A method widely used in order to measure populations of species is that of mark, release and recapture. Species that are small such as insects and mammals are often difficult to count therefore population numbers of such species are hard to establish. Due to the difficulty in this population estimates are made through what is known as the Lincoln Index (Chapman and Reiss, 2009). The method is carried out through capturing a number of individuals which are then marked so that they can be recognised again if they are recaptured after the initial release. The original marked individuals may be recaptured whereby the proportion of marked to unmarked individuals can then be calculated to estimate the population size through the following equation (Chapman and Reiss, 2009). N= CM R Whereby N refers to the whole population, C is the number of individuals captured, M is the number of individuals marked and R is the number of individuals released. 2.6.4 Counting Individual Species There are generally three different methods for counting individual species, with these being direct and indirect counting, along with look-see counting (Bibby 1993). et al, Direct counting involves the counting of all visible birds from a suitable vantage point whereby the birds are easily distinguished; for example waders breeding on a small island (Bibby 1993). Factors can influence the results of this method which may et al, impact upon the quality of the results. As Bibby (1993) examines accuracy can be et al affected by those undertaking counts with the naked eye or with binoculars. Indirect counting differs from direct as it relies upon counting signs of bird activity such as droppings, this however may only be useful where species live in burrows (Bibby et al, 1993). An example of this would be that of the Manx Shearwater whereby on the Island of Rum in the Inner Hebrides of Scotland they make their burrows in order to raise their young (Butt, 2012). It can however be argued that the number of droppings only indicates bird usage rather than population numbers (Owen, 1971).
A method widely used in order to measure populations of species is that of mark, release and recapture. Species that are small such as insects and mammals are often difficult to count therefore population numbers of such species are hard to establish. Due to the difficulty in this population estimates are made through what is known as the Lincoln Index (Chapman and Reiss, 2009). The method is carried out through capturing a number of individuals which are then marked so that they can be recognised again if they are recaptured after the initial release. The original marked individuals may be recaptured whereby the proportion of marked to unmarked individuals can then be calculated to estimate the population size through the following equation (Chapman and Reiss, 2009). N= CM R Whereby N refers to the whole population, C is the number of individuals captured, M is the number of individuals marked and R is the number of individuals released. 2.6.4 Counting Individual Species There are generally three different methods for counting individual species, with these being direct and indirect counting, along with look-see counting (Bibby et al, 1993). Direct counting involves the counting of all visible birds from a suitable vantage point whereby the birds are easily distinguished; for example waders breeding on a small island (Bibby et al, 1993). Factors can influence the results of this method which may impact upon the quality of the results. As Bibby et al (1993) examines accuracy can be affected by those undertaking counts with the naked eye or with binoculars. Indirect counting differs from direct as it relies upon counting signs of bird activity such as droppings, this however may only be useful where species live in burrows (Bibby et al, 1993). An example of this would be that of the Manx Shearwater whereby on the Island of Rum in the Inner Hebrides of Scotland they make their burrows in order to raise their young (Butt, 2012). It can however be argued that the number of droppings only indicates bird usage rather than population numbers (Owen, 1971).
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