Volume 2, Issue 1

The migration of monarch butterflies (Danaus plexippus) in North America has a number of parallels with long-distance bird migration, including the fact that migratory populations of monarchs have larger and more elongated forewings than residents. These characteristics likely serve to optimize flight performance in monarchs, as they also do with birds. A question that has rarely been addressed thus far in birds or monarchs is if and how wing characteristics vary within a migration season. Individuals with superior flight performance should migrate quickly, and/or with minimal stopovers, and these individuals should be at the forefront of the migratory cohort. Conversely, individuals with poor flight performance and/or low endurance would be more likely to fall behind, and these would comprise the latest migrants. Here we examined how the wing morphology of migrating monarchs varies to determine if wing characteristics of early migrants differ from late migrants. We measured forewing area, elongation (length/width), and redness, which has been shown to predict flight endurance in monarchs. Based on a collection of 75 monarchs made one entire season (fall 2010), results showed that the earliest migrants (n = 20) in this cohort had significantly redder and more elongated forewings than the latest migrants (n = 17). There was also a non-significant tendency for early migrants to have larger forewing areas. These results suggest that the pace of migration in monarchs is at least partly dependent on the properties of their wings. Moreover, these data also raise a number of questions about the ultimate fate of monarchs that fall behind

Animal migration is often defined in terms appropriate only to the ‘to-and-fro’ movements of large, charismatic (and often vertebrate) species. However, like other important biological processes, the definition should apply over as broad a taxonomic range as possible in order to be intellectually satisfying. Here we illustrate the process of migration in insects and other terrestrial arthropods (e.g. arachnids, myriapods, and non-insect hexapods) but provide a different perspective by excluding the ‘typical’ mode of migration in insects, i.e. flapping flight. Instead, we review non-volant migratory movements, including: aerial migration by wingless species, pedestrian and waterborne migration, and phoresy. This reveals some fascinating and sometimes bizarre morphological and behavioural adaptations to facilitate movement. We also outline some innovative modelling approaches exploring the interactions between atmospheric transport processes and biological factors affecting the ‘dispersal kernels’ of wingless arthropods

Two general migration strategies prevail among temperate-breeding migratory songbirds of North America. Most “Eastern” birds migrate relatively directly from breeding to wintering grounds immediately after molting, whereas a substantial proportion of “Western” species depart breeding grounds early, and molt during extended migratory stopovers before reaching wintering areas. The Lark Sparrow is one of a few Western Neotropical migrants with a breeding range that extends into regions dominated by Eastern species. We sought to determine whether Eastern Lark Sparrows migrated in a manner consistent with Western conspecifics or follow typical Eastern songbird migratory patterns. To do so, we tracked individual Eastern Lark Sparrows equipped with geolocators between their breeding grounds in Ohio and their unknown wintering locations. Data from three Ohio Lark Sparrows revealed 1) individual variation in the duration and directness of autumn migrations, 2) autumn departures that consistently preceded molt, 3) wintering grounds in the central highlands of Mexico, and 4) brief and direct spring migrations. These observations suggest that eastern populations of prevailingly Western migrants, such as Lark Sparrows, may be behaviorally constrained to depart breeding grounds before molt, but may facultatively adjust migration en route.

Theory predicts that if extending parental care delays migratory departure, and if later migration is more dangerous, then parental care should be curtailed to make an earlier departure. Adult western sandpipers ( Calidris mauri ) depart Alaska in July, and the presence of peregrine falcons ( Falco peregrinus ) along their route rises steeply during the migratory period. Pacific dunlins ( C. alpina pacifica ) are ecologically similar, but do not depart Alaska until October, after peregrine passage has peaked. Because peregrine migration begins earlier in years with early snowmelt, we predicted that the curtailment of parental investment by western sandpiper, but not of Pacific dunlins, should be more pronounced in these more dangerous years. We measured breeding phenology of these species on the Yukon Delta National Wildlife Refuge during three seasons with strongly differing snowmelt timing. We found that they initiated breeding simultaneously, and that western sandpipers, but not Pacific dunlins, ceased laying increasingly earlier, provided increasingly less parental care and departed increasingly sooner as snowmelt was earlier. Advancing departure date by the overall average of 5.2d relative to dunlin reduces migratory exposure to peregrines by an estimated 18%. Our results support the hypothesis that natural selection has favored curtailment of parental investment by western sandpipers to advance migratory departure.

Nocturnally migrating birds experience loss of sleep during the migratory period especially when undertaking long, non-stop flights. We report a field observation of daytime sleeping behavior in a Black-andwhite Warbler (Mniotilta varia) during spring migration. It is likely that this individual was compensating from sleep loss experienced during a trans-Gulf of Mexico flight. Only a few observations of daytime sleeping behavior have been reported in free-living migrants and all have been associated with long-distance flights in relation to ecological barriers.

Stopover behaviour is a central element of migration strategies. But in recent geolocator studies, despite now being able to track individual songbirds during their entire migration, their stopover behaviour has received little attention. We used light-sensitive geolocators to identify the migratory routes and schedules of 12 northern wheatears (Oenanthe oenanthe) breeding in Sweden. Three geolocators collected temperature data complementing inferences from light data by providing additional information on behaviour during migration. The wheatears performed a slow migration with considerable stopover time (84%/76% of autumn/spring migration), with short stops while traveling through Europe, and a prolonged stopover period in both autumn and spring in the Mediterranean region. Spring migration was faster than autumn migration, mainly because of decreased stopover time. Migration routes and time schedules were similar to those from a German breeding population. Compared to wheatears breeding in Alaska with a three-fold migration distance, Swedish wheatears spent more time during stopovers during autumn and spring migration, suggesting less time constraints and potential flexibility in migration schedules. The finding of prolonged stopovers, similar to other recent geolocator studies, shows that temporary residency periods may be common. This changes our current view on stopover ecology to one where temporary residency periods are part of spatio-temporal strategies optimising resource use during the entire annual cycle.

Twenty-eight species of migratory shorebirds rely on the coastlines of the northern Gulf of Mexico (NGOM) to fuel migrations to near-arctic breeding grounds. Shorebird species vary in their migration ecology: some species use a “jump” strategy, migrating long distances without stopping, while others use “skip” and “hop” strategies, stopping to refuel at shorter intervals along their journey. We compared stopover duration, body condition (fat scores and size-adjusted mass), and refueling rates (plasma metabolite concentrations), in three Calidrid sandpiper species (Calidris pusilla, C. mauri, and C. alpina) that differ in migration strategy after leaving the NGOM during spring. Results indicate that, while birds refueled at similar rates, C. alpina, an intermediate distance jump migrant, reached higher fuel stores before departing on migration than the hop and skip migrants, C. pusilla and C. mauri. C. alpina also spent more time on the NGOM than the other two species. Results suggest that NGOM habitats may be particularly important for migration success in C. alpina. This knowledge will help us predict the potential population level consequences of habitat loss due to global change on NGOM shorebird populations and develop conservation plans to mitigate these impacts.

Identification and characterization of seasonal migration routes and stopover sites has been recognized as important to the conservation of migratory species. This project utilizes multiple regression models including circular-linear regression to identify associations between route choice, travel speed, and environmental preferences using trajectory data of migratory Arctic Terns (Sterna paradisaea) and environmental data obtained through remote-sensing techniques. Results of this study suggest that route choice on the southward post-breeding migration route may be more dependent on underlying environment than the northward postwintering migration route. In contrast, travel speed was variably associated with underlying environment between southward and northward migrations, including several differences regarding the impact of interactions between environmental variables. These results reveal the importance of using multiple metrics in the estimation of spatial resistance and highlight conflicts between the theoretical resistance framework of GIS and movement analysis methods.

For long-distance migratory songbirds, morphological traits such as longer wings and a smaller body size are predicted to increase migration efficiency. Due to previous limitations in our ability to track the long-distance journeys of small-bodied birds, the relationship between morphology and start-to-finish migration performance has never been fully tested in free-living songbirds. Using direct-tracking data obtained from light-level geolocators, we examined the effects of morphological factors (wing and body size) on spring and fall migration performance (flight speed, duration of stopovers, total stopovers taken) of a widely distributed, trans-hemispheric migratory songbird, the purple martin (Progne subis) (n = 120). We found that smaller-bodied birds spent fewer days at stopovers along fall migration, but larger-bodied birds spent fewer days at stopover and took fewer stopovers during spring migration. More of the variation in fall migration performance was explained by morphology, as compared to spring migration, possibly indicating a larger influence of environmental conditions on spring performance. Overall, our results partially support long-standing and previously untested predictions regarding the influence of intrinsic factors on migration performance. Future research should examine the influence of environmental variation on migration performance as well as additional morphological traits that may contribute to migration performance.