I don't normally howl until late January, or so. I've not had much success with it this time of year.
December appears to be the start of the breeding season and choosing mates. Several years ago, I was coyote hunting in Mid-December and, way to the North on land I did not have permission to hunt, I spot 2 groups of coyotes laying on the snow, maybe 300yds apart. One group had 7-8 and the other, 5-6. Near each group was 2 coyotes, probably within 50yds of a main group. Every now and again, a member of a large group stood up and walked over and around the pair near them, then went back and laid down. This happened several times while I watched.
I was able to get to about 1/2 mile of them and started to call. They raised their heads and looked my way, but did not budge. Even howling did not get them to come any closer.
A week later, I was goose hunting the same property, and as it got light, I could see what might be the same 2 groups on the same hillside, doing the same thing. As before, they had no interest in my calls.
The next year, same place and Mid-December, I saw the same behavior.
I think the big groups were males and the pairs were females, and they were waiting for the females to be 'ready'. Once they pick mates,maybe early January, they get territorial and vocals work better for me.
Also, I have never had a coyote howl back at me during daylight in January through March. They just come in, quick and quiet.