The peak of the scrape making will be in the pre-rut. But the majority of those scrapes will never be used much, if at all, especially if they are on field edges. I like to use scrapes in conjunction with rub lines and funnels. In fact, over the years I've kind of refined my buck hunting strategy down to "find where the does are and that's where the bucks will be". That's not the only factor, but it's a primary one.
I also believe that while early rubbing is to remove velvet, a lot of the later rubs, especially along obvious "lines", are more of a signpost or territorial marker. I also don't believe that they do it to strengthen their neck muscles. The large necks that you see on rutting bucks is due to the increase in testosterone levels, and would occur whether they rubbed or not. That may be a side effect, but they don't think, "Hey! I need my daily neck work out today so I can be buff for the ladies!"
One more point.......while the bucks make the scrapes (although I have witnessed DOES opening scrapes on occasion), it's the does who determine which scrapes will be active. One more reason to focus on the ladies, especially when you see signs that they are coming into estrous.
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