Migratory routing and departure decisions of <i>Porzana carolina</i> (Sora): New insights from the Motus Wildlife Tracking System

ABSTRACT During migration, birds make a variety of decisions that may impact their overall survival and fitness. These decisions include but are not limited to their overall migration route as well as their departure timing considering variable weather conditions. Understanding how birds make these decisions can provide insight into not only their general migration strategy, but also the constraints they face during migration. Unfortunately, the migratory ecology of many members of the Rallidae family remains poorly documented. From 2017 to 2022, we fitted 202 Porzana carolina (Sora) with transmitters at Jug Bay, a critical stopover site along the Patuxent River, Maryland, USA, and tracked their migratory movements and decisions using the Motus Wildlife Tracking System. Tracking data revealed a tendency to follow the Atlantic coast in the fall. Spring migrants took variable paths, with routes primarily to the Great Lakes region, and had shorter stopovers. We also determined the timing and atmospheric conditions under which P. carolina initiated migration. Rising atmospheric pressure 24 hr before departure increased departure likelihood, as did wind profit (favorable tailwinds), while increased cloud cover slightly reduced departure probability, possibly due to disrupted nighttime navigation. Porzana carolina may select these conditions to maximize their travel speed and limit likelihood of disorientation while aloft. This time-minimization strategy is offset by their extended stopovers on the ground, which extend the duration of their migration. Porzana carolina needs to spend more time fueling to ensure they have enough energy to survive any obstacles they face while en route. By looking at the migration strategies of this understudied species, we can better understand the constraints birds face on migration.