DOI: 10.5061/dryad.wwpzgmsxg
title: Field margins as ecological corridors: Uncovering connectivity in agricultural landscapes using high-resolution tracking data and translocation experiments

description: Ecological corridors are key for reducing habitat fragmentation, yet their
 designation often relies on structural connectivity analysis based on
 expert opinion, land uses, and species occurrence rather than actual
 movement analysis, limiting our understanding of their effectiveness. This
 study aims to explore and experimentally test how different habitats
 facilitate or impede species movement in an intensive agricultural
 landscape designated as ecological corridors. Using a cutting-edge
 tracking system (ATLAS), we monitored the movement of 68 white-spectacled
 bulbuls (Pycnonotus xanthopygos) at high resolution (4 or 8-second
 intervals) and explored fine-scale habitat selection through integrated
 step selection analysis, focusing on movement segments while excluding
 static periods. To validate our observational findings, we conducted a
 translocation experiment with 64 bulbuls across three habitat treatments:
 natural, arable fields, and arable fields intersected by a main paved
 road. We compared return time, number of stops, the movement straightness
 of return flights across treatments, and the habitat selection during
 these flights. Bulbuls avoided arable fields, which significantly impeded
 their movement through the agricultural landscape. This was further
 confirmed in the translocation experiment, where bulbuls from the
 'arable field' treatment took the longest to return, made the
 most stops, and followed the most tortuous paths.  Bulbuls
 demonstrated a strong preference for vegetative features, such as narrow
 field-margins, which comprised only 2.2% of the study area, underscoring
 their importance as movement corridors. The translocation experiment
 reinforced this result, with bulbuls consistently selecting field-margins
 regardless of their treatment group. Additionally, bulbuls from the
 ‘natural’ treatment returned the fastest and followed the most direct
 paths.  Synthesis and applications: Our study demonstrates that
 field-margins can play a major role in maintaining connectivity and
 enhancing ecological corridor functionality in intensive agriculture
 landscapes, even for habitat generalist species like the bulbul. The use
 of high-resolution movement data enabled fine-scale habitat analysis,
 revealing the key role of these vegetative features in facilitating
 movement. Conservation efforts should prioritize maintaining these
 small-scale elements to enhance corridor effectiveness in agricultural
 landscapes.
description: # Field margins as ecological corridors: Uncovering connectivity in
 agricultural landscapes using high-resolution tracking data and
 translocation experiments Dataset DOI:
 [10.5061/dryad.wwpzgmsxg](10.5061/dryad.wwpzgmsxg) The data in this
 repository were collected as part of a study investigating the fine-scale
 habitat selection of the white-spectacled bulbul (*Pycnonotus
 xanthopygos*) within an intensively managed agricultural landscape. The
 study integrated high-resolution GPS tracking with experimental
 translocation to assess habitat selection and movement behaviour. The
 file `Field_Margins_Bulbul.zip` contains an R project
 (`fieldMargins.Rproj`) with all relevant data files, analysis scripts, and
 custom functions used to generate the results presented in the associated
 manuscript. ## Description of the data and file structure ### Files *
 `iSSA.tags.Info.RData`: Metadata associated with each tracked bulbul used
 in iSSA. - `iSSA.data.list.RData`: A list containing individual-level data
 frames of subsampled observed movement steps and matched simulated
 available steps used for integrated step selection analysis (iSSA). -
 `trans_info.RData`: A data frame containing metadata and movement
 summaries for experimentally translocated bulbuls. -
 `return.routes.list.RData`: A list of return trajectories from
 experimentally translocated bulbuls. - `beeLine_habitats.RData`:  A data
 frame quantifying the length of each land-use type along the straight-line
 (beeline) path between capture and release locations for each translocated
 bulbul. - `colorsCostum.RData`: A character vector of custom hexadecimal
 color codes used to represent individual birds in plots. ### Files content
 #### `iSSA.tags.Info.RData` *tag: *Unique identifier for each bulbul
 individual. *sample_rate*: Sampling rate of the ATLAS tags. *raw.data*:
 Total number of raw fixes collected. *valid.data*: Number of valid fixes
 after data filtering. *translocation*: Indicator of whether the bulbul was
 experimentally translocated (0 = no, 1 = yes). *bird.weight*: Body weight
 of the bulbul (in grams). *sex*: Sex of the bulbul (M = male, F = female,
 NA = unknown). *capture.location*: Name of the capture site.
 *iSSA.unique.dates*: Number of unique days with data used in iSSA.
 *iSSA.total.locs*: Total number of fixes used in the iSSA analysis. ####
 Variables `iSSA.data.list.RData` (per individual) *id*: Unique identifier
 for each bulbul. *burst_*: Segment identifier for a continuous sequence of
 movement. *x1_*,* y1_*: Coordinates (x, y) of the start location of the
 step. *x2_*, *y2_*: Coordinates (x, y) of the end location of the step.
 *sl_*: Step length, the distance between consecutive fixes (in meters).
 *direction_p*: Direction of the step in radians. *ta_*: Turning angle ,
 change in direction from previous step (in radians). *t1_*: Timestamp at
 the start of the step (POSIXct). *t2_*: Timestamp at the end of the step
 (POSIXct). *dt_*: Time interval between steps (in seconds). *step_id_*:
 Identifier for each unique movement step. *case_*: Indicates whether the
 step was used (TRUE) or available (FALSE). *cos_ta_*: Cosine of the
 turning angle. *log_sl_*: Log-transformed step length. *landUseStart*:
 Numeric code for the land-use category at the start of the step.
 *landUseEnd*: Numeric code for the land-use category at the end of the
 step. *landUse_start*: Land-use category name at the start of the step.
 *landUse_end*: Land-use category name at the end of the step. #####
 `trans_info.RData` *tag*: Unique identifier for each translocated bulbul.
 *sex*: Sex of the bird (M = male, F = female). *birdWeight*: Body weight
 at the time of capture (in grams). *treatment*: Description of the release
 habitat type (e.g., Natural, Arable field & road). *captureLoc*: Name
 of the capture location. *releaseSite*: Name/code of the site where the
 bird was released. *releaseDist*: Distance between capture and release
 sites (in kilometers). *returnDur*: Duration of the return journey (in
 hours). *stops*: Total number of stops recorded during the return. *si*:
 Straightness index of the return trajectory (0 = low straightness, 1 =
 high). *startEndLine*: Straight-line distance between start and end points
 of the return path (in kilometers). *log_returnDur*: Natural log of the
 return duration. *log_stops*: Natural log of the number of stops.
 *birdWeight_scaled*: Z-transformed bird weight. *releaseDist_scaled*:
 Z-transformed release distance. #### Variables in `return.routes.list`
 (per individual) ##### Used in analysis *TAG*: Unique identifier for each
 bulbul. *landUse*: Land-use category at the fix location (e.g., Natural
 Habitats). case_: Logical (TRUE = real point, FALSE = not used; all TRUE
 in this list). *ADP.ID*: Identifier for stationary segments. #####
 Additional variables (not used in analysis) *TIME*: Raw time value in
 milliseconds since epoch (Unix time). *X, Y*: Easting and northing
 coordinates (EPSG:2039, Israel TM Grid, in meters). *dateTime*: Timestamp
 of the fix (in POSIXct format). *date*: Calendar date of the fix. *DAY*:
 Day index of the trajectory. *distance*: Step length to the next point (in
 meters). *dT*: Time interval to the next fix (in seconds). *spd*: Speed
 between consecutive fixes (meters per second). *angl*: Turning angle
 relative to previous step (in degrees). *timeGapBurst*: Burst index
 assigned based on time gaps between consecutive fixes.
 *pointInBurst*: Number of fixes within the current burst. *ADP.ID, ADP.X,
 ADP.Y, ADP.start, ADP.end, ADP.duration, ADP.qlt*: Fields for identifying
 and describing stationary behavior segments. *seg.ID*: Identifier for
 movement segments. *Sun_angle*: Sun angle above the horizon (in degrees).
 *inDay*: Logical (TRUE/FALSE) indicating if the fix occurred during the
 day. *changeDay*: Logical indicator of a date transition in the tracking
 data. *dayIndex*: Sequential day index within the return period.
 *distFromRelease*: Distance from the release site to current fix (in
 meters). *distFromCapture*: Distance from the original capture location to
 current fix (in meters). *landUse*: Land-use category at the fix location.
 *LON*: Longitude coordinate (WGS84). *LAT*: Latitude coordinate (WGS84).
 *case_*: Logical (TRUE = real point, FALSE = not used; all TRUE in this
 list). #### `beeLine_habitats` *tag*: Unique identifier for each
 translocated bulbul. *landUse*: Land-use category along the beeline path.
 *habitat_length*: Total length of land-use type intersected by the beeline
 path (in meters). *beeLine_length*: Total length of the straight-line
 (beeline) path between capture and release locations (in meters). ###
 Scripts #### `iSSA.R`: Main script for conducting integrated Step
 Selection Analysis (iSSA). The script performs the following steps: * Fits
 individual-level iSSA models to assess habitat selection. * Summarizes
 model outputs at both individual and population levels. * Visualizes
 relative selection strength (RSS) across habitats. * Updates and compares
 step length and turning angle distributions by habitat. * Compares habitat
 selection patterns between translocated and non-translocated birds. *
 Produces model output tables and plots included in the manuscript and
 supplementary materials. #### `Translocation_analysis.R`: Script for
 analyzing translocation experiment data.  The analysis includes: * Fitting
 mixed-effects models to assess treatment effects on return time, number of
 stops, and path straightness. * Producing summary tables and diagnostic
 outputs (Table 1). * Visualizing return behavior metrics across treatment
 groups (Figure 4). * Comparing habitat use along actual return routes to
 habitat availability along straight-line (bee-line) paths using Wilcoxon
 tests (Table S3). * Visualizing log-transformed habitat selection ratios
 (ln(used/bee-line)) across land-use types (Figure 5). #### `functions.R`:
 Contains custom functions used in both scripts. ## Code/software The
 analysis was conducted in the R programming environment. All scripts are
 written in R and include explicit calls to load the required R packages.
 The analysis was conducted using R (version 4.5.0) within the RStudio
 integrated development environment. All scripts are written in R and
 include explicit calls to load the required packages.