Right off the bat, the world/setting that this takes place in is not the pinnacle of realistic, but I do want to have a bit of realism. Anyway, so in this story, really more of an idea,there is an action-figure named Rina that at times rides around on a talking and human-level intelligence seagull named Lafa she has befriended. And by rides on I mean like flies on, since she can walk on her own. So, putting aside obvious fantasy elements, can an average,let us say male ring-billed gull, still take-off and fly with an average plastic,6 inch tall action-figure mounted on his back?
This is pretty fantastic. What the heck were these two up to? If this video is faked, it faked me out good.
Maybe the ridden seagull is practicing with his buddy so Rina gets a smooth ride.
Yes it can.
Is your world hyper-realistic? No. Is it at least feasible? Yes. Then you have your answer I think, give yourself permission to draw your own lines.
...besides which, I've seen a seagull fly off with a cheeseburger that weighed more than a four ounces.
To ratchet it down, you can add some realism by discussing how Rina stays attached... how she stays on, how she limits the impact of her not-aerodynamic form on Lafa's flight capability.
Birds can typically carry about half their bodyweight, though only downhill.
This six inch action figure weighs 8 ounces, or 0.2 kilos. An average seagull might weigh a kilo to a kilo and a half for a male, or 0.7 kilos to 1.1 kilos for a female.
A female bird on the smaller size would probably struggle getting up with an action figure, since they're close to three times as big as an action figure, and so are close to the only fly down weight limit. A male bird on the larger size would have little trouble, weighing 7 times more than an action figure.
If depends on the species of "seagull", but a herring gull has been recorded as attacking and carrying off a chihuahua dog, weight around 1kg.
The usually live in flocks, so if one bird finds a substantial item of food its first reaction is to carry it away to somewhere safe, rather than be forced to share it with the other gulls.
Carrying a plastic figure would be no problem at all.