It's pretty tricky. The standard answer is by the black tailtip. Not much use here!
The important difference between the two species is that nivalis (weasels) have two litters a year, and erminea (stoats) have only one. It might sound esoteric, but it's the feature that explains most of the other differences. You need to be a small animal to breed that fast, so nivalis are smaller than erminea. You can't afford to miss a breeding season if you only get one shot at it per year, so erminea have the ability to put their pregnancies on hold (delayed implantation until the next spring. Being larger, erminea don't lose body heat quite as rapidly as nivalis, so they can be almost serpentine-slender. The nivalis have a somewhat plumper build and their muzzles aren't quite as sharp in profile. Also, the black tailtip is apparently also related to body size -- it's supposed to be a lure to distract predatory birds into attacking it rather than the animal's body while it flees across the snow. Nivalis are too small to have tails long enough for this to work, so the just have stubby little tails with no markings.
A fairly cosmetic difference is that the border between the brown fur and the white underparts is smooth in erminea and rather jagged in nivalis. I'm not entirely sure nivalis turn white in winter the way erminea do; I think it might be the case that they're just always white if they live far to the north, and always brown further south. You can see a little bit of brown on the top of the pictured animal's head, so it's certainly one that changes phase seasonally.
I'm pretty sure it's an erminea. But there if the picture was taken in north america, there's a third species, the long-tailed weasel (Mustela frenata) which looks more like erminea than nivalis does....
![[personal profile]](https://www.dreamwidth.org/img/silk/identity/user.png){kind=small}
(no subject)
Date: 2008-11-23 10:36 pm (UTC)(no subject)
Date: 2008-11-23 10:48 pm (UTC)(no subject)
Date: 2008-11-23 10:53 pm (UTC)STOAT!
(no subject)
Date: 2008-11-23 11:45 pm (UTC)(no subject)
Date: 2008-11-24 01:05 am (UTC)The important difference between the two species is that nivalis (weasels) have two litters a year, and erminea (stoats) have only one. It might sound esoteric, but it's the feature that explains most of the other differences. You need to be a small animal to breed that fast, so nivalis are smaller than erminea. You can't afford to miss a breeding season if you only get one shot at it per year, so erminea have the ability to put their pregnancies on hold ( until the next spring. Being larger, erminea don't lose body heat quite as rapidly as nivalis, so they can be almost serpentine-slender. The nivalis have a somewhat plumper build and their muzzles aren't quite as sharp in profile. Also, the black tailtip is apparently also related to body size -- it's supposed to be a lure to distract predatory birds into attacking it rather than the animal's body while it flees across the snow. Nivalis are too small to have tails long enough for this to work, so the just have stubby little tails with no markings.
A fairly cosmetic difference is that the border between the brown fur and the white underparts is smooth in erminea and rather jagged in nivalis. I'm not entirely sure nivalis turn white in winter the way erminea do; I think it might be the case that they're just always white if they live far to the north, and always brown further south. You can see a little bit of brown on the top of the pictured animal's head, so it's certainly one that changes phase seasonally.
I'm pretty sure it's an erminea. But there if the picture was taken in north america, there's a third species, the long-tailed weasel (Mustela frenata) which looks more like erminea than nivalis does....
(no subject)
Date: 2008-11-24 01:29 am (UTC)(no subject)
Date: 2008-11-24 03:52 am (UTC)>.>
Date: 2008-11-24 07:23 am (UTC)(no subject)
Date: 2008-11-23 11:02 pm (UTC)(no subject)
Date: 2008-11-23 11:25 pm (UTC)(no subject)
Date: 2008-11-24 01:14 am (UTC)(no subject)
Date: 2008-11-24 01:28 am (UTC)(no subject)
Date: 2008-11-24 04:13 am (UTC)(no subject)
Date: 2008-11-24 04:59 pm (UTC)