Justification of Red List Category
This species has a very small and declining population, and fledging success is very low. It is therefore listed as Endangered.
Wintering flocks of over 100 individuals have been observed in several occasions in Nuevo León (2014-2015), Coahuila (2010-2011) and San Luis Potosí (2010-2014), with a maximum flock size of 480 Worthen’s sparrows in San Luis Potosí (2010; Ruvalcaba-Ortega et al. in prep.). Precautionarily assuming that such flocks comprise the majority or even all of the remaining population, and given the very low productivity in the species, the total population size may be only best placed in the range 250-999 mature individuals; and their winter flocking behaviour would therefore suggest the species consists of one subpopulation. Previous smaller estimations (60-100; Canales del Castillo et al. 2010) recorded in 2006, may have been due to the lack of more widespread survey efforts.
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.
Spizella wortheni has suffered a major range contraction and currently only breeds at sites in Coahuila, Nuevo León, Zacatecas, and San Luis Potosí Mexico (Ruvalcaba-Ortega et al. in prep): More than 25 five localities have been recorded in these four states from recent intensive survey efforts, which can be grouped in 5 main regions: La Soledad Valley, Saltillo intermountain grasslands, Galeana agricultural lands around 57-highway, north-east Zacatecas-north-west San Luis Potosí grasslands, and Charcas-SantoDomingo grasslands (Canales-Delgadillo et al. 2015, Canale-Delgadillo 2011, Canales del Castillo et al. 2010, Scott-Morales et al. 2008, Garza de Leon et al. 2007, Behrstock et al. 1997, Wege et al. 1993, Ruvalcaba-Ortega et al. in prep.). Wintering flocks of >100 individuals have been observed in several occasions in Nuevo León (2014-2015), Coahuila (2010-2011) and San Luis Potosí (2010-2014), with a maximum flock size of 480 Worthen’s sparrows in San Luis Potosí (2010; Ruvalcaba-Ortega et al. in prep., R. Canales del Castillo, I. Ruvalcaba Ortega and J. González Rojas in litt. 2016). 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, Veracruz before 1957 and Chihuahua in 1959. The few records from Puebla and Veracruz were in the non-breeding season, and may refer to migrants, isolated individuals or extirpated populations (Wege et al. 1993).
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). In recently discovered breeding areas, 196 characterized nests showed a preference mainly for tarbush and four-wing saltbush (Atriplex canescens) as nesting shrubs (Ruvalcaba-Ortega et al. in prep., 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).
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 18.3% overall based on monitoring of 175 nests (R. Canales del Castillo, I. Ruvalcaba Ortega and J. González Rojas in litt. 2016); predation (Garza de Leon et al. 2007, Ruvalcaba-Ortega et al. 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, birds and coyotes are thought to predate nests (Ruvalcaba-Ortega et al. in prep., M. A. Cruz-Nieto in litt. 2007).
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), and Especies, Sociedad y Hábitat have protected and fenced a recently found breeding and wintering locality in Guadalupe Victoria, Coahuila (Ruvalcaba-Ortega et al. 2016). The final draft of the Conservation Program to conserve Worthen’s Sparrow in Mexico have been completed (Ruvalcaba-Ortega et al. 2015).Conservation Actions Proposed
Survey to identify additional breeding/wintering sites. Monitor known populations, and evaluate survival on natural and agricultural breeding areas (R. Canales del Castillo, I. Ruvalcaba Ortega and J. González Rojas in litt. 2016). 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.
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.
Text account compilers
Capper, D., Khwaja, N., Westrip, J., Mahood, S., Symes, A., Sharpe, C.J., Isherwood, I., Pople, R.
Ruvalcaba Ortega, I., Howell, S., Garza de León, A., Cruz-Nieto, M.Á., Canales del Castillo, R., González Rojas, J.I.
BirdLife International (2022) Species factsheet: Spizella wortheni. Downloaded from http://www.birdlife.org on 07/07/2022. Recommended citation for factsheets for more than one species: BirdLife International (2022) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 07/07/2022.