Question

why do desert animals having concentrated urine.

Answer 1

because they usually suffer from water scarcity...

Answer 2

Answer:

Desert mammals do not readily find water, hence they must excrete very less amount of water. They are able to produce highly concentrated urine.

To excrete nitrogenous waste products, mammals (and most amphibians) excrete urea diluted in water. Such xerocoles have adapted to make their urine as concentrated as possible (i.e. use the least amount of water) to dissolve urea.