Taxonomy [top]

Kingdom Phylum Class Order Family
Animalia Chordata Aves Passeriformes Emberizidae

Scientific Name: Spizella wortheni
Species Authority: Ridgway, 1884
Common Name(s):
English Worthen's Sparrow
Identification information: 12.5-14 cm. Dull sparrow with distinctive head pattern. Grey head with rufous crown (not extending on to forehead) and often brownish postocular stripe and wash on auriculars. Sandy grey-brown upperparts, streaked dark brown. Unstreaked grey rump. Dark brown wings and tail. Wings edged paler, with broad whitish to pale buff wing-bar, buffy-rufous tertial and secondary edging, and greyish lesser coverts. Whitish edging to tail. Pink bill. Juvenile is more nondescript. Head and chest washed brownish-buff, with dusky streaking on head and dark brown streaking on chest and flanks. Buff wing-bars. Similar spp. Sympatric Aimophila spp. have different head patterns and darker bills. Voice High, thin, fairly dry tssip or tsip, sometimes repeated rapidly. Song a dry, chipping trill of 2-3 second duration.

Assessment Information [top]

Red List Category & Criteria: Endangered B1ab(i,ii,iii,v); C2a(i); D ver 3.1
Year Published: 2013
Date Assessed: 2013-11-01
Assessor(s): BirdLife International
Reviewer(s): Butchart, S.
Contributor(s): Cruz-Nieto, M.Á., Howell, S., Canales del Castillo, R., González Rojas, J., Garza de León, A. & Ruvalcaba Ortega, I.
Facilitator/Compiler(s): Capper, D., Isherwood, I., Mahood, S., Pople, R., Sharpe, C J, Khwaja, N. & Symes, A.
This species has an extremely small and declining range and population, and fledging success is very low, but it qualifies as Endangered (rather than Critically Endangered) because it breeds at three sites and at least one subpopulation is larger than 50 mature individuals.

Previously published Red List assessments:
2012 Endangered (EN)
2008 Endangered (EN)
2004 Endangered (EN)
2000 Endangered (EN)
1996 Endangered (EN)
1994 Endangered (EN)
1988 Lower Risk/least concern (LR/lc)

Geographic Range [top]

Range Description: Spizella wortheni has suffered a major range contraction and currently only breeds at sites in Coahuila and Nuevo León, Mexico: La India, where it was discovered in 2004 (Garza de Leon et al. 2007); San José del Alamito (Canales del Castillo et al. 2010), and Tanque de Emergencia, where 100-120 individuals were found in January 1998 (S. N. G. Howell in litt. 1998) in Coahuila; and Las Esperanzas (Wege et al. 1993, Behrstock et al. 1997), La Carbonera and San Rafael in Nuevo León. Wintering flocks have been observed in Erial (100 individuals observed in February 2006), La Carbonera and San Rafael in Nuevo León, and Rancho los Angeles in Coahuila, where 60 individuals were observed in February 2006 (Canales del Castillo et al. 2010). Thorough surveys may find additional sites because suitable habitat remains within its historical range (M. A. Cruz-Nieto in litt. 2007). It was first described from New Mexico, U.S.A. in 1884, but it has only been recorded in Mexico since that date. There are records from eight states, but it was last recorded in Puebla in 1893, Tamaulipas in 1924, San Luis Potosí in 1951, Veracruz before 1957, Chihuahua in 1959 and Zacatecas in 1961. The few records from San Luis Potosí, Zacatecas, Puebla and Veracruz were in the non-breeding season, and may refer to migrants, isolated individuals or extirpated populations. However, since birds move only locally in the non-breeding season in Coahuila and Nuevo Leon and there has been a large breeding range contraction in the north, it seems more likely that these represent extirpated populations (Wege et al. 1993).

Countries occurrence:
Regionally extinct:
United States
Continuing decline in area of occupancy (AOO): Yes
Extreme fluctuations in area of occupancy (AOO): No
Estimated extent of occurrence (EOO) - km2: 25
Continuing decline in extent of occurrence (EOO): Yes
Extreme fluctuations in extent of occurrence (EOO): No
Number of Locations: 2
Continuing decline in number of locations: Unknown
Extreme fluctuations in the number of locations: No
Lower elevation limit (metres): 1200
Upper elevation limit (metres): 2450
Range Map: Click here to open the map viewer and explore range.

Population [top]

Population: Wintering flocks of 100 and 60 individuals were observed in February 2006 (Canales del Castillo et al. 2010). Precautionarily assuming that these comprise the majority or even all of the remaining population, the global population could therefore number as few as c.100 mature individuals.

Trend Justification:  There are no new data on population trends; however, the species is suspected to be declining at a slow rate owing to inappropriate grazing regimes.
Current Population Trend: Decreasing
Additional data:
Number of mature individuals: 100 Continuing decline of mature individuals: Yes
Extreme fluctuations: No Population severely fragmented: No
No. of subpopulations: 2 Continuing decline in subpopulations: Unknown
Extreme fluctuations in subpopulations: No All individuals in one subpopulation: No
No. of individuals in largest subpopulation: 1-89

Habitat and Ecology [top]

Habitat and Ecology: It is confined to open, arid shrub-grassland at elevations of 1,200-2,450 m (Wege et al. 1993, Behrstock et al. 1997) where breeding sites have been found in associations of tarbush (Flourensia cernua), creosotebush (Larrea tridentata), fourwing saltbush (Atriplex canescens) and short grassland (Garza de Leon et al. 2007, Canales del Castillo et al. 2010). It probably keys-in on certain vegetational structural components, such as open areas with low (grazed) grasses for foraging and a moderate complement of low, dense shrubs for cover and nesting (Behrstock et al. 1997, Garza de Leon et al. 2007, Canales del Castillo et al. 2010). Taller shrubs and trees may serve as observation or song perches, but a lack of shrubs over 0.5 m is not a deterrent to habitat occupancy (Behrstock et al. 1997). There are indications that it prefers the open-wooded area ecotone, but this is not the case at Las Esperanzas (Wege et al. 1993, Behrstock et al. 1997). In recently discovered breeding areas, 57 characterized nests showed a preference mainly for tarbush and Opuntia as nesting shrubs (Canales del Castillo et al. 2010). Nests of 3-5 eggs have been found between May and August (Garza de Leon et al. 2007, Canales del Castillo et al. 2010). Single-species flocks form after the breeding season (Wege et al. 1993) and are apparently strongly attracted to permanent water (Behrstock et al. 1997).

Systems: Terrestrial
Continuing decline in area, extent and/or quality of habitat: Yes
Generation Length (years): 3.8
Movement patterns: Not a Migrant

Threats [top]

Major Threat(s): Open shrub-grasslands have been greatly reduced by agriculture and grazing, and the rate of habitat conversion is increasing, primarily for production of potatoes (M. A. Cruz-Nieto in litt. 2007). There has been a progressive loss of habitat even on the Coahuila-Nuevo León border, especially in the El Potosí Valley (M. A. Cruz-Nieto in litt. 2007). Grazing and the use of chemicals modify and reduce the quality of the habitat and disturb nesting birds (Garza de Leon et al. 2007). It seems unlikely that large tracts of habitat remain near the currently known sites (Wege et al. 1993, Garza de Leon et al. 2007, Canales del Castillo et al. 2010). Reported reproductive success is very low, only 14% in La India and 0% in Carbonera; predation (Garza de Leon et al. 2007, Canales del Castillo and González-Rojas in prep.) and livestock disturbance (Canales del Castillo et al. 2010) seem to be the main causes, but it is not known how this affects populations (Garza de Leon et al. 2007). Snakes and coyotes are thought to predate nests (M. A. Cruz-Nieto in litt. 2007).

Conservation Actions [top]

Conservation Actions: Conservation Actions Underway
The north side of the valley near at Tanque de Emergencia (Rancho los Angeles), is managed appropriately by the Universidad Autónoma Agraria Antonio Narro, using a rotational grazing regime to ensure that the grass is always high in several pastures (Wege et al. 1993). The La India locality has been proposed as a protected natural area within the category of "sanctuary" by the Museo de las Aves de Mexico, Saltillo. Pronatura Noreste have fenced an important winter foraging locality for this species (M. A. Cruz-Nieto in litt. 2007).

Conservation Actions Proposed
Survey to identify additional breeding sites. Monitor known populations. Assess precise ecological requirements and understand local movements (Garza de Leon et al. 2007). Implement rotational grazing regimes at known sites (Wege et al.1993). Identify main predators and their impact over the reproductive success of the species. Develop an environmental education programme to promote the value of the ecosystem (Garza de Leon et al. 2007), and the importance of appropriate grazing regimes.

Citation: BirdLife International. 2013. Spizella wortheni. The IUCN Red List of Threatened Species 2013: e.T22721182A49935937. . Downloaded on 07 October 2015.
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