Chiffchaff song

Not sure if I’m imagining this (or if it’s already well-authenticated) but does chiffchaff song speed up in June?

The birds I have recently heard seem to have had a target number of chiffs and chaffs that they need to perform before the end of the singing season.

This is by contrast with the June call of the cuckoo which slows right down. The break between the cuck and the oo goes from less than half a second to two seconds.

Elsewhere in the bird orchestra, my experience is that the song thrush is at its richest and most powerful in mid-June.

The blackbird’s song becomes serener and less urgent.