Colony relocation of Greater Crested Terns Thalasseus bergii in Bass Strait, south-eastern Australia

A newly established Greater Crested Tern Thalasseus bergii colony was observed on Kanowna Island, northern Bass Strait, in December 2019 and was monitored through January 2020. A maximum of 532 ± 28 nests was counted,representing ~15–20% of the known northern Bass Strait breeding population. Resightings of 69 leg-banded individuals (from 3 to 24 years of age) demonstrated that founding individuals originated from colonies in Victoria [The Nobbies on Phillip Island (54%), Corner Inlet Barrier Islands (39%), Mud Islands in Port Phillip Bay (6%)] and one individual from South Australia. Breeding began 2 months later than usual for northern Bass Strait, perhaps because the birds only moved to Kanowna Island after failed nesting attempts elsewhere (Corner Inlet and Phillip Island). Individuals were observed to mainly feed their chicks with Barracouta Thyrsites atun and Jack Mackerel Trachurus declivis, contrasting with the usual predominance of Australian Anchovy Engraulis australis in the diet of this species in the Bass Strait region. This relocation may result from local changes in prey availability and/or a combination of potential human disturbance, predation and storm events. The recent 50% decrease in the number of breeding Greater Crested Terns in Victoria suggests substantial changes in the regional environmental conditions, highlighting the importance of understanding the impact of environmental variations on seabird species.