CM nature study with a 4 yr. old

I have a 4 year old son who loves “nature study.” We live on a farm, so it comes rather easy in some ways. He does spend a lot of time outside. My husband built him a nice bug box. He catches all sorts of critters and puts them in there and observes them and sometimes tries to draw them (we have to put a time limit on it though, he will forget and we’ve had quite a few dehydrated frogs). He does like to draw and has asked to have a nature notebook, but the problem there is that if I give him a notebook (spiral or otherwise bound) he will use every page in it – so We used a 3-ring binder and card stock paper and he’ll take a page outside and draw at his picnic table. When he gets older I’m sure we’ll move to a nicer one. He also does nature drawings with sidewalk chalk on the picnic table (we have no concrete – all gravel). We keep a calendar and note the weather and when certain flowers/trees leaf out/bloom. I have also tried some of the outdoor geography suggestons from Home Education – right now he is learning NSWE by the suns position. We recently got a bird song cd and he is trying to listen for what type of bird he hears. Field guides are also fun – he will look up whatever critter he finds. One book we found that was very fun is My First Nature Book by DK (we checked it out at the library but later bought a used copy online for $1). There are some fun nature projects for little ones in there. He also helps with the garden and we make mental notes of all of that. My husband has a degree in horticulture and grows landscape trees so he teaches him a lot about trees and plants – for now we work on the difference in evergreen and deciduous and identifying common trees by their bark and fruit (acorns, pecans, sweetgum balls, etc.). I’ve also given him nature scavenger hunts to go on – before he could read I would draw pictures of many things outside and give him a bag to collect them in – we’ve expanded it to certain numbers of each thing to sneak some math in 🙂 Off the top of my head, those are some of our daily outdoor activities. And just to clarify, this is by no means any formal setting where I say “okay we’re doing nature study now” but rather that because of where we live and what we do for a living the outdoors is a major part of our lives. These are some of the conversations we have, things my son likes to do (some of these are his ideas, some mine), and some fun things we do outside that I would think would qualify as “nature study” 🙂