I emailed Les Sims’ post (above) and my response to Richard Thomas, communications officer of Birdlife International.
He emailed back, with a few additional comments on Dr Sims’ post [I’ve added LS, RT to hopefully make clear]:

Thanks for this: like your reply, some comments of my own in his

LS: Poultry manure from infected farms does pose a potential
risk but the speculation that is currently occurring on this is no
different to the sort of speculation on the role of wild birds that
ornithologists have criticised.

RT: I disagree – there is some evidence to support these allegations, and
official recognition by FAO, WHO and OIE that these are “high risk
production practices”. We think that is worthy of further investigation
at the very least. It shouldn’t be our job to point this possibility
out: FAO should be looking into it, but don’t appear to be, at least

LS: Molecular studies on the Mongolian wild bird outbreak
reveal that the viruses, while still closely related to existing strains differ
somewhat from other circulating Eurasian H5N1 viruses, and this
outbreak cannot be explained by the use of poultry manure.

RT: As you [ie Martin] rightly point out – Guan Yi has identified around 250 varieties of H5N1, so I don’t understand his argument here. According to our Croatian official on Aiwatch, the Croatian strain is different to the
Romanian and Turkish one.

RT: Agreed, it’s very difficult to pin the Mongolian outbreak on poultry
manure, but there’s several explanations other than wild birds.

LS: These Mongolian cases remain the best available evidence
for spread by wild birds and it would seem remarkable if these were to be
the only such incidents.

LS: All possible routes of transmission should be explored but
this should be done in a manner that retains balance and objectivity.

RT: Agreed – not just focusing on wild birds. For whatever reason, FAO seem to have lost the plot, and need bringing back to it. That’s what we set out to do.