The solution could be pretty simple... Imagonem.
Most birds will recognize certain species within their realm as being egg-thieves. Crows and Owls both get this treatment by other birds. Attacked and driven off if at all possible. Crowded around if not.
It's in True Lineages, in the Mercere section
Thanks!
Vrylakos, the impression I got was that you wanted to it to be a CURSE, not a spell that achieves the same effect, is that right?
Well... I want a spell that creates a curselike effect. Does that make sense?
V
Yes- you want something Hermetic that acts like a curse, that follows the recipient. The apparent obstacle is that most spells have their one target (the recipient), and then would not magically effect the birds around that target at some later point.
But it seems that several valid approaches have been suggested. Take your pick.
(However, remember that Hermetic magic is not "all encompassing". It can't do "anything" that you can imagine, unlike in some other RPG's. Some magic systems simply have a spectrum of example effects, and suggest that the "level/magnitude" of the effect be roughly equivalent, as judged by the Game Master. Ars allows Players to build their spells to a desired level, and be fairly confident that the end product will be approved as designed.)
Well... it -is- .. .. just not yet ^^
Work harder and do more integration research!
And this is why, from a design perspective, Hermetic magic can't do everything. If it could already do anything, then player characters could never make a real contribution to Hermetic theory. So we have, quite deliberately, left spaces for your magi to fill.
But why no elder Terram rune?.. whyyyyy sobs .. .. damn lazy researchers.. missing runes out
Research is interesting though.. I suspect I'd try it more, if I wasn't worried about going into twilight ^^
(Or, at least, that's your story and you're sticking to it!) 
No, that's one thing I've always appreciated about Ars, and that many newcomers don't seem to grasp- that the Rules and Game World, while highly structured and richly detailed, are still very open-ended, allowing any Saga to pursue the direction that the players/SG are most comfortable with.
That is why I, myself, often display a lack of patience with some "What is the answer?" type questions (as opposed to philosophical exchanges) - there is no one answer, except for each troupe individually, that only they can answer. And that's a good thing. 
So, back to the topic - V, you have several suggested answers to choose from, or to use as starting points. Take your pick, and go from there, and good gaming!
I think the reason the authors didn't include it is that there is no rune that matches the properties of Terram very well. There are a few of the 22 Elder Futhark runes that could work-- Othila ("inheritance") probably being the best-- but all of the existing Verditius Runes are actually from the 16 Younger Futhark runes, and Othila does not appear in that alphabet.
The problem I imagine researchers in game have encountered there is that while it may be possible to unlock the properties of Terram, it was slightly more difficult than the other Arts because there isn't a good match, and so it was left for last. They've probably realized by now that they will need to introduce a new rune, or perhaps bring over a rune from the Elder Futhark or the Anglo-Saxon Futhorc. I doubt there's much information available about this; this could quickly lead to a story featuring the Rune Magic section of Ancient Magic.
Also, the researchers will need to choose a type of wood that is somehow associated with Terram, and perhaps that wood hasn't been discovered yet, or isn't particularly common in the part of the British Isles where the Mystery originated. What kind of tree would you imagine is most appropriate to Terram?
Iron wood?
Silver Aspen? Bronze Birch?
Perhaps the rare Molybdenum Larch?...
Ooh, got it! Petrified wood!
Yeah, I was gonna say petrified wood too ^^
Quercus Ilex - Stone Oak 
Change the Target to "individual". It is the person you're cursing that smells of food/egg thief to the birds.
Think of it as an animal version of "curse of the attraction of fire".
Or you leave the spell as is and go for target "special" like in Arm4.
Less fuss, more fun, and the spell level seems appropriate to the effect.
Doing this spell as ritual would be good for D:Permanent
There's no longer permanent duration rituals in fifth 
Anyway, this is a ReAn spell, it affects animals. In short, the victim is just the bearer of a spell that affect birds, it does nothing to him, thus the "group" target: it is a group of birds.
(Going on vacation, goodbye everyone!)
Which is much like saying that illusions and disguises must be Mentem and Group if they affect groups of humans. 
Have you not been reading along? There is more than one way to achieve this final effect. One is to magically change the victim, so that change sparks a natural reaction in the birds, another is to magically inspire the birds' reaction. Both are valid solutions to the same problem, as is so often the case in Ars.
(Have a good vacation!)
I answered speaking about my spell, and nothing else, that's all
Anyway, Verticius, what did you do?