Road noise reduction

The trouble with this is that the noise isn't anything like constant - and constant is what works when it comes to NR. Even if you try adaptive NR or DeNoise the results are no better, even though both of those are technically better for varying sources. Whatever you do, you end up with something that sounds more distracting than the traffic. Using a sound model and the Sound Remover worked even worse.

Unfortunately for you the only solution to this at all is to do what all nature recordists end up doing - persevere. Eventually you end up with the recording you want. There are some things you can do that may help though. One is to cut out as much intrusion as possible. Generally when it comes to birds (or surveillance in general) parabolic reflectors are your friend. Amazingly enough, so is recording in stereo. This helps because if you can get the sound you want central in the stereo field, sum and difference techniques can help you extract a lot of the stereo background without touching the part you want, and Audition can do that relatively easily.