Advancing an Owl

[NCSUCodeMonkey]

I feel silly posting this, but I have little experience with monster advancement.

I'm a Geomancer (Clr 3/Sor 4/Geo 2) with the Animal domain. I want to aquire some animal companions to use as scouts, watchmen, etc.

I was going to propose an advanced owl to my DM as one of my companions but I came across a problem. This is the advancement line from the Owl's statblock (MM 199):

1 HD (Medium-size); 2 HD (Large)

The only problem is that the owl already has 1 HD, and it's a Tiny creature, so the advancment line cannot be correct. The SRD entry is the same and the errata does not mention this.

Does anyone have a suggestion for a better advancement scheme? I would imagine the owl would be small for at least 1 HD, should it instead be: 2 HD (Small); 3 HD (Medium-size)?

NCSUCodeMonkey

 

[Celebrim]

The advancement is not correct, though making that claim is somewhat problematic because the HD of the owl as a tiny animal is probably incorrect as well.

Officially speaking, tiny animals should have 1/2 HD. Less officially, you could have a tiny animal with 1 HD so long as you reduced CON by 4 compared to similar creatures (which is how I tend to do it because I think it makes since that things with less mass will generally have lower Fort saves).

However, lets assume Owls are exceptional, 1 HD tiny animals. Since 1 HD animals are normally small, the Owl is approximately one size smaller than normal for creatures of it's HD. If we retain that attribute, for a triple advancement range we have then.

Owl 1 HD (4 h.p.): Tiny
Owl 2 HD (11 h.p.): Small
Owl 3 HD (19 h.p.): Medium

Which is exactly what logic would expect.