Asynchronous breeding and variable embryonic development period in the threatened Northern Leopard Frog (Lithobates pipiens) in the Cypress Hills, Alberta, Canada: conservation and management implications

Abstract

Understanding breeding phenology is critical for establishing monitoring strategies, comprehending population dynamics, and developing conservation actions for at-risk species, such as the Northern Leopard Frog (Lithobates pipiens). The timing of spawning and hatching in the Northern Leopard Frog may be highly variable depending on regional environmental conditions, which can make establishing the timing of surveys difficult. In spring 2006, eggs were laid over 30 days (24 April to 23 May) and hatching occurred over 2 weeks (14–28 May) at three neighbouring ponds in Cypress Hills, Alberta, Canada. Although spawning occurred over a month, all eggs hatched within a 2-week period, indicating variable embryo development rate. Among 26 egg masses, eggs laid later in the season developed approximately four times faster than those laid earlier, and Akaike information criterion-ranked models suggested that both Julian date and water temperature were important predictors of embryo development rate: later spawning date and warmer water were associated with faster rates. Some egg masses survived colder temperatures than previously reported for this species. Asynchronous breeding and variable development rates reveal the need to conduct multiple surveys over the breeding season, even within a small geographic area, to document reliably the presence of egg masses and identify breeding habitat. Identification of key breeding habitat is necessary to mitigate human-caused disturbances of such regionally imperiled species.