Where have all the Nightingales gone

First day of the Nightingale survey and up at the crack of dawn stumbling around my first Tetrad in Hamstreet Woods. The dawn chorus was in full swing with many birds singing.... but no Nightingales. My first area in which I have had Nightingales for the past 5 years was silent, even the one I had last weekend was not singing. I moved out of my first Tetrad into the second and in the distance I heard a Nightingale which was in the direction I had my second one last weekend. Then I had a slight distraction with a Lesser Spotted Woodpecker calling, it was in the tree right over my head but I could not find it so I moved on. This was the first one of the year in these woods. Down through the woods and to the Nightingale I heard singing in the distance and it was in the same area, I thought I heard two but could not locate the second at first but as I went around the track it popped up in front of me singing away. As I moved further around another Lesser Spot and this time I located it, but as for Nightingales that was it, only the 2 and so far this is the lowest count I have had for the past 5 years, hopefully another visit and covering the rest of my tetrad's will uncover some more.