Although a British saying believes that "one swallow does not a summer make," from Britain to the United States, residents tired of winter seek the sign of the first swallow to mark the beginning of spring. Before the 19th Century, many people in Britain believed that swallows spent the winter at the bottom of ponds buried in mud alongside frogs. The truth is almost as amazing. Swallows in Europe spend the winter in Africa while those in North America spend the winter South America. They make return journeys of up to 6,000 miles to help us welcome spring.
In Northern California, swallows arrive as early as mid-February, spending only from November to February in sunny South America. In Britain, they begin arriving in March with the first arriving in the far north, in Northern Scotland, at the end of March and the main influx at the beginning of May.
Swallow species identification is challenging, because they fly so fast that it is difficult to see them through binoculars. However, one clue is the shape and location of the birds' homemade grass-lined mud nests. Barn swallows, the only swallow in Northern California with the classic swallow-forked tail, create cup-like nests, typically upright, on beams inside barns or other old wooden structures. Cliff Swallows, in contrast, create gourd-like nests, often hanging upside down, on the underside of bridges over water or even over freeways.
You can find barn swallows in areas with open fields and wooden structures. To find cliff swallows, head for your nearest bridge (including road bridges over freeways). If it is safe, cross the bridge and then look down over the side. You may see dozens and dozens of nests, some with baby birds precariously and curiously looking out and down. I wonder how they hold on? Cliff swallows should really be called bridge swallows in honor of their amazing ability to adapt their nesting strategies to human structures. Their population has been expanding as they have moved to bridges from cliffs.
The above information and more about swallows can be found by visiting the websites below:
http://www.allaboutbirds.org/guide/Bank_Swallow/lifehistory