Long-term series of measurements of eggs and chicks of Caspian terns (Hydroprogne caspia) breeding in Lake Chany, Western Siberia, Russia, during 1985 and 2011

Caspian terns (Hydroprogne caspia (Pallas, 1770)) present a sub-cosmopolitan but scattered distribution, and many of its colonies are in a vulnerable state. The species has been listed in the Red Data Book of the Russian Federation and is covered by the Agreement on the Conservation of African-Eurasian Migratory Waterbirds (AEWA). We observed the colonies of Caspian terns repeatedly in the breeding season from May to June on the islands of Lake Chany from 1985 to 2011. We recorded clutch size, eggshell coloration and measured egg length and width to the nearest 0.1 mm with a caliper. Furthermore, we recorded the fate and hatching date of individual eggs and determined the clutch initiation date. Head, bill, tarsus length and body weight of newly hatched chicks was measured. Caspian tern colony size changed between years from 50 nests in 1985 to 513 in 1999, therefore, the sample size of measured eggs varied from 90 to 1,045. A total of 4,137 eggs and 570 chicks were measured. We provide new information for this species nesting in west Siberia, which is important to compare with other local results. The presented data set is a novel long-term data set on an isolated population of this species in center of Eurasian continent. The complete data set for this abstract published in the Data Article section of the journal is available in electronic format in MetaCat in JaLTER at http://db.cger.nies.go.jp/JaLTER/metacat/metacat/ERDP-2023-02.1/jalter-en.