A Study on Ecological Relationships between Crab Plover and Oystercatcher with prey Organisms in Sajjafi Mudflats

Ecological relations between foragers and their prey in two species of waders, crab plover (Dromas ardeola) and oystercatcher (Haematopus ostralegus), were studied in Zohre river mudflats over 9 months between summer 2004 to winter 2005. Seven line transects each with about 400 meters were detected in two sides of the river that four of which were located in the river estuary. The main food of crab plover and oystercatcher were determined via direct sighting, collection of shells scattered around nests, hunting and exploring the stomach contents Variable Circular Plot or VCP and distance to nearest neighborhood and quadrate methods were used for birds, crabs and cockles density and abundance estimation respectively. Then acquired data were analyzed by DISTANCE software. This study showed that the main food of crab plover and oystercatcher are Eurycarcinus orientalis and cockles from Cardidae family (Trachycardium and Laevicardium genuses) respectively. Crab populations are generally distributed in patches and the area between patches is taken to be devoid of prey. Foragers (Crab plover) must maximize their rate of energy intake and do not spend time and energy traveling between patches whereas tide is a time limiting factor. In this study it was found that crab plover should select the patch where they obtain the highest intake rates and its population is highly correlated with crab’s populations (= 0.875, P < 0.005). But there is no significant relationship between oystercatcher population density distributions with cockles (= 0.072, P < 0.005). The results suggest that measurement of prey availability can account for prey activity patterns.