Atmospheric advection of heat or cold: The formation of the false spring phenomenon in the spawning migrations of anuran amphibians (Amphibia, Anura) in Europe

The spawning migrations of four widespread species of anuran amphibians in European fauna (Pelobates vespertinus, Bombina bombina, Pelophylax ridibundus, and Rana dalmatina) were analyzed. In the years with an abnormally early start of the spawning migrations of the anuran amphibians and their passage through a false spring, powerful anticyclones over Central Asia, Trans-Urals or Western Siberia blocked the west–east atmospheric transfer. The second component forming the advection of air masses from low latitudes towards the north (cyclonic systems) was usually located over Western Europe, Scandinavia or the north of the European Russia. The opposite position (anticyclones over Western Europe and Scandinavia, and cyclones over Western Siberia, Trans-Urals, and the north and north-east of the European Russia) contributed to the advection of cold air from the Arctic Ocean basin to southern Europe. A sharp decrease in the average daily and average ten-day temperature of the surface air layer interrupted the spawning migrations of anuran amphibians. Between 1892 and 1995, false spring in Pallas’ spadefoot toad populations in the southeast of the European Russia occurred mainly as a result of medium-intensity heat waves, and after 1995 – almost exclusively as a result of high-intensity heat waves. The alternation of warm and cold air advections in the early spring (mid-March to early April) creates a meteorological basis that is fundamental to the intermittent nature of the spawning migration period of anuran amphibians (false spring pattern). A sharp advective increase in the surface air layer temperature determines the abnormally early start of the spring processes in anuran amphibians. Conversely, a gradual radiative increase in the temperature of local air masses, occurring even earlier than the phenological norm for certain species, causes the passage of the amphibian spawning migrations to occur continuously over time.