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Columbia Spotted Frog

Illustration of the Columbia Spotted FrogSince 1991, Spotted Frogs have been on Alberta's Blue List of species that current knowledge suggests may be at risk of declining to non-viable population levels in the province. The population status remains uncertain and investigation is required to determine if a possible decline in numbers or numbers of populations is occurring. The federal status of the species is currently under review by the Committee on the Status of Endangered Wildlife in Canada.

There has long been confusion regarding the appropriate taxonomic designation of this species. Recent analysis of the genetic makeup of the Spotted Frog complex has resulted in a revision of the earlier classification. The species of Spotted Frog which inhabits the mountainous regions of Alberta and most of British Columbia has been renamed as the Columbia Spotted Frog (Rana luteiventris). 

As this reclassification is very recent, much of the information available on these frogs is based upon its previous designation as a single species, simply the "Spotted Frog". 

Spotted Frogs have regularly been described as "highly aquatic". They are generally associated with cool, permanent water sources such as slow moving streams, rivers, marshes, springs, pools, and the margins of small lakes, usually with abundant aquatic vegetation. The species does make use of upland habitats, and will do so for long periods of time if enough water and cover is available nearby. Although adults may move a considerable distance from water following breeding, they generally prefer ponds or quiet water in subalpine forests, in grassland, and in brushland of sage and rabbitbush.

The majority of Spotted Frog sightings in Banff and Jasper National Parks were from the lower subalpine ecoregion, in ecosites which included a range of moisture regimes. Spotted Frogs were also reported from alluvial fans and terraces in the montane ecoregions and even the upper subalpine ecoregion. Salt (1979) described the general habitat preference of adult Spotted Frogs in the Rocky Mountain region of Alberta as follows:

Spotted Frogs in Alberta have been recorded to occur at elevations from around 995 metres in the Jasper area to over 2150 metres in the Kananaskis, Waterton and Crowsnest regions. 

Most of the wetlands used by Columbia Spotted Frogs in Waterton Lakes National Park are spring-fed. Known sites include beaver ponds, pothole ponds, fens and small lakes within a variety of coniferous, mixed-wood and deciduous forest types. Where emergent vegetation does occur, sedges and swamp horsetail are typical, although emergent vegetation is not always present. Occasionally, adults have been observed along slow-flowing creeklets after the breeding season has ended.

Spotted Frogs generally lay their eggs in the shallow, reedy water at the margins of ponds. In Alberta, Spotted Frogs prefer small ponds and river lowlands as breeding sites.

Other amphibian species which may be found along with Spotted Frogs in Alberta include the Long-toed Salamander, Western Toad, and at lower elevations, Striped Chorus Frog, Wood Frog and Tiger Salamander. Although Spotted Frogs have not generally been found to share breeding habitat with other Ranid species in Alberta. Spotted Frogs and Wood Frogs have recently been observed calling from the same wetland habitat in the Bow Valley corridor. However, Spotted Frogs have been found to share breeding habitat with Long-toed Salamanders in southwestern Alberta, as well as in the Kananaskis Valley and Jasper National Park. A recent report on the occurrence of Long-toed Salamanders in the northern and central regions did not find Spotted Frogs and Long-toed Salamanders within the same breeding ponds although three sightings of Spotted Frogs were documented.

Preferred Spotted Frog breeding areas in the Rockies are generally in shallow permanent pools. The depth of water in the areas where eggs were laid was between 3 and 30 centimetres. Nevertheless, Spotted Frogs may occasionally breed in very shallow, temporary water near more permanent water sources. Desiccation may be an important factor in tadpole mortality, implying that some breeding pools used are temporary.

Temperatures in Spotted Frog breeding ponds in Alberta's Rocky Mountain region are reported to be generally between 13 and 22 degrees Celsius. Spotted Frog tadpoles live in the warmest part of ponds and in larger breeding ponds such as those found at Leach Lake and Jasper National Park, where the average temperature of shallow water may sometimes fall below 13 degrees Celsius, tadpoles may seek warmer temperatures during the night and on cooler days by moving under partly submerged logs or burrowing into the mud at the bottom of the pond. 

In Alberta, Spotted Frogs are generally dark brown dorsally, with irregular darker brown spots. The spots may have rather indistinct borders and lighter centers. These frogs have a dark mask, running from the tip of the nose to the tympanum, although it may be faint. A light coloured stripe along the upper jaw, running from snout to forelimb, is a distinguishing feature, along with eyes that are angled somewhat upwards. Dorsolateral folds, distinct to Ranids, occur along the full length of the back. A red, salmon, or yellow colouring on the ventral surface, which appears almost superficially applied, also distinguishes the species. In Alberta, the throat or underside may be spotted or mottled with gray. Spotted Frogs can also be recognized by their stout form and rough skin. Males can be distinguished from females, during the breeding season, by their nuptual pads (swollen and darkened pads at the base of the thumb). Females are generally larger than males and juveniles are considered to be difficult to differentiate from young Wood Frogs.

Adults forage for worms, insects, spiders, molluscs, and crustaceans both aquatically and terrestrially. Molluscs, such as snails, made up the second largest component of the diet.

Spotted Frogs may overwinter underwater in Alberta and have been recorded to overwinter in their breeding ponds in the Cascade Mountains of Washington and in Montana. Females may move towards breeding ponds in the fall to overwinter nearby, in preparation for the following year's breeding season.

Spotted Frogs may make significant migrations overland in the spring and late summer. Spotted Frogs in Yellowstone National Park migrated to upland regions, with breeding adults seeking out suitable breeding pools in May, and returning to more permanent sources of water in July. Spotted Frogs were observed to move between separate stream courses, with a maximum recorded movement of 1281 metres. 

Spotted Frogs begin breeding in early spring, as soon as the ice in appropriate areas has melted. The males move together into a group, calling from within a few inches of one another. Males call while floating at the surface of the water, near the shoreline, but discontinue calling if temperatures drop to near freezing.

Spotted Frogs in Alberta become vocal during the mating season, as well as for a limited time beforehand. Their call is marked by a series of faint, rapid, low-pitched clicks, increasing in intensity, with some 4 - 50 clicks per call.  It has also been described as sounding similar to a distant helicopter. The low volume of the call does not carry further than about 30 metres. The relatively infrequent and low volume calls make this species difficult to detect with vocalization surveys. Male Spotted Frogs have been observed to call underwater, although more observations are required to assess how frequently this occurs. 

In Alberta, the earliest recorded breeding of Spotted Frogs in Banff and Jasper National Parks was 3 May, with egg masses being found until 27 May. Water temperatures must reach 10 to 11ºC before these frogs will emerge from hibernation. There could be as much as a three to four week difference in breeding dates, depending on the locality. 

Females lay their eggs in spherical masses, piled on top of each other, in shallow water. The masses may eventually float to the surface, forming a large frothy, floating mass. The upper eggs in these masses may be exposed at the surface of the water. Eggs hatch in 7 to 23 days, depending on temperature. Reports of the number of eggs in clutches vary from 444 to 1500 in the United States. 

In Peter Lougheed Provincial Park, Spotted Frog tadpoles were found between late May and early June, and mid-August. Within these sites, the total number of larvae varied from 1 to 75, with numbers appearing to peak in June and early July.  Tadpoles of Spotted Frogs grow very rapidly, developing limb buds and growing from an initial length of 8 millimetres up to 36 millimetres in about -30 days. Larvae generally metamorphose in the same year, but in more northerly populations, such as in Alberta, they may overwinter as tadpoles and metamorphose the following year. 

At least two years are required before the Columbia Spotted Frog reaches maturity in eastern Washington state. However, it has been determined that in Yellowstone National Park male Spotted Frogs may not breed until their fourth year, and females may not breed until their fifth or sixth year. This may be due to their slow growth rates and apparently long life spans. Growth rates are much slower at higher elevations. Female Spotted Frogs at lower elevations mature at two to three years of age and breed annually, while those at higher elevations reach sexual maturity after six years, and breed only bi- or tri-annually. Males in lower and higher elevation populations reach maturity at two and four years of age, respectively. As Alberta populations of these frogs belong to the same species as the populations in Wyoming, and also occur at relatively higher latitudes, if not at comparable altitudes, it is likely that the populations in Alberta exhibit similarly slow growth rates and limited reproductive potentials.

Reprinted from Alberta Wildlife Status Report No. 17 (1998), with permission from Alberta Sustainable Resource Development.

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