Frank R. Moore

Mapping migration in a songbird using high-resolution genetic markers

Neotropic migratory birds are declining across the Western Hemisphere, but conservation efforts have been hampered by the inability to assess where migrants are most limited—the breeding grounds, migratory stopover sites or wintering areas. A major challenge has been the lack of an efficient, reliable and broadly applicable method for measuring the strength of migratory connections between populations across the annual cycle. Here, we show how high‐resolution genetic markers can be used to identify genetically distinct groups of a migratory bird, the Wilsons warbler (Cardellina pusilla), at fine enough spatial scales to facilitate assessing regional drivers of demographic trends. By screening 1626 samples using 96 highly divergent single nucleotide polymorphisms selected from a large pool of candidates (~450 000), we identify novel region‐specific migratory routes and timetables of migration along the Pacific Flyway. Our results illustrate that high‐resolution genetic markers are more reliable, precise and amenable to high throughput screening than previously described intrinsic marking techniques, making them broadly applicable to large‐scale monitoring and conservation of migratory organisms.

Geographic position and landscape composition explain regional patterns of migrating landbird distributions during spring stopover along the northern coast of the Gulf of Mexico

ContextAnnual migration of landbirds across the Gulf of Mexico (GOM) presents a unique opportunity to examine extrinsic processes operating at various spatial scales in determining animal distributions.ObjectivesOur objectives were to comprehensively quantify bird stopover densities across the northern GOM coast and model broad-scale factors explaining distributional patterns.MethodsWe used weather surveillance radars to measure reflectivity of birds aloft at onset of nocturnal migratory flights and estimate bird stopover densities during four springs (2009–2012) for 6.7 million ha along the GOM. We aggregated bird densities to one longitudinal degree and 3xa0km of proximity to coast.ResultsBoosted Regression Tree models revealed that stopover density was related to year, longitude, proximity to coast, and amount of hardwood forest cover in the landscape. Average longitudinal patterns supported previous studies of broad-scale trans-Gulf migrant arrivals with highest density in Louisiana (92–93°W) and lowest in Alabama (88–89°W). Florida (83–84°W) supported a second peak in migrant density, suggesting an eastern trans-Gulf route or contribution from trans-Caribbean migrants. Longitudinal patterns in migrant distributions varied strongly between years and appear generally related to variability in GOM wind patterns. Densities increased with proximity to coast, highlighting constraints on migrants to travel inland, especially in Florida’s panhandle. Despite this, density was positively related to amount of forest cover more steeply along the immediate coast.ConclusionsBroad-scale stopover distributions of migrating landbirds along the GOM coast are heavily influenced by geographic constraints in the context of the GOM acting as a barrier to landbird migration.

Information acquisition during migration: A social perspective

ABSTRACT Information can enhance fitness, and the ways in which organisms acquire and use information are of heightened interest in ecological studies today. Migratory birds, as long-distance travelers of the globe, depend on rapid access to accurate information and thus provide particularly interesting study subjects for cognitive ecology. Yet, questions regarding how migratory birds collect information and make decisions en route remain to be answered. Here, we review the current status of this field of study and focus our attention on social learning (broadly defined as the use of inadvertently produced social information) as an important cognitive mechanism that can operate across taxonomic boundaries. We argue that social learning is critical to accelerate resource acquisition while reducing risks and uncertainties during migration. We put forward eight testable predictions in relation to when increased use of social information might be expected. Finally, we argue that migrant communities at stopover sites may serve as additional sources of information where transient associations with others may have important and long-lasting benefits.

Elevated Testosterone Advances Onset of Migratory Restlessness in a Nearctic-Neotropical Landbird

The primary cue for initiation of spring migratory restlessness (Zugunruhe) in landbird migrants is photoperiod. Gonadal hormones are known to have a role in the regulation of migratory disposition; however, the extent of their effect is not well understood. We examined the impact of exogenous testosterone on the onset of migratory restlessness in gray catbirds (Dumetella carolinensis). Catbirds were stratified by sex and randomly assigned to two rooms; individuals in one room were photoadvanced to initiate migratory restlessness and the other room was maintained on a 12:12 light/dark photoperiod. Each room had three groups (nu2009=u200910/group); males with testosterone implants, males with empty implants, and females. We predicted that in the photoadvanced room males with testosterone implants would initiate migratory activity earlier than empty-implanted males. We found that in the photoadvanced group, testosterone-implanted males initiated migration 2xa0weeks prior to empty-implanted males, and 3xa0weeks prior to females. In the non-photoadvanced males, the testosterone-implanted males initiated migration at the same time as the corresponding group in the photoadvanced room, while the empty-implanted males and females did not exhibit Zugunruhe. Our results illustrate that elevated testosterone can advance the onset of Zugunruhe, even in the absence of an extended photoperiod. Additionally, the onset of migratory restlessness observed in the photoadvanced, non-testosterone-implanted males and females further supports the importance of photoperiod as a cue for migratory restlessness. An interesting observation was the intersexual differences in the onset of migratory activity in gray catbirds, a species not previously known to exhibit protandry.

Seasonal gene expression in a migratory songbird

The annual migration of a bird can involve thousands of kilometres of nonstop flight, requiring accurately timed seasonal changes in physiology and behaviour. Understanding the molecular mechanisms controlling this endogenous programme can provide functional and evolutionary insights into the circannual biological clock and the potential of migratory species to adapt to changing environments. Under naturally timed photoperiod conditions, we maintained captive Swainsons thrushes (Catharus ustulatus) and performed RNA sequencing (RNA‐Seq) of the ventral hypothalamus and optic chiasma to evaluate transcriptome‐wide gene expression changes of individuals in migratory condition. We found that 188 genes were differentially expressed in relation to migratory state, 86% of which have not been previously linked to avian migration. Focal hub genes were identified that are candidate variables responsible for the occurrence of migration (e.g. CRABP1). Numerous genes involved in cell adhesion, proliferation and motility were differentially expressed (including RHOJ, PAK1 and TLN1), suggesting that migration‐related changes are regulated by seasonal neural plasticity.

Fuel stores, time of spring, and movement behavior influence stopover duration of Red-eyed Vireo Vireo olivaceus

AbstractnLong-distance migration is characterized by periods of flight, when energy stores are consumed, and periods of stopover, when energy stores are replenished. The duration of the migratory period is largely determined by time spent at stopover sites. The time constraints imposed on spring migrants should act to minimize the time spent on migration, yet spring migrants often remain at stopover sites for extended periods. We measured the influence of arrival fuel stores, arrival date, and foraging movement rate on the duration of Red-eyed Vireos (Vireo olivaceus) that remained at stopover sites for more than 1xa0day. We captured spring migrants in mist-nets as they arrived after crossing the Gulf of Mexico. We released them at an inland site and continuously followed (radio-tracked) their movements until departure. Departure time was confirmed with extensive ground searches and aerial surveys. Migrants remained at the stopover sites from 1 to 8xa0days (2.80xa0±xa00.14xa0days). Less than one-third of migrants were transient, leaving the night following release (32xa0%). Of the migrants that remained more than 1xa0day, those that arrived with low fuel stores remained longer than those that arrived with more fuel stores. Only migrants arriving early in the spring stayed for extended periods of time (>5xa0days). Further, migrants that moved faster within the stopover landscape presumably replenished fuel stores faster because they did not remain as long as migrants that did not move as quickly. When arrival fuel stores, arrival day, and departure day were known, we found multiple factors influenced the length of stay at spring stopover sites. Early spring migrants with low fuel stores that moved slowly through the landscape spent the most time at spring stopover sites.ZusammenfassungEnergiereserven, Frühjahrszeitpunkt und Bewegungsverhalten beeinflussen die Rastdauer beim RotaugenvireoVireo olivaceusn Der Langstreckenzug ist gekennzeichnet durch Flugphasen, in denen Energiereserven verbraucht werden, und durch Rastphasen, in denen diese Energiereserven wieder aufgefüllt werden. Die Gesamtlänge der Zugperiode wird zum großen Teil durch die Aufenthaltsdauer an den Rastplätzen bestimmt. Die zeitlichen Zwänge beim Frühjahrszug sollten eine Minimierung der Zugdauer bewirken; trotzdem verweilen Vögel auf dem Frühjahrszug oft längerfristig in den Rastgebieten. Wir bestimmten den Einfluss der Energiereserven bei Ankunft, des Ankunftsdatums und der Bewegungsmuster auf die Verweildauer von Rotaugenvireos (Vireo olivaceus), die sich länger als einen Tag im Rastgebiet aufhielten. Dazu fingen wir die Vögel auf dem Frühjahrszug mit Japannetzen bei ihrer Ankunft nach der Überquerung des Golfs von Mexiko. Danach ließen wir sie im Binnenland wieder frei und verfolgten ihre Bewegungen per Radiotelemetrie kontinuierlich bis zum Weiterflug. Der Abflugzeitpunkt wurde durch weiträumige Suche am Boden sowie durch Lufterkundung bestätigt. Die Zugvögel verweilten zwischen einem und acht Tagen (2.80xa0±xa00.14xa0Tage) in den Rastgebieten. Weniger als ein Drittel der Vögel waren Durchzügler, die bereits in der auf die Freilassung folgenden Nacht weiterflogen (32xa0%). Von den Zugvögeln, die sich länger als einen Tag aufhielten, blieben diejenigen, welche mit geringeren Energiereserven angekommen waren, länger als die, welche mit mehr Energiereserven eintrafen. Nur Zugvögel, welche im zeitigen Frühjahr ankamen, hielten sich über einen längeren Zeitraum (>fünf Tage) auf. Des Weiteren füllten Zugvögel, die sich in der Landschaft des Rastgebiets schneller bewegten, ihre Energiereserven vermutlich auch rascher wieder auf, da sie nicht so lange verweilten, wie Zugvögel, die sich weniger schnell bewegten. Waren die Energiereserven bei Ankunft, das Ankunftsdatum und der Abflugtag bekannt, fanden wir mehrere Faktoren, welche die Aufenthaltsdauer in den Frühjahrsrastgebieten beeinflussten. Zugvögel zu Beginn des Frühjahrs, die geringe Energiereserven hatten und sich langsam in der Landschaft bewegten, verbrachten somit die längste Zeit in den Frühjahrsrastgebieten.

Stopover biology of Ruby-throated Hummingbirds (Archilochus colubris) during autumn migration

ABSTRACT Surprisingly little is known about the migration and stopover biology of Ruby-throated Hummingbirds (Archilochus colubris), and even less is known about their sex- or age-dependent migration. First, we provide basic information on the migration and stopover biology of this species along the northern coast of the Gulf of Mexico during autumn, including phenology, stopover duration, fuel deposition rate (FDR), arrival mass, and estimated flight ranges. Second, we investigate whether these stopover variables are influenced by age or sex. Age-dependent migration is expected because young, hatch-year birds on their first migration lack the experience of older individuals. Sex-dependent migration is expected because of sexually dimorphic characteristics in wing morphology and body size. We obtained information on arrival mass, phenology, FDR, stopover duration, and estimated flight ranges through banding data, passive integrated transponder tags, radio telemetry, and color marking at a long-term migration station along the northern coast of the Gulf of Mexico. Our data provide strong evidence for age-dependent migration and only weak evidence for sex-dependent migration. Older birds arrived earlier, had larger fuel loads, and had shorter stopover durations than younger birds. In younger birds, we found no effect of sex on FDR, arrival mass, stopover duration, or phenology. Older males arrived with larger fuel loads than females. Finally, we used flight simulation software and our data to estimate that males and older birds were capable of longer potential flight ranges than either females or younger birds.

Patterns of testosterone in three Nearctic-Neotropical migratory songbirds during spring passage.

Preparation for breeding may overlap extensively with vernal migration in long-distance migratory songbirds. Testosterone plays a central role in mediating this transition into breeding condition by facilitating changes to physiology and behavior. While changes in testosterone levels are well studied in captive migrants, these changes are less well known in free-living birds. We examined testosterone levels in free-living Nearctic-Neotropical migrants of three species during their vernal migration. Testosterone levels increased during the migratory period in males of all three species but significantly so in only two. Testosterone levels in females remained the same throughout their migration. Our results support the extensive overlap between vernal migration and breeding preparation in male songbirds. The pattern of testosterone changes during vernal migration is far from clear in females.

Overlapping life-history stages in migrating songbirds: variation in circulating testosterone and testosterone production capacity

Understanding the extent of overlap between life-history stages is fundamental to understanding full-life cycle biology, especially for migratory species. Testosterone levels vary throughout the annual cycle in seasonally reproducing vertebrates. In migratory songbirds, testosterone increases associated with breeding preparation may overlap with the vernal migratory period; however, this overlap remains largely unexplored. We test the hypothesis that both circulating testosterone and the capacity to elevate testosterone increases throughout vernal migration in long-distance songbird migrants. Here we relate testosterone in songbirds sampled en route with the stable hydrogen isotope ratios in their feathers as a metric of breeding ground proximity. We determined the capacity to elevate testosterone using field gonadotropin-releasing hormone bioassays and related this to feather hydrogen ratios as well. Males that were closer to their breeding grounds had higher circulating testosterone, whereas there was no relationship between testosterone and breeding ground proximity in females. Similarly, while capacity to elevate testosterone was not related to breeding ground proximity in female migrants, this capacity was greater in males closer to their breeding grounds than those further away. These results reveal that male migrants prepare for breeding during their vernal migration, whereas the schedule for breeding preparation among females is less clear and may be more complex.ZusammenfassungÜberlappende Lebenszyklusstadien bei ziehenden Singvögeln: Variation im zirkulierenden Testosteron und in der Synthesekapazität für Testosteron Zu verstehen, in welchem Maße Lebenszyklusstadien überlappen, ist fundamental für ein Verständnis der Biologie des kompletten Lebenszyklus, und zwar besonders bei ziehenden Arten. Bei saisonal reproduzierenden Wirbeltieren variiert der Testosteronspiegel im Verlauf des Jahres. Bei ziehenden Singvögeln kann ein mit der Brutvorbereitung verbundener Anstieg des Testosteronspiegels mit dem Frühjahrszug überlappen, doch diese Überlappung ist bisher weitgehend unerforscht. Wir testeten die Hypothese, dass sowohl das im Blut zirkulierende Testosteron als auch die Kapazität, den Testosteronspiegel zu erhöhen, bei langstreckenziehenden Singvögeln auf dem Frühjahrszug ansteigen. Hierfür setzten wir die bei Singvögeln auf dem Zug gemessenen Testosteronspiegel in Beziehung zum stabilen Wasserstoffisotopenverhältnis in ihren Federn, welches als Maß für die Nähe zum Brutgebiet dient. Die Kapazität, den Testosteronspiegel zu erhöhen, haben wir ermittelt, indem wir im Freiland Gonadoliberin-Biotests durchgeführt haben. Diese Kapazität haben wir dann ebenfalls zu den Wasserstoffisotopenverhältnissen in den Federn in Beziehung gesetzt. Näher am Brutgebiet befindliche Männchen wiesen höheres zirkulierendes Testosteron auf, wohingegen bei Weibchen kein Zusammenhang zwischen Testosteron und der Nähe zum Brutgebiet bestand. Gleichermaßen hing die Kapazität, den Testosteronspiegel zu erhöhen, bei ziehenden Weibchen nicht mit der Nähe zum Brutgebiet zusammen, während sie bei näher am Brutgebiet befindlichen Männchen höher war als bei weiter vom Brutgebiet entfernten Männchen. Diese Ergebnisse zeigen, dass männliche Zugvögel sich bereits auf dem Frühjahrszug auf die Brut vorbereiten, während der Zeitplan der Brutvorbereitung bei Weibchen weniger klar und möglicherweise komplexer ist.