I would like to design a magic whistle. When blown, it summons all existing rabbits within a certain large radius (eg, 1 mile) to come to the whistle. This is done to the best of the rabbits' abilities. Once arriving at the whistle, they will stay at that location, completely docile. The basic idea is that this makes hunting rabbits extremely easy.
As near as I can tell, this item effectively casts two spells.
Detect all rabbits within a long distance (perhaps a mile) (Intellego Animal). Is this a "sight" (instead of hearing) version of Hunter's Sense, without detecting motivations? Would that suffice for a mile? Even in a forest?
Cause all rabbits to come to the item and stay at the location. Something along the lines of "Mastering the Unruly Beast". I assume that the intellego spell above would allow the targeting of the rabbits for this effect.
Is my logic here correct, in RAW?
How does the fact that this only targets rabbits (instead of any animal) affect the spell design? Does it? Can specific animals be targeted in RAW? Or would the effect have to target "small animals" instead and use size to make sure the whistle doesn't accidentally call a bear to the user's location?
Sight wouldn't suffice to target animals who aren't in line of sight due to being behind a tree. In fact, Sight wouldn't allow you to target an animal you don't already see. What you're thinking of, is vision. Vision would allow you to detect animals who are in line of sight but otherwise undetected (perhaps because they're hiding in a bush, or far away, or not moving). But Vision would still fail at detecting rabbits behind a tree, at least unless you're doing an effect with an herbam requisite that allows you to see through plants, etc. I'm not sure whether that effect could be built btw, the guideline exists in InTe, but not explicitly in InHe. A Hearing spell would let you hear their heartbeat from behind a tree, but would probably have a lower effective range.
There is a problem with your idea. Affecting a large quantity of rabbits could be done with group and size modifier... if there's a large group of rabbits. If you want to target "all rabbits in the forest", that just won't work. Rabbits don't travel in packs so there isn't a discernible group of large size to affect except perhaps a family raising young ones. What you're thinking about is Boundary, and boundary effects cannot be enchanted.
Weird targets from mystery cults may have better results here than normal results. Sensory Magic sound would be a nice alternative... except it can't be enchanted either. Symbol target would be nice... but like boundary, it's a ritual, and can't be put in an item.
Alternatively, if you target individual rabbits and you enchant an unlimited number of uses per day, make it a linked trigger that lasts for the duration of the activated intellego effect, you could bring the closest one that's detected to the item (or closest group, for a family). Once slain, and no longer detected, the effect would target the nearest alive one, and more rabbits would keep coming. This type of effect is possible, and keyed to, say, a sun effect, might be fairly effective if the intellego effect works as intended, but it implies the effect isn't stopping unless the duration runs out, however...
An alternative approach to automating the result is granting the senses to the item holder, and let him target the rabbits he sees with a separate, non-linked effect. Again, you're stuck with target individuals or small groups, because "all rabbits within a mile" isn't hermetic.
There is a big problem with your idea due to the limits of hermetic magic.
There is really no good way to detect all rabbits within a mile with standard hermetic magic. None of the standard ranges will suffice. (R:Sight requires that you can actually see your target)
If they were all within some well-defined boundary, then you could do it with a T:Boundary spell (+a few magnitudes for size), but just within a certain distance can't be done.
If you want the spell to just affect rabbits, then you design the spell so it only affects rabbits. And that is all there is to it.
Detecting all - or most - rabbits within a large distance is certainly possible without fancy effects: use the InTe 20 Terram guideline that makes your senses unhindered by earth, and add Herbam, Animal requisites to make anything Terram, Herbam or Animal-other-than-a-live-rabbit transparent to your Sight.
Having the whistle target said rabbits one per round in order of increasing distance is certainly a possibility (and for hunting purposes should be fine), though it probably costs you a magnitude in complexity (if you are persnickety, you can certainly extend the Intellego effect above with a Vim requisite so that you see through any Animal-other-than-a-live-rabbit-unaffected by this call).
In my troupe we have long debated whether all objects of a given type in sight qualifies as a Group (our current rule is in General no, but we agree it's not clear by the RAW). However, if not "the Group-sized set closest to you" probably qualifies as a slightly non-standard RDT priced at 1 magnitude higher than Group that you can't use in Spontaneous magic but that is otherwise fine to use in Formulaic spells or enchanted items.
But I would not design the whistle this way - it's far too expensive. Instead, I'd just say that the whistle transforms at Touch range the breath of the user (an Auram phenomenon) into a slightly unnatural phenomenon -- something that spreads far and smells delicious to rabbits. Panthers in mythic bestiaries are said to have exactly this prey-attracting "sweet" breath! This won't get you all the rabbits, and they'll probably still remain at what they feel is a "safe" distance (half a dozen paces), and it won't work well on very windy days, but it's much much cheaper (MuAu(An) Base 5, +1R:Touch, +1D:Conc comes at Level 15 + frequency and/or other modifiers and a relatively cheap Lesser enchantment).
This effect as designed requires access to Mystery magic techniques. There is a Mystery Virtue in the Bjornaer section of Mystery Cults called Sensory Magic (pg 27) that allows for design parameters for effects similar to how you describe.
It is not entirely impossible for similar secrets to be found in different sorts of places (Sensory Magic also exists for example in the hedge magic of the Bardic song magic) but it is not something I would expect to be common in the setting.
Usually Hermetic Magi without such specialized secrets simply approach their desired effect in a different way. You could instead make a whistle that when blown creates large amounts of rabbits and/or controls rabbits. (perhaps two different calls for different effects etc.)
Otherwise affecting targets outside of your perception, including detecting them, in large quantities over a large area generally falls under Boundary Target effects. This would also make the effect a Ritual effect and ineligible for inclusion in an item.
It is possible to augment your senses in different sorts of ways that might facilitate this but it seems like you want to reach out a bit with this effect.
One reason why people would tend to approach such things via a different design angle is it is frequently easier to achieve the desired effect by alternate approaches with few effects when you aren't trying to confront/design around a Limit of Magic.
Perhaps describe what you are trying to accomplish and we could help you design something that gets the job done?
Restricting the target to rabbits is certainly fine. I mean, after all if you use MuCo(An) to turn into a wolf or crow you can choose the type of animal, it's not left to chance or wizard's sigil or target's disposition.
You could also approach this as a more limited effect - given rabbits live in warrens, you should be able to detect those with InTe, and then affect them as Structures.
In principle tehspell could be done with target boundry plus some size boosts, but it would not be enchantable due to being a ritual spell. Unless of course you tether a spirit to the item to get past this limitation.
A Rusticanus (HoH:S p.131) enchanting the Major Supernatural Virtue (HoH:S p.105) Summon Animals into the whistle needs to have it.
So he is a pretty specialized guy - though still not as specialized as the poor draughtsman from Robert Graves' rhymes:
He found a formula for drawing comic rabbits:
This formula for drawing comic rabbits paid.
Till in the end he could not change the tragic habits
This formula for drawing comic rabbits made.
This effect creates a single rabbit. Any rabbits created are normal unaugmented rabbits though they are magical and must penetrate to affect anything protected by Magic Resistance. The rabbits are under the control of user of the whistle and will obey any commands unquestioningly.
This achieves the desired effect without having to detect rabbits or reach out to affect them. Though the effect level ends up being rather high as designed it could be lowered in a few different ways.
OP, do you have an intended use you want to put your item to when it is complete? What is your design goal?
This is for use by hunters. And since this is needed for nourishment, I did not think you could use CrAn without ritual magic, since the nourishment from eating the rabbit would disappear when the spell ended.
Is there a need to affect all rabbits within a mile radius? A whistle with R:Voice and unlimited uses could already be very helpful to a hunter.
Another option would be a box that casts a ReAn effect at R:Touch to force a rabbit to enter it (the hunter would still need to put the trap in an appropriate location and check on it latter).
I'd also point that from a narrative perspective, a Boundary effect seems a bad choice to me. You will cause an ecological imbalance on the area that is going to have bad implications. It's not different from creating gold and causing inflation.
I like InTe (plus any requisites) that targets/perceives the nearest rabbit, then sends it to the whistle with ReAn. And the item maintains concentration.
This item is part of a plot line and was created by a powerful magus, so if this is an expensive item, that is okay.
Also...
What about a CrIm effect that creates a sound that rabbits find irresistible?
And then an additional effect that makes them docile once close enough?