Workshop 1: Introduction to Distance Sampling

Mary Woodcock Kroble
Thursday 13 February 2014
Start date: 19 August 2014 - End date: 22 August 2014
Time: 12:00 am - 12:00 am


The general objective of this 4 day workshop is to give  wildlife managers, ecologists and statisticians a solid grounding in the basic  methods for design and analysis of distance sampling surveys. Teaching will be  a combination of lectures, computer sessions and discussion groups.

The course is intended for scientists who are carrying out population  assessments of wildlife. We anticipate a mix of marine and terrestrial mammalogists,  ornithologists and fisheries biologists, plus statisticians who have an  interest in the topic. To gain maximum benefit from the workshop, biologists  and ecologists should have some quantitative training, including basic  statistical methods (point and variance estimation and confidence intervals),  and some experience of survey design would be useful. Some familiarity with the  concepts of line or point transect sampling would be an advantage, although no  prior knowledge of these topics is assumed.

Much of the teaching will be through use of PCs, and some knowledge of  Microsoft Windows will be assumed. Participants are welcome to bring their own  portable computers (see Information for registrants for minimum requirements).

Distance sampling

The term ‘distance sampling’ covers a range of methods for assessing  wildlife abundance:

  • line transect sampling, in  which the distances sampled are distances of detected objects (usually animals) from the line along which the observer travels
  • point transect sampling, in  which the distances sampled are distances of detected objects (usually birds) from the point at which the observer stands
  • cue counting, in which the  distances sampled are distances from a moving observer to each detected cue given by the objects of interest (usually whales)
  • trapping webs, in which the  distances sampled are from the web centre to trapped objects (usually invertebrates or small terrestrial vertebrates)
  • migration counts, in which the ‘distances’ sampled are actually times of detection during the migration of objects (usually whales) past a watch point

Workshop content

The workshop will concentrate primarily on line and point transect sampling.  The concepts of distance sampling will be explained and the assumptions of the  methods discussed. Although the basic theory will be covered, the focus of the  workshop will be on practical application of the methods.

The workshop will start with an introduction to wildlife population   assessment methods, and demonstration of how line and point transect methods  are generalizations of sample count methods (strip counts and point counts  respectively). The underlying theory and assumptions of both line and point  transect sampling will be covered, and the relative merits of the two  approaches in different circumstances discussed. Computer sessions will follow,  to train participants in the use of Distance for straightforward data sets.

More complex issues will then be covered. Special methods are required when  animals occur in groups or “clusters”. For example, size bias can  occur – that is large clusters have a higher probability of detection than  small clusters, so that population size is overestimated. Methods for adjusting  for this bias will be given. Another issue is stratification, which is used to  improve the precision of estimates when animal abundance, detection probability  or clustering varies over time or space. Good survey design is an essential   ingredient of a successful survey so design issues and field methods will be  covered in detail. Some specialized applications of distance sampling such as  cue counting, migration counts, trapping webs and indirect counts (e.g., dung  or nests) will be mentioned.

Automated survey design (using Distance to assist in determining where survey effort will be allocated) as well as the incorporation of covariates in modelling of detection functions have moved from the advanced workshop to this introductory workshop.

Participants will be taught how to use the newest, windows-based version of  the industry-standard program Distance. Exercises in applications of Distance  will be set, and participants are encouraged to bring (a subset of) their own  data sets for preliminary analysis during the workshop.    Towards the end of the workshop, some time is put aside for informal  discussion groups composed of participants with common interests or problems.  In the past, these groups have included the following topics: population trend  analysis; transect surveys in rain forest; marine mammal surveys; songbird  surveys; seabird surveys; and dung surveys.

Participants interested in going beyond the basics of distance sampling are  encouraged to register for the advanced workshop, which takes place directly  after this workshop finishes.

The workshop will begin at 09:00 on Tuesday, 19th with registration at CREEM from 08:45. The workshop will finish at 17:00 on Friday, 22nd.

Materials provided

The following publications and software will be provided to  participants at no additional cost.

  • Introduction to Distance Sampling: Estimating Abundance of Biological Populations. S.T. Buckland, D.R. Anderson, K.P. Burnham, J.L. Laake, D.L. Borchers and L. Thomas. Oxford University Press, 2001.
  • Lecture notes containing all of the overheads and slides shown during the workshop. This material supplements and extends the distance sampling text book.
  • Distance software

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