The Wildlife Services-National Wildlife Research Center’s Mississippi Field Station working in conjunction with Alabama WS operations conducted 61 dispersal events on Double-crested cormorant (DCCO) night roosts. Approximately 93,200 DCCO (98 %) were dispersed using a combination of non-lethal and lethal harassment techniques.
We fit a sample of DCCOs with GPS transmitters to monitor their movements relative to night roost dispersal. We deployed a total of 38 transmitters from January-February 2020 and November 2020 to February 2021, of which 17 produced more than 1 month of location data. We have gathered data encompassing 494,874 DCCO locations in 2020, 2021 and 2022.
Six GPS-DCCOs were present at the night roosts during 14 roost dispersal events with some individual birds being dispersed from 1 to 4 times during February-March 2021 and one DCCO was present at the night roost harassed in early December 2020. These six DCCO used 10 or more nights roosts during the two weeks prior and after roost harassment. We calculated the daily average and maximum distance traveled from the harassed roosts two weeks before and after the harassment event.
The habitat of DCCOs during winters consisted of 14% wetlands, 22% waterbodies, 26% fish ponds, and 38% other types. After harassment we found that 3 of the 6DCCOs increased their daily distance from the harassed roost and foraged in different areas, containing other catfish ponds, than those prior to roost harassment. Four out of 6 DCCO did not increase their daily distance after harassment and foraged in the same areas before and after harassment. A DCCO stopped using fish ponds within a week after the night roost harassment. Another DCCO showed an initial reduction in the use of fish ponds followed by fluctuations in the use of fish ponds. We plan to deploy 10 additional GPS transmitters from November 2022-February 2023 to increase our sample size and more accurately assess the impacts of night roost harassment on the night roost use, foraging areas, and daily movements.