In canon it takes a year and a half, in which there are two generations, for birds to organize and start fighting humans. Five years after that they drafted their own declaration of independence. We're not given more detail on how their intelligence changes, so this is speculation, but -
Over the next, say, two months the initial survivors will reach a plateau in their development. Smarter than before, but we're talking... mmm, maybe corvid level? Remembering faces, individuals, and schedules, holding funerals for their dead, having a theory of mind, cooperating to get food, attacking threats to individuals as a group, making and using simple tools, playing. Also much more curious, but it's animal-curious, like crows. Young ones are more strongly affected and grow a little larger than their parents, but their sizes are well within normal pigeon size ranges.
They might have names for individuals and apply pigeon vocalizations to mean other things - food, humans, dogs, hawks. There are a number of animals that do this, it's not quite seen as language. The younger ones might be able to start to mimic some sounds, but it's still cooing. Also if someone could talk to them they would be more willing to follow suggestions out of curiosity.
The second generation will be smarter and more mimic-y. Pigeons can breed at any time of the year, but only if the setting is right. Wild, in around this area, they breed in spring and summer, when there's more food and keeping warm is easy. So, next spring there might be birds capable of learning and using words and simple phrases in the correct context, but they won't be human level. Depending on circumstances they might become shy of showing this around most people too.
Domestic individuals that catch the disease somehow might breed in the winter. Hatchlings become flightworthy after about a month and reach breeding age themselves at around six months. So in theory Locke could have a few pigeons who can speak intelligently and grasp somewhat more complicated topics by April, though they're still not at human levels of thinking, but the vast majority would be at crow level at that time.
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Over the next, say, two months the initial survivors will reach a plateau in their development. Smarter than before, but we're talking... mmm, maybe corvid level? Remembering faces, individuals, and schedules, holding funerals for their dead, having a theory of mind, cooperating to get food, attacking threats to individuals as a group, making and using simple tools, playing. Also much more curious, but it's animal-curious, like crows. Young ones are more strongly affected and grow a little larger than their parents, but their sizes are well within normal pigeon size ranges.
They might have names for individuals and apply pigeon vocalizations to mean other things - food, humans, dogs, hawks. There are a number of animals that do this, it's not quite seen as language. The younger ones might be able to start to mimic some sounds, but it's still cooing. Also if someone could talk to them they would be more willing to follow suggestions out of curiosity.
The second generation will be smarter and more mimic-y. Pigeons can breed at any time of the year, but only if the setting is right. Wild, in around this area, they breed in spring and summer, when there's more food and keeping warm is easy. So, next spring there might be birds capable of learning and using words and simple phrases in the correct context, but they won't be human level. Depending on circumstances they might become shy of showing this around most people too.
Domestic individuals that catch the disease somehow might breed in the winter. Hatchlings become flightworthy after about a month and reach breeding age themselves at around six months. So in theory Locke could have a few pigeons who can speak intelligently and grasp somewhat more complicated topics by April, though they're still not at human levels of thinking, but the vast majority would be at crow level at that time.