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

In 1950, David and Elizabeth Lack chanced upon a huge migration of insects and birds flying through the Pyrenean Pass of Bujaruelo, later describing the spectacle as combining both grandeur with novelty. The intervening years have seen many changes to land use and climate, posing the question as to the current status of this migratory phenomenon, while a lack of quantitative data has prevented insights into the ecological impact of this mass insect migration and into the factors affecting it. To address this, we revisited the site in autumn over a 4-year period and systematically monitored diurnal insect species and numbers. We document an annual mean of 17.1 million day-flying insects from 5 orders moving south, with ‘mass migration’ events associated with warmer temperatures, the presence of a headwind, sunlight, low windspeed, and low rainfall. Diptera dominated the migratory assemblage and annual numbers varied by more than fourfold with larger annual migration flows associated with..., , , # The most remarkable migrants: Systematic analysis of the Western European insect flyway at a Pyrenean mountain pass

[https://doi.org/10.5061/dryad.vq83bk40v](https://doi.org/10.5061/dryad.vq83bk40v)

This dataset is four years of insect migration observations during the months of September and October moving through the 30m wide Pass of Bujaruelo, 2300m up in the Pyrenees. We collected this data using a video trap and a malaise trap. Meteorological data was collected from meteoblue forecasting.

## Description of the data and file structure

The data is organised into an excel file with separate sheets for different aspects. These aspects are: Number of insects in the pass; Nutrient transfer calculations; Migratory strength data; Hoverfly species in the pass; Total assemblage; Butterfly migration data; Intercept trap data.

**Number of insects in the pass**

This dataset is an overview of the numbers of insects recorded migrating through the Pass of Bujaruelo. This contains all the d...