This shouldn't take more than an hour, tops. "Detect the power of a mystical aura" InVi Base2 R:Touch = Lv4
Halie can spont that non-fatiguingly (15In+3PuisIn+12Vi+2Sta+6Au=35, 38/5=7+), so in Heartbeast form she can just spam that spell while flying around.
If you have a 38 casting total, why not expend 1 fatigue and instead of going for level 4, use fatigue and bump up to level 15 sight and you can just look at the area and see. If you get 2+ on the roll (anything but botch check), you can do it for sight for 2 minutes and then 1 spell lets you survey the aura all around without even trying and no need for concentration checks to cast spell while moving.
Why are all birds, beaver and deer off limits and for what sort of area. I could see birds of prey off limits (since we have owl and crow familiars here but there are plenty of other birds that combined with deer are meat staples for food (I guess we could eat some sheep and goats but we need them for their wool).
Because it wouldn't BE lv15 at Sight range-- it would not be an Individual target at that point. And because fatiguing sponts don't have a risk of botch. And because you don't need a concentration check to cast Momentary spells while flying naturally.
How's about I play my character, and you don't? At least, as much as is possible, given that you'd already copied half my character's spell selection, anyway.
See my previous statement addressing you, at the top of this page. Thanks.
Going that route, you're going from InVi 4 (Base 2, +1 Touch, Momentary, Individual, although she could also do D: Diameter to make it a Level 5) to InVi 15 (Base 2, +3 Sight, Momentary, +2 Group since you're "affecting" multiple auras) - higher if she wants it to continue for Diameter to try to triangulate where the aura strength shift is. If she goes with the first option, even with a Diameter duration, she can just circle around and adjust her altitude to pinpoint how high up the M6 goes.
That was me trying to shoot off a quick answer between chores. Basically, until now, if they didn't know where Wallace or Eilid were, then no hunting of beavers or deer. Likewise, no crows unless they know where Beira is. With the newcomers, there are going to be strictures on hunting owls, eagles, and hedgehogs, as well. Sergeant Buttercup will make sure the word gets out.
it's base 3 to determine the magnitude of an aura. Also the target area is much bigger than Group would cover, (a size +3 lab is 1000 sqft) so it'd have to be Boundary (maybe could get away with "structure" if you were going to be really generous). So, it would be a minimum of lv30, which is moot anyway because my character wouldn't risk a mystical botch when it's completely unnecessary to do so.
Boundary spells must be rituals.
I thought there was an explicit exception for sensory spells that are effectively "as far as the eye can see"? Not at my books at the moment though.
Ahh. Context matters. Read the posts.
T:vision is equal to boundary. No ritual requirement.
Wouldn't R be personal, though? Intellego makes my head hurt.
That's why I tend to not use the "magical senses" variants very often...it gets too confusing. I prefer the generic Intellego "You know" stuff.
And, imo, it would be easier if Halie did the touch-range InVi with a duration. That way, she can tell just when she crosses from a +3 to a +6 to a 0, as opposed to having to re-spont Momentary versions every so often and trying to suss it out that way.
My reasoning on why that's preferable to the Sight-range variant that ladyphoenix was proposing is that, if there are more than one Aura strength, you would need a Group. And the spell would simply tell you that there is a M3, a M6, and an aura that is either null or not aligned with Magic within sight. Which wouldn't tell us what we're trying to figure out, since we already know that. Sometimes, simpler/easier is better.
Eyes of the Eagle (InIm25) has Vision as the Target instead of the Range. So, yeah, that's... weird. I hate building Intellego spells, no wonder no one ever plays Intellego specialists since 5th ed 
So at R: Personal, D: Diameter, R: Vision, it'd be lv15. Fatiguing-spontable, but doesn't save enough time to be worth the chance of botch.
So, Base 2, Range Touch, Target Individual, Duration Sun would be a level 5 spell, which she can easily spont with no fatigue. She casts it. She'll ask Aodhan to be on the ground, turns into a griffin, and carries a knotted rope in her talons such that when she calls out that she's reached a boundary of the aura's magnitude, he can count the knots to measure how high up. She'll loop around a few times to see if the aura extends up at the same height all around.
She'll skim across the water to check if the aura extend outside the island's edges any, and reluctantly take a couple dives in to see if it extends any below the water's surface. Reminder that wet cat = pissed off cat, and griffin falls firmly into the category of cat for these purposes. Anyway, if the aura's boundary at water level is the edge of the island, but there's a bit more +6 aura beneath the water's surface extending around the island, that would still cover Talia's shipboard lab. Which would be great, because then we don't have to worry about her destroying all our sancta by beaching her ship on top of the island when she has a lab project (and I wouldn't put it past 'er!).
Done.
Especially since she can just make another ship of identical configuration for 9 pawns of vis.
NO ONE ELSE WANTS A BOAT-LAB. IT'S JUST YOU.
Although... it would be pretty hilarious if the Tireless Servant could be wearin' his flippy-floppies, and start singing some Lonely Island...
youtube.com/watch?v=avaSdC0QOUM
Oh, I know, I was just thinking if necessary I could beach the ship, make another one, and then once I develop Arts sufficient to cast The Ambulatory Laboratory and then she can sail far and wide taking her lab with her...
headdesk
LOL
Flying around the edge of the island, the aura shifts from +6 to +3 at the waterline or at the edge of the dock on the north end of the island. Overhead, the aura extends up in a rough dome to a maximum height of 60 feet/20 paces.
When you hit the water, it is wicked cold and Halie needs to make a Stamina check vs. the cold vs. a Ease Factor of 9 or lose a Fatigue Level. The water is very murky (visibility about a pace), so she's going to have to proceed slowly carefully. Under the dock, the aura curves slightly in toward the island shelf (for lack of a better word) – not straight down, but not 45° either. So, directly under the dock, it's a Magic+6 in the water. If you go straight down from the edge, it soon shifts to M3, and when you angle back toward the island under the dock, it becomes M6 again.
How much time does Halie spend exploring under the water around the island (and risking Fatigue loss from the cold?)
6+3Stam+2Selkie=11.
She'll surface and call for Jeor to accompany her, just in case-- then she'll nose around for a while, until she loses two fatigue levels. Which is however long it takes to make three more checks.
(Seems like Soak from Thick Hide/Thick Fur should buffer against cold, but there's no mechanic for it :/)
Okay, that should be good for about half an hour of swimming and diving and what not. The loch bed runs out about ten or fifteen feet from the edge of Eilean Chon before it drops off. About ten feet below where it drops off, Halie thinks she sees a hole in the side of the island. Or it may be a shadow. If it is a hole, it's not very big...maybe a foot across. It's too dark and murky to see in, though.
Is she going to check anywhere else, or confine her exploration to the island?
Halie comes up, changes back into an eagle, back into a human, dries her skin off, and turns back into an eagle, swearing profusely like a fisherman's wife the whole time. She then tracks down Drystan: "I need to find a seal skin. It's a matter of great importance."
"We don't get seals very often," Drystan says. "And I don't believe that we have any seal skins here." He waves over a girl (who looks to be not quite a teen) and says something to her softly in Scots Gaelic. She promptly runs off, only to return a few minutes later. She shakes her head and says something to Drystan, who turns to Halie again.
"No, we don't have any seal skins in the stores."
((Iirc, Caoimhe ní Súilleabháin came with Talia. Has she stayed on the ship since she arrived a couple of days ago, is she around somewhere, does she have her sealskin somewhere obvious, like hanging from her belt or something?))