A technique to estimate white-tailed deer Odocoileus virginianus density using vertical-looking infrared imagery.
Sampling designs and methods have not been consistent among studies. Early aerial infrared imagery work for deer used strip transects and collected data with the imager in a fixed, vertical position (Croon et al. 1968, Graves et al. 1972). With the emphasis placed on determining demographic data (Wiggers & Beckerman 1993), circular plots with imagers in variable, oblique positions became more common.
The inability to calculate the area surveyed and time required to provide estimates of probability of detection have been two problems limiting the use of aerial infrared imagery for density estimation.
Haroldson et al. (2003) pointed out the difficulty in using circular plots with oblique angles to calculate an area. They used multiple oblique angles and were not able to provide reliable estimates of the areas surveyed. The difficulty in calculating the area was due to changing oblique angles and lack of an automated methodology for geo-referencing the area searched. The use of vertical imagery is required to be able to easily calculate linear and areal measurements (Paine & Kiser 2003). Borrowing from the field of photogrammetry, flight lines are essentially transects and the imagery data collected, if from a vertical position, provide strip transects. A probability of detection is required to compensate for the thermal targets missed, and distance sampling may provide a solution for this limitation.
It takes time to develop sightability models using telemetry techniques; Bernatas & Nelson (2004) required three years to collect a sufficient amount of data to provide a sightability model for counting bighorn sheep Ovis canadensis in canyonlands based on FLIR data. Distance sampling, however, provides a measure of detection probability (White 2005). Vertical-Looking Infrared (VLIR) imagery is a source of distance data that lends itself to distance sampling and may overcome the limitation of time required to sample large areas.
[FIGURE 1 OMITTED]
Our goal was to provide a method of collecting and analyzing infrared imagery data based on established remote sensing techniques (Paine & Kiser 2003) and common data analyses (Buckland et al. 2001) to estimate population density. VLIR imagery integrated with GPS and GIS data allows for distance calculations that may be used with distance sampling. Specifically, we wanted to determine: 1) if VLIR data, as opposed to FLIR data, were suitable to estimate density of a model species, white-tailed deer Odocoileus virginianus, using distance sampling, and 2) if the unaltered uniform model, which would indicate perfect detectability across the imagery, was the best model for all sites examined.
Material and methods
Our study area was located in the Mississippi Alluvial Valley of eastern Arkansas, USA (Fig. 1). We collected VLIR data in four sites: Choctaw Island Wildlife Management Area (CIWMA), Cut-Off Creek Wildlife Management Area (CCWMA), Lakeside Hunting Club (LHC) and Wingmead Farms (WMF). CIWMA and CCWMA were both owned by the Arkansas Game and Fish Commission, and LHC and WMF were privately owned.
CIWMA is located in Desha County, Arkansas, USA, within the Mississippi River levee system and is 3,360 ha in size. It contains bottomland hardwood forests and eastern cottonwood Populus deltoides plantations interspersed with old fields and food plots. Dominant tree species are oaks Quercus spp., pecan Carya illinoensis and eastern cottonwoods (Kissell & Tappe 2004). Elevation ranges from 32 to 41 m and is prone to winter and spring flooding.
CCWMA is located in Drew County, Arkansas, USA, and is 3,650 ha in size. Dominant overstory species are willow oak Quercus phellos, overcup oak Q. lyrata, southern red oak Q. falcata and American elm Ulmus americana (Fowler 2004). Food plots were dispersed throughout. Elevation ranges from 35 to 52 m and the area is prone to winter and spring flooding.
LHC, located in St. Francis County, Arkansas, USA, is 2,030 ha in size, and is dominated by agricultural fields, interspersed with bottomland hardwood forests and food plots. Sweetgum Liquidambar styraciflua, nuttall oak Q. nattallii, water oak Q. nigra, willow oak, pecan and hickory Carya spp. comprise the overstory. Elevation ranges from 50 to 60 m.
WMF is 2,310 ha in size and is located in Prairie County, Arkansas, USA. Agricultural fields, interspersed with food plots, and bottomland hardwood forests are the major cover types. Bottomland hardwood forests are dominated by cherrybark oak Q. pagoda, sweetgum, southern red oak, sycamore Platanus occidentalis, water oak and green ash Fraxinus pennsylvanica. Elevation ranges from 57 to 67 m. More detailed descriptions of the sites may be found in Gregory (2005).
We conducted flights along transects between 23:00 and 06:00 on 20-21, 21-22, 22-23 and 27-28 February 2004. The first transect was randomly placed at each site. All other transects were systematically placed parallel to the first transect and spaced approximately 400 m apart. We based transect orientation in each study site on the ability to maximize the area covered and to minimize the flight time. We sampled 21,14,13and 12 transects in the CIWMA, CCWMA, LHC and WMF, respectively, across the four nights, and we flew the same transects each night. We flew surveys at each site using a Cessna 182 at approximately 457 m above ground level (agl) and at approximately 120 km/ hour. Strip transect width and pixel size resulting from the altitude and aperture of the lens were approximately 110 m and 0.15 m, respectively. We recorded locations (latitude and longitude), flight paths, altitude, speed, date and time by an onboard global positioning system (GPS) unit and integrated GPS data into a geographic information system (GIS). We converted flight paths to a shapefile using ArcPad 6.0.3 NT to represent transect lines flown. The order in which the sites were visited was based on the most efficient route and the prevailing weather conditions. We did not conduct flights under conditions that reduced detectability of deer or were not suitable for flying, i.e. in heavy fog, rain or wind.
Camera specifications and imagery acquisition
We surveyed each site using a Mitsubishi IR-M700 thermal infrared imager (Mitsubishi Electric Corporation, Canada) equipped with a 50 mm lens mounted in the belly of the aircraft with the head oriented perpendicular to the flight path. We used mid-infrared and far-infrared wavelengths (1.25.9im). The detector array size was 801 (H) x 512 (V) pixels. The imager captured 50 frames per second in a field of view 14[degrees] (H) x 11[degrees] (V). We sent output to a digital video cassette recorder (Sony GV-D1000). We routed the GPS signal through a video encoder-decoder, and recorded it on the audio portion of the tape. Flight line spacing and GPS information minimized the potential for double counting. We reviewed and analyzed recorded video using a video-editing program (Avid Xpress DV, version 3.0) and a 33 cm black and white, 1,000 line monitor (Sony PVM-137). Thermal signatures of deer were identified by their unique shape and brightness relative to the background. No other species that had similar thermal signatures occurred in any of the sites. We exported images containing thermal signatures of deer as 8-bit tagged information file format (TIFF) images. We geo-referenced TIFF images using the encoded GPS data and transferred images into a GIS. We converted locations in decimal minutes to Universal Transverse Mercator coordinates for the purpose of calculating distances (Chang 2006).
We collected distance sampling data from TIFF images containing thermal signatures of deer. We delineated transects on images and measured the perpendicular distance from each deer to its associated transect (Fig. 2) to the nearest meter using GIS. We used individual deer instead of groups because thermal signatures of individual deer were detected independently of group affiliation. We truncated data as recommended by Buckland et al. (2001) to provide the best possible model to represent density. We determined deer density for each site using program DISTANCE 6.0, version 2 (Buckland et al. 2001, Thomas et al. 2002). We fit perpendicular distance data to uniform and half-normal key functions with no adjustments, cosine, simple polynomial and hermite polynomial adjustments. We used minimum Akaike Information Criterion (AIC; Akaike 1973) values to select the best model for each site. Based on competing models for each site, the density estimate, coefficient of variation (CV) of the density estimate and the probability of observing deer in the imagery were provided. We calculated the weight of each competing model based on AIC values.
[FIGURE 2 OMITTED]
[FIGURE 3 OMITTED]
We flew a total of 185.2 km, 204.3 km, 139.5 km and 218.2 km of transects and observed 572,213,76 and 405 individual deer on the CIWMA, CCWMA, LHC and WMF, respectively. We found that uniform models fit data best for each site (Fig. 3). The densities ranged from 0.042 to 0.125 deer/ha across sites, and the coefficients of variation decreased with an increasing number of transects (range: 14.3-33.4%). The probability of observing a deer in the imagery ranged from 0.82 to 1.00 ([bar.x] = 0.95 [+ or -] 0.05 SE) for the models from each site with the lowest AIC value; only models with [DELTA]AIC values [less than or equal to] 2 are reported (Table 1). The probability of detection was < 1.0 for the WMF site only.
We used a data collection method different from recent work (Dunn et al. 2002, Haroldson et al. 2003, Bernatas & Nelson 2004) in that we maintained a vertical position of the imager throughout each flight. Much of the recent work collecting infrared imagery from an aerial platform used a forward looking or oblique approach (Haroldson et al. 2003, Bernatas & Nelson 2004). Our approach allowed us to apply standard photogrammetry techniques (Paine & Kiser 2003) for calculating distances and using distance sampling (Buckland et al. 2001), as vertical imagery is preferred over oblique imagery for calculating distance and area measurements (Paine & Kiser 2003).
Vertical data collection provides the most consistent pixel resolution across the image, and allows for distance and area calculations (Paine & Kiser 2003). Data collected at view angles other than vertical increase the area of blind spots (Addison 1972). Thermal signatures of vegetation have the ability to hide target species under the vegetation. Even in open landscapes or under leaf-off conditions, oblique angles increase the area behind which target species may be obscured, while vertical views minimize the area of the blind spots.
Much of the recent research using infrared technology to provide counts or population size used FLIR data collected in circular plots or ' orbits' (Wiggers & Beckerman 1993, Haroldson et al. 2003, Bernatas & Nelson 2004). Haroldson et al. (2003) criticized area calculation using this method because of the labour intensity and inaccuracies of plotting field of view information on aerial photos. We avoided these issues by using the imager in a vertical position, collecting data along a transect line as recommended by Reynolds et al. (1995) and Haroldson et al. (2003), and using distances as our response variable, which we calculated through an automated process using GIS.
A uniform distribution is not reasonable when group size influences visibility or if surveys are conducted under different visibility conditions (Samuel et al. 1992). We eliminated group size influence by using distances to individual animals (Buckland et al. 2001). We minimized differences in visibility conditions by surveying only under similar, favourable conditions. Additionally, we addressed visibility by using strip widths based on 5-10% truncation as recommended by Buckland et al. (2001) which resulted in reduction of the half width by approximately 5 m at each of the four sites.
Distance sampling uses transects as replicates, and the greater the number of replicates the better the precision (Buckland et al. 2001). We sampled our four sites with economics taking precedence. The site with the most transects, CIWMA, provided the greatest precision of density, and the site with the least number of transects, WMF, the poorest precision. We believe that the extra cost of flight time would justify the precision obtained.
Probability of detection has been of concern and great importance in the development and use of aerial infrared imagery. High probability of detection (> 85%) should be expected where the vegetative cover is short (Parker & Driscoll 1972, Naugle et al. 1996). Addison (1972) first examined the probability of detection of cattle and described the trade-off between altitude and clarity of the thermal signature. As expected, lower altitudes (agl) yielded better results where all animals were detected. Parker & Driscoll (1972) assessed the detection of mule deer Odocoileus hemionus and pronghorn antelope Antilocapra americana confined to pens with no overhead canopy cover. Detection of the total number of animals varied by interpreter, but were high (92-99%). Haroldson et al. (2003), by contrast, reported low detection rates (31-89%) using circular flight patterns in a landscape containing deciduous hardwoods. They attributed the low detection, in part, to observer bias and methodology. Our study sites varied in amounts and proportions of deciduous hardwoods and agricultural land. Our use of transects and VLIR likely minimized the effect of deciduous hardwoods and maximized the probabilities of detection.
We found that the probability of detecting a deer was < 1 and resulted from an 'edge effect' when identifying deer in our imagery in one site. The probability of detection at the edge of the imagery likely declined as the radial distance from the center of the image increased. Increased distances from the center of the imagery caused an increased effect of vegetation; specifically, tree bolls increased blind spots. We did not quantify this source of variation, though it may be an important component of detection probability. Given that the uniform distribution provided the best fit for the other three sites, we did not find this source of variation influential on those sites; however, it is a source of error that should be considered when using VLIR.
Population closure is an important assumption for providing population estimates (White et al. 1982). We surveyed four sites each night, replicated each survey four times, and covered a total of > 11,000 ha. The methods we used provided for efficient data collection and likely maximized the likelihood of meeting the closure assumption. Most other estimation methods, such as mark-recapture (Gould et al. 2005) or even ground-based FLIR (Collier et al. 2007), often require considerably more time for data collection and increases the likelihood of violating the closure assumption.
Three basic assumptions are required for distance sampling (Buckland et al. 2001). The assumption that all objects on the transect line were always detected (i.e. g(0) = 1) was assumed to be valid, but we did not explicitly test for this. There are two forms of bias, availability and perception, related to g(0) = 1. Availability bias occurs when animals are not available for detection, such as in VLIR when deer are under canopy and are not visible from above. Perception bias occurs when the animal is present but the observer fails to detect the animal (Borchers 2004). The product of these forms of bias provide an estimate of the probability of detection on the line (i.e. g(0); Grunkorn et al. 2004). While we did not have estimates of availability bias for any site, we believe that we minimized the bias by conducting surveys during leaf-off conditions and utilizing the effect of parallax (Paine & Kiser 2003) in reviewing the imagery. We did, however, have an estimate of perception bias through a larger study (Gregory 2005) using independent double counts (Grankorn et al. 2004). For all the observations across the CIWMA, CCWMA, LHC and WMF, we estimated the detection bias as 0.97, 0.90, 0.91 and 0.96, respectively. More importantly, the thermal signatures that were identified by the secondary observer and not the primary observer were near the edges of the imagery for each site. Thus, we believe that objects on the transect line were detected with a probability very close to 1.0, if not 1.0 (Buckland et al. 2001) at all sites. We believe the second assumption, i.e. that objects were detected at their initial location, was met because deer were not disturbed by the aircraft flying at 457 m agl. Also, the distance between transects (approximately 400 m) and the short time required to fly one transect ([bar.x] = 1.33 minutes, SE = 0.03 minute) minimized the chance of double counting. We believe the third assumption, i.e. that measurements were exact, was met because we used geo-referenced images and perpendicular distances from deer to transect lines computed in a GIS. The pixel size of images was approximately 15 cm; therefore, distances measured from transect lines to deer were thought to be within 1 m.
We did not have density estimates over multiple years to determine if the detection probability changed over time in a site, but we did observe site-specific detection probabilities. Site-specific probabilities for visual surveys from the air for other ungulates have been addressed using sightability models (Unsworth et al. 1990, Bodie et al. 1995), and the probability of detection using VLIR also appeared to be site-specific. Even though a uniform detection function with no adjustments was found at three of four sites in our study, the validity of the assumption of detection being independent of distance would need to be verified before it could be used on different sites.
Reliable scientific studies require a CV of [less than or equal to] 0.051 for research purposes, 0.128 for accurate management purposes and 0.255 for rough management purposes (Skalski et al. 2005). Estimates that are more precise are more useful in managing ungulate populations. Our results indicate that VLIR data analyzed with distance sampling can provide levels of precision sufficient for long-term management practices when collected in bottomland hardwood forests and agriculturally dominated landscapes in winter.
Similar to sightability in visual aerial surveys, probability of detection varied across sites and a measure of detectability should be provided specific to the site sampled. Use of VLIR data for population estimation, if not using distance sampling for analysis, requires some other measure of probability of detection such as ground verification of animals observed in the imagery (Naugle et al. 1996). We hypothesize that other ungulate species, other cover types and other aerial platforms will yield different probabilities of detection as have been observed with sightability models for visual aerial surveys (Samuel et al. 1987, Noyes et al. 2000).
Acknowledgements--we thank the Arkansas Forest Resources Center, the School of Forest Resources, University of Arkansas-Monticello, the Arkansas Game and Fish Commission, R. Pearson of Lakeside Hunting Club and F. Lyon of Wingmead Farms for funding this research. An extended appreciation goes to T. Doepel, R. Murphy, R. Nimmo, N. Peterson, S. Parker and B. Tallant for assistance with ground work, and to L. Davis of Davis Aviation for his excellent flying and insights. We also wish to thank S. Focardi and an anonymous reviewer for providing suggestions that improved the manuscript.
Received 12 April 2010, accepted 22 November 2010
Addison, R.B. 1972: The possible use of infrared thermal imagery for wildlife census.--Proceedings of the North American Moose Conference Workshop 8: 301-325.
Akaike, H. 1973: Information theory and an extension of the maximum likelihood principle.--In: Petran, B.N. & Csaaki, F. (Eds.); International Symposium on Information Theory. Akadeemia, Kiadi, Budapest, Hungary, pp. 267-281.
Anderson, D.R. & Pospahala, R.S. 1970: Correction of bias in belt transect studies of immotile objects.--Journal of Wildlife Management 34: 141-146.
Bernatas, S. & Nelson, L. 2004: Sightability model for California bighorn sheep in canyonlands using forward-looking infrared (FLIR).--Wildlife Society Bulletin 32: 638-647.
Bodie, W.L., Garton, E.O., Taylor, E.R. & McCoy, M. 1995: A sightability model for bighorn sheep in canyon habitats.--Journal of Wildlife management 59: 832-840.
Borchers, D.L. 2004: Estimating detection probability from line-transect cetacean surveys when detection on the line is not certain: an overview.--In: Thomsen, F., Ugarte, F. & Evans, P.G.H. (Eds.); Proceedings of the workshop on estimation of g(0) in line-transect surveys of cetaceans. Kolmarden, Sweden, ECS Newsletter No. 44: 6-13.
Buckland, S.T., Anderson, D.R., Burnham, K.P., Laake, J.L., Borchers, D.L. & Thomas, L. 2001: Introduction to distance sampling: estimating abundance of biological populations.--Oxford University Press, Oxford, UK, 432 pp.
Chang, K. 2006: Introduction to geographic information systems. 3rd edition.--McGraw-Hill Companies, New York, New York, USA, 432 pp.
Collier, B.A., Ditchkoff, S.S., Raglin, J.B. & Smith, J.M. 2007: Detection probability and sources of variation in white-tailed deer spotlight surveys. --Journal of Wildlife Management 71: 277-281.
Croon, G.W., McCullough, D.R., Olson, C.E. & Queal, L.M. 1968: Infrared scanning techniques for big game censusing.--Journal of Wildlife Management 32: 751-760.
Dunn, W.C., Donnelly, J.P. & Krausmann, W.J. 2002: Using thermal infrared sensing to count elk in the southwestern United States.--Wildlife Society Bulletin 30:963967.
Fowler, A.T. 2004: Winter relative abundance and habitat characteristics of swamp rabbits in the Mississippi alluvial plain of eastern Arkansas.--M.Sc. thesis, University of Arkansas-Monticello, Monticello, Arkansas, USA, 120 pp.
Gould, W.R., Smallidge, S.T. & Thompson, B.C. 2005: Mark-resight superpopulation estimation of a wintering elk Cervus elaphis canadensis herd. Wildlife Biology 11(4): 341-349.
Graves, H.B., Bellis, E.D. & Knuth, W.M. 1972: Censusing white-tailed deer by airborne thermal infrared imagery. Journal of Wildlife Management 36: 875-884.
Gregory, S.G. 2005: Comparison of density estimators for white-tailed deer using aerial thermal infrared videography.--M.Sc. thesis, University of Arkansas-Monticello, Monticello, Arkansas, USA, 111 pp.
Grunkorn, T., Diederichs, A. & Nehls, G. 2004: Aerial surveys in the German Bight--Estimating g(0) for Harbour Porpoises (Phocoena phocoena) by employing independent double counts.--In: Thomsen, F., Ugarte, F. & Evans, P.G.H. (Eds.); Proceedings of the workshop on estimation of g(0) in line-transect surveys of cetaceans. Kolmarden, Sweden, ECS Newsletter No. 44: 26-32.
Haroldson, B.S., Wiggers, E.P., Beringer, J., Hansen, L.P. & McAninch, J.B. 2003: Evaluation of aerial thermal imaging for detecting white-tailed deer in a deciduous forest environment.--Wildlife Society Bulletin 31: 1188-1197.
Kissell, R.E., Jr. & Tappe, P.A. 2004: An assessment of thermal infrared detection rates using white-tailed deer surrogates.--Journal of the Arkansas Academy of Science 58: 70-73.
Naugle, D.E., Jenks, J.A. & Kernohan, B.J. 1996: Use of thermal infrared sensing to estimate density of white tailed deer.--Wildlife Society Bulletin 24: 37-43.
Noyes, J.H., Johnson, B.K., Riggs, R.A., Schlegel, M.W. & Coggins, V.L. 2000: Assessing aerial methods to estimate elk populations: a case study.--Wildlife Society Bulletin 28: 636-642.
Paine, D.P. & Kiser, J.D., II. 2003: Aerial photography and image interpretation. 2nd edition.--John Wiley and Sons, Inc., Hoboken, New Jersey, USA, 632 pp.
Parker, H.D., Jr. & Driscoll, R.S. 1972: An experiment in deer detection by thermal scanning.--Journal of Range Management 25: 480-481.
Reynolds, P., Duck, C., Youngson, D. & Clem, D. 1995: An evaluation of airborne thermal imaging for the census of red deer Cervus elaphus populations in extensive open habitats in Scotland.--In: Thompson, I. (Ed.); Proceedings of the International Union of Game Biologists, XXI Congress, Halifax, Nova Scotia. Canadian Forest Service, Chalk River, Ontario, Canada, pp. 162-168.
Samuel, M.D., Garton, E.O., Schlegel, M.W. & Carson, R.G. 1987: Visibility bias during aerial surveys of elk in northcentral Idaho.--Journal of Wildlife Management 51: 622-630.
Samuel, M.D., Steinhorst, R.K., Garton, E.O. & Unsworth, J.W. 1992: Estimation of wildlife population ratios incorporating survey design and visibility bias. Journal of Wildlife Management 56: 718-725.
Skalski, J.R., Ryding, K.E. & Millspaugh, J.J. 2005: Wildlife demography: Analysis of sex, age, and count data.--Elsevier Academic Press, San Diego, California, USA, 636 pp.
Thomas, L., Laake, J.L., Strindberg, S., Marques, F.C., Buckland, S.T., Borchers, D.L., Anderson, D.R., Burn ham, K.P., Hedley, S.L. & Pollard, J.H. 2002: DISTANCE. Version 4.0 Release 1.--Research Unit for Wildlife Population Assessment, University of St. Andrews, UK. Avaliable at http://www.ruwpa.st-and.ac.uk/distance/ (Last accessed on 12 August 2009).
Unsworth, J.W., Kuck, L. & Garton, E.O. 1990: Elk sightability model validation at the National Bison Range, Montana, USA.--Wildlife Society Bulletin 18: 113-115.
White, G.C. 2005: Correcting wildlife counts using detection probabilities.--Wildlife Research 32: 211-216.
White, G.C., Anderson, D.R., Burnham, K.P. & Otis, D.L. 1982: Capture-recapture and removal methods for sampling closed populations.--Los Alamos National Library, Los Alamos, New Mexico, USA, Report number LA-8787-NERP, 235 pp.
Wiggers, E.P. & Beckerman, S.F. 1993: Use of thermal infrared sensing to survey white-tailed deer populations.--Wildlife Society Bulletin 21: 263-268.
Robert E. Kissell, Jr. & Susan K. Nimmo
Robert E. Kissell, Jr. & Susan K. Nimmo *, School of Forest Resources, Arkansas Forest Resources Center, University of Arkansas, Monticello, Arkansas 71656, USA--e-mail addresses: firstname.lastname@example.org (Robert E. Kissell, Jr.); email@example.com (Susan K. Nimmo)
* Present address: Arkansas Game and Fish Commission, South Central Regional Office, 500 Ben Lane, Camden, Arkansas 71701, USA
Corresponding author: Robert E. Kissell, Jr.
Associate Editor: Leif Egil Loe
Table 1. Distance sampling results for white-tailed deer based on vertical looking infrared imagery data collected across four nights on four sites (CCWMA = Cut-off Creek Wildlife Management Area, CIWMA = Choctaw Island Wildlife Management Area, LHC = Lakeside Hunting Club and WMF - Wingmead Farms) in eastern Arkansas in February 2004. Site Model (b) AIC (c) [DELTA]AIC CCWMA Uniform 763.290 0.000 UniformSP2 764.349 1.059 Half normal 764.365 1.076 CIWMA Uniform 1841.197 0.000 Half normal 1843.181 1.984 LHC Uniform 389.872 0.000 Half normal 391.872 2.000 WMF UniformC2 1295.863 0.000 Half normal 1295.869 0.006 UniformSP2 1296.027 0.164 UniformHP2 1296.027 0.164 Density Site Model (b) LCL (d) Estimate UCL (e) CCWMA Uniform 0.065 0.104 0.168 UniformSP2 0.069 0.112 0.183 Half normal 0.069 0.112 0.183 CIWMA Uniform 0.230 0.309 0.415 Half normal 0.228 0.311 0.423 LHC Uniform 0.030 0.056 0.105 Half normal 0.029 0.056 0.108 WMF UniformC2 0.114 0.232 0.472 Half normal 0.111 0.225 0.457 UniformSP2 0.109 0.222 0.451 UniformHP2 0.109 0.222 0.451 Probability of observation (a) Site Model (b) LCL (d) Estimate UCL (e) CCWMA Uniform 1.000 1.000 1.000 UniformSP2 0.809 0.930 1.000 Half normal 0.801 0.929 1.000 CIWMA Uniform 1.000 1.000 1.000 Half normal 0.905 0.994 1.000 LHC Uniform 1.000 1.000 1.000 Half normal 0.775 1.000 1.000 WMF UniformC2 0.730 0.817 0.914 Half normal 0.760 0.842 0.933 UniformSP2 0.780 0.853 0.933 UniformHP2 0.780 0.853 0.933 GOF (f) Site Model (b) p-value CV (g) Weight (h) CCWMA Uniform 0.782 0.222 0.592 UniformSP2 0.827 0.233 0.205 Half normal 0.824 0.235 0.202 CIWMA Uniform 0.884 0.143 0.879 Half normal 0.765 0.151 0.121 LHC Uniform 0.551 0.296 0.881 Half normal 0.349 0.325 0.119 WMF UniformC2 0.969 0.334 0.271 Half normal 0.969 0.333 0.269 UniformSP2 0.938 0.332 0.230 UniformHP2 0.938 0.332 0.230 (a) Probability of observing a deer in the defined area under the selected model. (b) Models included Uniform, UniformSP2 = Uniform key function with a simple polynomial adjustment of 2nd order, Half normal, UniformC2 = Uniform key function with a cosine adjustment of 2nd order, UniformHP2 = Uniform key function with a hermite polynomial adjustment of 2nd order. (c) AIC = Akaike information criterion value. (d) LCL = Lower confidence limit (95%). (e) UCL = Upper confidence limit (95%). (f) GOF = Goodness-of-fit. (g) CV = Coefficient of variation. (h) Weight based on AIC values.
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|Author:||Kissell, Robert E., Jr.; Nimmo, Susan K.|
|Date:||Mar 1, 2011|
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