Volume 3, Issue 1

Effective conservation of short-distance migrants requires an understanding of intraspecific variation in migratory patterns across small spatial scales. Until the advent of ultra-light geolocation devices, our knowledge of the migratory connectivity of songbirds was limited. For the Hermit Thrush (Catharus guttatus), subspecies delineations and connectivity patterns have been unclear in the portion of their breeding range in western North America from southeastern Alaska to northwestern Washington, where individuals wintering in the San Francisco Bay Area of California purportedly breed. To determine breeding locations and migratory timing of the Bay Area’s wintering Hermit Thrushes, we deployed geolocators at sites to the north and south of the San Francisco Bay. We compared results from these two regions to one another and to connectivity patterns suggested by subspecies definitions. We collected morphometrics to identify regional differences. Hermit Thrushes that wintered in the North Bay had a wider and more southerly breeding distribution from the British Columbia coast to northwestern Washington, whereas South Bay thrushes migrated to southeastern Alaska and the British Columbia coast. In general, North Bay thrushes departed wintering grounds and arrived on breeding grounds earlier than South Bay thrushes, but we cannot eliminate sex as a factor in these differences. Regional morphology differed only in bill length. Intraspecific isolation in glacial refugia during the Late Pleistocene may explain these fine-scale geographic variations in migration patterns and morphology.

Little is known about common bottlenose dolphin (Tursiops truncatus) seasonal migration along the United States southeastern Atlantic coast, or what factors influence migratory patterns. Therefore, our objectives were to: 1) document evidence for seasonal movement of dolphins in this region (that would indicate migratory behavior) and 2) determine if seasonal changes in abundance and temporary emigration (i.e., migration indicators) for dolphins along South Carolina and Georgia coasts are related to changes in water quality variables. Previously collected capturerecapture data (from visual sightings of individual dolphins) and water quality data from Charleston, South Carolina and St. Catherine’s Island, Georgia were used to achieve our objective. Robust design models were used to estimate seasonal abundance and temporary emigration for the Charleston population, whereas closed population capture-recapture models were used to estimate seasonal abundances for the St. Catherine’s Island population. The Charleston population showed seasonal abundance and temporary emigration patterns with low estimates in winter, which increased in spring, peaked in summer, and decreased in fall. Seasonal temporary emigration was best explained by water temperature, which followed the same general pattern. Seasonal abundance in the St. Catherine’s population was best explained by salinity, but no consistent pattern in abundance was observed. Our results not only provide the first evidence of a clear seasonal migration of dolphins in this region, but can aid in conservation and management efforts by increasing accuracy of abundance estimates.

Long-distance migration can be seen throughout the animal kingdom and can have large impacts on population dynamics and species distributions. The act of migration itself also affects the evolution of a species, as evolutionary forces select for certain characteristics in animals conducting long-distance migration. Monarch butterflies are best known for their annual migration from Canada and the northern United States to central Mexico, but some populations of monarchs have lost the ability to migrate. Previous research found that migratory monarchs had larger, more elongated wings than their non-migratory counterparts and it was hypothesized that these traits were beneficial for migration. However, Bergmann’s rule - which predicts larger body sizes with increasing latitude - could also explain this pattern as migratory populations are found at higher latitudes. To understand the role of wing dimensions in migration, we examined forewing size and shape of migratory and non-migratory monarchs from seven worldwide populations varying in latitude. Results showed that larger forewing size was indeed correlated with migratory status rather than latitude. However, migratory monarchs did not have more elongated forewing shape than non-migratory monarchs across the globe. Our study indicates that size may play a larger role than shape in long-distance migratory capability.

Migration strategies may change in response to climate change with consequences for conservation efforts. We used 80 years (1934−2014) of band recovery data (N = 1,057) to describe spatial and temporal patterns in the migration behavior of American Robins. The distribution of recoveries suggests strong continental scale connectivity with distinct separation between eastern and western North America, with a more moderate degree of connectivity within these regions. We also found little evidence of differential migration between males and females. Despite previous studies that suggest the winter distribution of robins has shifted northward, our analysis shows no obvious change in migration distance over time. Surprisingly, we found that a significant proportion of across season band recoveries occurred locally (20%), in close proximity to the original banding locations. It’s well known that large numbers of robins linger in northern breeding grounds well into the winter of some years, but the proximity of these birds to breeding areas was previously unknown. We found little evidence that the winter latitude of migrants or local recoveries shifted over time. However, there was a trend for increased frequency of local recoveries in recent decades, providing an alternative hypothesis for the northward shift in winter distribution.

Knowledge of migratory connectivity is critical to understanding the consequences of habitat loss and climate change on migratory species. We used light-level geolocators to determine breeding locations and migratory routes of wintering Golden-crowned Sparrows (Zonotrichia atricapilla) in two regions of California, USA. Eight out of 9 birds tagged at coastal-wintering sites in Marin County went to breeding sites along the Gulf Coast of Alaska, while 7 out of 8 inland-wintering birds in Placer County migrated to interior sites in the Yukon, Northwest Territories, and British Columbia, Canada. Our estimate of the strength of migratory connectivity was relatively high (rm = 0.66). Coastal-wintering birds followed a coastal migration route while inland-wintering birds migrated inland. Coastalwintering birds migrated significantly farther than inland birds (3,624 km versus 2,442 km). Coastal birds traveled at a greater rate during spring migration (179 km/d) than did inland birds (118 km/d), but there was no statistical difference in the rate of fall migration (167 km/d and 111 km/d, respectively). Dates of arrival and departure, and duration of spring and fall migration, did not differ between groups, nor did return rates. Rates of return also did not differ between tagged and control birds. The distinct migration routes and breeding areas suggests that there may be more structuring in the migratory geography of the Golden-crowned Sparrow than in a simple panmictic population.