When I saw this juvenile Cardinal with his feathers fluffed out, I was sure it was in distress from the 90 degree weather. After a short time, though, the bird flew away without any problem. I've since noticed several more juveniles doing the same thing. They all seem to have their baby down, so maybe this is just their way of keeping cool. Here's a juvenile Blue Jay doing the same thing.
This is a juvenile Mockingbird with his feathers fluffed.
A lot of juveniles in the yard means it was a successful nesting season. I just hope these youngsters can cope with the early heat wave.