The importance of survey design in distance sampling: field evaluation using domestic sheep
Tom A. Porteus A B , Suzanne M. Richardson A and Jonathan C. Reynolds A
+ Author Affiliations
- Author Affiliations
A Game & Wildlife Conservation Trust, Fordingbridge, Hampshire, SP6 1EF, UK.
B Corresponding author. Email: tporteus@gwct.org.uk
Wildlife Research 38(3) 221-234 https://doi.org/10.1071/WR10234
Submitted: 19 December 2010 Accepted: 6 April 2011 Published: 13 July 2011
Abstract
Context: Sampling methods to estimate animal density require good survey design to ensure assumptions are met and sampling is representative of the survey area. Management decisions are often made based on these estimates. However, without knowledge of true population size it is not possible for wildlife biologists to evaluate how biased the estimates can be if survey design is compromised.
Aims: Our aims were to use distance sampling to estimate population size for domestic sheep free-ranging within large enclosed areas of hill country and, by comparing estimates against actual numbers, examine how bias and precision are impaired when survey design is compromised.
Methods: We used both line and point transect sampling to derive estimates of density for sheep on four farms in upland England. In Stage I we used limited effort and different transect types to compromise survey design. In Stage II we increased effort in an attempt to improve on the Stage I estimates. We also examined the influence of a walking observer on sheep behaviour to assess compliance with distance sampling assumptions and to improve the fit of models to the data.
Key results: Our results show that distance sampling can lead to biased and imprecise density estimates if survey design is poor, particularly when sampling high density and mobile species that respond to observer presence. In Stage I, walked line transects were least biased; point transects were most biased. Increased effort in Stage II reduced the bias in walked line transect estimates. For all estimates, the actual density was within the derived 95% confidence intervals, but some of these spanned a range of over 100 sheep per km2.
Conclusions: Using a population of known size, we showed that survey design is vitally important in achieving unbiased and precise density estimation using distance sampling. Adequate transect replication reduced the bias considerably within a compromised survey design.
Implications: Management decisions based on poorly designed surveys must be made with an appropriate understanding of estimate uncertainty. Failure to do this may lead to ineffective management.
References
Bergstedt, R. A., and Anderson, D. R. (1990). Evaluation of line transect sampling based on remotely sensed data from underwater video. Transactions of the American Fisheries Society 119, 86–91.| Evaluation of line transect sampling based on remotely sensed data from underwater video.Crossref | GoogleScholarGoogle Scholar |
Biswas, S., and Sankar, K. (2002). Prey abundance and food habit of tigers (Panthera tigris tigris) in Pench National Park, Madhya Pradesh, India. Journal of Zoology 256, 411–420.
| Prey abundance and food habit of tigers (Panthera tigris tigris) in Pench National Park, Madhya Pradesh, India.Crossref | GoogleScholarGoogle Scholar |
Borchers, D. L., Buckland, S. T., and Zucchini, W. (2002). ‘Estimating Animal Abundance: Closed Populations.’ (Springer-Verlag: London.)
Borralho, R., Rego, F., and Vaz Pinto, P. (1996). Is driven transect sampling suitable for estimating red-legged partridge Alectoris rufa densities? Wildlife Biology 2, 259–268.
Buckland, S. T., Anderson, D. R., Burnham, K. P., Laake, J. L., Borchers, D. L., and Thomas, L. (2001). ‘Introduction to Distance Sampling: Estimating Abundance of Biological Populations.’ (Oxford University Press: Oxford.)
Carbyn, L. N., Oosenbrug, S. M., and Anions, D. W. (1993). ‘Wolves, Bison and the Dynamics Related to the Peace-Athabasca Delta in Canada’s Wood Buffalo National Park.’ (Canadian Circumpolar Research Institute, University of Alberta: Edmonton, AB.)
Cassey, P., and McArdle, B. H. (1999). An assessment of distance sampling techniques for estimating animal abundance. Environmetrics 10, 261–278.
| An assessment of distance sampling techniques for estimating animal abundance.Crossref | GoogleScholarGoogle Scholar |
Clark, P. J., and Evans, F. C. (1954). Distance to nearest neighbor as a measure of spatial relationships in populations. Ecology 35, 445–453.
| Distance to nearest neighbor as a measure of spatial relationships in populations.Crossref | GoogleScholarGoogle Scholar |
Croston, D., and Pollott, G. (1994). ‘Planned Sheep Production.’ 2nd edn. (Blackwell Scientific: Oxford.)
Dique, D. S., de Villiers, D. L., and Preece, H. J. (2003). Evaluation of line-transect sampling for estimating koala abundance in the Pine Rivers Shire, south-east Queensland. Wildlife Research 30, 127–133.
| Evaluation of line-transect sampling for estimating koala abundance in the Pine Rivers Shire, south-east Queensland.Crossref | GoogleScholarGoogle Scholar |
Fewster, R. M., Buckland, S. T., Burnham, K. P., Borchers, D. L., Jupp, P. E., Laake, J. L., and Thomas, L. (2009). Estimating the encounter rate variance in distance sampling. Biometrics 65, 225–236.
| Estimating the encounter rate variance in distance sampling.Crossref | GoogleScholarGoogle Scholar | 18363772PubMed |
Fewster, R. M., Southwell, C., Borchers, D. L., Buckland, S. T., and Pople, A. R. (2008). The influence of animal mobility on the assumption of uniform distances in aerial line-transect surveys. Wildlife Research 35, 275–288.
| The influence of animal mobility on the assumption of uniform distances in aerial line-transect surveys.Crossref | GoogleScholarGoogle Scholar |
Freilich, J. E., Camp, R. J., Duda, J. J., and Karl, A. E. (2005). Problems with sampling desert tortoises: a simulation analysis based on field data. The Journal of Wildlife Management 69, 45–56.
| Problems with sampling desert tortoises: a simulation analysis based on field data.Crossref | GoogleScholarGoogle Scholar |
Heydon, M. J., Reynolds, J. C., and Short, M. J. (2000). Variation in abundance of foxes (Vulpes vulpes) between three regions of rural Britain, in relation to landscape and other variables. Journal of Zoology 251, 253–264.
| Variation in abundance of foxes (Vulpes vulpes) between three regions of rural Britain, in relation to landscape and other variables.Crossref | GoogleScholarGoogle Scholar |
Hiby, L., and Krishna, M. B. (2001). Line transect sampling from a curving path. Biometrics 57, 727–731.
| Line transect sampling from a curving path.Crossref | GoogleScholarGoogle Scholar | 1:STN:280:DC%2BD3MrgtFOitQ%3D%3D&md5=53b92ac285184bb62db923ae5d47f425CAS | 11550921PubMed |
Hounsome, T. D., Young, R. P., Davison, J., Yarnell, R. W., Trewby, I. D., Garnett, B. T., Delahay, R. J., and Wilson, G. J. (2005). An evaluation of distance sampling to estimate badger (Meles meles) abundance. Journal of Zoology 266, 81–87.
| An evaluation of distance sampling to estimate badger (Meles meles) abundance.Crossref | GoogleScholarGoogle Scholar |
Johnston, R. G. (1983). ‘Introduction to Sheep Farming.’ (Granada: London.)
Langbein, J., Hutchings, M. R., Harris, S., Stoate, C., Tapper, S. C., and Wray, S. (1999). Techniques for assessing the abundance of brown hares Lepus europaeus. Mammal Review 29, 93–116.
| Techniques for assessing the abundance of brown hares Lepus europaeus.Crossref | GoogleScholarGoogle Scholar |
le Mar, K., Southwell, C., and McArthur, C. (2001). Evaluation of line-transect sampling to estimate nocturnal densities of macropods in open and closed habitats. Wildlife Research 28, 9–16.
| Evaluation of line-transect sampling to estimate nocturnal densities of macropods in open and closed habitats.Crossref | GoogleScholarGoogle Scholar |
Lynch, J. J., Hinch, G. N., and Adams, D. B. (1992). ‘The Behaviour of Sheep: Biological Principles and Implications for Production.’ (C.A.B. International: Wallingford, UK.)
Marques, F. F. C., and Buckland, S. T. (2003). Incorporating covariates into standard line transect analyses. Biometrics 59, 924–935.
| Incorporating covariates into standard line transect analyses.Crossref | GoogleScholarGoogle Scholar | 14969471PubMed |
Marques, T. A., Buckland, S. T., Borchers, D. L., Tosh, D., and McDonald, R. A. (2010). Point transect sampling along linear features. Biometrics 66, 1247–1255.
| Point transect sampling along linear features.Crossref | GoogleScholarGoogle Scholar | 1:STN:280:DC%2BC3M%2FislWltw%3D%3D&md5=de8366325fb0df4a40aaf8adaae3642aCAS | 20105157PubMed |
Ortega, Y. K., and Capen, D. E. (2002). Roads as edges: effects on birds in forested landscapes. Forest Science 48, 381–390.
Otto, M. C., and Pollock, K. H. (1990). Size bias in line transect sampling: a field test. Biometrics 46, 239–245.
| Size bias in line transect sampling: a field test.Crossref | GoogleScholarGoogle Scholar |
Péroux, R., Mauvy, B., Lartiges, A., Bray, Y., and Marboutin, E. (1997). Point transect sampling: a new approach to estimate densities or abundances of European hare (Lepus europaeus) from spotlight counts. Gibier, Faune Sauvage 14, 525–529.
Preston, J., Prodöhl, P., Portig, A., and Montgomery, I. (2003). ‘The Northern Ireland Irish Hare Lepus timidus hibernicus Survey 2002.’ The Queen’s University of Belfast, School of Biology & Biochemistry for the Environment and Heritage Service. (DoE: Northern Ireland.)
Purser, A. F., and Roberts, R. C. (1959). The relationship of hogg weight to the subsequent performance of Scottish Blackface ewes. Animal Science (Penicuik, Scotland) 1, 107–111.
Reid, N., Harrison, A. T., and Robb, G. N. (2008). ‘Northern Ireland Irish Hare Survey 2009.’ Natural Heritage Research Partnership for the Northern Ireland Environment Agency. (Quercus: London.)
Ruette, S., Stahl, P., and Albaret, M. (2003). Applying distance-sampling methods to spotlight counts of red foxes. Journal of Applied Ecology 40, 32–43.
| Applying distance-sampling methods to spotlight counts of red foxes.Crossref | GoogleScholarGoogle Scholar |
Seddon, P. J., Ismail, K., Shobrak, M., Ostrowski, S., and Magin, C. (2003). A comparison of derived population estimate, mark-resighting and distance sampling methods to determine the population size of a desert ungulate, the Arabian oryx. Oryx 37, 286–294.
| A comparison of derived population estimate, mark-resighting and distance sampling methods to determine the population size of a desert ungulate, the Arabian oryx.Crossref | GoogleScholarGoogle Scholar |
Southwell, C. (1994). Evaluation of walked line transect counts for estimating macropod density. The Journal of Wildlife Management 58, 348–356.
| Evaluation of walked line transect counts for estimating macropod density.Crossref | GoogleScholarGoogle Scholar |
Thomas, L., Buckland, S. T., Rexstad, E. A., Laake, J. L., Strindberg, S., Hedley, S. L., Bishop, J. R., Marques, T. A., and Burnham, K. P. (2010). Distance software: design and analysis of distance sampling surveys for estimating population size. Journal of Applied Ecology 47, 5–14.
| Distance software: design and analysis of distance sampling surveys for estimating population size.Crossref | GoogleScholarGoogle Scholar | 20383262PubMed |
Trenkel, V. M., Buckland, S. T., McLean, C., and Elston, D. A. (1997). Evaluation of aerial line transect methodology for estimating red deer (Cervus elaphus) abundance in Scotland. Journal of Environmental Management 50, 39–50.
| Evaluation of aerial line transect methodology for estimating red deer (Cervus elaphus) abundance in Scotland.Crossref | GoogleScholarGoogle Scholar |
Tsujino, R., Noma, N., and Yumoto, T. (2004). Growth of the sika deer (Cervus nippon yakushimae) population in the western lowland forests of Yakushima Island, Japan. Mammal Study 29, 105–111.
| Growth of the sika deer (Cervus nippon yakushimae) population in the western lowland forests of Yakushima Island, Japan.Crossref | GoogleScholarGoogle Scholar |
Valeix, M., Fritz, H., Dubois, S., Kanengoni, K., Alleaume, S., and Saïd, S. (2007). Vegetation structure and ungulate abundance over a period of increasing elephant abundance in Hwange National Park, Zimbabwe. Journal of Tropical Ecology 23, 87–93.
| Vegetation structure and ungulate abundance over a period of increasing elephant abundance in Hwange National Park, Zimbabwe.Crossref | GoogleScholarGoogle Scholar |
Varman, K., and Sukumar, R. (1995). The line transect method for estimating densities of large mammals in a tropical deciduous forest: an evaluation of models and field experiments. Journal of Biosciences 20, 273–287.
| The line transect method for estimating densities of large mammals in a tropical deciduous forest: an evaluation of models and field experiments.Crossref | GoogleScholarGoogle Scholar |
Venturato, E., Cavallini, P., and Dessì-Fulgheri, F. (2010). Are pheasants attracted or repelled by roads? A test of a crucial assumption for transect censuses. European Journal of Wildlife Research 56, 233–237.
| Are pheasants attracted or repelled by roads? A test of a crucial assumption for transect censuses.Crossref | GoogleScholarGoogle Scholar |
Ward, A. I., White, P. C. L., and Critchley, C. H. (2004). Roe deer Capreolus capreolus behaviour affects density estimates from distance sampling surveys. Mammal Review 34, 315–319.
| Roe deer Capreolus capreolus behaviour affects density estimates from distance sampling surveys.Crossref | GoogleScholarGoogle Scholar |
White, G. C., Anderson, D. R., Burnham, K. P., and Otis, D. L. (1982). ‘Capture–Recapture and Removal Methods for Sampling Closed Populations.’ (Los Alamos National Laboratory: Los Alamos, NM.)
White, G. C., Bartmann, R. M., Carpenter, L. H., and Garrott, R. A. (1989). Evaluation of aerial line transects for estimating mule deer densities. The Journal of Wildlife Management 53, 625–635.
| Evaluation of aerial line transects for estimating mule deer densities.Crossref | GoogleScholarGoogle Scholar |
Williams, B. K., Nichols, J. D., and Conroy, M. J. (2002). ‘Analysis and Management of Animal Populations.’ (Academic Press: San Diego, CA.)
Williams, R., Hedley, S. L., and Hammond, P. S. (2006). Modelling distribution and abundance of Antarctic baleen whales using ships of opportunity. Ecology and Society 11, 1.
Williams, R., and Thomas, L. (2009). Cost-effective abundance estimation of rare animals: testing performance of small-boat surveys for killer whales in British Columbia. Biological Conservation 142, 1542–1547.
| Cost-effective abundance estimation of rare animals: testing performance of small-boat surveys for killer whales in British Columbia.Crossref | GoogleScholarGoogle Scholar |
