OBSERVATIONS ON THE BREEDING IMMIGRATION OF WOOD FROGS RANA-SYLVATICA REINTRODUCED IN EAST-CENTRAL MISSOURI

The wood frog Rana sylvatica was successfully reintroduced into a portion of western St. Louis County, Missouri, in 1980. In 1987 we followed the immigration of adults of this population to the breeding pond by capturing individuals in drop cans associated with a drift fence. Immigration began on 26 February and terminated on 28 March. The modal class of both sexes immigrated on 28 February. Male immigrants were more abundant than females (1.57:1). The mean snout-vent length (SVL) of males was 51.5 +/- 0.21 mm and that of females was 60.3 +/- 0.36 mm. The relationship between SVL and mass was linear (female mass = 1.82 SVL - 89.31; male mass = 0.67 SVL - 20.11) but different between the sexes. The frogs were more likely to be captured in drop cans associated with ravines. Data from this southern population and seven other populations obtained from the literature permitted us to quantify the relationship between data of immigration and latitude. In general, the mean date of breeding increased 5.2 days per degree of latitude.