DOI: 10.5061/dryad.t1g1jwtfs
title: Data from: Come from away: Reconstructing the long-range migratory flight of spruce budworm moths to Newfoundland, Canada

description: In this study, we combined Lagrangian atmospheric models with
 ecophysiological factors to reconstruct a migratory flight of spruce
 budworm (SBW, Choristoneura fumiferana) moths. This insect is a major
 defoliator in boreal forests in Eastern Canada and was captured in large
 numbers in a light trap on the night of 26-27 July 2017 at Sally's
 Cove, on the west coast of Newfoundland, Canada.  First, we used
 a simple trajectory model in backward mode in time to identify the most
 likely source region of the SBW moths south of Anticosti Island, in the
 Gulf of St. Lawrence, where moth take-off was likely facilitated by
 orographic lift.  Second, using a thermo-circadian model of
 take-off flight and the dispersion model MLDP (Modèle lagrangien de
 dispersion des particules), we determined that, during their 375 km
 journey, moths travelled a few hundred meters above surface level, under
 windy and low-humidity conditions. Although the moths followed a
 trajectory too low to be tracked by a nearby weather radar, potential
 bioscatter reflectivities that could potentially be SBW bioscatter were
 detected at higher altitudes, suggesting that the moths that landed in
 Sally’s Cove could have been part of a larger dispersal event. 
description: Data file: Using the R package ‘terra’, the time series of raster
 maps in Azimuthal Equidistant Projection describing maximum reflectivity
 (calculated from the lowest 5 elevation scans) for each 10-minute interval
 from Jul 26 2000 UTC to Jul 27 0900 UTC were collated as a SpatRaster.
 This data object was then saved as a netCDF file. Ground clutter (but not
 precipitation) had been filtered from each raster using a radar-specific
 clutter mask. Background: In 27 July 2017, a large
 increase in spruce budworm moths was detected in traps located along the
 east coast of Newfoundland (REF) and near the radar station located at
 Marble Mountain, Newfoundland (48.9303 N, -57.83462 E). Computer
 simulations indicate that these moths may have been derived from a mass
 dispersal event with a source population on Anticosti Island.
 Ground clutter mask: Ground clutter was identified using scans
 from July 26, 0000-0900 UTC.  Ground clutter on the two lowest elevation
 scans (0°, 0.2°) was identified on the east coast of Quebec (NNW of the
 radar station) and around the radar station itself in Newfoundland. On the
 three higher elevation scans (0.4°, 0.6°, 0.8°), there were small,
 scattered areas of ground clutter around the radar station (Figure
 1). Results: Sufficient data were available to search
 for migrating SBW on two nights: (a) Jul 26 0000 to 0900 UTC and (b) Jul
 26 2000 to 0900 UTC: (a) Jul 26 0000 to 0900 UTC: Two
 distinct patches of targets were identified (Figure 2):
 1. At 0010hrs UTC there was a small area of moderate reflectivity
 (&gt; 2dBZH) north of the radar station (west of Hawkes Bay) on the
 three lowest elevation scans (0°,0.2°, 0.4°). This patch moved towards the
 west and disappeared from view at 0220hrs over the Atlantic Ocean
 . 2. At 0530hrs, scattered low reflectivity (&lt;
 -0.1 dBZH) over the Gulf of St Lawrence to the NNW of the radar station
 was present on the lowest elevation scan (0°). At 0620hrs this area of low
 reflectivity substantially increased in size and began to move SSE towards
 the radar station. At first these targets were only detected using the
 lowest elevation scan, but as the targets moved closer to the radar
 station they were also detected by higher elevation scans. This patch was
 still present on the final scan at 0900hrs UTC. (b) Jul
 26 2000 to Jul 27 0900 UTC: Four distinct patches of targets were
 identified (Figure 3): 1. Ground clutter was very
 poorly filtered from the scans, with large areas of high reflectivity
 remaining around the radar station, and on the Quebec mainland.
 2. A patch of high reflectivity was detected on all elevation
 scans approximate 220km to the north of the radar station at 0010 UTC.
 This patch moved slowly to the east over time and disappeared from scans
 by 0810 hrs UTC. This patch describes precipitation clutter.
 3. Patches of high reflectivity were detected on the two lowest
 elevation scans (0°, 0.2°) approximately 200km to the SSW of the radar
 station between 0010-0220 hrs, 0250-0510 hrs, and 0640-0820 hrs
 UTC. 4. A patch of high reflectivity over the Gulf of
 St Lawrence approximately 150km WNW of the radar station, was detected by
 the lowest elevation scan (0°) between 0010-0810 hrs UTC. This patch was
 also detected within the 0.2° elevation scans from 0100-0810 hrs UTC and
 on the 0.4° elevation scan between 0200-0.250 and between 0620-0810. On
 the composite scan, the relative density of high reflectivity cells, and
 the width of the high reflectivity patch, were both highest between
 0120-0240 hrs. Additional small areas of moderate
 reflectivity were detected within the 0.6° elevation scan (but not lower
 scans), close to the Quebec mainland between 0440-0600 hrs.
 Discussion: The characteristics of this radar are not conducive
 to detecting SBW. At low elevations, most sectors are blocked by terrain
 (Figure 4), leaving only small segments to the south, west and north
 visible. Within these available sectors, the radar poorly samples the
 volume below 1000m where migrating SBW are typically located. The lowest
 radar beam (0°) does not sample air space below approx 500m a.s.l. (Figure
 5), and at a distance of 150km from the radar station, does not sample
 airspace below 1000m a.s.l. The potential SBW targets in the fourth group
 are located in the 1000 to 3000m elevation range at 150m from the radar
 station, but because of blocked sectors it is not possible to determine
 where they departed from or landed. Radial velocity of these potential SBW
 on the 1.5° elevation Dopplar scan are between -2 &lt; v ≤ 0 m/s,
 indicating stationary objects or objects with very slow radial movement
 toward the radar station. Wind direction during this period was WSW (257°)
 at an average wind speed of 10 m/s (NCEP reanalysis data).
description: # Data from: Come from away: Reconstructing the long-range migratory
 flight of spruce budworm moths to Newfoundland, Canada Dataset DOI:
 [10.5061/dryad.t1g1jwtfs](10.5061/dryad.t1g1jwtfs) ## Description of the
 data and file structure The present study focuses on a dispersal event
 detected by Rhainds et al. (2022) on the night of 26-27 July 2017, close
 to the town of Sally’s Cove, located on the west coast of Newfoundland
 (49.73 ° N, 57.93 ° W). We hypothesized that, because SBW populations were
 at low density levels everywhere on the island of Newfoundland at the
 time, the immigrants observed in Sally’s Cove must have come from high
 population density areas on the mainland. To test this hypothesis, we
 developed and applied a methodology to reconstruct SBW dispersal events
 from observed arrival location and time. Since the per capita rate of
 dispersal is density-dependent, the potential sources of migrants are
 generally assumed to be areas of high population density (Anderson and
 Sturtevant, 2011; Sturtevant et al., 2013; Garcia et al., 2024). We used
 annual forest defoliation levels as an indicator of population density
 (Rhainds & Therrien, 2025). To simulate the atmospheric dispersal of
 SBW, we used the Lagrangian modelling approach, which consists of tracking
 the motion of air parcels as they move through the atmosphere.  A
 comprehensive explanation of the conceptual approach and applications of
 Lagrangian modelling, including air parcels, can be found in Lin et al.
 (2013). We used two Lagrangian models: a trajectory model executed in
 backward mode in time to identify the most likely source area and a
 dispersion model run in forward mode in time to reconstruct the
 moths' flight. Both models assume that the moths travel passively
 with the wind. The trajectory model, described in D’Amours et al. (2015),
 is a simple tool designed to quickly calculate a few air parcel
 trajectories (typically of the order of about ten) moving in the 3-D wind
 field of the atmosphere. In this model, only the advection by the mean
 wind (that is, atmospheric transport) is considered. The dispersion model
 used was the Lagrangian stochastic particle dispersion model MLDP (Modèle
 lagrangien de dispersion de particules). In MLDP, dispersion is modelled
 by calculating the trajectories of a large number of air parcels,
 typically several million, in two parts: 1) 3-D displacements due to the
 transport by the synoptic (non-turbulent) component of the mean wind
 provided by the meteorological model, and 2) 3-D displacements due to
 turbulent stochastic motions that are unresolved (at subgrid scale) by the
 meteorological model. Therefore, unlike the trajectory model, MLDP
 simulates the dispersion of a tracer, which allows the computation of
 concentrations of this tracer in the atmosphere, typically expressed as
 mass per unit volume of air. We analyzed single-polarization C-band radar
 data from the region of interest to detect the presence of reflectivity
 signals resembling those of insects. Anticosti Island and the Jacques
 Cartier Strait lie outside the coverage of Canadian mainland radars, while
 the western region of Newfoundland is covered by the Marble Mountain radar
 (CXME), located at 48.930 ° N and 57.835 ° W, 90 km south of Sally’s Cove.
 Consequently, we extracted raw data from the Marble Mountain radar station
 (559 m above sea level, ASL; wavelength: 5.33 cm, beam width: 0.62°) for
 26-27 July 2017, thus covering the night preceding the insect captures at
 Sally’s Cove as well as the night of capture. We processed the radar scans
 as described by Boulanger et al. (2017) using the BUGTRACKER package
 (Fabry and Hogg, 2020). In short, the four lowest elevation radar volume
 scans (0°, 0.2°, 0.4°, 0.5°) were read into Python, and signals from
 ground clutter (calculated using scans between 00 to 09 UTC on Jul 26),
 precipitation, and potential vertebrates (reflectivity &gt; 25 dBZ) were
 censored. Scans were projected onto a 500 m x 500 m Cartesian grid, and a
 composite image of potential SBW activity within each grid cell was
 calculated using the maximum reflectivity across elevation scans. ###
 Files and variables #### File: About_the_NF_data_file.pdf
 **Description:** Description and interpretation of the Mable Mountain
 (Newfoundland, Canada) radar data  #### File:
 SBW_reconstructed_migratory_flight.zip **Description:** 3D position and
 environmental data of the reconstructed migratory flight trajectory of
 spruce budworm moths from the island of Anticosti to Sally's Cove
 (Newfoundland)   #### File:
 Meteorological_profiles_along_SBW_trajectory.zip
 **Description:** Meteorological vertical profiles along the migratory
 flight of the spruce budworm moths. A text file is included that describes
 the data.  #### File: Backward_trajectories.zip **Description:** Raw
 results from the backward trajectories starting at Sally's Cove. A
 text file is included that describes the data. ## Access information Other
 publicly accessible locations of the data: *
 [https://www.donneesquebec.ca/recherche/fr/dataset/donnees-sur-les-perturbations-naturelles-insecte-tordeuse-des-bourgeons-de-lepinette](https://www.donneesquebec.ca/recherche/fr/dataset/donnees-sur-les-perturbations-naturelles-insecte-tordeuse-des-bourgeons-de-lepinette) Data was derived from the following sources: * [https://www.canada.ca/en/environment-climate-change/services/weather-general-tools-resources/weather-tools-specialized-data.html](https://www.canada.ca/en/environment-climate-change/services/weather-general-tools-resources/weather-tools-specialized-data.html)