Volume 135, 2018, pp. 572–582 DOI: 10.1642/AUK-17-224.1 RESEARCH ARTICLE Classic pattern of leapfrog migration in Sooty Fox Sparrow (Passerella iliaca unalaschcensis) is not supported by direct migration tracking of individual birds Kevin C. Fraser,1*Amelie´ Roberto-Charron,1 Bruce Cousens,2 Michael Simmons,3 Ann Nightingale,3 Amanda C. Shave,1 Renee´ L. Cormier,4 and Diana L. Humple4 1 Department of Biological Sciences, University of Manitoba, Winnipeg, Manitoba, Canada 2 Georgia Basin Ecological Assessment and Restoration Society, Nanaimo, British Columbia, Canada 3 Rocky Point Bird Observatory, Victoria, British Columbia, Canada 4 Point Blue Conservation Science, Petaluma, California, USA * Corresponding author: [email protected] Submitted November 22, 2017; Accepted February 22, 2018; Published May 9, 2018 ABSTRACT Leapfrog migration systems, whereby more-northern breeding populations overwinter the farthest south, provide unique opportunities to further our understanding of how environmental variation shapes migratory behavior and the seasonal distributions of birds. Leapfrog migration in a western Fox Sparrow subspecies complex (Passerella iliaca unalaschcensis, Sooty Fox Sparrow) was described as early as 1920, and has served as an exemplar of leapfrog systems in subsequent theoretical work. However, migration behavior within P. i. unalaschcensis has never been studied directly, nor has the proposed leapfrog pattern been confirmed through the tracking of individuals. Using light-level geolocators and GPS tags, we tested the long-standing pattern of leapfrog migration in Sooty Fox Sparrows by determining spatiotemporal movement patterns for individuals originating from a northern (Vancouver Island, British Columbia) and a more southern (Point Reyes, California) overwintering region, where migratory timing, routes, and breeding locations were predicted to differ. Our results did not support the proposed leapfrog migration pattern in several ways. Individuals overwintering on Vancouver Island were predicted to be sedentary and/or breed locally, but we found they traveled more than 3,000 km to breeding sites in coastal northwestern British Columbia and southern Alaska. Birds overwintering in California had breeding locations that overlapped those of birds from British Columbia, as well as the predicted breeding regions of 4 other subspecies. Lastly, spring and fall migration routes were largely coastal for both groups, and we found no evidence of a proposed transoceanic fall migration route between Alaskan breeding sites and Californian overwintering sites. Thus, our results do not support the long-held pattern of leapfrog migration in Sooty Fox Sparrows and further highlight that bio-logging tools can reveal important new insights into patterns of migratory behavior, even in relatively well-studied systems. Keywords: bio-logging, geolocator, migration ecology, migratory connectivity, movement ecology, songbird Le patron classique de migration en saute-mouton chez Passerella iliaca unalaschcensis n’est pas appuye´ par le suivi de la migration directe des oiseaux RESUM´ E´ Les systemes` de migration en saute-mouton, selon lesquels les populations nichant le plus au nord passent l’hiver le plus au sud, fournissent des occasions uniques de mieux comprendre comment la variation environnementale fa¸conne le comportement migrateur et les distributions saisonnieres` des oiseaux. La migration en saute-mouton chez Passerella iliaca unalaschcensis (complexe de sous-especes` de l’Ouest de P. iliaca)aet´ ed´ ecrite´ des` 1920 et a servi d’exemple de systemes` de saute-mouton dans les travaux theoriques´ subsequents.´ Toutefois, le comportement de migration au sein de P. i. unalaschcensis n’a jamais et´ e´ etudi´ e´ directement et le patron de saute-mouton propose´ n’a pas et´ e´ confirme´ par le suivi d’individus. A` l’aide de geolocalisateurs´ legers´ et de balises GPS, nous avons teste´ le modele` etabli´ de longue date de la migration en saute-mouton chez P. iliaca unalaschcensis en determinant´ les patrons de deplacement´ spatio-temporels des individus provenant de regions´ d’hivernage nordiques (ˆıle de Vancouver, en Colombie- Britannique) et plus meridionales´ (Point Reyes, en Californie), ouonpr` edisait´ des differences´ dans la periode´ de migration, les voies migratoires et les aires de reproduction. Nos resultats´ n’appuyaient pas le patron de migration en saute-mouton propose´ de plusieurs fa¸cons. Nous avions predit´ que les individus qui hivernaient sur l’ˆıle de Vancouver etaient´ sedentaires´ et/ou se reproduisaient localement, mais nous avons trouve´ qu’ils se depla¸´ caient sur plus de 3 000 km jusqu’aux aires de reproduction sur les cotesˆ du nord-ouest de la Colombie-Britannique et du sud de l’Alaska. Les oiseaux qui hivernaient en Californie avaient des aires de reproduction qui chevauchaient celles des oiseaux de Q 2018 American Ornithological Society. ISSN 0004-8038, electronic ISSN 1938-4254 Direct all requests to reproduce journal content to the AOS Publications Office at [email protected] K. C. Fraser, A. Roberto-Charron, B. Cousens, et al. No leapfrog migration in Sooty Fox Sparrow 573 Colombie-Britannique, de memeˆ que les regions´ de reproduction predites´ de quatre sous-especes.` Enfin, les routes migratoires au printemps et a` l’automne passaient principalement le long des cotesˆ pour les deux groupes et nous n’avons trouve´ aucune preuve d’une voie migratoire transoceanique´ en automne entre les sites de reproduction en Alaska et les sites d’hivernage en Californie. Ainsi, nos resultats´ n’appuient pas le modele` etabli´ depuis longtemps de la migration en saute-mouton chez P. i. unalaschcensis et soulignent davantage que les outils de bio-logging jeter un important nouvel eclairage´ sur les patrons de comportements migratoires, memeˆ dans des systemes` relativement bien etudi´ es.´ Mots-cles:´ ecologie´ de la migration, ecologie´ des deplacements,´ bio-logging, oiseau chanteur, geolocalisateur,´ connectivite´ migratoire INTRODUCTION The Fox Sparrow (Passerella iliaca) is one of the most widely distributed migratory passerines, with a breeding The spatiotemporal patterns of long-distance songbird range that spans continental North America. Owing to migration have fascinated generations of researchers great geographic variation in plumage, structure, and and provide important test beds for investigating the behavior, up to 18 subspecies of Fox Sparrow have been evolution of seasonal distributions and migration proposed (Weckstein et al. 2002), with 4 officially behavior. Intraspecific variation in migration timing, recognized (American Ornithologists’ Union 1998). Ge- routes, and seasonal distributions may arise through netic (mtDNA) evidence supports P. i. unalaschcensis competition, variation in the degree of seasonality, and/ (Sooty Fox Sparrow) as one of the 4 recognized North or habitat quality across species’ ranges (Newton 2008). American subspecies (Zink 1994). Sooty Fox Sparrow has Leapfrog migration is one such intraspecific pattern that been further divided into 6 or 7 subspecies, based upon has been reported in a diverse array of avian taxa in both morphological and plumage characteristics (Swarth 1920, New and Old World migration systems (Newton 2008). Webster 1983, Rising 1996, Weckstein et al. 2002). A In a leapfrog system, the most-northern breeding leapfrog migration system was described for the Sooty populations within a species have the longest migration group (Swarth 1920), and this system has since served as distance and overwinter the farthest south, leapfrogging an ‘‘exemplar’’ of leapfrog migration in numerous theoret- over more-southern breeders and their overwintering ical works as well as textbooks devoted to migration regions. Several hypotheses for the evolution of leapfrog ecology and animal behavior (Bell 1997, Alerstam and migration systems have been proposed. This pattern may Hedenstrom 1998, Newton 2008, Alcock 2009). Sooty Fox arise through competitive interactions, such as when Sparrows breed from the Canada–United States border to more-northern breeding individuals encounter non- the Alaskan Peninsula and winter from southern British breeding areas already occupied by more-southern Columbia to southern California (Weckstein et al. 2002). breeders that completed breeding earlier, and therefore Fox Sparrows overwintering in the southern British journey farther to acquire available sites (Newton 2008). Columbia region were ascribed to the P. i. fuliginosa Alternatively, this pattern may be driven by variation in subspecies of Sooty Fox Sparrow, and were described as habitat quality and/or seasonality at overwintering areas, ‘‘hardly migratory at all’’ with the exception of altitudinal or where higher-quality habitats may support longer local movements (Swarth 1920). Sooty Fox Sparrows migration distances, allowing birds that overwinter overwintering in California were expected to be the most farther south to leapfrog over more-southern breeders migratory and to leapfrog the more sedentary northern to sites farther north (Bell 1997); this was recently groups as they journeyed to and from breeding sites suggested for leapfrog migration in Wood Thrushes distributed across coastal areas of northwestern British (Hylocichla mustelina; McKinnon et al. 2015). New Columbia and southern Alaska (Swarth 1920). Within direct-tracking technologies now offer additional means these Californian overwintering subspecies, an east-to- of addressing critical knowledge