Kevin C. Fraser

Repeat tracking of individual songbirds reveals consistent migration timing but flexibility in route.

Tracking repeat migratory journeys of individual animals is required to assess phenotypic plasticity of individual migration behaviour in space and time. We used light-level geolocators to track the long-distance journeys of migratory songbirds (wood thrush, Hylocichla mustelina), and, for the first time, repeat journeys of individuals. We compare between- and within-individual variation in migration to examine flexibility of timing and route in spring and autumn. Date of departure from wintering sites in Central America, along with sex and age factors, explained most of the variation (71%) in arrival date at North American breeding sites. Spring migration showed high within-individual repeatability in timing, but not in route. In particular, spring departure dates of individuals were highly repeatable, with a mean difference between years of just 3 days. Autumn migration timing and routes were not repeatable. Our results provide novel evidence of low phenotypic plasticity in timing of spring migration, which may limit the ability of individuals to adjust migration schedules in response to climate change.

Continent-wide tracking to determine migratory connectivity and tropical habitat associations of a declining aerial insectivore

North American birds that feed on flying insects are experiencing steep population declines, particularly long-distance migratory populations in the northern breeding range. We determine, for the first time, the level of migratory connectivity across the range of a songbird using direct tracking of individuals, and test whether declining northern populations have higher exposure to agricultural landscapes at their non-breeding grounds in South America. We used light-level geolocators to track purple martins, Progne subis, originating from North American breeding populations, coast-to-coast (n = 95 individuals). We show that breeding populations of the eastern subspecies, P. s. subis, that are separated by ca. 2000 km, nevertheless have almost completely overlapping non-breeding ranges in Brazil. Most (76%) P. s. subis overwintered in northern Brazil near the Amazon River, not in the agricultural landscape of southern Brazil. Individual non-breeding sites had an average of 91 per cent forest and only 4 per cent agricultural ground cover within a 50 km radius, and birds originating from declining northern breeding populations were not more exposed to agricultural landscapes than stable southern breeding populations. Our results show that differences in wintering location and habitat do not explain recent trends in breeding population declines in this species, and instead northern populations may be constrained in their ability to respond to climate change.

Connectivity of wood thrush breeding, wintering, and migration sites based on range-wide tracking

Many migratory animals are experiencing rapid population declines, but migration data with the geographic scope and resolution to quantify the complex network of movements between breeding and nonbreeding regions are often lacking. Determining the most frequently used migration routes and nonbreeding regions for a species is critical for understanding population dynamics and making effective conservation decisions. We tracked the migration of individual Wood Thrushes (Hylocichla mustelina) (n = 102) from across their range with light-level geolocators and, for the first time, quantified migration routes and wintering regions for distinct breeding populations. We identified regional and species-level migratory connectivity networks for this declining songbird by combining our tracking results with range-wide breeding abundance estimates and forest cover data. More than 50% of the species occupied the eastern wintering range (Honduras to Costa Rica), a region that includes only one-third of all wintering habitat and that is undergoing intensive deforestation. We estimated that half of all Wood Thrushes in North America migrate south through Florida in fall, whereas in spring approximately 73% funnel northward through a narrow span along the central U.S. Gulf Coast (88-93°W). Identifying migratory networks is a critical step for conservation of songbirds and we demonstrated with Wood Thrushes how it can highlight conservation hotspots for regional populations and species as a whole.

Tracking from the tropics reveals behaviour of juvenile songbirds on their first spring migration.

Juvenile songbirds on spring migration travel from tropical wintering sites to temperate breeding destinations thousands of kilometres away with no prior experience to guide them. We provide a first glimpse at the migration timing, routes, and stopover behaviour of juvenile wood thrushes (Hylocichla mustelina) on their inaugural spring migration by using miniaturized archival geolocators to track them from Central America to the U.S. and Canada. We found significant differences between the timing of juvenile migration and that of more experienced adults: juveniles not only departed later from tropical wintering sites relative to adults, they also became progressively later as they moved northward. The increasing delay was driven by more frequent short stops by juveniles along their migration route, particularly in the U.S. as they got closer to breeding sites. Surprisingly, juveniles were just as likely as adults to cross the Gulf of Mexico, an open-water crossing of 800–1000 km, and migration route at the Gulf was not significantly different for juveniles relative to adults. To determine if the later departure of juveniles was related to poor body condition in winter relative to adults, we examined percent lean body mass, fat scores, and pectoral muscle scores of juvenile versus adult birds at a wintering site in Belize. We found no age-related differences in body condition. Later migration timing of juveniles relative to adults could be an adaptive strategy (as opposed to condition-dependent) to avoid the high costs of fast migration and competition for breeding territories with experienced and larger adults. We did find significant differences in wing size between adults and juveniles, which could contribute to lower flight efficiency of juveniles and thus slower overall migration speed. We provide the first step toward understanding the “black box” of juvenile songbird migration by documenting their migration timing and en route performance.

A Trans-Hemispheric Migratory Songbird Does Not Advance Spring Schedules or Increase Migration Rate in Response to Record-Setting Temperatures at Breeding Sites

The decline of long distance migratory songbirds has been linked to an increasing mismatch between spring arrival date and timing of food availability caused by climate change. It is unclear to what extent individuals can adjust migration timing or en route rate in response to annual variation in temperature at breeding sites. We tracked the ca. 7300 km spring migration of 52 purple martins Progne subis from the Amazon basin to two breeding sites in eastern North America. Spring 2012 was the warmest on record in eastern North America, but contrary to predictions, this did not result in earlier departure, faster migration, or earlier arrival at breeding areas compared with earlier years. Temperatures and rainfall in the Amazon basin at the time of departure were not higher in 2012, and conditions along migration routes did not give consistent signals of a warmer spring at the breeding site. Once in North America, individuals likely had limited opportunity to speed up their migration because this final portion of the journey was already very rapid (570 km/d; 4–5 d in duration). Migration timing over the entire journey was best predicted by breeding latitude and sex and was not sensitive to ecological cues (temperature and rainfall amount) at departure from South American overwintering sites or en route, in contrast to recent studies of other songbirds. Our results provide the first direct evidence for a mismatch between higher spring temperatures at breeding sites and departure schedules of individual songbirds, and suggest phenotypic responses to short-term climatic warming may be limited for some species. Further direct-tracking data with greater geographic and temporal scope is needed to test for individual plasticity in response to temperature and rainfall along migratory routes for this, and other, species.

Combining direct and indirect tracking techniques to assess the impact of sub-Saharan conditions on cross-continental songbird migration

Understanding how events throughout the annual cycle interact to influence individual fitness and hence population dynamics is crucial to optimize conservation strategies for migratory birds. Despite major advancements in technology, direct tracking devices for passerine songbirds are still limited by the need for recapturing tagged individuals. Stable-isotope analysis of bird tissue has the opportunity to supply information on a larger number of individuals, although it is limited by the indirect knowledge of the geographical position of the birds. In this study, we provide a first attempt to combine annual spatio-temporal data achieved from direct tracking with information on local environmental conditions by using stable isotopes (δ13C and δ15N). We use this approach to investigate if environmental conditions at the wintering area in southern Africa influence timing of spring migration and carry-over to affect breeding performance in a long-distance migratory passerine bird, the Red-backed Shrike (Lanius collurio). We found that individuals wintering in relatively moist conditions (depleted in δ13C) and at lower latitudes (closer to the breeding grounds) departed later on spring migration than individuals in more xeric habitats. However, the effect of non-breeding area conditions and latitude were not found at subsequent migration stages and late departing individuals spent fewer days on migration towards the breeding grounds. Although conditions in the non-breeding range have previously been suggested to influence population fluctuations in Red-backed Shrikes, we found no evidence of a carry-over effect on breeding performance. This study highlights the potential of combining different approaches when investigating seasonal interactions in migratory animals.ZusammenfassungKombination von direkten und indirekten Ortungsmethoden zur Bewertung des Einflusses der Bedingungen in der Subsahara auf den interkontinentalen Zug von Singvögeln Das Verständnis dafür, wie die diversen Ereignisse im Verlauf eines ganzen Jahres miteinander zusammenhängen und die individuelle Fitness und damit die gesamte Populationsdynamik beeinflussen, ist ausschlaggebend für die Optimierung von Strategien zum Schutz von Zugvögeln. Trotz erheblicher technischer Fortschritte besteht die Einschränkung, dass Geräte zur direkten Ortung davon abhängig sind, damit ausgestattete Vögel wiederfangen zu müssen. Die Analyse stabiler Isotope aus Vogelgeweben bietet die Möglichkeit, Informationen von einer großen Anzahl Individuen zu sammeln, ist aber dadurch eingeschränkt, dass sie keine direkten Informationen über die geographische Position der Vögel liefert. In dieser Untersuchung stellen wir einen ersten Versuch vor, räumlich-zeitliche Daten aus direkten Ortungen mit Informationen über lokale Umgebungsbedingungen, gewonnen aus Bestimmungen stabiler Isotopen (δ13C and δ15N), zu kombinieren. Dieser Ansatz wurde gewählt, um herauszufinden, ob die Umgebungsbedingungen an den Überwinterunsgplätzen im südlichen Afrika den Beginn des Frühjahrszugs beeinflussen und beim Langstreckenzieher, dem Neuntöter (Lanius collurio), eventuell noch auf den Bruterfolg durchwirken. Wir stellten fest, dass Vögel, die in einer relativ feuchten Umgebung (wenig δ13C ) und in geringeren geographischen Breiten (näher an den Brutgebieten) überwintert hatten, den Frühjahrszug später begannen als Vögel aus trockeneren Gebieten. Eine Auswirkung von Umgebungsbedingungen außerhalb der Brutgebiete und/oder von der geographischen Breite auf spätere Stadien des Zugs konnte jedoch nicht festgestellt werden; später startende Individuen verbrachten weniger Tage auf dem Zug in die Brutgebiete. Obwohl schon früher vermutet wurde, dass sich beim Neuntöter die Bedingungen außerhalb der Brutgebiete eventuell auf Populationsfluktuationen auswirkten, konnten wir keinen Beweis für derartige „carry-over“-Effekte auf den Bruterfolg feststellen. Diese Studie unterstreicht das Potential, das bei der Untersuchung saisonaler Interaktionen bei Tieren mit Zugverhalten in der Kombination unterschiedlicher Ansätze liegt.

Classic pattern of leapfrog migration in Sooty Fox Sparrow (Passerella iliaca unalaschcensis) is not supported by direct migration tracking of individual birds

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.

Tracking the Conservation Promise of Movement Ecology

From butterflies to elephants, the rapidly developing science of movement ecology is providing increasingly detailed spatio-temporal data on a wide array of mobile animals. Thus, this discipline also holds great promise for improving the conservation of wildlife. To measure progress towards this promise, we investigated the degree to which movement ecology research is connected to conservation goals as well as the proportion of studies that were incorporated into federal and international status assessments for mobile species at risk. We examined 13,349 “movement ecology” papers published between 1990 and 2014 and found that explicit connections to conservation and management were made in 35% (n = 4, 672) of these papers, with the number of connections increasing over time. We then measured the uptake of movement ecology research into species status assessment and recovery plans (n = 72 documents) produced by three different governance agencies for 12 endangered mobile species. We found that on average 60 % of available movement ecology research was used in the status assessment process, demonstrating that when movement ecology research is available, it is generally being utilized in conservation planning. However, for 25% of these species, there was little movement research available to be used, highlighting that knowledge gaps remain for some at-risk species despite the general growth of movement ecology research. We outline opportunities for movement ecology to promote more effective conservation of taxa that move.