Scan Sampling and Waterfowl Activity Budget Studies: Design and Analysis Considerations

Abstract

SummaryScan sampling is a common technique used to quantify the activities of animals, including waterfowl. When large numbers are present, it is often impractical to record the activities of each individual, and sub-sampling is employed. We present a method for the design and analysis of scan sampling studies involving sub-sampling, based on an actual study of waterfowl activity on a waste stabilisation pond. The design we propose avoids subjectivity in the selection of individuals,is truly random rather than haphazard, and is adaptable to other situations. It allows for the population on each sampling occasion to be divided into separate strata with samples taken from each. The method of analysis addresses the statistical issues arising from such designs. In estimating the proportion of individuals engaged in an activity, it uses the information from observations in which some of the individuals are counted but their activities not recorded, and estimates the sampling variance introduced by sub-sampling. In comparing the mean proportions for different levels of a factor, such as time of day, the method uses restricted maximum likelihood (REML), an algorithm which can account for the sampling variance as well as for missing data. It is anticipated that the methods described

REVIEW: Perspectives on wastewater treatment wetlands and waterbird conservation

“…The main action taken to meet this requirement was the installation of two activated sludge plants and, as a result, the treated water, which now supplies most of the WSP systems, is substantially lower in organic C and N than raw sewage whilst the concentration of P has remained largely unchanged (Hamilton 2002). An activity budget study monitored the diurnal activities of eight waterbird species over the two years preceding the treatment process change (Hamilton, Taylor & Hepworth 2002), and subsequent monitoring (Mustoe & Waugh 2006; Mustoe 2009) using the same protocol (Hepworth & Hamilton 2001), confirmed statistically significant ( P < 0·05) declines in the time spent feeding for all eight species (Mustoe & Waugh 2006; Mustoe 2009). Understanding the reasons for these declines would require food and bird condition data, which are not available.…”

Activity budgets of waterfowl (Anatidae) on a waste-stabilisation pond

“…The analysis of the activity data is described in detail by Hepworth and Hamilton (2001). Briefly, data were analysed using restricted maximum likelihood (REML) (Patterson and Thompson 1971) in the statistical package GenStat (Lawes Agricultural Trust, IACR-Rothamsted).…”

A comparative study of the diurnal behaviour of the Northern Shoveller (Anas clypeata) during the wintering season at Garaet Hadj-Tahar (North-East Algeria) and Garaet Timerganine (Algerian highlands)

“…Days of inclement weather (persistent rain, high winds, poor visibility) were avoided. Hepworth and Hamilton (2001) undertook sampling at approximately monthly intervals.…”

“…A solution to this problem is to divide the site into nonoverlapping sections that are observed separately. The data then need to be weighted according to the numbers of birds observed in the different sections (Hepworth and Hamilton, 2001). It took approximately 1 h to sample the entire pond.…”

“…The purpose of these sections was only to aid surveying. Each of the 5 sections was scanned from left to right (Hepworth and Hamilton, 2001). One of the following activity classes was assigned to each individual without distinction of sex: feeding, sleeping, swimming, grooming, flying, and courtship.…”