Migration strategies of the Baltic dunlin: rapid jump migration in the autumn but slower skipping type spring migration

Abstract

Migration during spring is usually faster than during autumn because of competition for breeding territories. In some cases, however, the costs and benefits associated with the environment can lead to slower spring migration, but examples are quite rare. We compared seasonal migration strategies of the endangered Baltic population of the dunlin Calidris alpina schinzii using light‐level geolocator data from 26 individuals breeding in Finland. Autumn migration was faster, with individuals showing a ‘jump’ and ‘skipping’ migration strategy characterised by fewer stationary periods, shorter total stopping time and faster flight. Spring migration was slower, with individuals using a ‘skipping’ strategy. The duration of migration was longer for early departing birds during spring but not during autumn suggesting that early spring migrants are prevented from arriving to the breeding areas or that fueling conditions are worse on the stopover sites for early arriving individuals. Dunlins showed high migratory connectivity. All individuals had one long staging at the Wadden Sea in the autumn after which half of the individuals flew 4500 km non‐stop to Banc d’Arguin, Mauritania. The other half stopped briefly on the Atlantic coast on their way to Mauritania. One bird wintered on the coast of Portugal. Nine individuals that carried geolocators for two years were site faithful to their final non‐breeding sites. Based on the strategies during the non‐breeding period we identified, Baltic dunlin may be especially vulnerable to rapid environmental changes at the staging and non‐breeding areas. Consequently, the preservation of the identified non‐breeding areas is important for their conservation.

Finish with a sprint: Evidence for time‐selected last leg of migration in a long‐distance migratory songbird

“…Geolocator‐tracked swifts Apus apus showed no clear pattern of changes in travel rate between early and late stages of migration, while, similar to our tracked flycatchers, the swifts showed increased speed during the barrier crossing (Åkesson, Klaassen, Holmgren, Fox, & Hedenström, ). Rapid crossing of ecological barriers have also been demonstrated in other songbirds (Adamík et al., ; Ouwehand & Both, ) as well as waders (Klaassen, Alerstam, Carlsson, Fox, & Lindström, ; Pakanen et al., ). However, a comprehensive comparison of migration speeds in songbirds over different parts of their journey is still lacking due to former weight limitations of tracking devices.…”

Survival probability in a small shorebird decreases with the time an individual carries a tracking device

“…methods. The difference may be due to different migratory behaviour as hoopoes use multiple stopovers (Bächler et al 2010, van Wijk et al 2015, whereas southern dunlins may fly up to 4500 km nonstop during autumn migration (Pakanen et al 2018). Our results suggest that such a relatively small load may not be sustainable in the long term, especially when facing adverse conditions.…”

“…Multiple renesting may cause a substantial increase in energy expenditure via egg laying (Monaghan and Nager 1997), and females may therefore be in a poor condition at the start of migration. Interestingly, females also depart on migration earlier than males, leaving less time for preparation (Pakanen et al 2018). Therefore, the additional energy expenditure and stress caused by a tracking device during migration may be fatal.…”

“…In 2013 and 2014, we deployed light-level geolocators (Intigeo-W65A9, Migrate Technology Ltd) with plastic (Salbex) leg-flags on the tibia of 53 breeding southern dunlins (Pakanen et al 2015(Pakanen et al , 2018. The device including the flag weighed 0.8 g, which is about 1.5-2.0% (mean mass 46.4 g, SD 3.69) of their body mass.…”

“…Geolocators are the main tracking devices for studying migration of smaller species (Briedis et al 2018, Procházka et al 2018. We deployed geolocators in 2013-2014 to document migration of a southern dunlin Calidris alpina schinzii population that has been studied in detail since 2002 (Pakanen et al 2011(Pakanen et al , 2015(Pakanen et al , 2018. Our previous analyses found no strong effects on return rates or reproduction in the year after deployment in this long-distance migratory shorebird (Pakanen et al 2015, Weiser et al 2016.…”