EMBARGOED UNTIL:
August 4, 2014; 2pm Central
Field Museum PR Contact:
media@fieldmuseum.org
312.665.7107
The Evolution of Migration
Ancestral songbirds headed south for the winter
Each year, millions of birds migrate thousands of miles between the locations where they breed
and raise young, and the areas where they spend the winter. Each migration is a trip fraught with
danger—many birds die before they reach their final destination. To scientists, long distance
migration still holds many mysteries, one of which is: where did migration begin and how did it
evolve? This question has long been a debated topic among scientists, but thanks to new research
from Field Museum scientists, we may have an answer for one of the largest groups of migratory
birds. The scientists’ research will be published in the Proceedings of the National Academy of
Sciences (PNAS).
Traditionally, there have been two schools of thought: one, that ancestors of migratory birds
spent the whole year in North America and evolved migration by moving their winter range to
the tropics. The other theory suggested that these ancestors were originally found in the tropics,
and evolved migration by moving breeding grounds to more temperate locales like North
America.
To uncover this mystery of migration Resident Graduate Student Ben Winger (University of
Chicago) and Associate Curator of Botany Rick Ree created a model that uses a phylogeny (a
“family tree” of species) to infer how the breeding and winter ranges of migratory species
changed through time. They applied the model to a large group of migratory birds that include
warblers, cardinals, sparrows, tanagers, orioles, and others. “We named it the 'domino model'
because the breeding and winter ranges of species were coded in 3x2 grids of binary values, like
dots on domino pieces. The computational challenge was to reconstruct the most probable
evolutionary shifts from one domino to another,” explains Ree. Tracing back through time and
examining common ancestors of migratory and non-migratory species, they were able to
conclude that there was more evidence supporting the idea that birds lived year-round in North
America and began migrating further and further south, resulting in today’s birds migrating
thousands of miles every year.
Another result of the study suggests that many tropical species of birds are descendants of
migratory ancestors that lost migration and stayed in the tropics year-round. “This is an
interesting result because species diversity in this group is much higher in the tropics. Previously,
more species in the tropics led to the assumption that temperate species are derived from tropical
ancestors; however, the results of our phylogenetic study suggest that the opposite pattern
happened often in this group.”
The paper Temperate origins of long-distance seasonal migration in New World songbirds will
be published by PNAS the week of August 4 and is available to media. Contact
media@fieldmuseum.org for access to the paper, and to arrange interviews.
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