Fat, weather, and date affect migratory songbirds' departure decisions, routes, and time it takes to cross the Gulf of Mexico.

Approximately two thirds of migratory songbirds in eastern North America negotiate the Gulf of Mexico (GOM), where inclement weather coupled with no refueling or resting opportunities can be lethal. However, decisions made when navigating such features and their consequences remain largely unknown due to technological limitations of tracking small animals over large areas. We used automated radio telemetry to track three songbird species (Red-eyed Vireo, Swainson's Thrush, Wood Thrush) from coastal Alabama to the northern Yucatan Peninsula (YP) during fall migration.

Low metabolism and inactive lifestyle of a tropical rain forest bird investigated via heart-rate telemetry.

Birds in the lowland tropical rain forest are expected to have low energy turnover. Here, we used heart rate telemetry to estimate nighttime resting metabolic rate (RMR), daily energy expenditure (DEE), and locomotor activity of a small, long-lived tropical rain forest-understory bird, the spotted antbird (Hylophylax naevioides). Heart rate was linearly related to oxygen consumption in respirometry measurements that encompassed 96% of heart rates measured in wild birds.

Wingbeat frequency and flap-pause ratio during natural migratory flight in thrushes.

Powered flapping flight has evolved independently in many different taxa. For flapping fliers, wingbeat parameters such as frequency and amplitude are the primary determinants of these animals' energetic expenditure during flight. Here we present data on wingbeat frequency and amplitude for three New World thrush species during 15 entire nocturnal migratory flights over the Midwestern United States.

Navigation: bat orientation using Earth's magnetic field.

Bats famously orientate at night by echolocation, but this works over only a short range, and little is known about how they navigate over longer distances. Here we show that the homing behaviour of Eptesicus fuscus, known as the big brown bat, can be altered by artificially shifting the Earth's magnetic field, indicating that these bats rely on a magnetic compass to return to their home roost. This finding adds to the impressive array of sensory abilities possessed by this animal for navigation in the dark.

Biotelemetry of New World thrushes during migration: Physiology, energetics and orientation in the wild.

Billions of songbirds migrate between continents each year, but we have yet to obtain enough information on in-flight physiology and energetics to fully understand the migratory behavior of any one species. New World Catharus thrushes are common nocturnal migrants amenable to biotelemetry, allowing us to measure physiological parameters during migratory flight in the wild. Here, we review work by the authors on Catharus thrush in-flight physiology during spring migration in continental North America and present new data on individual variation in energy use during migratory flight.

Migrating songbirds recalibrate their magnetic compass daily from twilight cues.

Night migratory songbirds can use stars, sun, geomagnetic field, and polarized light for orientation when tested in captivity. We studied the interaction of magnetic, stellar, and twilight orientation cues in free-flying songbirds. We exposed Catharus thrushes to eastward-turned magnetic fields during the twilight period before takeoff and then followed them for up to 1100 kilometers.