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1 December 2019 Migration tactics of a long-distance migratory songbird from across a continental breeding range
Rosalind Renfrew, Dan Kim, Noah Perlut, Michael D. Cadman
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Migration strategies in the avian world are often compared at the species level and evaluated relative to general ecology and constraints such as molting and breeding timetables. The advancement of tracking technology provides an opportunity to explore variation in more specific migration tactics within species and their populations as it relates to demographic and environmental factors throughout the annual cycle. We compare migration timing among 4 populations of Bobolink (Dolichonyx oryzivorus) from across the breeding range using data from light-level geolocators. The date of departure from the breeding grounds and the duration of southbound migration differed among breeding populations, and were more variable for eastern breeding populations compared to western populations farther from the main migration corridor. Despite variation in both timing and distance from the corridor among breeding populations, date of arrival at the major southbound stop in the Llanos of South America remained synchronous, but less so than previously described. Weekly flight distances were highly variable and did not differ among populations. Duration of northbound migration did not differ among populations and was half as long as the southbound migration. Our findings show Bobolink populations breeding near the species' relatively narrow migration corridor in the southeastern United States were more variable in terms of how they reached the first lengthy stop in the Llanos, suggesting more flexibility in migration tactics. Breeding locations were not associated, however, with the timing or duration of the remainder of their migratory schedule. Our findings support the hypothesis that food resources, both historical and present, drive and also modify the endogenous migration schedule of this flocking species with a split migration.

Rosalind Renfrew, Dan Kim, Noah Perlut, and Michael D. Cadman "Migration tactics of a long-distance migratory songbird from across a continental breeding range," The Wilson Journal of Ornithology 131(4), 735-749, (1 December 2019).
Received: 26 September 2017; Accepted: 23 December 2018; Published: 1 December 2019

Dolichonyx oryzivorus
migration tactics
molting grounds
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