One tough chick

Last Saturday my 11 white leghorn chicks were ~3.5 weeks old. It was nice and sunny out and in the 50s so I let a few outside their coop for a bit to see how they'd do. Well, one of our puppies decided to chase one. Unfortunately, it was around the side of the coop and the chick took off and I didn't see where. I ddin't see it the rest of the day or that night or the next two days and nights. I wrote it off. Today my kids found it wandering arond about 75 yards away from the coop, near our playset and some trees. The first night it got down in the low thirties, the next in the 40's and rainy, even more rain and in the 40's again last night. The chick had a dirty beek and feet, but that was about it - totaly unscathed. I know it wasn't under the chicken coop (I had checked there the first couple of nights), probably in the under brush somewhere. This got me to thinking - why do I have that heat lamp pugged in anymore.