Water Balance During Real and Simulated Long-Distance Migratory Flight in the Bar-Tailed Godwit

We examined Bar-tailed Godwits (Limosa lapponica), a long-distance migratory shorebird, for evidence of dehydration toward the end of their 4,300-km migratory flight from West Africa to the Dutch Wadden Sea. Bar-tailed Godwits are ideal subjects for research on flight range constraints because they can readily be caught in migratory flight. Because godwits are capable of long nonstop travel, we hypothesized that they are physiologically adapted to minimize en route water loss, and therefore, do not experience water imbalance under standard migratory conditions. To test this hypothesis, we compared the hydration state of flying Bar-tailed Godwits at the end of a long bout of migratory flight to that of recently-landed godwits. Flying godwits were hydrated to the same degree as birds with free access to water, suggesting that godwits maintain water balance during migratory flight. To corroborate these empirical results, we ran a theoretical simulation of flight-incurred loss of water and energy in a male Bar-tailed Godwit based on the published model by Klaassen et al. (1999). When a low body drag is assumed, model output suggests that Bar-tailed Godwits flying at altitudes ranging from sea level to 3,000 m will avoid dehydration, and that flight at about 3,000 m will result in the longest possible flight range.