Beyond refueling: Investigating the diversity of functions of migratory stopover events

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.

Fall and Winter Movements of Newfoundland Graycheeked Thrushes (Catharus Minimus Minimus)

The Newfoundland subspecies of Gray-cheeked Thrush (Catharus minimus minimus) has declined since the 1980s and degradation of winter habitat has been suggested as a contributing stressor. However, the winter range of this subspecies is not well understood, so we fitted 29 males with archival GPS tags during summer 2016. Four tagged thrushes were recaptured in summer 2017 and, though all tags had missing locations and broken antennae, the data retrieved showed that one thrush wintered in the Sierra Nevada de Santa Marta (SNSM) in northern Colombia, one in the nearby Sierra de Perija in Venezuela, and a third may have settled in the same region. One tag provided locations until April 21 and that thrush was consistently detected within a ~1 ha area through the winter. Locations obtained during fall migration indicated that thrushes travelled to South America via Central America and possibly by directly crossing the Caribbean. Contemporary research indicates that the SNSM is an important migratory stopover for Northern Gray-cheeked Thrushes (C. m. aliciae) but a historical report coupled with our observations suggest winter use of the SNSM and adjacent areas in northern South America by C. m. minimus, though numbers may be lower than during the 1900s.