Breeding Data
First Egg Dates
When do these birds breed?
One measure of when a bird species breeds is the date when it lays
its first egg. This table shows the first-egg date for 13
cavity-nesting species in the Southwest region according to data
collected by participants of The Birdhouse Network for the 2003 season.
Within that region, first egg dates ranged from February 28 (Western
Bluebird) to May 30 (Violet-green Swallow). This information might lead
us to ask questions about two types of trends, "what is it about the
environment that causes such large differences between sites?" and
"what is it about the biology and behavior of these birds that causes
such large differences within the same region?"