Methodology           

III   WATERFOWL CENSUS AND MONITORING

 Birds are the easiest of all animals to census as they are often brightly coloured, relatively easy to see and highly vocal. The bird census and monitoring is an extremely cost-effective way of monitoring the overall health of the ecosystem. The censusing methods are broadly of two types: those for censusing species that are evenly distributed across the landscape and those for species that are not (i.e., highly clumped).

 Waterbirds are broadly defined as: “birds ecologically dependent on wetlands” and include traditionally recognised groups popularly known as wildfowl, waterfowl and shorebirds and waders. In addition to these groups there are other species that are dependant on wetlands such as kingfishers, passerines, etc.

 Wetland and water birds make use of a variety of conditions, from dry zones and meadows bordering lakes to open water zones. On the basis of their size, the availability of food and suitable foraging conditions, different birds can occupy different parts of the lake. Generally there are five major groups of water birds found based on the wetland zones they frequent. They are: (i) Open water birds, (ii) Waders and shoreline birds, (iii) Meadow and grassland birds, (iv) Birds of reed bed and other vegetation, and (v) Birds of open air space above wetlands.

 Ducks, geese, grebes, cormorants, kingfishers, terns, gulls and pelicans represent the open water birds. Stilt, greenshank, sandpipers, storks, ibises, spoonbill, herons and egrets tend to frequent shallow waters. The vegetated portions of the wetland are represented by rails, bitterns, coots, jacanas, moorhens, snipe, painted snipe etc.

 Birds in the lakes are enumerated using either point counts or line transects.

 Point Counts

Method: A point count is a count undertaken from a fixed location for a fixed time period. It can be undertaken at any time of the year, and is not restricted to the breeding season. Point counts can be used to provide estimates of the relative abundance of each species or when coupled to distance estimation can yield absolute densities.

 Point – count stations can be laid out in a systematic or random manner, but they should not be close to each other, with a minimum distance of 200m maintained between each of them. As a reasonably large number of point counts will be needed from each study plot, point counting is not a suitable technique for small study areas. Counts must be done for a fixed amount of time at each station. All birds that are seen or heard are recorded. In areas with a very rich bird fauna or where species are hard to detect or identify, it may be necessary to count longer than 10 minutes.

 If only relative indices of abundance are required, then counts are made only in an unlimited distance or within an arbitrary range, such as 25m. Bird detectability decreases with distance from the observer, and to use point-counts to estimate density a few assumptions are made. In practice, there are three ways of incorporating distance estimation into point counts to enable density calculation. The simplest, and recommended method is to have two counting bands and to record birds up to a fixed distance and beyond that distance separately. Increasingly complex methods require either several distance bands rather than just two or attempting to estimate the distance to every contact. It is often advisable to undertake at least two separate counts at each counting station, one in the first half of the season and one in the second. This not only ensures that both early and late breeders are recorded during the counts, but also takes into consideration seasonal variations in the detectability, since a species though present may be more detectable during one part of the season than the other. In general, the maximum value of each species at each counting station should be used in the density analyses. Point-counts are widely used to census songbirds, but are of little use for less detectable species. However, they have been used to census waders, waterfowl and nocturnal birds.

 Line Transects

Line transects are undertaken by observers moving along a fixed route and recording the birds they see on either side of the route. Transects can be walked on land, or flown in the air or sailed in water. The transects are most suitable for large areas of open habitat. First, the transect routes need to be chosen. A transect route could even be a square or rectangle allowing the observer to end up at the starting point. In principle, a transect could be circular, though it might be difficult to follow such a route in practice and to use exactly the same route on subsequent visits.

 The total length of the transect route varies depending upon the study in question. Practical considerations include the time available to spend in the field and the size of the area to be censused. Ideally, the total length is split down to shorter lengths. These could either be continuous or wholly independent of one another. If several different transects are to be undertaken on a plot, they should be sufficiently far apart to ensure that the same individual is not counted on different transects. The appropriate distances might be 250-500 m in open habitats. Once the transect routes have been planned, it is then necessary to decide how many visits are to be made to each route and the distance up to which the count has to be made.

 Simple indices of the number of birds recorded per unit of length of transect can be obtained by counting birds up to an unlimited distance or to a single fixed distance, on either side of the transect. Approximate densities can be calculated from the fixed strip transect but rely on the assumption that all birds are detected. More reliable measures of density can be obtained from a fixed – line distance transect in which birds are recorded separately in a central zone (the ‘near belt’) and beyond (the ‘far belt’).

 Waterfowl are sometimes counted from the air while flying along transects of known length and width. The width of the transect will vary with particular application, but an overall width of about 200m is appropriate. The plane should be flown at the lowest safe speed (e.g., 150 km/hour). In practice this will be often fast to count every individual bird, and quick estimates of flock size are often done. Bird density is then calculated from the number of birds counted and the overall area of the transect (from its width, the speed of the plane and the time taken to complete the transect).

 Disadvantages: Density can only be estimated on the assumption that birds on the transect line are not missed (e.g., if one was walking too fast), do not move before detection (e.g., if they are disturbed by the observer), are not counted twice (if one was walking too slowly), distance is estimated without error and that all observations are independent events. In practice, many of these assumptions will not be met and may lead to biases.