Reproduction in an Introduced Population of <i>Elaphe schrenckii</i> (Strauch, 1873) in Eelde, the Netherlands

Abstract

In 1994 an unknown number of captive bred Russian rat snakes, Elaphe schrenckii (Strauch, 1873) were introduced near Groningen Airport Eelde (Drenthe Province), the Netherlands. Research in 2016/2017 confirmed that the species has become established and is expanding slowly, as recent sightings are known at distances up to 5.3 km from the initial release site. Although the continuous presence over two decades and sightings of different life stages of E. schrenckii specimens indicate successful reproduction, no reproductive data existed. To gain more insight, we conducted field surveys between 2014 and 2016 to collect data on oviposition sites and reproduction. Eggs of E. schrenckii were encountered in three compost heaps. Twenty-two clutches were found in these heaps in total, comprising a total of 332 eggs. Additionally, 42 loose eggs were found, totaling the number of retrieved eggs to 374. Minimum clutch sizes range from 10 – 21 eggs and average 15.1 ± 3.2 eggs (N = 22). Total individual egg hatching rate is 87.8% (N = 271). Clutch hatching rate varied between 46.2% and 100% with a mean value of 86.7 ± 18.8% (N = 16). Our findings indicate the importance of compost heaps for this species regarding reproduction as suitable sites for oviposition within this non-native range. Also, fecundity does not seem to be negatively affected by conditions in its invasive range; clutch size is on the high side. Because hatching rates can be high, its reproduction does not seem to be a limiting factor for further expansion within Eelde and surroundings.