Bird on a cactus

Why would a bird sit on a cactus?

I have no answers that suit my mind. But, in deserts, birds have no better trees to sit on. When summer heat gets hotter and there is less water, they take the water even from the thorny cactus. But, only for some time. Then, as the summer gets hotter, they migrate to a water land across seven seas.

Maybe the reason is the same as when tired people sit under the shade of a huge green tree, even near a lake.

Guess, be it a cactus or a huge green tree, are there for similar purpose.

A bird on a cactus is a fairly accpeted concept in dry areas, just as sitting under a shaded tree, and relaxing., till rejuvenate to fly ahead.