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Lower Colorado River Multi-Species Conservation Program Balancing Resource Use and Conservation

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Yuma Hispid Cotton Rat

      (Sigmodon hispidus eremicus)

Yuma Hispid Cotton RatYuma Hispid Cotton Rat JuvenileYuma Hispid Cotton Rat Habitat
  • DESCRIPTION
  • DISTRIBUTION
  • HABITAT
  • CONSERVATION
  • MULTIMEDIA

General Description

Cotton rats are members of the genus Sigmodon. Species within this genus are described as rodents that are thick bodied, with a medium-length tail slightly shorter than its head and body. Their ears barely project above their fur, and their tail is sparsely haired. There are two subspecies of Sigmodon along the Lower Colorado River (LCR); the Yuma hispid cotton rat (Sigmodon hispidus eremicus) and the Colorado River cotton rat (Sigmodon arizonae plenus). The two subspecies cannot be distinguished by the way they look, but can readily be identified using skull measurements. They are also identified using molecular techniques including DNA sequencing. It is likely that the two subspecies ranges do not overlap along the LCR.

Legal Status

The Yuma hispid cotton rat is listed as a California Species of Special Concern.

Taxonomy

The Yuma hispid cotton rat was first discovered in 1804 by Cienega Wells in Mexico. The Yuma hispid cotton rat (Sigmodon hispidus eremicus) is a geographically isolated subspecies of the hispid cotton rat (S. hispidus). The Yuma subspecies is not considered to be markedly differentiated from the main species, which occurs in eastern Arizona and likely shares most of the life history traits with the rest of the species.

Reproduction

Hispid cotton rats breed throughout the year. They have been observed to have a gestation period of 27 days and produce precocial young (fully furred, eyes open, active, and need little parental care), which are weaned after 15 to 25 days. The average litter size is 5-6 young, and one captive female in a laboratory was recorded to have produced nine litters in a 10-month period. Breeding starts after 2 to 3 months of age, and the average life span is 6 months. Maximum densities have been recorded in the fall, with smaller population peaks occurring in spring. The lowest densities have been documented to occur in winter and summer.

Diet

Hispid cotton rats are active all year, feeding mainly on grasses and vegetation with insects making up a small portion of the diet on a seasonal basis.

Threats

Backwater habitat along the lower Colorado River has been altered by channelization, agricultural use, and storage of water, invasion by saltcedar, and decreased flow regimes due to dam construction. These alterations all may have contributed to a decline in the population of cotton rats along the lower Colorado River.

Population density is regulated by disease and avian predators; mammal predation is considered to be incidental. The principal competitors for resources for hispid cotton rats include other rodents.

More Information

Additional information on this species, as well as source documentation, can be found in the species accounts located at this link (PDF). Technical Reports on this species can be found here.

Updated December 15, 2014

The hispid cotton rat (S. hispidus) is widespread and its range includes northern South America, Mexico, Central America, and the southeastern and south central United States. However, the Yuma (S. h. eremicus) subspecies is geographically isolated from the rest of the species.  It is considered to be restricted to areas along the LCR, south of the Palo Verde Mountains, and small, isolated areas of suitable habitat west of Yuma, Arizona, in Imperial County, California. Although the Yuma hispid cotton rat may have historically occurred in the western part of the Gila River Valley east of Yuma, no evidence exists indicating that the Yuma hispid cotton rat is currently present in these areas. The range of the subspecies is limited to areas near Yuma, Arizona, where is has been trapped in Mexico close to the border, but may overlap with that of the Colorado River cotton rat on the northern edge of its range.

Click on the map below to see the distribution range of the Yuma hispid cotton rat using the interactive GIS map.

Click here to see the distribution range of the Yuma hispid cotton rat

 

There is limited information available specific to the life history and habitat requirements of the Yuma hispid cotton rat. The Yuma subspecies is not considered to be markedly differentiated from the main species, which occurs in eastern Arizona and likely shares most of its traits with the rest of the species.  Grass height and density have been documented as important habitat components for hispid cotton rats; they utilize runways through dense herbaceous growth and nests are built of woven grass.  They have small home ranges, which radio-telemetry studies have shown that hispid cotton rats utilize in a systematic manner, over multiple days.

 

LCR MSCP Conservation Measures

The Habitat Conservation Plan provides conservation measures specific to each species. Listed below are the species specific conservation measures for the Yuma hispid cotton rat. Click on the arrows to expand the table.

YHCR1—Conduct research to better define Yuma hispid cotton rat habitat requirements

Conduct research, if needed, to better define the elements of Yuma hispid cotton rat habitat and provide information necessary to design and manage created habitat.

YHCR2—Create 76 acres of Yuma hispid cotton rat habitat

Of the 5,940 acres of cottonwood-willow to be created as habitat for covered species, at least 76 acres will be designed to provide habitat for the Yuma hispid cotton rat in Reaches 6 and 7 near occupied habitat. Created Yuma hispid cotton rat habitat will be designed and managed to support a moist herbaceous understory, an element of the species' habitat.

MRM2—Monitor and adaptively manage created covered and evaluation species habitats

Created species habitats will be managed to maintain their functions as species habitat over the term of the LCR MSCP. Created habitat will be monitored and adaptively managed over time to determine the types and frequency of management activities that may be required to maintain created cottonwood-willow, honey mesquite, marsh, and backwater land cover as habitat for covered species. This conservation measure applies to those species for which comparable measures are not subsumed under species-specific conservation measures (Section 5.7 in the HCP). They are not applicable to species for which habitat would not be created under the LCR MSCP Conservation Plan, such as the desert tortoise, relict leopard frog, humpback chub, and threecorner milkvetch.

CMM1—Reduce risk of loss of created habitat to wildfire

Management of LCR MSCP conservation areas will include contributing to and integrating with local, state, and Federal agency fire management plans. Conservation areas will be designed to contain wildfire and facilitate rapid response to suppress fires (e.g., fire management plans will be an element of each conservation area management plan).

CMM2—Replace created habitat affected by wildfire

In the event of created-habitat degradation or loss as a result of wildfire, land management and habitat creation measures to support the reestablishment of native vegetation will be identified and implemented.

AMM1—To the extent practicable, avoid and minimize impacts of implementing the LCR MSCP on existing covered species habitats

To the extent practicable, establishment and management of LCR MSCP–created habitats will avoid removal of existing cottonwood-willow stands, honey mesquite bosques, marsh, and backwaters to avoid and minimize impacts on habitat they provide for covered species. Temporary disturbance of covered species habitats, however, may be associated with habitat creation and subsequent maintenance activities (e.g., controlled burning in marshes and removal of trees to maintain succession objectives). LCR MSCP conservation measures that could result in such temporary disturbances will, to the extent practicable, be designed and implemented to avoid or minimize the potential for disturbance. In addition to implementing AMM3 and AMM4 below, these measures could include conducting preconstruction surveys to determine if covered species are present and, if present, implementing habitat establishment and management activities during periods when the species would be least sensitive to those activities; or redesigning the activities to avoid the need to disturb sensitive habitat use areas; staging construction activities away from sensitive habitat use areas; and implementing BMPs to control erosion when implementing ground disturbing activities.

AMM5—Avoid impacts of operation, maintenance, and replacement of hydroelectric generation and transmission facilities on covered species in the LCR MSCP planning area

To the extent practicable, before implementing activities associated with OM&R of hydroelectric generation and transmission facilities, measures will be identified and implemented that are necessary to avoid take of covered species where such activities could otherwise result in take. These measures could include conducting surveys to determine if covered species are present and, if so, deferring the implementation of activities to avoid disturbance during the breeding season; redesigning the activities to avoid the need to disturb covered species habitat use areas; staging of equipment outside of covered species habitats; delineating the limits of vegetation control activities to ensure that only the vegetation that needs to be removed to maintain infrastructure is removed; stockpiling and disposing of removed vegetation in a manner that minimizes the risk of fire; and implementing BMPs to control erosion when implementing ground disturbing activities.

AMM6—Avoid or minimize impacts on covered species habitats during dredging, bank stabilization activities and other river management activities

To the extent practicable, before initiating activities involved with river maintenance projects, measures will be identified and implemented that avoid or minimize take of covered species where such activities could otherwise result in take. Such measures could include alternative methods to achieve project goals, timing of activities, pre-activity surveys, and minimizing the area of effect, including offsite direct and indirect effects (e.g., avoiding or minimizing the need to place dredge spoil and discharge lines in covered species habitats; placing dredge spoils in a manner that will not affect covered species habitats).

In the event of created-habitat degradation or loss as a result of wildfire, land management and habitat creation measures to support the reestablishment of native vegetation will be identified and implemented.


Research and Monitoring Activities

LCR MSCP conduct a variety of research and monitoring activities along the LCR encompassing both MSCP and non-MSCP species. For a complete list of all activities, please see the Research and Monitoring Activities web page.

The following list includes different research and monitoring activities for small mammals. Click on the link for more information.

This gallery includes photos of this species. If you require larger photos, please contact our webmaster Michelle Reilly at mreilly@usbr.gov.