The sun was shining abundantly early morning April 19th.
From appr. 8 AM onwards the sunrays shone into my outdoor terrarium. At 8.15 AM 1 of the female T. radix became active. At 9 AM my male T.s.pickeringii became active as well. At 10 AM it started to get cloudy, but despite that the male T.radix also became active. At 11 AM there was some light rain. T.s.pickeringii and the female radix remained visible, but the male T.radix had crawled away. At 11.30 AM the rain had stopped and the sun became a bit more powerful (through the clouds).
The radix female and the T.s.pickeringii had remained visible. The male T.s.pickeringii had even heated up sufficiently to quickly crawl away every time he saw me. Air temperatures were approximately 10 – 11 °C. AT 2 PM it was still 100% cloudy and all the snakes had disappeared. It got too cold. But from 3 PM onwards the sun became strong again in a clear blue sky. Unfortunately the location of my outdoor terrarium is such that the sun hardly can reach the terrarium after 3 PM in this time of the year. Despite that the female T.radix and the male T.s.pickeringii had become active again after 3 PM until appr. 3.30 PM.
The sun was very bright and almost continuously (just a few scattered clouds) on April 20th. The day started very cold: 3 – 4 °C. At 7.45 the first sunbeams entered the terrarium and at 9 AM the male T.s.pickeringii became visible. I had to leave the house early but upon my return at 2.30 PM the sun could still warm the last 1 m² of the terrarium. The couple T.radix appeared to be mating in the sun. The male T.s.pickeringii was basking together with 2 N.sipedon. So the 2nd N.sipedon had become active this year! At 3.15 PM the sun had disappeared out of the terrarium. Only the male pickeringii remained active until the last sunrays disappeared out of the terrarium. The others were gone around 2.50 PM. After 3.20 PM no snakes were active, it was too cold. Maximum air temperatures were 10 – 11 °C, but I expect the snakes were able to reach their optimal temperatures of around the 30 °C while basking in the powerful sun..