Identifying an organism's migratory strategies and routes has important implications for conservation. For most species of European ducks, information on the general course of migration, revealed by ringing recoveries, is available, whereas tracking data on migratory movements are limited to the largest species. In the present paper, we report the results of a tracking study on 29 Eurasian Teals, the smallest European duck, captured during the wintering period at three Italian sites. The departure date of spring migration was determined for 21 individuals, and for 15 the entire spring migratory route was reconstructed. Most ducks departed from wintering grounds between mid-February and March following straight and direct routes along the Black Sea-Mediterranean flyway. The breeding sites, usually reached by May, were spread from central to north-Eastern Europe to east of the Urals. The migratory speed was slow (approximately 36 km/day on average) because most birds stopped for several weeks at stopover sites, mainly in southeastern Europe, especially at the very beginning of migration. The active flight migration segments were covered at much higher speeds, up to 872 km/day. Stopover duration tended to be shorter when birds were closer to their breeding site. These results, based on the largest satellite tracking effort for this species, revealed for the first time the main features of the migratory strategies of individual Teals wintering in Europe, such as the migration timing and speed and stopover localization and duration.

The migration starting date (MSD) of 30 Eurasian teal and 8 Eurasian stone-curlews was estimated by processing tracking data with four methods. A significant difference was found for teal, with methods fitting models on Net Square Displacement postponing MSD compared to distance threshold methods. In stone-curlews the four methods provided comparable MSD estimates. The reliability of teal MSD was evaluated comparing the estimated ratio between time at stopover/time in flight with the ratio expected from the optimal migration theory. Threshold methods provided estimates closer to the ratio expected for time-minimizing migrants and therefore seems the most reliable approach, especially for datasets with irregular sampling and variable migratory strategies.

Migratory behaviour allows individuals to inhabit areas with optimal environmental conditions throughout the year. To reduce energy expenditure and the risk of mortality while migrating, birds may schedule their departures basing on environmental cues that provide seasonal and/or local information. In this study, we aimed to identify the possible effect of environmental factors on the spring migration of 30 Eurasian teal Anas crecca tracked between 2014 and 2018 from Italian wintering areas. We used Cox proportional hazard and generalized estimating equation models to evaluate the environmental cues that affect teal's decision to start migratory movements from the wintering grounds and continue migration from stopover sites. Apart from the anticipated effect of photoperiod, the onset of spring migration was not substantially influenced by environmental variables, whereas the speed of migration seemed to be influenced by both seasonal (increased ground temperature, an indicator of spring advancement) and local (low cloud cover and northward blowing winds, which support migratory flight) environmental cues. The slow migration observed in teal may favour a strategy in which migratory timing is modulated mainly by the conditions encountered during the journey rather than at the start of the migration. This suggested low impact of local environmental variables on the onset of spring migration could have important consequences both for the management of this species for hunting purposes and for the way the species might respond to the ongoing climatic change.

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