DOI: 10.5061/dryad.5dv41nsd0
title: Disturbance-related redistribution of Western capercaillie (Tetrao urogallus) away from woodland tracks

description: Wild vertebrates usually avoid ground disturbed by humans with uncertain
 effects on their distribution and density. We report on a natural
 experiment that confirms and extends previous conclusions about how the
 local distribution of capercaillie is affected by track-based disturbance.
 We surveyed the birds’ droppings in two periods, before and after a
 predicted increase in disturbance adjacent to an expanding Scottish
 village, and model the probability of finding droppings in relation to
 period plus two disturbance gradients – distance to a much disturbed
 ‘entry zone’ with a high density of tracks lying adjacent to the village,
 plus distance to the nearest track. Throughout the study, no droppings
 were found within the entry zone and their density was depressed up to 400
 m from it. Density of droppings was also depressed within 100–120 m of
 tracks but, compared to a notional scenario without tracks, was threefold
 greater on ground 120–250 m from tracks. Although the number of cocks
 counted at the lek in spring showed a small increase, there was an almost
 threefold decline in the probability of finding capercaillie droppings on
 and within about 40 m of tracks. We infer that, after the development,
 birds were less likely to use or cross tracks in pursuit of their daily
 living requirements, with unknown consequences for their population
 dynamics and vital rates. Our results have implications for refuge design.
 Birds on roughly half of a 50 ha refuge should be undisturbed by direct
 effects of track-based activities. However, birds shifting away from
 tracks may themselves cause local increases in density and associated,
 indirect disturbance such that a refuge would need to be over 300 ha
  to keep half of it undisturbed.
description: Capercaille droppings were surveyed along fixed N-S transects
 100m apart during 14 surveys in 2006-2021. These fell into two periods:
 Period 1 before the adjacent housing development and Period 2 after it. 
 Each observation was assigned to a 100 x 20m grid based on the transect
 lines. These observations were then used to prepare the heat map Figure 1.
 The distances from each grid point to the 'entry zone' dE and to
 the nearest track dT were measured via GIS. The probability of finding
 droppings Pf (response variable) was then modelled as (explanatory
 variables) a cubic polynomial in dE and a quadratic in dT plus the
 category period and its interactions with each of the polynomial terms
 via  the SAS (ver 9.1) Glimmix macro to enact a logistic GLMM with survey
 as a random effect. Temporal and spatial autocorrelations were accounted
 for as explained in the paper.
description: # Disturbance-related redistribution of Western Capercaillie Tetrao
 urogallus away from woodland tracks
 ## BoG data
 WLB-2023-01151.R2 The data are on an Excel file with three worksheets:
 Droppings 2006-21 entry_zone_distances_dE track_­distances_dT **Droppings
 2006-21** contains the positions and other details of each observation of
 droppings. Each column is headed by a short title with an associated
 explanatory note. "." in a cell denotes no data.
 **entry_zone_distances_dE** contains the positions (easting and northing)
 of each grid point within the main study area plus the distance dE to the
 entry zone. Each column is headed by a short title with an associated
 explanatory note. **track_­distances_dT** contains the positions (easting
 and northing) of each grid point within the main study area plus the
 distance dT to the nearest track. It includes distances to old tracks that
 were present throughout  (column D,  t_dist (dT)) plus distances that
 include the new tracks of Period 2 (column E, t_dist_P2). A new ‘easy
 access’ track, the ‘Capercaillie trail’ was constructed in the entry zone
 between surveys 10 and 11 and so dT for each of these surveys is provided.
 It had no effect on the results because – being close to the village in
 the entry zone – it was not the nearest track to any observation of
 droppings. Each column is headed by a short title with an associated
 explanatory note. The data were processed as described in the paper. ##
 BoG\_GIS\_data The data are three shapefiles
 BoatofGartenWood_newtracks.shp BoatofGartenWood_oldtracks.shp
 BoatofGartenWood_surveyboundaries.shp **BoatofGartenWood_newtracks**
 contains the tracks which were mapped as occurring after the development,
 as polylines. **BoatofGartenWood_oldtracks** contains the tracks which
 were mapped as being present prior to the development, as polylines.
 **BoatofGartenWood_surveyboundaries** contains the survey boundaries as
 polygons.