Continental-scale patterns in diel flight timing of high-altitude migratory insects

Abstract

Many insects depend on high-altitude, migratory movements during part of their life cycle. The daily timing of these migratory movements is not random, e.g. many insect species show peak migratory flight activity at dawn, noon or dusk. These insects provide essential ecosystem services such as pollination but also contribute to crop damage. Quantifying the diel timing of their migratory flight and its geographical and seasonal variation, are hence key towards effective conservation and pest management. Vertical-looking radars provide continuous and automated measurements of insect migration, but large-scale application has not been possible because of limited availability of suitable devices. Here, we quantify patterns in diel flight periodicity of migratory insects between 50 and 500 m above ground level during March-October 2021 using a network of 17 vertical-looking radars across Europe. Independent of the overall daily migratory movements and location, peak migratory movements occur around noon, during crepuscular evening and occasionally the morning. Relative daily proportions of insect migration intensity and traffic during the diel phases of crepuscular-morning, day, crepuscular-evening and night remain largely equal throughout May-September and across Europe. These findings highlight, extend, and generalize previous regional-scale findings on diel migratory insect movement patterns to the whole of temperate Europe. This article is part of the theme issue ‘Towards a toolkit for global insect biodiversity monitoring’.

The most remarkable migrants—systematic analysis of the Western European insect flyway at a Pyrenean mountain pass

“…Similar southward movements occur along the Atlantic seaboard [ 51 , 52 ]. To accurately quantify the total number of migratory insects crossing the Pyrenees, extensive deployment of monitoring resources and techniques is needed, including the use of vertical-looking radars [ 2 , 53 ].…”

Monitoring aerial insect biodiversity: a radar perspective

“…Using a network of small-scale radars for monitoring at large spatial extent, Haest et al . [ 59 ] demonstrate the surprising consistency of these diel activity patterns along a European gradient from southern France to Finland.…”

“…Small-scale radars have mostly been used for dedicated biological/ecological purposes such as fundamental or applied research in local or regional settings. Most devices are run in Europe ( figure 3 ), where an informal network of 17 small-scale radars has been set up recently [ 59 ] and only a handful more devices exist elsewhere in the world. Yet, as some models of small-scale radars have been developed into commercial off-the-shelf products, networks of small-scale radars could be set up nationally and internationally as standardized aerial biodiversity monitoring systems.…”

Towards a toolkit for global insect biodiversity monitoring

“…Haest et al . [ 62 ] use a European network of small-scale radars to exemplarily investigate diel activity patterns of insects. On a yet larger spatial scale, Tielens & Kelly [ 63 ] use the network of weather-radars in the contiguous USA to identify a latitudinal gradient in insect flight activity, and its variation across biomes.…”