Inyo California Towhee

Pipilo crissalis eremophilus

Description

The Inyo California towhee, Pipilo crissalis eremophilus, is a grey-brown, sparrowlike songbird. It is medium sized, approximately 7-7.5 in (17.8-19 cm) in length, and the sexes are similar in size and color. Inyo California towhees are slightly smaller than the Sacramento California towhee, its nearest geographic relative, whose range extends east to the Sierra Nevada Mountains; there are significant differences in bill length, middle toe, wing, and tail lengths. Plumage coloration of the Inyo California towhee is a slightly paler ash gray than other members of this species, a difference not readily discernable to the naked eye.

Behavior

Inyo California towhees mate for life, and only when one bird dies does the other pursue another mate. Sexual maturity is generally attained in the first breeding season after hatching. Initiation of nesting coincides with local plant growth and flowering periods, which are influenced by rainfall and temperature that also affect insect abundance. The breeding season generally starts early in spring, with courtship and nest building commencing in March. The first clutches are laid in April, but can be laid as early as late, March; replacement clutches may be laid as late as May or early June. If the first clutch falls the pair will recycle, but breeding behavior usually ceases for the pair when the first clutch is successful. Clutch sizes range from two to four eggs, with four eggs occurring most frequently. Only the female incubates the eggs, but both parents share in the brooding and feeding of the young. Eggs hatch after 14 days of incubation, and the young fledge 8 days after hatching.

Parents continue to feed young for at least four weeks after fledging. The young are fully independent of the parents at six weeks, but remain within their natal nest area through the following fall and winter. Inyo California towhees nest in both riparian habitat and a variety of desert shrubs in adjacent upland communities. Their nests are bulky cups made of thin twigs, grasses, and forb stems with leaves and flower heads. The nests are lined with fine stems, grasses, and hairs. Nests are constructed in a variety of plants that include shining willow, arroyo willow, desert olive, antelope brush, bladder sage, four-winged saltbush, and green ephedra. These plant types help provide nest sites off the ground that offer protection from ground predators and dense canopies that hide nests from aerial predators. These trees also provide shade from extreme desert temperatures. Territories are defended by both the male and female from intruders year-round, but more vigorously during the breeding season. Territories include nest sites, foraging areas, roosts, and perches. Territories range from 25 to 62 acres (10.1 to 25.1 hectares) and decrease in size during the breeding season. Towhees will move outside their territories during the non-breeding season to forage in the open desert. Inyo California towhees are omnivorous (feeding on plants and animals), opportunistic feeders, foraging primarily in open rocky and sandy desert hillsides on just about any seed or invertebrate they encounter. They will also forage on the low branches of large shrubs and in the leaf litter and foliage of dense riparian vegetation. Towhees primarily peck and glean when foraging but will also engage in scratching, flycatching, chasing, and harvesting to find or capture food. Their primary food source is weed seeds, followed by grain, invertebrates, and fruit. Plant food items include seeds from grasses, annuals, perennial forbs, and deciduous and evergreen shrubs and trees. Both adults and young towhees eat seeds year round. Small fruit from willows, desert olive, desert tomato, and grasses are consumed by adults in the spring and summer. Insects consumed include unidentified insect larvae and winged and crawling insects such as moths, flies, grasshoppers, and beetles. The diet changes as availability of food changes. More invertebrates are eaten during the spring and summer months when invertebrates are most active, while seeds are the main food in the towhee's diet during the fail and winter. Nestlings and young fledglings are fed invertebrates, exclusively.

Little is known about competition between Inyo California towhees and other species. Ground foraging birds such as mountain quail, California quail, and chukar may forage on the same desert hillsides and feed on a common and important food source, seeds. Although spotted towhees nest at different heights, they require the same dense riparian shrub cover for nest construction. Spotted and Inyo California towhees do not tolerate each other during the breeding season. Little evidence is available to indicate that Inyo California towhees are taken in significant numbers by natural predators. Only one record of predation on Inyo California towhees, by a gopher snake preying on a nest containing two nestlings. Potential predators include the sharp-shinned hawk, coyote, bobcat, badger, gray fox, and a variety of snake species.

California towhees are nonmigratory, holding their territories year-round. However, if snow cover does not allow towhees to forage for seeds, they may migrate to lower elevations within their range to find food.

Habitat

The Inyo California towhee occurs in the southern Argus Mountains of the Mojave Desert, a north-south oriented range located between the Sierra Nevada to the west and the Panamint and Slate Ranges to the east. These mountains range from approximately 2,680 to 5,630 ft (816.8 to 1,716 m) above sea level. The climate is severe, with summer temperatures regularly exceeding 100°F (37.8°C) accompanied by frequent strong winds and infrequent rainfall. Winter conditions axe equally extreme, with temperatures often below freezing and some snowfall. The substrate is mainly decomposed granite with little soil or litter. Surface water is limited to springs and the resulting seeps and creek flow. Inyo California towhees nest and forage in areas of dense riparian vegetation dominated by willows, Fremont cottonwood, and desert olive with associated rubber rabbit brush and squaw waterweed. They also nest in shrubs of the upland community adjacent to riparian habitat and use the upland habitat as their principal foraging grounds. This habitat consists of Mojave creosote bush scrub or Mojave mixed woody scrub. Plants associated with the creosote bush community include burrobush, allscale, and indigo bush.

Distribution

The Inyo California towhee is a relict population of a species that was historically widespread in the southwestern United States and northern Mexico. This subspecies became restricted to mountain areas in the northern Mojave Desert as a result of prehistoric climatic changes beginning in the Pliocene. The primary range of the Inyo California towhee is limited to riparian habitats located within the southern Argus Range, Inyo County, California.

From surveys conducted between 1978 and 1986, approximately 111 Inyo California towhees occurred on the Naval Air Weapons Station (NAWS), China Lake. In 1992 and 1994, all suitable Inyo California towhee habitat east of NAWS was surveyed and 83 towhees were observed. From this count, the estimate was placed at 92 towhees in an area that constitutes approximately one-third of the sub-species' range. Inyo California towhees are located in a 107,520-acre (43,513.3-hectare) area between LaMotte Spring to the north and Indian Joe Spring to the south. The Naval Air Weapons Station supports approximately 68% of this subspecies' range. The remaining 32% of the population is located on adjacent Bureau of Land Management and California Department of Fish and Game land. The most recent population surveys (1995) for this subspecies indicate that no more than 200 individuals exist.

Threats

Degradation or destruction of riparian habitat is the primary threat to the continued existence of the Inyo California towhee. Grazing of grasses, shrubs, and forbs, and trampling of riparian and adjacent upland scrub habitats by feral burros, and to a lesser extent by feral horses and cattle, have significantly reduced the ability of these habitats to support towhees. Plants that are not grazed are trampled, and supporting soils are compacted. Feral burros are particularly destructive due to their practice of creating "burro baths", which can be up to 10 ft (3.3 m) in diameter, destroy all vegetation, and create miniature dust bowls. Altering riparian habitat in this manner also encourages the disproportionate growth of native species that are not preferred by this towhee subspecies, such as squaw waterweed, and the invasion of exotics like salt cedar and carrizo. The invasion of salt cedar in particular threatens to replace native plant species preferred by Inyo California towhees. Agency records indicate that the controlled burning of willows surrounding desert springs was conducted as late as the 1970s to increase surface water for bighorn sheep. Human habitation and activities in desert riparian habitats or in close proximity also threaten the Inyo California towhee's existence. Excessive diversion of water from riparian habitats used by this subspecies is a real and immediate threat. Water diversion is the result of mining activities, recreation, irrigation, livestock, and rural development. Water is currently being diverted from springs located in three of the eleven designated critical habitat areas.

Off-road vehicle use has resulted in the direct loss of desert scrub and riparian habitat. Springs such as Austin, Christmas, Mumford, North Ruth Springs, and Peoples Springs that can be reached by vehicle are affected by public use. Peoples Spring, which is accessible by two-wheel drive vehicles, is so badly disturbed that only rushes and grasses grow there, although water is plentiful. Unmanaged recreational use, including camping, hiking, and biking, has resulted in the degradation of some riparian habitats. The NAWS, which encompasses approximately two-thirds of the towhee's range, has developed a program emphasizing the protective management and restoration of endangered and threatened species. This program has reduced grazing and trampling threats to Inyo California towhees by initiating management prescriptions to eliminate burros and wild horses from riparian habitats. The NAWS has also been withdrawing all mineral extraction operations and has closed Navy lands to most public uses.

The Bureau of Land Management (BLM) administers federal lands that include approximately one-third of the Inyo California towhee's current range. These federal lands include seven towhee critical habitat areas: five springs and two water courses. The BLM, recognizing the sensitivity of these critical habitat areas and their importance to the towhee, designated the Great Falls Basin Area of Critical Environmental Concern primarily for their protection. Management prescriptions that benefit the towhee include the protection of all water sources, removal of burros, management of off-road vehicles use, and removal of exotic vegetation.

Conservation and Recovery

Under management by the NAWS and the BLM, threats to the Inyo California towhee have been reduced. However, strict adherence to management prescriptions over a longer period of time is necessary before recovery goals can be met. In 1994 the State of California purchased Indian Joe Canyon, the only parcel of critical habitat under private ownership, and is in the process of developing a management plan that will address the recovery needs of the towhee. Overgrazing of grasses, shrubs and forbs, and the trampling of vegetation by feral burros and horses is a principal threat. Feral burros and horses should be removed or managed in a manner that the Inyo California towhee and the riparian habitat on which it depends is protected throughout its range. The water table and flows should be restored; if necessary, water rights should be secured. Water diversions should be eliminated whenever possible by limiting the use of water for domestic and industrial development. Water diversions, which can include spring boxes, should be removed from the following critical habitat areas: Mumford Spring, Alpha Spring, North Ruth Spring, Bainter Spring, and Indian Joe Canyon. A program to remove exotic salt cedar and carrizo, an invasive native, from riparian habitat should be established throughout the range of the Inyo California towhee. Degradation of the riparian habitat at Austin Spring has allowed carrizo to invade the area. To increase the area's suitability as Inyo California towhee breeding habitat, the carrizo should be removed and replaced with arroyo willows.

Contacts

U.S. Fish and Wildlife Service
Regional Office, Division of Endangered Species
Eastside Federal Complex
911 N.E. 11th Ave.
Portland, Oregon 97232-4181
(503) 231-6121
http://pacific.fws.gov/

U.S. Fish and Wildlife Service
Ventura Fish and Wildlife Office
2493 Portola Rd., Suite B
Ventura, California 93003-7726
Telephone: (805) 644-1766

References

U.S. Fish and Wildlife Service. 3 August 1987 "Determination of Threatened Status and Critical Habitat Designation for the Inyo Brown Towhee." Federal Register 52 (148): 28780-28788.

U.S. Fish and Wildlife Service. 10 April 1998. "Recovery Plan for Inyo California Towhee." U.S. Fish and Wildlife Service, Portland, 32 pp.