The urge to migrate is building as the breeding season approaches.

Laura Erickson

Hormones are surging. The drive to establish a territory, mate, and raise young is increasingly strong.

"Robins have an internal clock, and they know that soon it is time to start moving north. Their restlessness becomes irresistible depending on the length of day, but birds wait for the weather and temperature to be right. Robins generally follow behind the spring thaw and they wait for favorable winds. They want a tail wind. They wait for the south wind to come along and help them move north. So, knowing when to migrate involves an internal clock, a feel for temperature, and the right weather patterns that create south winds," says Cornell University biologist Martha Fischer.

Unseasonably Warm
Observers are reporting unseasonably warm temperatures for February and robins on the move.

"Robins are everywhere! Record warm yesterday and almost record warm today, so many fields are exposed and robins are all over the place feeding," observed Don Davis on February 19th near Presqu'ile Provincial Park in Ontario.

Watch carefully to see how robins respond to this warm spring:

• Will they move north earlier than normal?
  
• Will their breeding habitat be ready?
• What if cold and freezing temperatures return?
  

Ecological Mismatch?
Scientists studying climate change watch for a mismatch between events that are driven by temperature (spring thaw) and those driven by photoperiod (migratory restlessness). These days, temperatures are varying more widely than normal. In contrast, climate change does not affect photoperiod; it's caused by the earth rotating around the sun.