| We examined the fasting migration hypothesis for Swainson's Hawks (Buteo swainsoni) by estimating the length, duration, and speed of the migration between North and South America and measuring changes in their body masses at various times throughout the year. We instrumented 34 adult Swainson's Hawks with satellite radios on their breeding grounds in western North America to determine the duration, length, and speed of the migration. Migrating south at 188 km/day, it took Swainson's Hawks 51 days to complete their 13504 km migration to their austral summer grounds. Averaging only 150 km/day on their return migration, it took them 60 days to complete the shorter 11952 km migration back to North America. Adult male and female Swainson's Hawks had average... |
