How big would a bird have to be to carry a human if gravity were halved?

How large would a bird have to be to still be able to fly, while carrying a human, specifically if gravity is half as strong as it is on Earth?

Most riders would be less than 140 pounds and under 5'10. They live mostly in the desert and would often have favorable wind conditions with few clouds. The composition of the atmosphere is essentially the same as Earth's, and the atmospheric pressure is also the same as Earth's.

The birds need to be able to both take off and effectively fly while carrying their rider. They also need to be able to reach a height of 2000 feet above the ground and maintain it for at least 1 hour while carrying the rider. Manuverability, combat ability, and speed are not the main focus, but would be nice advantages.

The birds primarily glide and soar while in the air, like most raptors. The birds have a body structure similar to that of a Bald Eagle and their bones are also just as heavy and strong as an eagle's. Otherwise they might be strained under the additional weight of a rider.

I'd prefer it if magic was not taken into account much, and answers tried to be realistic as possible. The one main exception would be to possibly ignore the square-cube law, which almost nobody in the fantasy genre seems to care much about anyways, and would likely make this creature impossible.

Okay - so let us start with some Baselines:

According to Google - the most weight lifted by a Bird is apparently 18 Kg, lifted by the Harpy Eagle. Halving the gravity gives us a weight of 36 Kg - which is a bit light, considering your goal weight is just over 60 Kg.

However, in terms of Wingspan, they are not as big as say an Albatross or Condor - so this suggests that the relationship between the size of bird and absolute lifting power is not strictly linear.

But for the sake of argument, let us say it is, they have a current wingspan of about 2 metres, so doubling that - 4 metres. Something Something Cube Law something - we will need to increase this again, I CBF doing the maths - but let us consider that to accomodate the musculature to power such an impressive wingspan that it is cubed - so 8 metres.

Interestingly enough - that is approaching the size of a small light aircraft wingspan (The humble Cessna clocking in at 11 metres)

So - an Eagly like bird of Prey - with an 8 metre wingspan is my answer.

For bonus worldbuilding points - If you have the animal primarily feeding on something like Baby Camels (which weigh in at over 30 Kg at Birth) and have its hunting method effectively Boom-and-Zoom (Swoop in, grab the Baby Camel, carry it off to eat) - then you can probably get close enough to justify carrying a human.