I broke each month into categories where we would read, talk about, or watch videos on the topic. I had them do some work for their science notebook, and wrapped up each section with a notebook page on the topic relevant to the bird they chose to study. Naturally, we went into the field when we could, though it was far less than I wanted to thanks to illness, a surgery, and timing in general.
I created a pdf for my bird study plans instead of listing it all below, but here are the monthly topics:
January: Bird Classification
February: Bird Anatomy
March: How Birds Live (Habitats and Diet)
April: How Birds Live (Communication, Mating/Nesting)
This is a perfect study to get into the field. Buy or borrow at least one pair of binoculars to take along with you, as well as a field guide. I like this one for the field (it's nice and light), and my boys liked this one to get them started and for checking off. Of course, my favorite book to flip through is The Sibley Guide to Birds, though it's heavy to carry around with you.
Another resource my kids thoroughly enjoyed was the game Bird Bingo. This game is always a favorite, but this set is extremely well-made, gorgeous, and seems durable. (Really, it looks and feels luxurious!) It was definitely a nice respite during winter, waiting for migration to begin.
Through it all, I read aloud to them from The Burgess Book of Birds for Children. I found it both informative and fun to read, as did my children, especially the boys. We have also started to watch the David Attenborough's The Life of Birds.
There are so many sites online to utilize to see nesting cams, bird songs, bird identification, etc. I listed some in my plans that we specifically used. I also created a list of county and state parks near me that were of particular interest for local (or migrating birds). That takes a bit of time to research but it's nice knowing where it's best to see birds at certain times. I found a state group that did most of the research for me so all I had to do was copy the info and tuck it into our science folder.
Be sure to get out even in the winter! As you can see, we enjoyed ourselves!
If you use the plans, and have questions, ask away!