Surveying large areas of habitat just got a whole lot easier, as a team of scientists ditch traditional on-foot fieldwork and take to the skies. By using high resolution photographs taken by aerial drones, scientists from the Technical University of Munich (TUM) have gathered information about habitat suitability for the larvae of two declining butterfly species.
As butterflies change throughout their life cycle, so their ecological requirements change too. A variety of different micro-habitats must be available to ensure successful survival. A micro-habitat is an extremely localised, small scale environment on which an organism depends. For example, the imago (adult) butterfly may need an abundance of flowers as a nectar source and a certain amount vegetation-cover for egg oviposition. In comparison, a larvae may prefer low vegetation height and a large amount of bare soil.
This study, recently published in Landscape Ecology, analysed the micro-habitat requirements of two members of the Lycaenid family: the common blue (Polyommatus icarus) and adonis blue (Polyommatus bellargus). These small, azure-coloured butterflies both occur in calcareous grasslands across Europe. Both species largely depend on horseshoe vetch (Hippocrepis comos) or bird’s-foot trefoil (Lotus corniculatus) for their survival. These plants not only serve as nectar sources for adult butterflies, but are larval host plants too. Unfortunately, due to large-scale agricultural intensification, these species are undergoing the same fate as so many other grassland species. Disappearance and fragmentation of their habitat has lead to severe declines over past decades.
For conservation strategies to be effective, it is important to take a closer look at these species needs – by understanding and assessing micro-habitat requirements at all life stages.
Starting in-situ, the scientists collected data on the distribution of eggs and caterpillars on the host plants. Furthermore, they collected thorough and detailed information on the corresponding micro-habitat characteristics. This included flower bud density, vegetation height, percentage of bare soil, availability of shadow, and distance to surrounding vegetation.
Taking to the air
Then, by employing an aerial drone equipped with a high-res camera, the scientists were able to extend their study to the landscape scale. “The high resolution of just a few centimetres per pixel – made possible by low-altitude overflights – provides information of micro-habitat structures over a relatively large area,” said Jan C. Habel, lead author of the study. By combining the information collected from field observations with images from the drone, the scientists calculated habitat suitability models (HSMs). These enabled them to predict suitable micro-habitats for the butterfly larvae with a considerable degree of success.
The use of drones in detecting and identifying micro-habitats has exciting potential for the future of conservation. The ability to project knowledge from small-scale field observations onto a much larger area will make habitat conservation more proficient and effective. Conservationists will be able to fine-tune their efforts by identifying areas of high value, and so target specific areas for management.
Furthermore, the study made some important findings about the habitat preferences of the common and adonis blue butterflies. A heterogeneous habitat, one with a mosaic of open grassland and shrubs, may positively affect the two species. “Our study also demonstrates that the entire life cycle of organisms, such as butterflies, should be taken into consideration when making recommendations for conservation measures,” says Habel on his findings, “because the study shows how sensitively organisms react, even to minimal changes.”
Jan Christian Habel, Mike Teucher, Werner Ulrich, Markus Bauer, Dennis Rödder: Drones for butterfly conservation: larval habitat assessment with an unmanned aerial vehicle. Landscape Ecology 2016, 1-11. DOI: 10.1007/s10980-016-0409-3
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