Recoveries by Condition for Caspian Tern

Although ringing of this species has started in the early 20th century, most encounters have been obtained after the 1960s. They come mainly from the breeding season and especially from Jun – nearly half of all records (48%). Majority of encounters (65%) are recorded in N Europe. The encounters based on dead birds considerably decreased over time – from 86% pre-1960 to 14% after 1991; those based on alive birds markedly increased – from 1% pre-1960 to 84% after 1991. The latter is mostly due to ringing recoveries, and especially to metal ring readings in the field and colour mark encounters. Shooting constituted 58% of all cases before 1960, it is currently reduced to about 3%. Birds are locally trapped in W Africa (especially in the Inner Niger Delta in Mali) for sport, food and income (Zwarts et al. 2009).

Annual Movements for Caspian Tern

Post-breeding dispersal starts in late Jul, the autumn movements are evident from Aug – numerous encounters (both coastal and inland) from W, C & E Europe. Mediterranean region is reached mainly Sep-Oct. Most breeding sites are left by Oct. The African wintering grounds (mostly Senegal, Mali & Ghana, but scattered records throughout the Sahel E to Chad) are occupied as early as Oct, but mostly in Nov.

First-year birds commonly remain in W Africa during the summer (Zwarts et al. 2009), some undertaking partial return migration (Kilpi, Saurola, 1984). Recent satellite-tracking study identified (based on 39 birds) W Sahel (69%), lake Chad (10%), Nile River Delta & Basin (8%); as main wintering regions in Africa; 13% remained to overwinter in S Spain (Rueda-Uribe et al. 2021).

Spring migration starts in Mar-Apr and the breeding sites are reached back in Apr-May.

Connectivity by Month by Region for Caspian Tern

Unlike most other tern species, Caspian Terns routinely fly overland on their way to and from the wintering grounds (Zwarts et al. 2009). In Europe, the Fennoscandian population undertakes the longest distance migration (Shiomi et al. 2015).

Baltic Sea population takes mainly SW & S routes, while the Black Sea region breeders – mostly SW. Dispersal movements after the breeding season start in late summer, lots of encounters are spread throughout Europe. Most birds reach S Europe & N Africa early to mid-autumn. A small part of them stay to overwinter (S Spain), while the bulk continues to the wintering grounds (mostly in W Africa, but also in C & E Africa) which are reached mainly in late autumn. Return migration takes place primarily in mid- to late spring.

A vagrant bird marked in USA has been encountered in UK during the 1930s.