Roosting patterns and daily activity of migratory shorebirds at Grand Pré, Nova Scotia

Daily activity and roosting patterns of four species of migratory shorebirds, Semipalmated Plover, Black-bellied Plover, Semipalmated Sandpiper and Short-billed Dowitcher were studied at Grand Pré, Kings County, Nova Scotia from May to November, 1975. Movements of birds to and from roosts were recorded on field maps and later transferred to acetate overlays on the basis of the height of the tide at the time of flight. Factors related to the behavior of roosting shorebirds and the type of site selected for roosting were determined. Roost—types in descending order of preference were: i) sand and pebble beach; ii) inland plowed field; iii) salt marsh} and iv) pasture. Preferred roost-sites generally had the following characteristics which were related to roost quality: i) they remained uncovered by the tides; ii) they were relatively close to foraging areas; iii) they were away from areas of high disturbance; and iv) they permitted the birds unobstructed lateral vision of adjacent areas. Birds of the four species congregated at staging areas on the upper shore as the tide covered the foraging areas. Subsequently, they collected at roosts on the beach or flew in large flocks to inland sites. This pattern was reversed as the tide ebbed. Black-bellied Plover and Short-billed Dowitcher generally roosted in plowed fields or, less frequently, in salt marsh. Semipalmated Sandpiper and Semipalmated Plover usually roosted on the beaches. At night, most shorebirds were observed roosting on the beaches. Disturbance of roosting shorebirds was monitored and the sources grouped into the categories of: i) birds and dogs; ii) human activity; and iii) vehicles and machines. The responses of the shorebirds to these sources of disturbance were also evaluated and categorized. Response to direct human disturbance was most intense, followed by disturbance due to birds and dogs. The least response was elicited by vehicles and machines. The preferred beach roosts were subject to such intense human disturbance during August that they were largely abandoned until September in favour of inland roosts. The responses to disturbance were similar for birds of all four species although Short-billed Dowitcher and Black-bellied Plover were the first to respond. They were also more susceptible to the different types of disturbance than the smaller shorebirds.