Chrome Browser system requirements [support.google.com]:

To use Chrome Browser on Mac, you'll need:

• OS X Yosemite 10.10 or later

Ok thank you - I take it then that if it doesn't have Chrome in the UA then it must be Safari. And for the second part of my question - does Safari give the referrer URL? Or is it variable?

Both of the user agents are likely to be legit. Not everyone updates as soon as the next best thing comes out. Some recent OSX updates have not been viewed as improvements by some people and since some useful functions are lost, people may just keep using what they prefer, what works for them.

To determine whether a visitor's UA is legit, it is more useful to see what they're doing. Requesting only .html or only images without the rest of the resources such as .css of a particular URL piques my interest for example. Unless the UA is a known/named bot or a really outdated version of a browser that can't work on the platform it claims, I assume the visitor to be human if their activity is human.

Referers are iffy on any browsers.

To use Chrome Browser on Mac, you'll need:

Nonsense. Those are simply the requirements for the most recent Chrome. I'm on 10.9 and they will no longer let me download new versions--in fact they've retroactively subtracted a few numbers, so if I try to download now, I'll be given a lower version than what I've actually got installed. Whether the system requirement is truly valid is, as always, a whole different question.

I'm trying to figure out if I am indeed seeing a change in behavior (over the past few weeks or months) in terms of seeing hits from MAC OSX systems with no referer but that otherwise look like legit hits.

I found no matches for the exact string

Mozilla/5.0 (Macintosh; Intel Mac OS X 10_11_0) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/59.0.3071.115 Safari/537.36

so I checked for

Mac OS X.+?Chrome/59.0.3071.115 Safari/537.36

... and yes, you may have stumbled across something. Apart from a few isolated image requests, 100% of hits were robots--in fact, all of them in my logs were blocked robots, most of them using familiar request patterns, so take a closer look at your blocking criteria.

The second of your quoted UA strings--which is Safari, not Chrome--is human.

Edit: I backtracked and looked for the element “Chrome/59.0.3071.115 Safari/537.36” without reference to OS. The last human visits (assorted Windows) were in March.

And while searching these patterns, I found a slew of highly suspect requests from 120.92.11 and 120.92.72 (just those two, but many of each), so now I'm off to investigate more closely.

To use Chrome Browser on Mac, you'll need:

Nonsense.

Agreed. There's a lot of misinformation about Chrome support on Mac.