dragchute
You've spoilt it by using the word 'mass'!!
In the answer in Pilot, our hoistee says that the 'total weight of the aircraft does not alter one iota'. The 'mass' doesn't, but weight is 'the force of attraction of the earth on a given mass'. As altitude increases, mass remains constant but weight decrases as gravitational force decreases. When the geese take off and gain additional distance from the centre of the earth, their weight will decrease (their mass will of course stay the same).
The decrease in overall weight (albeit only by an iota) will lead to a decrease in wing loading.
As an aside, we always need less than 1g of lift to maintain straight and level flight - and less lift the higher we go!