Computing Foraging Paths for Shore-Birds Using Fractal Dimensions and Pecking Success from Footprint Surveys on Mudflats: An Application for Red-Necked Stints in the Moroshechnaya River Estuary, Kamchatka-Russian Far East

Abstract

Foraging strategies for Red-necked Stints (Calidris ruficollis) at migration staging sites are virtually unknown, nor exist any methods to achieve such crucial knowledge. Here, for the first time a non-invasive and quantitative computing method of foraging paths is presented from a study carried out during fall migration 1999 for fine-sediment mudflats of the Moroshechnaya River Estuary (56° 50’ N, 156° 10’ E), eastern Sea of Okhotsk, Russian Far East. Footprint surveys on a mudflat were used in order to compute the distances and angles between foraging patches, including pecking success information. It was then analyzed how the pecking success at a foraging patch affects the selected distance between foraging patches and turning angles; no correlations were found. However, with increasing scale (size of divider to measure the foraging path) the fractal dimension of the foraging path generally increases, peaking at intermediate scales and then decreases at larger scales. This indicates for the working scale (grain size 1cm, extend 40cm) that Red-necked Stints make their foraging decisions using a static approach (< 20cm step-length, and 10-40° absolute change of angle). On a smaller scale, and once prey was located, they forage in food patches along ‘cracks’ of the mudflat. It is suggested that fractal dimensions of foraging paths can serve as a basic and quantitative description for the arrangement and distribution of prey patches in mudflats relevant to shorebirds. The presented approach has large potential to describe the efficiency of foraging shorebirds when analyzing pecking success at mudflats along their entire flyways.