Master of Science (MS)
Semester of Degree Completion
Jill L. Deppe
CHAPTER I: A Comparison of Diel Movement Patterns in Three Bird Species at a Stopover Site on the Northern Coast of the Gulf of Mexico
During migration, birds require stopover habitats where they stop en route to rest, refuel, and prepare for the next stage of their migration. For songbirds, many short movements made within a stopover habitat are known to be costlier than a single long migratory flight, as it takes a considerable amount of energy to initiate flight. This indicates that migrating birds should strive to balance the energy expenditure made in movement during stopover and energy gains they might be able to make while active at a stopover site. In this paper we examine the movement levels of three different species (Red-eyed Vireos [Vireo olivaceous], Swainson's Thrushes [Catharus ustulatus], and Wood Thrushes [Hylocichla mustelina]) throughout the day at a fall stopover site in southern Alabama on the coast of the Gulf of Mexico. We used automated radio telemetry to investigate how birds might change their movement patterns based on four variables influential to an individual's energy needs to complete their migration and their foraging abilities: age, fat stores, local wind speed, and wind direction. Our results demonstrate that each species has a unique pattern of movement, that wind direction was the strongest predictor of the proportion of time Red-eyed Vireos and Wood Thrushes spend moving, and that fat is the strongest predictor of movement in Swainson's Thrushes. The degree to which these variables influenced movement, however, was relatively small, and we posit that this might indicate that the habitat at this site is relatively poor and the potential for energy gain is too low to make altering movement patterns a viable strategy for optimizing energy use and fat gain.
CHAPTER II: Migratory Quiescence in Three Bird Species at a Stopover Site on the Northern Coast of the Gulf of Mexico
Migratory quiescence is a behavior characterized by a period of reduced activity occurring before birds depart from a stopover site during migration. It has been documented in captive studies but has not yet been observed in the wild. This study documents and characterizes migratory quiescence at a stopover site along the Gulf Coast in southern Alabama during fall migration in three species of songbirds, Red-eyed Vireo (Vireo olivaceus), Swainson's Thrush (Catharus ustulatus), and Wood Thrush (Hylocichla mustelina). We found that of these three species, only Red-eyed Vireos displayed a period of quiescence prior to migratory departure that differed significantly from other periods of stillness that occurred throughout the day. To investigate the purpose of this behavior, we examined morphological, physiological, and environmental correlates with the quiescent period to gain insight into its function. Only age and surface wind-speed at the time of departing a stopover site were related to quiescence. The purpose of migratory quiescence remains unclear, but our data suggest that some aspect of the physiology of a species (particularly their diet and the need to expel waste prior to initiating migration), and the experience of the individual are the factors most likely to be influencing quiescence.
Schofield, Lynn, "Daily Activity Patterns in Three Migratory Bird Species at a Stopover Site on the Northern Coast of the Gulf of Mexico" (2015). Masters Theses. 2402.