Bird migration in space and time: chain migration by Eurasian curlew (Numenius arquata arquata) along the East Atlantic Flyway

Migration patterns in birds vary in space and time. Spatial patterns
include chain, leap frog, and telescopic migration. Temporal patterns such
as migration duration, number and duration of stopovers may vary according
to breeding latitude, sex and season. This study aimed to verify these
patterns in a long-distance migrant, the Eurasian curlew (Numenius arquata
arquata), and to provide a synopsis of spatio-temporal migration patterns
in this species of concern throughout the East Atlantic Flyway. We tagged
85 adults with GPS-data loggers in Germany, Poland, France, and Estonia
between 2013 and 2019. We computed the distance flown, linear loxodromic
distance, duration, stopover number, total stopover duration, mean
stopover duration, departure time, and arrival time for 177 out of 187
tracks. On average (± standard deviation), spring migration occurred from
April 4–14 (10.2 ± 8.4 days), curlews flew 3,623 ± 1,366 km, and had 5.8 ±
3.6 stopovers, with a duration of 29.4 ± 38.2 h per stopover, while autumn
migration occurred from June 18–29 (10.9 ± 9.9 days), curlews flew 3,362 ±
1,351 km, and had 5.4 ± 4.0 stopovers, with 31.8 ± 32.3 h per stopover.
Curlews displayed chain migration, because wintering curlews maintained
the latitudinal sequence to their breeding sites. Southern curlews had a
longer nesting period due to their earlier arrivals. While spring arrival
at breeding sites did not differ between the sexes, in autumn females
departed earlier than males. Migration duration and distance, as well as
stopover number and duration showed a significant increase with breeding
site latitude but did not differ between the sexes or between spring and
autumn migrations, suggesting that curlews took a comparable amount of
time migrating during both seasons. The high site faithfulness in curlews
suggests that rapid autumn migration allows them to return to defend their
winter foraging areas.