PBS
Pbs: Parenthood (Birds)
This article from the companion site to "The Life of Birds" by PBS is full of examples of parenting birds. There is astonishing variety in nest building, offspring rearing, care, and even manipulation and deceit.
Other
Ornithology: Avian Development
A good page devoted to the development process of birds. Discusses the incubating process and the stages of development.
Other
Ornithology: Avian Reproduction
Provides a good discussion of the reproductive behaviors and systems of birds. Contains information on everything from nests to incubation times.
University of Pittsburgh
Univ. Of Pittsburgh/seasonal Decline in Tree Sparrow
A HIGH level science article written about the change in clutch size through a mating season and the possible science base for this phenomena.