I lost two boilers in two days

Sometimes things happen and you don't have explanation for it.
I was so sad yesterday when i lost one of my birds that i have been rearing for the past 2months. i bought them when they were 4weeks old and since then the chickens have been doing fine.

Today again i lost another bird and i was told that it is due to the excessive heat that we are experiencing now. I was surprise because the boilers did not show any sign of sickness when i was feeding them.

My plan is to have them sold by Easter; but losing 2 at this point is really disturbing. Each of them weighed at least 3kg.