Couch’s Spadefoot (Scaphiopus couchii)

Photo by Jim Rorabaugh

Couch's Spadefoot, Yuma Co., AZ. Photo by Jim Rorabaugh

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Description

This is a moderate-sized (< 91 mm) anuran that is green or yellowish-green dorsally.  The eyes are large and the pupils are vertical.  A dark, sickle-shaped tubercle, distinctly longer than wide, is found on the inside of the ventral surface of each hind foot.  No cranial crests or parotoid glands are present.  Females possess dark reticulations, whereas the somewhat smaller males are lighter overall with faint dark spots, reduced reticulations, or they may lack dark markings altogether.  The other spadefoots in the 100-Mile Circle – Mexican Spadefoot and Plains Spadefoot – are brown, tan, grayish, or grayish-green, and lack the dark reticulations.  They also have wedge-shaped tubercles on the hind feet (rather than sickle-shaped).  In our area, Couch’s Spadefoot is widespread in the valleys, bajadas, and foothills, but absent from the higher mountains above about 1,875 m.  In the 100-Mile Circle, it occurs primarily in Sonoran and Chihuahuan desertscrub and semi-desert grassland, and less commonly in oak woodland and Plains grassland.  Couch’s Spadefoot is only rarely associated with agriculture, usually on the edge of croplands.

This is a classic, explosive breeder, in that it lies dormant, underground until the first substantial monsoon storm, then emerges for a few nights of frantic breeding and foraging when its plaintive “Whaaaa! Whaaaa!” call announces the beginning of the summer rainy season.  Its call can be heard here: http://amphibiaweb.org/cgi-bin/amphib_query?special=call&genus=Scaphiopus&species=couchii

Breeding aggregations can occur throughout the summer, but they are rarely as large or noisy as those that form after the first rains of summer.  Couch’s Spadefoot breeds in low-lying temporary pools filled by summer storms.  Breeding sites are frequently modified in some way, either intentionally as catchments for livestock, or unintentionally, such as where water pools up along railroad tracks or road shoulders.  The species also breeds in water that collects in arroyos and tinajas in desert mountain ranges.  It may also be found breeding in ditches and other places where water collects on the wildland margin with agriculture. Clutches of often more than 3,000 eggs are deposited into rain pools. The eggs hatch and the tadpoles develop rapidly, metamorphosing in as little as 7.5 days post-hatching, but metamorphosis may take as much as 16 days.  Tadpoles are herbivorous, but some become cannibalistic and are significant predators on anuran eggs.  Metamorphs are 9-13 mm SVL.  Because of its very short larval period and its ability to wait out the dry periods underground, Couch’s Spadefoot is one of our most arid-adapted amphibian species, occurring in the western deserts in areas that receive less than an average of 70 mm of precipitation per year.

Couch’s Spadefoot will often stay active through the summer as long as conditions are moist.  They may retreat underground temporarily during dry periods, only to emerge again after the rains resume.  These spadefoots may stray considerable distances (probably kilometers) from the breeding pond late in the summer.  Adults are nocturnal, but small juveniles and metamorphs are often found active by day.  In the 100-Mile Circle, Couch’s Spadefoot is only rarely found active outside of the late June to September period.

The diet of metamorphosed Couch’s Spadefoots consists of invertebrates.  Small Couch’s Spadefoots eat spiders and insects, whereas adults consume mostly winged and nymphal termites early in the summer, which are common after the first rains.  Later they eat beetles, bugs, ants, grasshoppers, crickets, and spiders.  One or two full stomachs of insects are enough to sustain a Couch’s Spadefoot through dormancy to the next summer season.

Couch’s Spadefoot is listed as a species of least concern on the IUCN’s Red List.  Threats to this species are minimal, although it has been eliminated from expanses of urban and agricultural development.  It has benefited from construction of cattle tanks and charcos, as well as surface disturbance that results in berms or depressions that allow water to pool during the summer rains.

Suggested Reading:

Brennan, T.C., and A.T. Holycross. 2006. Amphibians and Reptiles in Arizona. Arizona Game and Fish Department, Phoenix, AZ.

Dimmitt, M.A. 1992. Biology of desert toads with emphasis on spadefoots.  Pages 51-54 in Collected Papers of the Tucson Herpetological Society 1988-1991.

Morey, S.R. 2005. Scaphiopus couchii Baird, 1854 Couch’s Spadefoot.  Pages 508-511 in M.J. Lannoo (ed.), Amphibian Declines: The Conservation Status of United States Species.  University of California Press, Berkeley.

Morey, S.R., and D.N. James. 1994. Variation in larval habitat duration influences metamorphosis in Scaphiopus couchii. Pages 159-165 in P.R. Brown and J.W. Wright (editors), Herpetology of the North American Deserts.  Special Publication No. 5, Southwestern Herpetologists Society, Van Nuys, California.

Author:  Jim Rorabaugh

For additional information on this species, please see the following volume and pages in the Sonoran Herpetologist: 2006 Jan:8-9, 2014 March:4-7.

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