Only the last one even has a reverse DNS entry (at the moment, from here). It appears to be ads.perlmonks.org, a hostname that I know nothing about. It appears to host a bad version of the site (scary).

It's one of the three addresses I get for perlmonks.org.

$ nslookup perlmonks.org
Server:         192.168.3.125
Address:        192.168.3.125#53

Non-authoritative answer:
Name:   perlmonks.org
Address: 216.92.34.251
Name:   perlmonks.org
Address: 66.39.54.27             <-------
Name:   perlmonks.org
Address: 209.197.123.153
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