If it is through our understanding and interpretation of language (as much as their more concrete existence) that our worlds are defined, to lose it would be apocalyptic.
There is a great deal of discussion, and an acceptance that the answer might encompass a range rather than an absolute, around how similar the intelligence and interiority of animals that can mimic and approximate human speech are to our own. In the natural world this ability, at least as it applies to recreating a variety of sounds, seems to occur mainly in avian species. This talent appears most famously in parrots, although there are actually more numerous and more complex examples within the Corvidae family, particularly within the Corvid genus which includes crows and ravens, rooks and jackdaws (amongst others).
While the intelligence of many of these species is still being charted, it is the use of language - albeit borrowed - which is of particular interest. Although, clearly, there is a distinction and a meaningful difference between recreation and comprehension, their innate potential has been exploited in the apparently deliberate creation of empowered counterparts which have built upon what already exists in nature. Perhaps the strangest of these are the Jaw-Jaw Birds, most similar in aspect and appearance to ravens except that their plumage, beaks and legs are a uniform and deep India-ink blue, who use their speech to ensnare their prey.
Where other birds of their associated family have been known to learn and repeat words and phrases that they have been exposed to - sometimes going so far as to show some understanding of the context in which their repetition is apropos - Jaw-Jaw Birds have not only demonstrated vocabularies roughly equivalent to those of a typical five year old but are able to employ them in naturalistic and meaningful conversation. These talents though, as remarkable as they are, are not natural marvels; they represent the convergence of several factors necessary for Jaw-Jaw Birds to draw out the unique fare on which they feast.
Migrating between chill autumns and colder winters, Jaw-Jaw Birds (which are believed to number in the hundreds at most) will fly near to people who are alone or on the very fringes of small groups. At first they attempt to draw attention by means of their unusual colouration, pulling the more curious observer out of relative safety and into harm’s way to get a closer look, but where this does not work they will speak. Only a word or two at this point, enough to intrigue but not enough to indicate the extent of their intelligence, and will persist until they have isolated their target or unless additional attention is brought upon them.
Once they have isolated their prey, the Jaw-Jaw Bird will begin to talk more freely; slowly revealing the extent of their ability and engaging the person in conversation. Most people, entirely unfamiliar with a world in which a creature of such inexplicable talent is even possible, cannot help but respond - and within a few minutes they have unknowingly trapped themselves. What this unique predator seeks is not physical sustenance but a linguistic enrichment, the vocabulary of their prey, which is a bounty they want greedily and horde jealously. They don’t absorb new words through mimicry, they siphon away what they take; sound and meaning and memory altogether.
They take more than they are shown; the substance and text of the conversation opening some kind of channel through which the seat and source of language is accessible to them. It starts with the words that someone might not consciously remember knowing - a pathway into the language centres which is unlikely to be immediately noticed - before gorging itself on the unusual, interesting and uncommon until it finally reaches and consumes most of the everyday. Over the course of one conversation the Jaw-Jaw Bird will take almost all of someone’s language, leaving only disconnected dregs and the basest banalities.
Absent the terms and terminology to properly define and understand their world, those who have been drained are nonetheless - and rather cruelly - left with the compulsion to talk incessantly; fragments of thoughts that run only occasionally and only coincidentally along the same channels as a relevant stream of consciousness. What remains are those elements the Jaw-Jaw Birds cannot consume, let alone process: The words that people misuse, mispronounce or could not have accurately defined. The resulting inane aphasia that sprouts from the fallow fields of their harvests are, as a consequence, peppered with the unique idiosyncrasies and malapropisms of their victims’ prior vocabulary and speech patterns.
Worse than the heavy-handed burglary is the damage left behind in its wake: the parts of the brain that are responsible for processing language - both as a physical mechanism and as a way of conceptualising the world and the self - are bludgeoned and battered. What is not destroyed outright atrophies away; most language learnt, and the ability to learn anew, disappears. The condition is medically irreversible, the best-case scenario being those occasions when the instinctive and unconscious minds are able to reconstruct a relatively high-functioning animalistic self. Victims might never be independent again, they will certainly not be themselves, but they can live lives of a certain, uncomplicated happiness if properly cared for.
The specific origins of the Jaw-Jaw Bird are unknown, but it is generally accepted that something other than the vicissitudes of natural selection and evolution must have played a part in their genesis and later proliferation. There is clearly a deliberate and targeted intent behind what they take, which perhaps makes the surest defence against them the most unlikely: They only feed on monoglots. If one is sufficiently versed (to the point of being passably conversant) in one or more other languages, they are apparently immune to the attentions and thus the dangers of the Jaw-Jaw Birds. If were they meant to take away language, it seems strange that its abundance would confound them.
The motive behind the first deliberate killing of a Jaw-Jaw Bird was not recorded in any form of which we are aware or to which we have access. It might have been an act of revenge carried out by an aggrieved relative of one of the birds’ victims, or an attempt to claim their loot and - in killing and consuming the Jaw-Jaw Bird’s body - take the stolen words into themselves in a rush of unearned learning. Perhaps the act was unconnected with the uniqueness of the bird’s deeds and it was felled at the hands of an indiscriminate hunter who came upon it by chance.
No matter how the blow was dealt, and regardless of the reasoning that drove it, in this instance death was an unanticipated restorative. What had been stolen was restored in an immediate, unrelenting and bewildering torrent to the person from which it had been taken. The cause and effect of it all would have been unknown at the time, of course; it was only much later (and with the anecdotal knowledge that some victims had gone through the apparently spontaneous regeneration into their prior completeness) that the Jaw-Jaw Birds were deliberately hunted so that any of their still-living prey might be made whole again.
The acclimatisation to a more complex sense of the world and of the self, especially since it comes all at once and involves the rapid regeneration of neural tissue, is extremely disorientating. What someone was once and is becoming again collides with the sensation-driven and instinctual being that had replaced it; many are rendered near-catatonic with the shock, though this tends to pass within a few days. In the gap between the initial encounter with the Jaw-Jaw Bird and the restoration there is often very little memory - a vagueness somewhere between the sensation of lost time and the faded recollection of a nightmare.