That depends. Normally, a pidgeotto can carry about ten to fifteen pounds maximum, depending on how they’re trained.
On the other hand, if they know Fly (a move that greatly enhances a flying-type’s wing strength using the same sort of physics that allows those same flying-types to generate hurricane-level gusts of wind), then they can carry the weight of a fully grown adult man.
{Short note of explanation: The following is a complete rewrite of the pidgey line’s pokédex entries, rather than simply an entry for mega pidgeot. This probably won’t be a common thing but rather just a thing that might happen from time to time with the least funny entries. Sorry! Carry on!}
Pidgey
The Tiny Birb Pokémon
Type: Normal/Flying
Official Registration #: 16
Entry: A small, extremely common bird-like pokémon native to Kanto. This pokémon is popular among younger trainers, not only for how easy it is to catch and train but also because humans apparently take delight in calling a nearly direct descendant of the majestic dinosaur pokémon “birb,” “smol boi,” and/or “four pounds of whoop-[EXPLETIVE].”
Pidgeotto
The Birb Pokémon
Type: Normal/Flying
Official Registration #: 17
Entry: The evolved form of pidgey, by battle experience. The crest on its head is a set of feathers that help stabilize this pokémon during high-speed flight. However, the author will not discourage anyone from assuming that they are “leafs” that pidgeotto “wears on its head to enhance its beauties.”
Pidgeot
The Birb Pokémon
Type: Normal/Flying
Official Registration #: 18
Entry: The evolved form of pidgeotto, by battle experience. The author can neither confirm nor deny whether or not this pokémon would sell its trainers to Giratina for one corn chip, but he can say it’s more likely for pidgeot to do it than honchkrow.
Mega Pidgeot
The Birb Pokémon
Type: Normal/Flying
Official Registration #: 18+
Entry: The advanced form of pidgeot, via pidgeotite. This bird-like pokémon keeps itself in the air by sheer force of anger alone. You may think the author is quoting yet another bird-themed meme, but actually, no, that is a literal and scientifically accurate statement.
Pidgey
The Tiny Bird Pokémon
Type: Normal/Flying
Official Registration #: 16
Entry: A small, normally docile pokémon that is extremely common to Kanto and Johto. As such, along with rattata, pidgey are typically among the first pokémon a beginning Kantonian trainer captures. This is made all the easier thanks to the fact that pidgey also prefer kicking up sand using low-powered gusts of wind at ground level before fleeing, rather than engaging in a proper battle, but its small wings and the amount of energy it expends in blinding its foe make it difficult to get away quickly. Still, as a pokémon not known for either its battle prowess or its defensive capabilities, it, too, tends to be permanently stored rather quickly, but as of late, it has enjoyed an upsurge in popularity, partly because of pidgeot’s newly discovered mega evolution and partly because, according to the internet, it is “an adorable birb” who “wears leaf for enhance its beauties.”
Pidgeotto
The Birb Bird Pokémon
Type: Normal/Flying
Official Registration #: 17
Entry: The evolved form of pidgey, by battle experience. Like many other pokémon, evolution grants pidgeotto more confidence and aggression. It goes from being a docile pokémon to a highly territorial one that tends to claim a large swath of land as its home. Additionally, it possesses keen eyesight and the ability to swoop down onto prey from great heights and snatch its target with deadly claws. However, what it has not outgrown from its days as a pidgey is its love for bread, so travelers hiking through Kanto should beware when carrying sandwiches.
Pidgeot
The Bird Pokémon
Type: Normal/Flying
Official Registration #: 18
Entry: The evolved form of pidgeotto, by battle experience. While pidgeotto’s aggression calms a bit upon evolution, its hunting behaviors otherwise remain the same. In fact, pidgeot’s sharpened eyesight, its ability to fly at Mach-2 speeds, and its capacity to generate hurricane-strength winds make pidgeot far more deadly than its much more hostile pre-evolution. Luckily, pidgeot only exist naturally in the mountains around Victory Road, so most trainers needn’t worry about the fate of their sandwiches. Strong trainers thinking of challenging the Elite Four, however, are a different matter, but by then, you might already be aware of the sizable list of pokémon that would also do unspeakable things to you for a sandwich and any fish-like meat inside it. In short, the deadliest object a trainer can carry with them throughout their journey is a tuna fish sandwich.
The Pokédex According to Bill 