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

Abstract

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)(2014)(2015)(2016)(2017)(2018)(2019)(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.RESUMEN. Chonrrohierax uncinatus es una ave rapaz Neotropical especializada y sigilosa que ha recibido poca atención en la investigación. A pesar de los registros dispersos de los movimientos de C. uncinatus, por largo tiempo se ha pensado que esta especie no es migratoria. Estudiamos la migración de otoño hacia el sur de C. unicnatus en Veracruz, México y Belice e investigamos si las condiciones ambientales en la zona de reproducción influencian la migración. Colectamos datos de conteos migratorios durante 8 años (2013-2020) en Belice y 25 años en Veracruz. En Belice registramos 39,928 individuos durante su migración de otoño hacia el sur durante un total de 3093.1 horas de conteo, con un promedio de los conteos de otoño estacionales (±SE) de 4991 ± 1083 aves/ año, con bandadas compuestas por hasta 200 individuos. En comparación, durante un total de 42,531 horas de conteo en dos sitios en Veracruz, registramos 3870 C. uncinatus con un promedio en los conteos estacionales (±SE) de 154.8 ± 12.1 ave...