events can be distinguished, as can “transmigration,” the passage overhead of populations originating elsewhere. Movement distances can be inferred, and broad source and (more tentatively) destination regions are identified. Movements were typically over distances of up to 400 km. Interpretation of radar observations requires judgment, and the present two units provide only partial coverage of the locust infestation area, but their capacity to detect major population movements promptly, and to provide information between necessarily infrequent surveys, has proved valuable.

The Australian Plague Locust—Risk and Response

Abstract Locust plagues are natural hazards that have been historically regarded as disasters because of their impact on agricultural production. In Australia during the nineteenth and early twentieth centuries, the impacts of locusts led to significant hardships among farmers struggling to establish viable individual livelihoods. The use of pesticides for locust control and the establishment during the 1970s of coordinated response arrangements has significantly mitigated the economic and social impact of plagues. The main risk now is of control failure, which could lead to major economic losses, but significant concern also exists about unnecessary interventions; contamination of nontarget crops, pastures, and livestock; effects on natural ecosystems; and injuries and health hazards for control staff and the general public. Establishment of a national specific-purpose locust control organization with expert staff and formal links to regional stakeholders has allowed development of appropriate and effective responses to these risks. These responses have now been formalized as defined operating procedures. Mitigating the risks of locust control is ultimately as important as mitigating the impact of the locust plagues themselves.

Riders on the Wind: The Aeroecology of Insect Migrants

Migratory flight close to the Earth’s surface (within the so-called flight boundary layer) occurs in some insects, but the vast majority of migrants ascend above this layer and harness the power of the wind for transport. The resulting displacements range from dispersive movements over a few tens of metres to seasonal migrations covering thousands of kilometres. In this chapter, we summarize knowledge of the use of the aerosphere by insects, focusing particularly on longer migrations, in relation to: the height and duration of flight, direction and speed of movement, seasonal and diel patterns, and responses to atmospheric conditions and phenomena. The seasonal mass movements have major ecological consequences in the invaded areas, and these are discussed briefly. We also highlight recent comparisons of insect movement strategies with those of flying vertebrates and mention interactions between these groups in the atmosphere. We conclude with some suggestions for the future development of these topics.

The Effort–Outcomes Relationship in Applied Ecology: Evaluation and Implications

&NA; Knowing the outcome(s) of management efforts in applied ecology is topical and useful. The effort‐outcomes principle states that there is a cause‐and‐effect relationship between the desired outcomes of management and the effort applied (the inputs) but with diminishing returns. A question addressed by this relationship is the following: How much management effort is enough to achieve a desired outcome? We evaluate the relationship—namely, how it is described or estimated—give empirical examples, and outline a novel and explicit conceptual framework that connects management efforts to outcomes. We conclude that the relationship has been described three ways previously: in stylized graphs, from computer algorithms, and in observational studies. We recommend a fourth way employing manipulative experiments carried out as part of an adaptive management program and designed explicitly to estimate the relationships parameters.

Evaluating wildlife management by using principles of applied ecology: case studies and implications

Abstract Context. The broad concepts and generalisations that guide conduct of applied ecology, including wildlife management, have been reviewed and synthesised recently into 22 prescriptive and three empirical principles. Aims. The aim of this study was to use these principles to evaluate three on-ground wildlife management programs and assess the utility of the principles themselves. Key results. Case studies of long-term management of national park biodiversity impacted by feral pigs (Sus scrofa), and of conservation and harvest of red kangaroos (Macropus rufus) and mallards (Anas platyrhnchos), were selected to provide a representative range of management objectives, spatial scales and land tenures, and to include both native and introduced species. Management documents and a considerable scientific literature were available for all three programs. The results highlight similarities and differences among management activities and demonstrate the 25 principles to differing degrees. Most of the prescriptive principles were demonstrated in both the management and the scientific literature in all three programs, but almost no use was made of the three empirical principles. We propose that use of the prescriptive principles constitutes evidence that these programs meet both societal and scientific expectations. However, the limited use of the empirical principles shows gaps in the three programs. Conclusions. The results suggest that evaluating other wildlife management programs against the principles of applied ecology is worthwhile and could highlight aspects of those programs that might otherwise be overlooked. Little use was made of the empirical principles, but the the Effort–outcomes principle in particular provides a framework for evaluating management programs. Implications. The effort–outcomes relationship should be a focus of future applied research, and both prescriptive and empirical principles should be integrated into wildlife management programs.

Ascent and descent rates of high-flying insect migrants determined with a non-coherent vertical-beam entomological radar

ABSTRACT Vertical-beam radars employing non-coherent transmission and reception provide an effective means of detecting insects migrating at heights of hundreds of metres. Current units can determine the insects’ horizontal velocities, orientations, and some characteristics indicative of the targets’ identities; however, they are not able to detect the vertical component of the targets’ motion. It has generally been presumed that more sophisticated radar technology, employing Doppler processing and requiring coherent operation, would be needed to observe ascent and descent of targets, but we show here that with modern, high-speed, data-acquisition technology it is possible to determine these quantities from the echo signals produced by current non-coherent transceivers. A specially developed data-analysis algorithm that extracts precise target ranges from each of the radar’s pulses and calculates averages over multiple samples forms an essential component of this new capability. An upgraded Insect Monitoring Radar (‘IMRU’) incorporating these elements can estimate target heights with a precision of 0.13 m up to heights of 1 km (and 0.2 m from 1 to 2.5 km), and it does so every 0.13 s. This allows ascent and descent rates to be estimated to a precision of 0.4 m s‒1 at lower altitudes and to 0.1 m s‒1 at the greatest heights, where the broader beam produces echoes with longer duration. Brief case studies are presented that show IMRU observations of ascending and descending insects in daytime convective thermals, around dusk (when nocturnal migration commences with a take-off flight), during an established nocturnal migration, and at the leading edge of a mesofront. Some limitations and potential biases of the method are identified, and its utility relative to alternative methods is considered.

Aeroecological Observation Methods

Observation of animals flying in the atmosphere is the core empirical process of aeroecology. For species that are small, or that fly by night or at high altitudes, this presents a considerable challenge. Even for the more visible species and for flights near the ground, recording the animals’ movements requires specialised techniques. Fortunately, continuing rapid advances in radio and optical technologies, electronics, and computing are providing numerous opportunities for developing new and improved observing capabilities. The larger, more complete, and more precise observational datasets that these new technologies are providing underlie the current wave of discovery and growth in this novel discipline. This chapter is mainly concerned with methods for detecting and studying insects, birds, and bats flying in the open air, i.e. above the vegetation layer. Detection of these animals, and estimation of their numbers, can be achieved through in-flight capture or by remote sensing, with the latter comprising visual observation (including technologies for augmenting human sight), aural monitoring, radar, and laser/lidar. Remotely sensed animals can be identified, though sometimes only to a group of species, from characteristic features of the signals or images received. Information about the animals’ activities—their mode of flight, orientation, etc.—can be obtained either by remote sensing or from sensors mounted on the animals. The latter method, which relies on radio-telemetry or archival logging to record the acquired data, may also be used to monitor the animal’s physiological state, the environment it is moving in, and its trajectory. The chapter also examines how information about the timing and geographical extent of movements, and the environmental conditions the animals are experiencing, can be obtained. Finally, the particular challenges of observational aeroecology are identified, the multidisciplinary nature of the observing task is recognised, and some possible developments are proposed.