Unusual evening activity of toad-headed agamas (Phrynocephalus mystaceus) on the Sarykum dune (Republic of Dagestan, Russian Federation)

In different seasons of 2019 and 2021, dusky activity was detected in toad-headed agamas (Phrynocephalus mystaceus) on the Sarykum dune (Dagestan), although they are considered to be typical daytime species. With the onset of evening, lizards first burrowed into the sand or went into holes (primary evening activity). But after about 50 minutes, often already at deep dusk, they came to the surface again and continued their activity sometimes in almost complete darkness for about 30 minutes more (secondary evening activity, twilight). During twilight activity, toad-headed agamas do almost everything that they do during the daytime: they ate, the males tried to mate with the females, chased each other and adolescents, carried out other social communications, etc. The main motivation for twilight activity on the Sarykum may be related to the need for additional nutrition, since there are not enough food facilities for them on the dune during the daytime for a number of reasons, and in the evening there is a massive flight of small forage insects. Twilight activity was also noted in the toad-headed agamas in the Astrakhan region, but there the motivation for it was clearly different. Evening or even nocturnal activity is described in the literature for some other usually diurnal reptile species. Some of them warmed up at night under incandescent lamps used in anthropogenic landscapes (anoles, some agamids). In this case, the lamps allowed them to heat up to body temperatures that allowed them to realize full activity. Other species remained active after sunset, as long as the ambient temperatures allowed them to keep their body temperature close to the minimum limit of the temperature of their full activity (anoles, monitor lizards, some agamids). The cardinal difference between the twilight activity of the toad-headed agamas described by us was that at that time they did all the things they did in the daytime, only their body temperatures were in the range of about 10° lower than during the day.