Stopovers comprise a significant proportion of the time that many birds spend migrating, and researchers have long relied on these events to define and classify broader migratory strategies. Analyses of stopovers often assume that individuals stop primarily or exclusively in order to replenish energy stores, but other non-fueling behaviors have also been described during stopover events and can influence stopover incidence and duration. Here, we discuss the growing demand for understanding these non-fueling behaviors and for restoring the inherent behavioral complexity to stopover events. We begin by describing how light-weight tracking technologies allow researchers to follow individuals along their entire migratory journeys, capturing stopovers that controvert the traditional stop–refuel–resume paradigm. We then discuss 5 well-identified non-fueling behaviors—recovering, sleeping, waiting, information gathering, and social interactions—and examine how including these behaviors can alter interpretations of individual movement paths. Finally, we outline emerging directions for identifying these behaviors and look to larger implications for population management and site conservation along migratory flyways.

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Background Conditions encountered en route can dramatically impact the energy that migratory species spend on movement. Migratory birds often manage energetic costs by adjusting their behavior in relation to wind conditions as they fly. Wind-influenced behaviors can offer insight into the relative importance of risk and resistance during migration, but to date, they have only been studied in a limited subset of avian species and flight types. We add to this understanding by examining in-flight behaviors over a days-long, barrier-crossing flight in a migratory shorebird. Methods Using satellite tracking devices, we followed 25 Hudsonian godwits (Limosa haemastica) from 2019–2021 as they migrated northward across a largely transoceanic landscape extending > 7000 km from Chiloé Island, Chile to the northern coast of the Gulf of Mexico. We identified in-flight behaviors during this crossing by comparing directions of critical movement vectors and used mixed models to test whether the resulting patterns supported three classical predictions about wind and migration. Results Contrary to our predictions, compensation did not increase linearly with distance traveled, was not constrained during flight over open ocean, and did not influence where an individual ultimately crossed over the northern coast of the Gulf of Mexico at the end of this flight. Instead, we found a strong preference for full compensation throughout godwit flight paths. Conclusions Our results indicate that compensation is crucial to godwits, emphasizing the role of risk in shaping migratory behavior and raising questions about the consequences of changing wind regimes for other barrier-crossing aerial migrants.

The rufa red knot (Calidris canutus rufa) is a migratory shorebird that performs one of the longest known trans-hemispheric migrations of any bird species - from their breeding grounds in the Canadian Arctic to their nonbreeding grounds as far south as Tierra del Fuego - and they have experienced a population decline of over 85% in recent decades. During migration, they rest and refuel at stopover sites along the Atlantic Coast, including Kiawah and Seabrook islands in South Carolina. Here, we document the importance of Kiawah and Seabrook islands for knots by providing population and stopover estimates during their spring migration. We conducted on-the-ground surveys between 19 February - 20 May 2021 to record the occurrence of individually marked knots. In addition, we quantified the ratio of marked to unmarked knots and deployed geolocators on knots captured in the area. Using a superpopulation model, we estimated a passage population of 17,247 knots (~41% of the total rufa knot population) and an average stopover duration of 47 days. Our geolocator results also showed that knots using Kiawah and Seabrook islands can bypass Delaware Bay and fly directly to the Canadian Arctic. Finally, our geolocators, combined with resighting data from across the Atlantic Flyway, indicate that a large network of more than 70 coastal sites mostly concentrated along the coasts of Florida, Georgia, South Carolina, and North Carolina provide stopover and overwintering habitat for the knots we observed on Kiawah and Seabrook islands. These findings corroborate that Kiawah and Seabrook islands should be recognized as critical sites in the knot network and, therefore, a conservation priority. As a result, the threats facing the sites - such as prey management issues, anthropogenic disturbance, and sea level rise - require immediate attention.

Do constant environments produce ecological specialists? Wang et al. test this common assumption in Drosophila melanogaster and find that the converse may be true: constant environments sometimes produce robust generalists that can withstand change. In this study, increased tolerance to change may be best explained as a by‐product of adaptation to a particularly harsh salt‐enriched environment.