Bregnballe, Thomas4; Vinas, Marta Mas3; Gregersen, Jens3
1 Department of Bioscience - Biodiversity and Conservation, Department of Bioscience, Science and Technology, Aarhus University2 Department of Bioscience - Wildlife Ecology, Department of Bioscience, Science and Technology, Aarhus University3 unknown4 Department of Bioscience - Wildlife Ecology, Department of Bioscience, Science and Technology, Aarhus University
Like other seabirds Great Cormorants Phalacrocorax carbo sinensis are known to prospect in potential breeding colonies during their first years of life before they settle to breed. Based on daily resightings of colour-ringed cormorants in the old Vorsø colony we examined the difference between native and non-native birds with respect to their timing and pattern of colony attendance during the breeding season. We also explored how colony location influenced the tendency of first-year birds and 1-3-year-old cormorants ringed in eighteen different Danish cormorant colonies to visit the study colony. We found that juveniles from colonies close to Vorsø were approximately up to 12 times more likely to visit the Vorsø colony than birds originating from colonies located further away. We looked at changes over an 18-year-period in the proportion of individuals visiting the colony and in their duration of stay. We observed a decline in the duration of stay for both natal and non-natal birds, but immature natal birds always stayed far longer on average than visiting non-natal birds.