Identification of Little Tern (Sternula albifrons) Prey in Inland Andong Lake, Korea Using Video Image Analysis

Abstract

Little Tern (Sternula albifrons) prey composition was studied on a sandy islet in inland Andong Lake, Republic of Korea, during the breeding season (April to July 2018). Two remote-control video cameras with 4K-resolution were set on the islet to identify prey and determine whether prey species composition or size differed among breeding stages. On still images in which terns had prey in their bills (n = 1,275), prey species were identified, classified to five length-categories, and compared among breeding stages. Freshwater fishes dominated the observed diet (100%; 11 species overall), where the landlocked pond smelt (Hypomesus nipponensis; 80.8%) and largemouth bass (Micropterus salmoides; 13.7%) were main prey species. The mean prey length was 51.0 ± 20.89 mm, where 50.1–75.0 mm prey was the most frequent in the diet (42.2%) and varied significantly among breeding stages; 50.1–75.0 mm prey were most frequent during courtship and incubation stages, whereas 1.0–25.0 mm prey were most frequent at the chick-rearing stage. Surface water temperatures exceeded the upper thermal tolerance of the primary prey species at a date coincidental with tern departure from the colony.