Seasonal habitat use and site fidelity of the mountain yellow-legged frog in Sierra Nevada high-elevation lakes
Research Project Summary
Site fidelity, the tendency to return and reuse previously occupied habitats, is considered to be an important life history strategy. Site fidelity is predicted to increase survival because animals can efficiently relocate suitable habitats for important activities such as breeding, feeding and overwintering. However, problems might arise if frogs have a strong fidelity to altered or impacted sites.
For 10 years (1997-2006), we have tagged and recaptured mountain yellow-legged frogs (MYLF-Rana muscosa) at specific water bodies in Dusy Basin, Kings Canyon National Park, California.
Rana muscosa, endemic to the California Sierra Nevada, has dramatically decreased in number during the past century (>90%), due in part to the introduction of predatory trout (Oncorhynchus spp.) into the historically fishless lakes of the high Sierra Nevada . The strong detrimental effects of trout on MYLF are well documented, and it is likely that the presence of fish severely limits a lake as breeding habitat for MYLF. In addition, MYLF is unique in requiring 2-4 years of continuous water before tadpoles can metamorphose into terrestrial subadults (Figure 1). Because of the self-sustaining introduced fish in Dusy Basin ’s larger, deeper lakes, frogs may be restricted to breeding in smaller, shallower lakes prone to drying. Breeding site fidelity to ephemeral lakes (in addition to predation in permanent lakes) would severely limit recruitment of new adults. This could lead to population decline and local extinction due to repeated tadpole mortality from summer lake drying.
- To determine if MYLF shows site fidelity during breeding, feeding, or overwintering.
- To quantify habitat use and movement between preferred habitats.
- To explore the link between site fidelity, lake drying and recruitment.
METHODS AND DESIGN
In a ten-year study from 1997-2006, we used PIT (passive integrated transponder) tags to determine the site fidelity and habitat use of 1250 mountain yellow-legged frogs (MYLF) in Dusy Basin (3460 m), Kings Canyon National Park during their three main activity periods of overwintering, breeding, and feeding.
MYLF use of water bodies changed throughout the active period: during overwintering and breeding, frogs were primarily found in five main water bodies, but during feeding periods, frogs were more widely distributed throughout the basin.
To quantify site fidelity we are first using the % of frogs captured two or more years and exclusive to one water body during a specific activity period. Analyses to date show that overall site fidelity is high and 58% of frogs are exclusive to one water body during breeding periods, 55% of frogs during feeding and 78% of frogs during overwintering. The % exclusive to each lake during the breeding period is shown in Figure 2.
We are also using multi-strata models to quantify site fidelity. Preliminary analyses show that the probability of returning to previously used water bodies during all activity periods is typically greater than 80% when compared to moving to new water bodies.
APPLICATION OF RESEARCH RESULTS
Preliminary results show that site fidelity is high in particular lakes during breeding and overwintering periods. Breeding site fidelity may have been a useful strategy in the past when fish were not present but may now be disrupting frog populations. In Dusy Basin frogs are restricted from some of the deeper, permanent lakes due to successfully breeding fish populations. Site fidelity analysis has shown that frogs have high site fidelity for lakes with the highest number of egg masses ( Lake 2 and 20 – Fig. 2 and 3) during the breeding period. However, some lakes with the highest breeding activity are also more prone to drying. Analyses will determine how lake drying influences recruitment.
Mark-recapture surveys on the Dusy Basin population are providing information on growth rates, seasonal movement patterns, site fidelity, reproduction, population structure and environmental effects on survival. The results will help policy makers and land managers in formulating effective management strategies using the best available science.
Dusy Basin, Kings Canyon National Park, California
1.)Matthews, Kathleen R. 1.) Feldman, Krishna 2.)
1)USDA Forest Service
Pacific Southwest Research Station
Sierra Nevada Research Center
2) USDA Forest Service
Pacific Southwest Research Station
PUBLICATIONS AND PRODUCTS