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Intensive radio-tracking during August-December enabled us to collect detailed information on digging behaviors of a small sample of black-footed ferrets (Mustela nigripes) occupying colonies of white-tailed prairie dogs (Cynomys leucurus). A sample of 33 prairie dogs, also radio-tagged, progressively ceased aboveground activity during late summer and fall, presumably as they descended into burrows to hibernate. Most of the time ferrets spent digging was in November-December when >95% of the radio-tagged prairie dogs were inactive, suggesting that digging was primarily to excavate hibernating prey. Although 43.9% of the burrow openings were estimated to be in large mounds, which are common on colonies of white-tailed prairie dogs, all of a sample of 17 deposits of soil (diggings) made by ferrets were excavated at small mounds or nonmounded openings. The average duration of 23 nocturnal sessions of digging by ferrets was 112.2 minutes. A digging session consisted of multiple bouts of soil movement typically lasting about 5 min, and sessions were separated by pauses above- or belowground lasting several minutes. Bouts of moving soil from a burrow involved round-trips of 12.5-30.3 s to remove an average of 35 cm3 of soil per trip. These digging bouts are energetically costly for ferrets. One female moved 16.8 kg of soil an estimated 3.3 m during bouts having a cumulative duration of 178 minutes, removing a soil plug estimated to be 178 cm long. Increasing evidence suggests that some behaviors of ferrets and prairie dogs are coevolutionary responses between this highly specialized predator and its prairie dog prey. RESUMEN.—Mediante el uso intensivo del monitoreo por radio desde agosto hasta diciembre, logramos colectar informacion detallada sobre la conducta de excavacion de una pequena muestra de hurones de patas negras (Mustela nigripes) que habitan colonias de perros llaneros de cola blanca (Cynomys leucurus). Una muestra de 33 perros llaneros, tambien monitoreados por radio, cesaron gradualmente su actividad sobre el suelo durante finales del verano y el otono, probablemente debido a que descendieron a sus madrigueras para hibernar. De noviembre a diciembre fue cuando los hurones pasaron la mayor parte de su tiempo cavando y cuando mas del 95% de los perros llaneros monitoreados por radio no se encontraban activos, lo cual indica que las excavaciones se hacian primordialmente para extraer presas que estaban hibernando. A pesar de que se estima que el 43.9% de las madrigueras se encuentra en los monticulos grandes que son comunes en las colonias de perros llaneros de cola blanca, de una muestra de 17 depositos de tierra (excavaciones) realizados por hurones, todos se habian excavado en monticulos pequenos o en madrigueras sin monticulos. La duracion promedio de 23 sesiones nocturnas de excavacion realizadas por hurones fue de 112.2 minutos. Una sesion de excavacion consistio de varios ratos de movimiento de tierra que tipicamente duraban alrededor de 5 minutos, separados por pausas tanto sobre el suelo como en el subsuelo que duraban varios minutos. En estos ratos, se realizaban viajes de 12.5-30.3 segundos para remover 35 cm3 de tierra por viaje. Estas excavaciones de tierra consumen mucha energia de los hurones. Una hembra removio 16.8 Kg de tierra a lo largo de una distancia de aproximadamente 3.3 m durante sus ratos de excavacion, los cuales duraron 178 minutos en total y en los que logro remover un taponamiento de 178 cm de largo. Existen cada vez mas evidencias que indican que algunos comportamientos de los hurones y los perros llaneros son respuestas coevolutivas entre este depredador altamente especializado y su presa, el perro llanero.

Ecologically equivalent species serve similar functions in different communities, and an ecological surrogate species can be used as a substitute for an equivalent species in a community. Siberian polecats (Mustela eversmanii) and black-footed ferrets (M. nigripes) have long been considered ecological equivalents. Polecats also have been used as investigational surrogates for black-footed ferrets, yet the similarities and differences between the 2 species are poorly understood. We contrasted activity patterns of radiotagged polecats and ferrets released onto ferret habitat. Ferrets tended to be nocturnal and most active after midnight. Polecats were not highly selective for any period of the day or night. Ferrets and polecats moved most during brightly moonlit nights. The diel activity pattern of ferrets was consistent with avoidance of coyotes (Canis latrans) and diurnal birds of prey. Similarly, polecat activity was consistent with avoidance of red foxes (Vulpes vulpes) in their natural range. Intraguild predation (including interference competition) is inferred as a selective force influencing behaviors of these mustelines. Examination of our data suggests that black-footed ferrets and Siberian polecats might be ecological equivalents but are not perfect surrogates. Nonetheless, polecats as surrogates for black-footed ferrets have provided critical insight needed, especially related to predation, to improve the success of ferret reintroductions.

The two living species of black-tailed prairie dogs Cynomys mexicanus and C. ludovicianus are found in Mexico. Cynomys mexicanus, a Mexican endemic, is restricted to a 600-km2 region in northwestern Mexico. It is found in six large arid grassland valleys associated with gypsum soils and surrounded by arid scrub. Due to the small geographic range and destruction of its habitat this species is considered endangered. Cynomys ludovicianus is found in northwestern Mexico. Its present distribution comprises a very large complex covering approximately 55 000 ha, eight major dogtowns, and more than one million prairie dogs. Indeed, this population represents the largest continuous prairie dog complex left in North America. However, its present conservation status is considered as threatened, mainly because of the rapid deterioration of its habitat.

The black-footed ferret (Mustela nigripes) (Figure 27.1) is a small, secretive, nocturnal member of the family Mustelidae (Hall, 1981; Honacki, Kurman and Koeppl, 1982). Ferrets have an obligate dependence on the prairie dog (Cynomys spp.) community, utilizing the prairie dog for food and its burrows for shelter (Campbell et al., 1987).

Yuma clapper rails (Rallus longirostris yumanensis) are protected under the Endangered Species Act, and 90% of the U.S. population occurs within 2 wetland complexes. Assessment of impacts on, and mitigation measures for, Yuma clapper rails are required by law, yet managers lack quantitative information on habitat requirements. Seasonal habitat requirements provide resource managers with the information necessary to assess effects of development and water use practices on Yuma clapper rails in the Southwest. Playback recordings are commonly used to survey rail populations, yet their accuracy has not been evaluated. Consequently, we examined survey techniques and seasonal habitat requirements of Yuma clapper rails during 1985-87 on the lower Colorado River in southwestern Arizona to provide the recovery team and resource managers with reliable population estimates and habitat requirements