MOVEMENTS OF DOUBLE-CRESTED CORMORANTS AMONG WINTER ROOSTS IN THE DELTA REGION OF MISSISSIPPI

From 12 Jan.-9 Apr. 1993, 25 Double-crested Cormorants (Phalacrocorax auritus) were captured, fitted with radio-telemetry transmitters, and monitored to determine night-roost fidelity and movements in the Delta Region of Mississippi. Transmitter-equipped cormorants were located a t 15 different roost sites during the study. The mean number of roosts used by cormorants was 2.08 +/- 0.172 SE. The mean number of transmit ter-equipped cormorants located each week was 8.25 +/- 0.87 SE. The di stances moved by cormorants among night roosts ranged from 0-398 km. I n the eastern part of the Delta Region two studies were conducted conc urrently with this telemetry study to determine if repeated harassment of roosting cormorants using pyrotechnics would cause cormorants to a bandon selected roosts and nearby aquaculture facilities. Dispersed ro osts were repeatedly harassed with pyrotechnics in the eastern part of the Delta Region and non-dispersed roosts in the western part of the Delta Region were not harassed. There was no significant difference in cormorant movement to more than one roost after transmitter attachmen t between birds captured in dispersed roosts versus non-dispersed roos ts. Three transmitter-equipped cormorants were located on the Gulf coa st approximately 390 km from the study area. One subsequently moved ba ck to the study area These observations provide evidence that in Missi ssippi wintering populations of cormorants show no strong fidelity to a primary roost, but shift throughout the Delta Region and to the Gulf coast.