Overland Migration Research Articles

Out of Africa: Linked continents, overland migration and differential survival explain abundance of Proteaceae in Australia

The centres of diversification of the iconic family Proteaceae are in South Africa and southern Australia. Since the ancestors of the family can be traced to NW Africa our task was to explain how all subfamilies (Proteoideae, Grevilleoideae, Persoonioideae) managed to reach Australia and we propose the pathway: (Africa (N South America (S South America (Antarctica (Australia))))). Our dated molecular phylogeny shows that the family arose 132 million years ago (Ma), and by 125 Ma had separated into the three subfamilies that remain dominant today. The age and location of records for 420 fossil pollen with Proteaceae affinities were collated per continent and submitted to curve-fitting analysis. This showed spread of early Proteaceae into N South America from ∼121 Ma that was able to continue for another 20–25 My. These three subfamilies (plus Carnarvonia) travelled south through South America and Antarctica, crossing the Weddellian Isthmus from ∼110 Ma, to reach southern Australia by ∼104 Ma. The history of Proteaceae in South America mimics that of Africa, where Grevilleoideae diversified instead of Proteoideae that died out. Entry to Australia via Antarctica was possible until ∼70 Ma at its SW corner and 45 Ma at its SE (Tasmanian) corner enabling the three subfamilies (and Carnarvonia) restricted entry into Australia over 35–60 million years. The SW Australian sclerophyll flora became the centre of diversification and emigration at the species level of all but the rainforest (mesophyll) Grevilleoid/Proteoid clades within Australia. Close genetic links between clades in South Africa (the centre of diversification of the sclerophyll flora in Africa) and SW Australia are the product of disparate migratory histories from their common ancestor in NW Africa, differential survival among subfamilies and parallel evolution in matched environments. SE Australia became the centre of diversification at the subtribe level. Close genetic links between clades in South America and SE Australia are the product of long-distance dispersal from their common ancestor in N South America, genetic stability in matched environments and eventual vicariance.

Flight Capacity and Response to Habitat Drying of Endemic Diving Beetles (Coleoptera: Dytiscidae) in Arkansas (USA)

The ability to colonize new habitat is essential for wild populations affected by disturbance or other forms of habitat change. For aquatic insects in small streams, overland flight is an important strategy for dispersal when barriers to in-stream migration exist and when populations are isolated in upland habitats. Two Ozark-endemic water beetles (Heterosternuta sulphuria and Heterosternuta phoebeae) have shown little overlap in distributions, with the former frequently occurring in small upland watersheds and the latter occurring in aquatic habitats farther downstream in larger watersheds. Because H. sulphuria has been associated with perennial aquatic habitats, we hypothesized that H. sulphuria individuals could exhibit low capacity for flight, thereby affecting population distributions over time. Laboratory flight observations showed that zero individuals of H. sulphuria flew (n = 67), whereas 17 of 76 individuals of H. phoebeae were observed to fly. Stream habitat drying experiments provided further evidence of the weak capacity for flight and overland migration of H. sulphuria, with low probabilities of survivorship in microhabitats exposed to drying. Weak flight capacity and apparent intolerance to habitat drying have important implications for the evolutionary history and conservation of H. sulphuria in small Ozark streams exposed to variable flow regimes and stream margins vulnerable to disturbances.

Fossil pollen resolves origin of the South African Proteaceae as transcontinental not transoceanic.

The prevailing view from the areocladogenesis of molecular phylogenies is that the iconic South African Cape Proteaceae (subfamily Proteoideae) arrived from Australia across the Indian Ocean during the Late Cretaceous (100-65 million years ago, Ma). Since fossil pollen indicates that the family probably arose in North-West Africa during the Early Cretaceous, an alternative view is that it migrated to the Cape from North-West-Central Africa. The plan therefore was to collate fossil pollen records throughout Africa to determine if they are consistent with an African (para-autochthonous) origin for the Cape Proteaceae, and to seek further support from other palaeo-disciplines. We used palynology (identity, date and location of records), molecular phylogeny and chronogram preparation, biogeography of plate tectonics, and palaeo-atmospheric and ocean circulation models. Our collation of the rich assemblage of Proteaceae palynomorphs stretching back to 107 Ma (Triorites africaensis) in North-West Africa showed its progressive overland migration to the Cape by 75-65 Ma. No key palynomorphs recorded in Australia-Antarctica have morphological affinities with African fossils but specific clade assignment of the pre-Miocene records is not currently possible. The Cape Proteaceae encompass three molecular-based clades (tribes) whose most recent apparent ancestors are sisters to those in Australia. However, our chronogram shows that the major Adenanthos/Leucadendron-related clade, originating 54-34 Ma, would have 'arrived' too late as species with Proteaceae affinities were already present ~20 million years earlier. The Franklandia/Protea-related clade arose 118-81 Ma so its distinctive pollen should have been the foundation for the scores of palynomorphs recorded at 100-80 Ma, but it was not. Also, the prevailing winds and ocean currents trended away from South Africa rather than towards, as the 'out-of-Australia' hypothesis requires. Based on the evidence assembled here, we list three points favouring an Australian origin and nine against; four points favouring an Antarctic origin and seven against; and nine points favouring a North-West-Central African origin and three against. We conclude that a gradual migration of the Proteaceae from North-West-Central Africa southeast→south→southwest to the Cape and its surroundings occurred via adaptation and speciation during the period 95-70 Ma. We caution that incorrect conclusions may be drawn from literal interpretations of molecular phylogenies that neglect the fossil record and do not recognize the possible confounding effects of selection under matched environments leading to parallel evolution and extinction of bona fide sister clades.

Out of Africa: Linked Continents, Overland Migration and Differential Survival Explain Abundance of Proteaceae in Australia

Out of Africa: Linked Continents, Overland Migration and Differential Survival Explain Abundance of Proteaceae in Australia

From Private Dreams to Public Damnings

From Private Dreams to Public Damnings

Flight Performance of Migrating Juvenile Barn Swallows Hirundo rustica in Relation to Fat Load and Wing Morphology

Migratory birds have evolved the ability to accumulate fat reserves to fuel their migratory journeys. However, increased fuel load leads to an increased body mass, which is expected to impair flight performance and increase predation risk. Results of previous research are contradictory, with some studies reporting detrimental effects of fat load on flight performance, while others showing no such influences. Furthermore, no studies have investigated the relationship between fat load and flight performance in obligate aerial insectivores, which are known to accumulate only moderate fat loads while migrating overland and not crossing wide ecological barriers such as oceans or deserts. In this study we investigated the inter-individual variation in short-term flight performance (flight manoeuvrability, velocity and acceleration) in juvenile Barn Swallows Hirundo rustica in relation to fat load in Poland (central Europe), during the initial stages of autumn southward migration. We evaluated individual swallow fat loads by means of a Total Body Electrical Conductivity (TOBEC) scanner. In order to evaluate short-term flight performance in a standardised manner we used flight tunnels. We controlled statistically for the independent effect of wing morphology, which can be expected to influence flight performance. Juvenile fat loads were on average 7.5% (range 0.2–20.5) of lean body mass, but we found no negative effect of the fat mass on short-term flight performance traits. Individuals with larger fat mass reached higher velocity compared to leaner ones, which is in line with theoretical expectations. However, fat mass did not significantly predict flight manoeuvrability or acceleration. The results indicate that relatively small fat loads accumulated by juvenile Barn Swallows during overland migration do not impair short-term flight performance.

Enshrining Gender in Monuments to Settler Whiteness: South Africa’s Voortrekker Monument and the United States’ This Is the Place Monument

This essay examines two monuments: the Voortrekker Monument in South Africa and the American This is the Place Monument in Utah. Similar in terms of construction and historical purpose, both employ gender as an important tool to legitimize the settler society each commemorates. Each was part of a similar project of cultural recuperation in the 1930s−1940s that chose as their object of commemoration the overland migration in covered wagons of a group of white settlers that felt oppressed by other white settlers, and therefore sought a new homeland. In a precarious cultural moment, descendants of these two white settler societies—the Dutch Voortrekkers of South Africa and Euro-American Mormons (Latter-day Saints or LDS) of Utah—undertook massive commemoration projects to memorialize their ancestors’ 1830s−1840s migrations into the interior, holding Afrikaners and Mormons up as the most worthy settler groups among each nation’s white population. This essay will argue that a close reading of these monuments reveals how each white settler group employed gendered depictions that were inflected by class and race in their claims to be the true heart of their respective settler societies, despite perceiving themselves as oppressed minorities.

The Cherokee and Wyandot Companies on the Overland Trails to California: Histories of Indigenous Migration and the Settler Gaze, 1849–1856

The popular memory of the nineteenth century American West has long fixated on the thousands of trail emigrants who famously crossed the North American continent in search of wealth, adventure, and new lives. Historical and scholarly narratives have explored the ways that these massive overland migrations threatened, altered, and devastated Native American societies of the West. Often neglected in these historical narratives, however, are the many Native Americans who participated in these migrations, founded their own overland companies, and blazed some of the most important trail routes across the continent. Among the most numerous were several companies of Cherokee and Wyandot people who left Indian Territory for California, where they would participate in the Gold Rush. This article explores the complex histories and memories of these Indigenous migrants and settlers, from their journeys across the trails, their experiences in Gold Rush California, and their relations with other Native and settler communities.

Overland and oversea migration of white storks through the water barriers of the straits of Gibraltar

Soaring landbirds typically exploit atmospheric uplift as they fly overland, displaying a highly effective energy-saving locomotion. However, large water bodies lack thermal updrafts, potentially becoming ecological barriers that hamper migration. Here we assessed the effects of a sea surface on the migratory performance of GPS-tagged white storks (Ciconia ciconia) before, during and after they crossed the straits of Gibraltar. Oversea movements involved only flapping and gliding and were faster, traversed in straighter, descending trajectories and resulted in higher movement-related energy expenditure levels than overland, supporting the water barrier hypothesis. Overland movements at both sides of the sea straits resulted in tortuous routes and ascending trajectories with pre-crossing flights showing higher elevations and more tortuous routes than post-crossing, thus supporting the barrier negotiation hypothesis. Individual positions at both ends of the sea narrow were predicted by zonal winds and storks´ location at entry in the European hinterland, and birds did not show compensational movements overland in anticipation to subsequent wind displacements oversea. The length of the water narrow at departure shore, the elevation therein and the winds on route affected major components of sea crossing performance (such as distances and times overwater, minimum elevations, climb angles, speeds and energy expenditure), supporting the departure position and oversea winds hypotheses. In summary, our study provides a prime example at high temporal resolution of how birds adjust their behavior and physiology as they interact with the changing conditions of the travelling medium, reallocating resources and modifying their movement to overcome an ecological barrier.

Relative Severity of Food Insecurity During Overland Migration in Transit Through Mexico.

Despite anecdotal reports of food insufficiency in the overland migration through Mexico, little is known about the frequency and extent of food insecurity during this transit. In a shelter in north central Mexico, we interviewed 95 Central American migrants traveling overland to the US regarding their experiences of food insecurity in transit. 74% experienced some degree of food insecurity, ranging from having only one meal to no food at all in one or several consecutive 24h periods. Factors associated with relatively more severe food insecurity included more days in active transit, more severe illness impacting mobility, or travel companion illness in the prior 2 weeks. Illness was predicted by a pre-migration diagnosis of chronic disease. Understanding the factors associated with relative severity of food insecurity during overland migration can inform policies for prioritizing assistance and prevention.

Phylogeny and biogeography of Pachygoneae (Menispermaceae), with consideration of the boreotropical flora hypothesis and resurrection of the genera Cebatha and Nephroia

The tribe Pachygoneae consists of four genera with about 40 species, primarily distributed in tropical and subtropical Asia and America, also in Australasia and Africa. This tribe presents an ideal model to investigate the origin of the tropical and subtropical amphi-Pacific disjunction pattern. More specifically, it allows us to test whether the tropical lineages diverged earlier than the subtropical ones during the fragmentation of the boreotropical flora. In this study, we reconstructed the phylogeny of Pachygoneae using five plastid (rbcL, atpB, matK, ndhF, trnL-F) and one nuclear (26S rDNA) DNA regions. Our results indicate that Pachygoneae is not monophyletic unless Cocculus pendulus and Cocculus balfourii are excluded. We resurrected the genus Cebatha to include these two species and established a new tribe for this genus. Within Pachygoneae, the species of Cocculus are distributed in three different clades, among which two are recognized as two distinct genera, Cocculus s.str. and Nephroia resurrected, and one species is transferred into Pachygone. Our molecular dating and ancestral area reconstruction analyses suggest that Pachygoneae began to diversify in tropical Asia around the early-middle Eocene boundary (c. 48 Ma) and expanded into the New World by c. 44 Ma. In the New World, tropical Hyperbaena originated in the late Eocene (c. 40 Ma), whereas the subtropical Cocculus carolinus and Cocculus diversifolius originated later, in the early Oligocene (c. 32 Ma). These two timings correspond with the two climatic cooling intervals, which suggests that the formation and breakup of the boreotropical floral may have been responsible for the amphi-Pacific disjunct distribution within Pachygoneae. One overland migration event from Asia into Australasia appears to have occurred in the early to late Miocene.

Analysis of atmospheric circulation situation and source areas for brown planthopper immigration to Korea: a case study

AbstractRice planthoppers and related viral diseases have become one of the most important factors affecting rice production in Asian countries, and the resulting abuse of pesticides is laying a hidden danger for future food security. As the most economically devastating species, the brown planthopper, Nilaparvata lugens (Stål), moves from the tropical Indochina Peninsula to temperate regions where it cannot overwinter annually with the feature of long‐range migration, and eventually appears in paddy fields of most East Asian countries. Compared with the overland migration that has been studied in more detail, there is relatively less understanding of N. lugens’ performance in transnational movement, especially in the representative overseas migration between China and Northeast Asia. Based on the light‐trap data from China and Korea and the matched meteorological data of East Asia in 2016, a typical overseas migration event was basically analyzed. The results are as follows. First, the source area of the N. lugens population in this migration was in southeastern Jiangsu and eastern Shanghai. They took off at dusk on 1 August, flying at the altitude of 1700–2200 m, and landed in southwestern Korea at 02:00–11:00 UTC on 3 August. Second, a southerly airflow belt was the main weather factor for population's overseas migration, and the confrontation between the western Pacific subtropical high and a northern high pressure in southern Korea was the main reason for population to land. Besides, we discussed the one‐off feature of overseas migration compared to overland migration. These results show the close relation between weather systems and the migration dynamics of N. lugens and may extend the perception for N. lugens’ behavioral chain in the long‐range migration between China and Northeast Asia, thus allowing a sufficient time for reasonable and effective control measures.

Geographic range and habitat reconstructions shed light on palaeotropical intercontinental disjunction and regional diversification patterns in Artabotrys (Annonaceae)

AbstractAimThe biogeographical and habitat history of the species‐rich angiosperm genus Artabotrys is reconstructed to assess hypotheses relating to processes that underlie palaeotropical intercontinental disjunction (PID) and regional diversification patterns.LocationPalaeotropics.TaxonArtabotrys (Annonaceae).MethodsPhylogenetic relationships were estimated based on 53 Artabotrys species, using four chloroplast and 10 nuclear markers (c. 15.7 kb). Divergence times were estimated using two fossil calibrations and an uncorrelated lognormal relaxed clock model. Ancestral range estimation was performed under a dispersal–extinction–cladogenesis model while ancestral habitat reconstruction was conducted using the BAYAREALIKE model.ResultsArtabotrys is unequivocally monophyletic, with a species‐rich main Artabotrys clade (MAC) comprising distinct African and Asian sister clades, and an early divergent grade (EDG) comprising two African species. An ancestral range in Africa is inferred, with a single dispersal to Asia. The PID at the MAC crown occurred in the Miocene. A broad habitat tolerance spanning rain forests and seasonally dry forests/savannas was inferred at the MAC stem and crown nodes. Several shifts from rain forests to seasonally dry habitats were inferred, but there is no indication of a reverse transition.Main conclusionsThe most plausible explanation for the PID involves overland migration across Arabia in the Miocene, prior to subsequent climate deterioration. Long‐standing differences in climatic niche may have resulted in a significant yet porous biogeographical divide at the Isthmus of Kra, but Wallace's line does not reflect differences in climatic niches. Niche conservatism is an underlying pattern in Artabotrys, with local niche shifts occurring rather recently.

Overland movement and migration phenology in relation to breeding of Arctic Terns Sterna paradisaea

It is often implicitly assumed that seabirds migrate using marine environments, but this assumption is increasingly being challenged by electronic tracking data. The arrival and departure routes of Arctic Terns breeding on the North Sea coast of the United Kingdom (UK) are unknown but there has been speculation about the possibility of overland migration. Analysis of light‐level geolocator data from birds breeding on the Farne Islands suggests that these birds arrived and left their North Sea colony overland via the Irish Sea, rather than taking coastal routes along the east coast of the UK and through the English Channel. In addition, some departing birds may enter the North Atlantic by crossing Ireland rather than through the Irish Sea. The direction of arrival in spring had a more southerly orientation than the direction of autumn departure. The geolocator data allow migration phenology in relation to breeding to be defined and indicated that the birds arrived around 15 days before the first eggs were laid in the colony. Departure timing may be determined by seasonal progression and not markedly influenced by breeding success. This study supports the idea that overland migration may be a more widespread and consistent strategy for seabirds than has been realized.

A 2000-year sediment record reveals rapidly changing sedimentation and land use since the 1960s in the Upper Mara-Serengeti Ecosystem

The Mara River basin is a trans-boundary basin of international importance. It forms the headwaters of the Nile River and serves as the primary dry season water source for an estimated 1.1 million rural people and the largest remaining overland migration of 1.4 million wildebeest in the Serengeti-Mara Ecosystem. Changes throughout the basin are impacting the quantity and quality of the Mara River, yet the historical context of environmental conditions in the basin is not well known. We collected sediment cores throughout the wetland at the mouth of the Mara River, and we used isotopic dating methods and a suite of analyses to examine historical patterns of sediment quantity and source, mercury contamination, and carbon and nutrient loading. Our results show that ecological conditions in the Mara River basin were fairly stable over paleoecological time scales (2000–1000 years before present), but there has been a period of rapid change in the basin over the last 250 years, particularly since the 1960s. A shift in the source and quantity of sediments in the river began in the late 1700s and became much more pronounced in the 1950s and 1960s, coincident with increasing mercury concentrations. The quantity of sediment from the Upper Mara increased, particularly since 1960, but the proportion of total sediment from this region decreased as the Talek and Middle Mara portions of the basin began producing more sediment. The decadal oscillation in sediment accumulation was congruent with known periods of extreme precipitation events. Carbon and nitrogen loading also increased since the 1960s, and the shift in the isotopic ratio of nitrogen provides evidence for increased anthropogenic loading. Altogether, these data likely reflect patterns of change also experienced in other basins throughout East Africa.

A bridge between oceans: overland migration of marine birds in a wind energy corridor

Located at the shortest overland route between the Gulf of Mexico and the Pacific Ocean, Mexico's Tehuantepec Isthmus is a globally important migratory corridor for many terrestrial bird species. The Pacific coast of the Isthmus also contains a significant wetland complex that supports large multi‐species aggregations of non‐breeding waterbirds during the boreal winter. In recent years, extensive wind energy development has occurred in the plains bordering these wetlands, directly along the migratory flyway. Using recent studies of movement patterns of three marine‐associated bird species – reddish egrets Egretta rufescens, brown pelicans Pelecanus occidentalis, and red knots Calidris canutus – from the northern Gulf of Mexico, we assess the use of the isthmus as a migratory corridor. Our data provide evidence that marine birds from the Gulf region regularly overwinter along the Pacific coast of Mexico and use the isthmus as a migratory corridor, creating the potential for interaction with terrestrial wind farms during non‐breeding. This study is the first to describe migration by marine‐associated bird species between the Gulf of Mexico and Pacific coast. These data contribute new information toward ongoing efforts to understand the complex migration patterns of mobile marine species, with the goal of informing integrated conservation efforts for species whose year‐round habitat needs cross ecoregional and geopolitical boundaries.

Dangerous Subjects: James D. Saules and the Rise of Black Exclusion in Oregon by Kenneth R. Coleman

429 Reviews REVIEWS DANGEROUS SUBJECTS: JAMES D. SAULES AND THE RISE OF BLACK EXCLUSION IN OREGON by Kenneth R. Coleman Oregon State University Press, Corvallis, 2017. Illustrations, notes, bibliography, index. 240 pages. $19.95, paper. Discussions of race in Oregon almost inevitably return to the origins of the state’s overwhelming whiteness. Scholars and nonacademics who seek to explain Oregon’s striking lack of racial diversity look to the distant past, to its 1840s and 1850s statutes that prohibited African American migration and residence. Although the Oregon judiciary rarely enforced these anti-Black laws, and the Fourteenth Amendment nullified them in the 1860s, they seemingly cast a long shadow. African Americans continued to view Oregon as a bastion of white supremacy and largely avoided settling there. In Dangerous Subjects, historian Kenneth Coleman investigates this narrative of Oregon’s racial history and complicates it substantially. Coleman uses the life of James D. Saules, an early Black migrant to the Oregon Country, as a vehicle for exploring the origins of racial exclusion in the Pacific Northwest. Prior to Coleman’s research, Saules stood as a shadowy figure in the region’s early history. His involvement in the Cockstock Affair — an 1844 skirmish between Euro-Americans and Mollala people in Oregon City — and his later alleged threat to join Native resistance against neighboring whites, has long led historians to speculate that he was the inspiration for Oregon’s first Black exclusion laws. Coleman not only examines these two incidents and the anti-Black sentiment that swirled around them, he also reconstructs Saules’s life and places it in the broader context of settler colonialism that gave rise to a distinctly white supremacist legal and political regime in Oregon. What emerges from Coleman’s analysis is a complicated portrait of Saules as both an agent of empire who helped advance the United States’ conquest of the Pacific Northwest and a man who suffered from the colonial racial regime that arrived with Euro-American settlers. The documentary record on Saules is frustratingly thin, but Coleman conducts impressive detective work in genealogical sources, government records, and personal manuscripts to piece together the life of his enigmatic subject. He traces Saules’s origins to the burgeoning maritime industry of the U.S. Atlantic seaboard during the first third of the nineteenth century. Saules was a sailor whose career and travels frequently intersected with American imperial ventures. As a crew member aboard American whaling ships, Saules helped extend U.S. commercial power across the Pacific. Later, he played a more direct role in American imperialism by joining the United States Exploring Expedition (U.S. Ex. Ex.) as a ship’s cook. The voyages of the U.S. Ex. Ex. aimed both to collect data that could advance American commercial interests in the Pacific and to present a show of U.S. force to Indigenous people. As a member of the expedition , Saules may have participated in a string of violent encounters with Pacific Islanders, including massacres in Fiji and the Drummond Islands. When Saules finally deserted the expedition after his ship ran aground in the Oregon Country, he was already well versed in the workings of American colonial violence. Coleman ably demonstrates how Saules stood at the cusp of two modes of colonization in the Oregon Country. The first, merchant capitalism, had as its central aim the extraction of the Pacific Northwest’s wealth in animal pelts and exploited a diverse pool of non-white laborers. This was the world of the Hudson’s Bay Company with its small British population, multiracial workforce, and “middle ground” policies of compromise and accommodation with Native people. Overland migrations from the United States brought a new mode of settler colonialism, in which invading newcomers 430 OHQ vol. 119, no. 3 431 Reviews sought to displace and dispossess Native people , seize and settle their land, and exclude all but whites from access to productive property and political rights. Saules was able to make his way in the first colonial society by marrying a Native woman and engaging in small-scale commercial ventures such as ferrying and family farming. He fit less well in the new American regime that made whiteness a prerequisite...

Annual mass drownings of the Serengeti wildebeest migration influence nutrient cycling and storage in the Mara River

The annual migration of ∼1.2 million wildebeest (Connochaetes taurinus) through the Serengeti Mara Ecosystem is the largest remaining overland migration in the world. One of the most iconic portions of their migration is crossing of the Mara River, during which thousands drown annually. These mass drownings have been noted, but their frequency, size, and impact on aquatic ecosystems have not been quantified. Here, we estimate the frequency and size of mass drownings in the Mara River and model the fate of carcass nutrients through the river ecosystem. Mass drownings (>100 individuals) occurred in at least 13 of the past 15 y; on average, 6,250 carcasses and 1,100 tons of biomass enter the river each year. Half of a wildebeest carcass dry mass is bone, which takes 7 y to decompose, thus acting as a long-term source of nutrients to the Mara River. Carcass soft tissue decomposes in 2-10 wk, and these nutrients are mineralized by consumers, assimilated by biofilms, transported downstream, or moved back into the terrestrial ecosystem by scavengers. These inputs comprise 34-50% of the assimilated diet of fish when carcasses are present and 7-24% via biofilm on bones after soft tissue decomposition. Our results show a terrestrial animal migration can have large impacts on a river ecosystem, which may influence nutrient cycling and river food webs at decadal time scales. Similar mass drownings may have played an important role in rivers throughout the world when large migratory herds were more common features of the landscape.

“Farewell to America”

Historians have long tethered American overland migration to U.S. westward expansion, and they have presumed that Americans who left U.S. borders for Oregon and California in the early 1840s desired—and even assumed—that the United States would soon conquer the Far West. This article examines the words and actions of western migrants before U.S. expansion in 1846. It argues that, in fact, migrants left U.S. borders because their economic prospects were poor in the United States and thus that most migrants cared little whether the United States conquered the West in the near future. Indeed, some of the more ambitious migrants were even hostile to U.S. expansion, for they longed for a western republic of their own. Ultimately, Americans who traveled west did not ascribe to the idea of the United States’ Manifest Destiny but instead were seeking their own individual destinies.

Convergence of broad-scale migration strategies in terrestrial birds.

Migration is a common strategy used by birds that breed in seasonal environments. Selection for greater migration efficiency is likely to be stronger for terrestrial species whose migration strategies require non-stop transoceanic crossings. If multiple species use the same transoceanic flyway, then we expect the migration strategies of these species to converge geographically towards the most optimal solution. We test this by examining population-level migration trajectories within the Western Hemisphere for 118 migratory species using occurrence information from eBird. Geographical convergence of migration strategies was evident within specific terrestrial regions where geomorphological features such as mountains or isthmuses constrained overland migration. Convergence was also evident for transoceanic migrants that crossed the Gulf of Mexico or Atlantic Ocean. Here, annual population-level movements were characterized by clockwise looped trajectories, which resulted in faster but more circuitous journeys in the spring and more direct journeys in the autumn. These findings suggest that the unique constraints and requirements associated with transoceanic migration have promoted the spatial convergence of migration strategies. The combination of seasonal atmospheric and environmental conditions that has facilitated the use of similar broad-scale migration strategies may be especially prone to disruption under climate and land-use change.