Comparative breeding behavior of the red-legged frog (Rana aurora aurora) and the western spotted frog (Rana pretiosa pretiosa) in southwestern British Columbia

Abstract

The breeding behavior of Rana aurora aurora and R. pretiosa pretiosa from an area of sympatry in southwestern British Columbia is described and compared. A 7-ac field near White Rock, B.C., was closely observed during the 1968 and 1969 breeding seasons.Both species arrived at breeding sites and began breeding activities within 2 weeks after emergence from hibernation in February and March. They both used the same temporary pond and slow-moving stream, and breeding occurred simultaneously.Male pretiosa gather into small groups with individuals vocalizing within inches of each other. The mating call is given in air as the frogs float on the surface of water only a few inches deep at the margins of the pond and river. Male aurora call several feet apart while completely submerged in 2 ft or more of water, and 3 ft or more from the pond and river edges. Descriptions of the mating calls of both species, as well as a call peculiar to amplectic male aurora, are given.Female pretiosa spawn mainly during daylight and the eggs are placed on top of, or immediately adjacent to, the first mass present. As many as 26 separate masses were laid on top of one another in the same place, unattached to vegetation in only a few inches of water. Female aurora spawn only at night and deposit their eggs attached to submerged vegetation in a minimum of 12 in. of water, and at least 3 ft from the pond and river shore; masses are several feet apart. The eggs of both species are laid in those areas where conspecific males vocalize.Peculiar aspects of both species' breeding behaviors are discussed, as well as those factors leading to successful reproductive isolation. Observations of breeding aurora in allopatry indicate no major differences from those on aurora sympatric with pretiosa.