Agriculture creates subtle genetic structure among migratory and non-migratory populations of burrowing owls throughout North America

Population structure across a species distribution primarily reflects
historical, ecological and evolutionary processes. However, large-scale
contemporaneous changes in land use have the potential to create changes
in habitat quality and thereby cause changes in gene flow, population
structure, and distributions. As such, land-use changes in one portion of
a species range may explain declines in other portions of their range. For
example, many burrowing owl populations have declined or become extirpated
near the northern edge of the species’ breeding distribution during the
second half of the 20th century. In the same period, large extensions of
thornscrub were converted to irrigated agriculture in northwestern Mexico.
These irrigated areas may now support the highest densities of burrowing
owls in North America. We tested the hypothesis that burrowing owls that
colonized this recently created owl habitat in northwestern Mexico
originated from declining migratory populations from the northern portion
of the species’ range (migration-driven breeding dispersal whereby
long-distance migrants from Canada and the U.S. became year-round
residents in the newly created irrigated agriculture areas in Mexico). We
used 10 novel microsatellite markers to genotype 1,560 owls from 36 study
locations in Canada, Mexico, and the United States. We found that
burrowing owl populations are practically panmictic throughout the entire
North American breeding range. However, an analysis of molecular variance
provided some evidence that burrowing owl populations in northwestern
Mexico and Canada together are more genetically differentiated from the
rest of the populations in the breeding range, lending some support to our
migration-driven breeding dispersal hypothesis. We found evidence of
subtle genetic differentiation associated with irrigated agricultural
areas in southern Sonora and Sinaloa in northwestern Mexico. Our results
suggest that land-use can produce location-specific population dynamics
leading to subtle genetic structure even in the absence of dispersal
barriers.