Young Songbirds: Lazy Travelers or Clever Learners?
Juvenile Wood Thrushes arrive much later to spring breeding grounds than adults. Here's why.
Like human teenagers, the juvenile songbird likes to dawdle. This is especially true for juvenile Wood Thrushes during spring migration, a new study finds. While adult and juvenile Wood Thrushes travel the same migration routes, it takes the younger birds almost twice as long to get to the breeding site.
Emily McKinnon, biologist at York University in Canada, learned about these migration differences by attaching geolocator "backpacks" to the birds, which record flight data that, once retrieved, show scientists the Wood Thrushes flight paths.
At first, scientists thought the young birds' slow pace could be attributed to their lower physical fitness and shorter wingspan. But McKinnon says that's not the case. "It doesn't seem that juveniles couldn't get there faster." So why don't they have a speedy flight?
Turns out its not youthful laziness—it all comes down to survival instincts. "The juveniles have just evolved to migrate later so they don't have to compete with the adults for breeding territory," McKinnon says. Essentially, the younger birds delay their arrival by taking more days at stopover sites—along the northeastern United States and the central Gulf coast—as an adaptive strategy to ensure they have a chance to make babies too. This strategy hasn't helped them in recent years, however, since the Wood Thrush population has been steadily declining.
Some scientists suspect habitat reduction at stopover sites play a key role in shrinking Wood Thrush numbers. McKinnon and her colleagues think learning more about these locations could help scientists understand what's causing the population drop. They compiled their migration data to pinpoint stopover sites to help future researchers and conservationists find a solution.
While this research is all about the Wood Thrush, McKinnon believes that the reason for delayed juvenile migration holds true for many other songbird species. Scientists just need to strap some more "backpacks" on other birds to learn the nuances for individual species.