Temporal Migration Patterns Research Articles

Spatial and Temporal Migration Patterns of Wilson’s Warbler (Wilsonia Pusilla) in the Southwest as Revealed by Stable Isotopes

AbstractWe used stable hydrogen isotopes (δD) to identify the breeding locations of Wilson’s Warbler (Wilsonia pusilla) migrating through five sites spanning a cross-section of the species’ southwestern migration route during the springs of 2003 and 2004. Determining the temporal and spatial patterns of migration and degree of population segregation during migration is critical to understanding long-term population trends of migrant birds. At all five migration sites, we found a significant negative relationship between the date Wilson’s Warblers passed through the sampling station and δD values of their feathers. These data were consistent with a pattern of “leap-frog” migration, in which individuals that bred the previous season at southern latitudes migrated through migration stations earlier than individuals that had previously bred at more northern latitudes. We documented that this pattern was consistent across sites and in multiple years. This finding corroborates previous research conducted on Wilson’s Warbler during the fall migration. In addition, mean δD values became more negative across sampling stations from west to east, with the mean δD values at each station corresponding to different geographic regions of the Wilson’s Warblers’ western breeding range. These data indicate that Wilson’s Warblers passing through each station represented a specific regional subset of the entire Wilson’s Warbler western breeding range. As a result, habitat alterations at specific areas across the east-west expanse of the bird’s migratory route in the southwestern United States could differentially affect Wilson’s Warblers at different breeding areas. This migration information is critical for management of Neotropical migrants, especially in light of the rapid changes presently occurring over the southwestern landscape.Patrones Espaciales y Temporales de la Migración de Wilsonia pusilla en el Sudoeste Detectados Mediante Isótopos Estables

Migration patterns in a population of cottonmouths (Agkistrodon piscivorus) inhabiting an isolated wetland

AbstractFew studies have examined the spatial and temporal migration patterns of snakes to and from active‐season habitats. We conducted a year‐long population‐level analysis of cottonmouth Agkistrodon piscivorus migration patterns by monitoring snakes entering and leaving a Carolina bay wetland that was encircled by a continuous terrestrial drift fence. Cottonmouths used the wetland during the active season and left the bay in the fall to overwinter in other habitats. Adults and juveniles did not differ in time of arrival at the bay but juveniles left the bay earlier than adults. Spatially, captures of adult cottonmouths entering and leaving the bay were distributed non‐randomly, with capture peaks corresponding to the directions to the nearest permanent aquatic habitats. Juveniles' immigration patterns in the spring were biased in the same directions as those of the adults, but they left non‐directionally in the fall. This suggests that neonates do not rely on adult scent trailing to locate hibernacula, and that in a region with moderate winter temperatures, suitable overwintering sites may not be a limited resource. Additionally, our study demonstrates that cottonmouths make extensive use of upland habitats and underscores the importance of both critical upland habitat and forested corridors between wetlands and hibernacula for the conservation of wetlands herpetofauna.

Assessing migration patterns of sharp‐shinned hawks Accipiter striatus using stable‐isotope and band encounter analysis

Intraspecific migration patterns in birds have both spatial and temporal components. Two commonly reported spatial patterns are leap‐frog and chain migration. Temporal migration patterns refer to the timing of migration of populations from different breeding latitudes. We investigated the spatial and temporal migration patterns of hatching‐year (HY) sharp‐shinned hawks Accipiter striatus of interior North America using stable‐hydrogen isotope and band encounter analyses. Feather samples were collected from hawks migrating through New Mexico, USA and measured for their stable‐hydrogen isotope ratios (δD) to distinguish individuals originating from relatively high and low natal latitudes. We then examined the relationship between feather δD values and passage dates through New Mexico, USA. We also gathered band encounter data from the Bird Banding Lab of the United States Geological Survey to determine the wintering latitudes of HY sharp‐shinned hawks relative to their passage date through migration banding sites in interior North America. Combining these data, we found that during fall migration HY sharp‐shinned hawks used a chain migration pattern, that is, hawks originating from lower latitudes wintered further south than those from higher latitudes. In addition, birds originating from lower latitudes passed through interior North America earlier than those from higher latitudes. We also found that hawks from higher latitudes were significantly larger than those from lower latitudes, and that females from higher latitudes had significantly higher estimated fat levels than females from lower latitudes.

Calibration of Radiocarbon Ages and the Interpretation of Paleoenvironmental Records

Calibration of the radiocarbon timescale of paleoecological records is essential if they are to be explained correctly in terms of their governing ecological or climatological controls. The differences between calendar ages and radiocarbon ages that arise from variations in 14C production through time can distort the chronologies of individual records and the interpretations based on them. Misleading impressions of synchrony or diachrony of events among multiple records can result, and estimates of the apparent duration of episodes and rates of sedimentation and local population changes can be biased. Displays of the temporal patterns of migration or extinction may also be affected. Spurious correlations may arise between records with radiocarbon-controlled chronologies and time series of potential controls that are expressed on a calendar time scale. Support for particular explanations of features in a paleoecological record may vary depending on whether radiocarbon ages are calibrated or not. This situation is illustrated using the eastern Beringian Populus subzone as an example. When the radiocarbon ages that control the timing of the Populus subzone are calibrated, the contemporaneous decrease in ice volume and increase in summer insolation are implicated as the ultimate controls of the occurrence of the subzone.

ON THE ROAD AGAIN: SEASONAL MIGRATION TO A SUNBELT METROPOLIS

Seasonal migration to Sunbelt locales in recreational vehicles (RVs) has emerged as a major form of cyclical movement among Americans and Canadians. Using Phoenix, Arizona, as a case study, this paper addresses three questions. Who participates in this lifestyle? What are their geographical and temporal patterns of migration? What are the distinguishing characteristics of RV resort communities? Results highlight that older Americans and Canadians are defining new lifestyles and forms of retirement living based on seasonal movement in RVs.

RURAL-URBAN MIGRATION IN CHINA, 1950–1982: ESTIMATES AND ANALYSIS

The objectives of this study are to construct a series of annual net rural-urban migration estimates for post-1949 China and to examine the temporal patterns of rural-urban migration and urbanization and their relationship with economic growth. The paper begins with a review of the problems in previous estimations of China's net rural-urban migration. By tackling the various problems identified, a set of reasonably accurate migration estimates is presented. The trends and special features of rural-urban migration in post-1949 China are then examined. It is shown that the volume of net rural-urban migration since 1949, accounting for about half the urban population increase, is by no means small and is certainly more than was previously realized. The tremendous variation in migration rates reflects the heavy interventionist role of the government in this area. The periods of high net migration generally coincide with the periods of better economic performance. It is argued that the temporal patterns of migration and urbanization have been shaped mainly by the economic development strategy pursued by China. Finally, the current trend of rural-urban migration is examined.

Preliminary Studies on the Visible Migrations of Adult Salmon

Techniques have been developed for observing and recording the behaviour of migrating adult salmon. Daytime movement through slow water (less than 5 ft/sec (1.5 m/sec)) is by steady swimming in schools. Such steady swimming is interrupted with resting periods at velocities between 3 and 5 ft/sec (1.0–1.5 m/sec) but can be sustained over long periods at velocities less than 3 ft/sec (1 m/sec). Movement through slow water in the Somass River system normally occurs along the line of the deepest channel, wherever this is well defined. Movement through rapids (velocities more than 5 ft/sec or 1.5 m/sec) is by darting interspersed with holding, salmon moving individually rather than in schools. Migration through pools, and through other obstructions such as fishways shows diurnal rhythms, modifications of which are associated with numbers of salmon moving, the time within the migratory season, and the species concerned. Nocturnal migration occurs.Entry of salmon into rivers during the migratory season occurs at intervals, the initiating stimulus for which is frequently related to the passage of atmospheric warm fronts over the river estuary.Techniques for field behaviour studies of salmon migration have a potential for management in that it is possible to undertake such studies in areas scheduled for industrial development and to utilize the revealed spatial and temporal migration patterns in the design of fish diversion facilities.