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Scale dependence of the numerical response in Knots (Calidris canutus)

Vahl, W.K. (1999) Scale dependence of the numerical response in Knots (Calidris canutus). Master's Thesis / Essay, Biology.

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The numerical response between foraging waders and their prey species depends on the scale on which it is studied. The lack of a fixed numerical response is due to heterogeneity in the distribution of their food supply. In this study, the numerical response of Knots (Calidris can utus) is studied on three different scales on a single mud flat in the western Wadden Sea (the Netherlands); the largest scale concerns the entire mud flat, whereas the other two concern the scales of between and within corners of this mud flat. The distribution of flocks of Knots is observed on a daily basis, by checking 67 quadrants for the presence of a flock of Knots several times a week. Food supply in these quadrants is measured on a regular basis. Diet composition is measured both through direct observations in the field and by collecting Knot-droppings. On neither of the three different scales a strong numerical response is observed. On the largest scale our rough measurements of Knot abundance only indicate that Knots can distinguish patch quality on this level. On the scale of interest, the between corners of the mud flat scale, neither significant nor strong relations with the biomass-density of a specific prey species is found, probably due to the small sample size. The average relation between Knot abundance and biomass-density of Carcinus maenas on the smallest scale of observation is significant though very weak. Despite of problems following from an incomplete design, it can be concluded that Knots forage on Carcinus rnaenas when this prey is abundant. Otherwise they forage on Cerastoderina edule even though Macoma baithica is present at rather high densities as well. The ignorance of Macoma baithica to the diet might be due to the use of a foraging mode specific for Carcinus maenas and Cerastoderma edule; the consumption of these shallow living prey species does not require the deep probing of the bill needed for capturing Macoma baithica.

Item Type: Thesis (Master's Thesis / Essay)
Degree programme: Biology
Thesis type: Master's Thesis / Essay
Language: English
Date Deposited: 15 Feb 2018 07:44
Last Modified: 15 Feb 2018 07:44

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