strike straight across the Caribbean Sea to Florida (Fig. 3), while the 

 swallows begin their journey by a westward flight of several hundred 

 miles to Panama (Fig. 4). From there they move leisurely along the 

 western shore of the Caribbean Sea to Mexico, and, continuing to 

 avoid a long trip over water, go completely around the western end of 

 the Gulf of Mexico. This circuitous route adds more than 2,000 miles 

 to the journey of the swallows that nest in Nova Scotia. The question 

 may be asked: "Why should the swallow select a route so much longer 



Cliff Swallow 



_ Isochronal Migration Lines 

 Migration Route 



Figure 4. Migration of the cliff swallow. A day migrant that, instead of flying across 

 the Caribbean Sea as does the black-poll warbler (see Fig. 3), follows the coast 

 of Central America, where food is readily obtained. 



23 



