Status of Northern Leopard Frogs in the Southwest

Science Center Objects

Although it is not listed on the Federal Endangered Species list, there is considerable concern over northern leopard frog declines in western North America. It is listed as a “special concern” species by some state wildlife agencies (e.g., Arizona Game and Fish Department 1996) and declines have been reported in Arizona, Colorado, New Mexico, and other areas across the west.  Leopard frogs have become very rare in the northern Arizona and southern Utah region, but their current status is poorly known. A major aim of this work is to determine the present distribution, population status, and habitat occurrence of the northern leopard frog in Glen Canyon, Grand Canyon, and surrounding areas. Careful surveys of the distribution and numbers of leopard frogs in the region provide important information on long-term population trends, and the effects of population fragmentation and isolation on leopard frog populations in the southwestern part of their range. 

Background & Importance

Over the last three decades, there has been increasing recognition and concern about declines in amphibian populations in areas throughout the world. The cause of many of these declines is unknown, but they have even occurred in national parks and other protected areas, suggesting widespread regional causes. The western United States is one of the areas that has seen widespread declines and local extinctions. This project focuses on the current status and population changes in leopard frogs in the southwestern United States.

Northern leopard frog floating in the water in Glen Canyon.

Northern leopard frog in Glen Canyon. (Credit: Charles Drost, USGS. Public domain.)

Major issues addressed by this study are:

1) current distribution of leopard frog populations;

2) estimated population sizes at occupied sites;

3) degree of geographic and genetic separation of these populations; and

4) overall status and population trends.

General Methods

Field surveys cover all accessible areas of perennial water that may provide suitable habitat for northern leopard frogs, in northern Arizona, southern Utah, and adjacent areas of western Colorado and northwestern New Mexico.  In the Glen Canyon area, specifically, surveys cover selected tributary canyons on the north side of Lake Powell from Glen Canyon Dam up the lake to the area of Bullfrog.  This represents a linear distance along the Colorado River corridor of nearly 500 km.  We use a combination of spotlight surveys at night, when amphibians are most active, and diurnal searches for adult amphibians, eggs, and larvae.  Owing to the linear nature of the side canyon habitats and generally sparse vegetation cover, such visual surveys provide a reasonable index of population size.

In our surveys, we also search for evidence of chytridiomycosis.  Occurrence of chytrid fungi in this region has not been extensively examined, so we collect tissue samples from all amphibian species encountered to evaluate the presence of this highly pathogenic fungus.  We follow a standard protocol used by the Arizona Game and Fish Department, involving a simple swab of the abdominal skin of captured frogs.  The swabs are analyzed with polymerase chain reaction techniques (PCR) to determine presence or absence of chytrid fungus.