Lourenço P.M. (2007) Analysing the faecal samples of Ragworm predators: not just a matter of counting mandibles. ARDEA 95 (1): 151-155

Ragworms Hediste diversicolor are an important prey item in the diet of many estuary dwelling animals. The standard method for estimating the number of Ragworms in faeces or pellets is simply dividing the counted the number of Ragworm mandibles by two, which can easily lead to an underestimation of the real number of Ragworms present. Here, I present two alternative methods, which can lead to less biased estimates of the number of Ragworms in samples. I compared the three methods by applying them on faecal samples of Grey Plover Pluvialis squatarola and Redshank Tringa totanus from the Tagus estuary, Portugal. The alternative methods yielded significantly higher estimates of the number of Ragworms present in each sample, a difference that can have repercussions on dietary studies of Ragworm predators. The pros and cons of each method are discussed in the with regard to the use of faeces and pellets for ecological research, and the situation in which each method should be applied is discussed.