DOI: 10.5061/dryad.3r2280gg0
title: Estimating density of mountain hares using distance sampling: a comparison of daylight visual surveys, night-time thermal imaging and camera traps

description: Surveying cryptic, nocturnal animals is logistically challenging.
 Consequently, density estimates may be imprecise and uncertain. Survey
 innovations mitigate ecological and observational difficulties
 contributing to estimation variance. Thus, comparisons of survey
 techniques are critical to evaluate estimates of abundance. We
 simultaneously compared three methods for observing mountain hare (Lepus
 timidus) using Distance sampling to estimate abundance. Daylight visual
 surveys achieved 41 detections, estimating density at 14.3 hares km-2
 (95%CI 6.3–32.5) resulting in the lowest estimate and widest confidence
 interval. Night-time thermal imaging achieved 206 detections, estimating
 density at 12.1 hares km-2 (95%CI 7.6–19.4). Thermal imaging captured more
 observations at furthest distances, and detected larger group sizes.
 Camera traps achieved 3,705 night-time detections, estimating density at
 22.6 hares km-2 (95%CI 17.1–29.9). Between the methods, detections were
 spatially correlated, although the estimates of density varied. Our
 results suggest that daylight visual surveys tended to underestimate
 density, failing to reflect nocturnal activity. Thermal imaging captured
 nocturnal activity, providing a higher detection rate, but required fine
 weather. Camera traps captured nocturnal activity, and operated 24/7
 throughout harsh weather, but needed careful consideration of empirical
 assumptions. We discuss the merits and limitations of each method with
 respect to the estimation of population density in the field.
description: Please refer to the manuscript for more information. The data has
 been prepared for loading in to software distance.  
description: <b>META DATA DESCRIPTIONS     </b>
 Data are prepared ready for loading in to Software Distance. 
   <b>_____DAYLIGHT VISUAL
 SAMPLING_____</b> STUDY AREA = HOLME MOSS for all
 sites SITE = Sites within the study, numbered 1 through
 6 as per the manuscript.  AREA KM^2 = 8.17KM^2 per site
 square which sums to 49 KM^2 for the whole area of Holme Moss. 
 LINE_LENGTH _KM  = Per site what distance was walked in
 kilometres. PERP_DISTANCE_M = Perpendicular distance to
 the transect line in metres. CLUSTER_SIZE = How many
 mountain hares were observed.  _____<b>NIGHT-TIME THERMAL IMAGING_____</b> STUDY AREA = HOLME MOSS for all sites SITE = Sites within the study, numbered 1 through 6 as per the manuscript.  AREA KM^2 = 8.17KM^2 per site square which sums to 49 KM^2 for the whole area of Holme Moss.  OBSERVATION POINT = Unique ID for each vantage point.  Some of these received multiple visits so appear several times. SURVEY_EFFORT = 1 per vantage point. RADIAL_DISTANCE_M = Radial distance to the mountain hare detection in metres. CLUSTER_SIZE = How many mountain hares were observed.  _____<b>CAMERA TRAPS_____</b> STUDY AREA = HOLME MOSS for all sites SITE = Sites within the study, numbered 1 through 6 as per the manuscript.  AREA KM^2 = 8.17KM^2 per site square which sums to 49KM^2 for the whole area of Holme Moss.  CAM_ID = Unique ID for each camera trap.  These are "point transect labels" for software distance. SURVEY_EFFORT_SECONDS = Expressed with "1k" i.e. one second is the effort unit.  The value shown is the sum of the effort units for each individual camera i.e. the total number of seconds the camera was deployed for. RADIAL_DISTANCE_M = Radial distance to the mountain hare detection in metres. CLUSTER_SIZE = How many mountain hares were observed.