Winter connectivity and leapfrog migration in a migratory passerine

Aim: Every year birds prepare for their migration journey, and
understanding how this phenomenon is carried out allows us to infer
whether human activities have influenced and modified the way in which the
birds migrate. Many bird species perform long-distance movements to find
sites with better conditions and optimize the use of resources during the
annual cycle. These migration movements in birds have been studied using
different methods, from mist nets, mark and recapture techniques,
geolocators to document movements, and stable hydrogen isotopes. In this
study, we used a genetic tool to create a graphic representation of the
genetic variation across the species breeding range or genoscape as a
reference to assess the connectivity of a migratory bird across its annual
cycle. The advantage of the genoscape approach is that it allows us to
identify distinct genetic units in the breeding range and then detect the
migration pattern of those units through time and space. Methods: We
studied migration in the Painted Bunting (Passerina ciris) using genetic
data from 386 individuals across the breeding range, 230 samples from 28
migration stopover locations, and 178 samples from 16 wintering locations.
We also combined population and individual-level genetic assignments to
breeding areas in order to study migratory connectivity patterns in
greater depth. Results: Our results show the existence of four main
genetic groups within the species: Eastern, Southwestern, Central, and
Louisiana. We also found that most of the individuals migrate during the
fall towards Western Mexico and Central America and return to their
breeding sites through the coastal plains of the Gulf of Mexico; the
Louisiana breeding unit migrates to the Yucatan Peninsula and Central
America, returning to their breeding sites in the spring through the
coastal plains of the Gulf of Mexico. We found strong support for the
existence of a Leap-frog migration pattern. Main conclusions: We use a
genoscape approach to investigate population structure and broad-scale
migration patterns in the Painted Bunting. By screening samples from
across the annual cycle, we can reveal clear patterns of population
structure across the breeding range and provide strong support for the
existence of leapfrog migration.