Scientists have discovered that five species of North American songbirds experience a second breeding season as they head south towards their wintering habitat in Central and South America. After initially breeding in temperate regions of Canada and the United States, the birds stop over in western Mexico and breed again.

This is the first time that biologists have documented so-called “migratory double-breeding” among birds in this hemisphere, though it’s been known to occur in Europe.

From Environment Canada’s most recent quarterly e-newsletter:

It has been long known that yellow-billed cuckoo, yellow-breasted chat, orchard oriole, Cassin’s vireo and hooded oriole travel to northwest Mexico following breeding in the north to molt and make use of the seasonal monsoonal rains in the area. Now, a subpopulation of these species clearly breeds again in Mexico before moving further south to winter.

Why is this important? First, it suggests that some bird species have begun to depend on areas outside their traditional breeding range to sustain their numbers. Secondly, it reinforces the notion that conserving bird populations requires connectivity — conserving multiple habitat areas along a migratory bird’s flyway. As migratory birds journey from point A to B, their stopovers are crucial locations that also must be preserved — particularly if they’re doubling as breeding areas.

The need to approach bird conservation from a transborder, complete flyway perspective is, of course, why Nature Canada works with BirdLife International partners in places like Haiti, Panama and Brazil.

Here is Environment Canada’s news update. The full scientific paper by Queen’s University researchers appeared in the Proceedings of the National Academy of Sciences.