I woke up two days ago to a strange sound. At first, I thought it was just the radiator, which usually makes fizzing and hissing and cranking and burbling noises. (I do note the first coming on of the radiator in my old (1905) apartment building. Apparently it is not turned on by a human hand but related to some complicated measuring of temperature, which makes it a true phenological sign. It first came on September 19 last year; it would be harder to measure when it goes off, since one is never quite certain, until some time has passed what was the last day it was on.)
But no, this sound was not the radiator. It took me a while before I recognized it: a bird chirping. Sweet and low, quiet but cheerful. Have no idea what kind of bird it was but I realized that I haven't heard that sound for quite a while. Spring is here!