Related by Orlgandi Kulbrastsson of the Squirrel Eater Clan.

“One thing the visitor to one of the steads of the Narrow Stream Clan will notice straight off is that compared to all other Orlanthi (and that, of course is an Orlanthi all) their longhouses are… well, less long. They’re often a little less wide as well. Of course when asked, they’ll tell you that it’s because that’s just the way it’s always been. You’ll notice too that they don’t take their animals in with them when the cold comes. Instead they have special houses just for their cattle! Can you believe that? My old dad always told me they was weird.”

This secret was inspired by Jörg Baumgartner's (www.sartar.de) comments to me about the size of the houses in the photographs compared to the size of traditional Orlanthi housing.
The answer to the secret is (select the invisible text in the area below to reveal it):

When the original clan members arrived in the Narrow Stream Valley and began to build themselves a life, one of their earliest discoveries was the ancient barrow.

The clan was lucky enough to number a shaman among them. He spoke to the spirits of the barrow, who told him that they in some ways were the ancestors of the clan, and in some ways were not, and that the barrow was now the clan’s, and the spirits within were to be honoured as ancestors. To be successful they said, the clan must build its longhouses so that there was no room for animals, for in the dark past animals and men had shared houses in Dragon Pass before. That, they said, is what begat the half-man half-beast peoples of parts of the Pass. This they said was wrong, and must never be allowed to happen again.

The clan took this knowledge and said they were blessed to find ancestors here who could guide them in this way. Thus you will never find a Narrow Stream clan member taking their animals into their houses – instead they build stables and barns for their beasts.

The durulz say that what the clan was told is true in one way, but in another way is a lie. But they only say that amongst themselves as they value their friendship with the Narrow Stream Clan too much to risk it with loose talk – even if it is true!

Related by Iristhus the Dour, an Issaries pedlar.

“You noticed that up in the Narrow Stream lands they let durulz run about as iffen they was real Orlanthi? I mean, I ain’t got nothing against ducks personal like – I’ll sell ’em pegs or sharpen their knives just like I would for anyone – but they ain’t real folks like you an’ me now, are they? It ain’t decent, but don’t go sayin’ so up there unless you want a lump on your head and a boot up your arse!”

The reason why is (select the invisible text in the area below to reveal it):

When the clan first came to the valley and claimed the land as their tula, they found that from spring through autumn durulz would come downstream into the valley (from the north west) to fish the steam and hunt in the marshes. At first there was some conflict, but the chief at the time (Heortarl the Founder) realised they could not fight another clan so soon after their journey, so he made peace instead.

The durulz were eager for peace, and it was revealed that they were not a large clan, but that they had been here, upstream from the valley since before the Dragonkill War.

After some decades of peace, the durulz rewarded the Narrow Stream Clan’s defending of them against the Squirrel Eater Clan, who would love to raid the ducks but must pass through the more powerful Narrow Stream Clan’s tula to get to them. They let them in on a great secret, one that had been entrusted to the durulz clan of Featherfalls in the Second Age. It is the secret that makes the current chief Oddi Oddisson sure that the clan will be a king-maker one day.

What that secret is… You’ll have to wait and see.