Tropical Birds Waited For Land Crossing Between North And South America, Study Finds

[Nicholas]

ScienceDaily (Dec. 9, 2009) — Despite their ability to fly, tropical birds waited until the formation of the land bridge between North and South America to move northward, according to a University of British Columbia study published this week in the Proceedings of the National Academy of Sciences (Early Edition).

Find it HERE!

[Auspex]

The researchers believe the inability of many tropical birds to fly long distances across open water -- some are reluctant even to cross rivers as narrow as 200 metres -- may have contributed to the few north-bound movements prior to the land bridge completion.

My take is that, since these homebodies had everything they needed right where they were (how else would a sedentary habit have evolved and persisted?), they needed to be "led" north by the migration of the plants and insects (which couldn't go the distance before the bridge) that they had co-evolved with.