The path to success: Foraging paths and behaviour of oystercatchers in relation to their food supply

In this research the influence of food distribution on the walk patterns of oystercatchers Haematopus ostralegus was studied. Oystercatchers feed on bivalves and worms that live below the surface in the sediment of mudflats. Oystercatchers were expected to follow different walk paths on basis of their foraging success. Oystercatchers are expected to follow a more sinuous path in a patch with a lot of food and a straighter path in a patch with a low food availability. When an oystercatcher performs a more sinuous, random walk the chance that it walks out of a patch is smaller, which would be profitable in a high quality patch. Soil samples were taken to determine the food distribution of one mudflat and films were made to study the foraging success and walk paths of individual oystercatchers. The hitrate (number of hits per second of foraging) of individual oystercatchers was calculated. For individual walk paths we looked at the turning angle, average interval distance (distances an oystercatcher walked until it stood still or changed direction) and average walk speed. There was no significant relation between foraging success and food distribution on the mudflat, oystercatchers did not find more food in patches with more food available. The results show that oystercatchers turned more and walked shorter interval distances during foraging when the hitrate was higher. An analysis on a smaller scale showed that oystercatchers made a larger turning angle after a successful interval. The walk speed was significantly related to the presence of other oystercatchers and wind speed.