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Understanding insect migration behaviour and pathways using individual tracking and radar

Periodic Reporting for period 1 - InsectMigration (Understanding insect migration behaviour and pathways using individual tracking and radar)

Reporting period: 2019-02-01 to 2021-01-31

Insects are the most diverse and abundant group of terrestrial migrants often involving the movement of billions to trillions of individuals in a single season. Insects play a critical role in ecosystems worldwide, both as ecosystem service providers (e.g. pollination and biocontrol), as well as causing detrimental effects (e.g. huge invasions of migratory pest species, such as locusts). Insect migration also involves the immense movement of biomass, resulting in significant nutrient transport between habitats. However, despite their significant role in ecosystems, the migratory pathways and mechanisms behind large-scale population connectivity of insects, is poorly understood. Migration involves movement across large spatial scales, which can pose challenges for studying this phenomenon, particularly when tracking small migratory animals, such as insects. Therefore, remote sensing methods such as radar combined with remote technology that can be carried by the animals themselves, can prove particularly useful for studying this fascinating phenomenon.

This will be the first study of its kind to combine the state-of-the-art methods of individual insect tracking (using radio-telemetry) and radar methods to record migratory behaviour and direction, while also investigating departure decisions along the migratory route. Therefore, results from the proposed research will have wide-ranging impacts for understanding the mechanisms behind insect migrations and the movement patterns of both species of conservation concern and pest species, and facilitate effective management actions. Understanding insect movements and landscape use will also have significant implications for identifying the mechanisms that contribute to the observed patterns of insect population decline.

Using a unique combination of individual tracking, vertical-looking radar and trapping data, we investigated the migratory behaviour of hawkmoths to provide insight into migratory routes and departure decisions. In this project, we aimed to investigate two main sets of objectives, which provide the basis for three work packages:

Objective 1 (Work Package 1): Our objective was to investigate the influence of radio-transmitters on the flight behaviour of hawkmoths in the field and the laboratory. Secondly, we investigated the movement behaviour of hawkmoths to gain important baseline information on flight behaviour, movements and home range size.
Objective 2 (Work Packages 2 and 3): Our objectives were to elucidate the migratory pathways of hawkmoths, to understand migratory flight and orientation behaviour in relation to topography and weather conditions along these routes. Furthermore, we aimed to investigate which factors influence individual departure decisions and stopovers en route.
Using individual-borne radio-telemetry, we successfully tracked migrating death's-head hawkmoths (Acherontia atropos) from the air using a Cessna 172 airplane. Hawkmoths were able to be followed continuously for up to 3.5 hrs during which we collected high resolution data on their headings in relation to local wind conditions. This represents the first study to track a nocturnally migrating insect in detail and the longest distance that an insect has been followed continuously. We compared the migratory tracks to high-resolution wind data to investigate whether migrating hawkmoths had their movements primarily dictated by wind. We have also collected data on local movements of hawkmoths using radio-telemetry, and will compare this to local weather data to determine which factors may influence departure decisions prior to migration.

During the course of the project, we operated a specialised entomological radar to investigate the behaviour of migrating insects, in particular hawkmoths, in relation to local wind conditions. The radar data complements the individual tracking data that we have collected and will be used to elucidate patterns of insect behaviour across the migration season. In addition to the radar data, we have continued to collect data on the migration phenology of hawkmoths through high-altitude passes in the Swiss Alps, a key bottleneck for flying migrants. In combination, our data will allow us to gain a unique insight into the ecology and behaviour of these enigmatic migrants.

Results of this project have been disseminated to scientific audiences at conferences (in Germany and the United Kingdom) and via presentation at workshops and invited seminars, and lectures to students (in Germany, Russia, Switzerland and the United Kingdom). Results of the project have also been disseminated to the broader public via articles in magazines and newspapers. We have also published a number of scientific papers throughout the course of the project, relating to the migration behaviour of insects in response to winds, quantification of insects using techniques such as radar, and interpreting patterns of insect decline.
This project is one of the first to combine individual tracking and radar to investigate insect migration behaviour. As technology improves, individual tracking devices continue to get smaller, opening up the range of accessible species. The project has highlighted the utility of using individual tracking to study migrating insects and provides a solid footing for understanding how insects respond to wind conditions while on route. Furthermore, high-resolution individual tracking can provide information on how individuals maintain course and the mechanisms by which they navigate. Through individual tracking, we have revealed that migrating hawkmoths are not just being directed by the wind to undertake their migration but will also migrate in what were previously considered to be unfavourable conditions. These results provide further evidence that insect migration is not just a passive phenomenon and have implications for forecasting the movements of migratory insects.
Death's-head Hawkmoth with radio-transmitter being released. Photo: Christian Ziegler.