Intratropical migration of the Hook-billed Kite ( Chondrohierax uncinatus ) in Middle America

The Hook-billed Kite (Chondrohierax uncinatus) is a specialized and secretive Neotropical raptor that has received little research attention. Despite scattered records of Hook-billed Kite movements, this species was long thought to be non-migratory. We studied the southbound autumn migration of Hook-billed Kites in Veracruz, Mexico, and Belize and investigated whether environmental conditions on their breeding grounds influenced migration. We collected migration count data over 8 years (2013–2020) in Belize and 25 years (1995–2019) in Veracruz. In Belize, we recorded 39,928 Hook-billed Kites on their southbound autumn migration during a total of 3093.1 count hours, with an autumn seasonal mean (±SE) count of 4991 ± 1083 kites/year, with flocks consisting of up to 200 individuals. In comparison, during a total of 42,531 count hours at two count sites in Veracruz, we recorded 3870 Hook-billed Kites with a seasonal mean (±SE) count of 154.8 ± 12.1 kites/year. Most kites in Veracruz migrated as single individuals or groups of < 4 birds and the largest flock ever recorded had 12 individuals. The mean 95% seasonal passage window of Hook-billed Kites in Belize lasted 44.9 ± 2.5 d (N = 8 years) from 26 October to 9 December compared to an earlier passage from 13 September–11 November in Veracruz (N = 25 years). Precipitation on the breeding grounds had no influence on the timing or magnitude of the kite migration through Belize; whereas, in Veracruz, migration timing occurred later as precipitation north of the count site increased. Notably, age, sex, and color morph classes migrated in mixed flocks; therefore, we detected no signs of differential migration, which is uncommon among raptors. Our study describes, for the first time, the largest known southbound autumn migration of Hook-billed Kites. Working to understand the life histories of tropical raptors provides critical ecological information, which can aid in identifying potential threats, conservation needs, and population statuses.