Cassin's Sparrow

Peucaea cassinii


Demography and Populations

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Figure 4. Relative abundance of Cassin's Sparrow during the breeding season in the United States.

Based on data from the North American Breeding Bird Survey, 2011–2015. See Sauer et al. (2017) for details.

Figure 5. Regional trends in Cassin's Sparrow breeding populations in the United States.

Based on data from the North American Breeding Bird Survey, 1966–2015 (Sauer et al. 2017). Data show estimates of annual population change over the range of the survey; areas of increase are shown in blue and declines are shown in red. See Sauer et al. (2017) for details.

Measures of Breeding Activity

Age at First Breeding

Presumably in year after hatching but no data.


In southeastern Arizona, mean clutch size 3.3 eggs ± 0.48 SD (range 3–4, n = 22) (RKB). On fields enrolled in Conservation Reserve Program, Southern High Plains, Texas, 4.4 eggs ± 0.61 SE (n = 34) (125). In Oklahoma, 4.2 eggs (range 3–5, n = 6) (126). In Nebraska, 3 nests with 5 eggs each (54).

Annual and Lifetime Reproductive Success

No comprehensive studies with large sample sizes. Several studies estimate reproductive success for small numbers of nests. In a 2-year study in west-central Texas, 13 fledglings were produced by 6 pairs, with 54% of eggs laid resulting in successful fledging event (7). In Southern High Plains, Texas, Berthelsen and Smith (125) found 46% of 30 nests in Blue Grama (Bouteloua gracilis)/Sideoats Grama fields successfully raised ≥ 1 young to fledging (1988–1989). At Tucson, Arizona, of 19 nesting attempts in 1983, 10 were successful in rearing ≥ 1 young to fledging, 6 were documented as failures, fate of 3 nests unknown (RKB). Only two of 21 males studied over 2 years in west-central Texas remained unpaired through summer (29). Such studies may suggest levels of true annual reproductive success but larger samples needed.

Following wildfire in Texas panhandle mesquite grasslands, higher nest success in recently burned (within 2 years) areas compared to unburned plots; ranging from 0.20 (Mayfield index) in unburned plots vs. 0.53 in burned plots three years after wildfire (127). Despite large and intense fires, few overall effects on nest success by 2 years post-fire, largely because woody vegetation had recovered.

Daily nest survival rate 0.97 ± 0.03 SE, higher for Cassin’s Sparrow than for Field Sparrow (Spizella pusilla) or Lark Sparrow (Chondestes grammacus) in grazed and burned sagebrush grassland in Oklahoma. More Cassin’s Sparrow nests were found in patch-burn grasslands than in areas treated with traditional seasonal grazing regimes (19).

No information on lifetime reproductive success.

Number of Broods Normally Reared per Season

Limited studies document only 1 brood/season, but skylarking by male after fledging of first brood suggest that double-brooding is at least possible (7).

Proportion of Females that Rear at Least One Brood to Nest Leaving

No information.

Life Span and Survivorship

Not banded in sufficient numbers for verified longevity records to be maintained by Bird Banding Laboratory. From 1960 to 2017, only 1,400 Cassin's Sparrows were banded within their normal breeding range (including Mexico). An average of < 21 birds were banded annually, mostly in Arizona and Texas (U.S.G.S Bird Banding Lab data).

Disease and Body Parasites

One bird collected in Kansas had large mass on nares and upper bill, arising from loral skin and filling both nares. Diagnosed as fowl pox (128).

Study of blood parasites in 40 Arizona monsoon breeders detected following prevalences: Haemoproteus, 1 bird (2.5%); microfilarie, 1 bird (2.5%); Trypanosoma avium, 6 birds (15%). No detections of Plasmodium or Leucocytozoan species. Overall infection rates 7/40 birds (17.5%). Infection levels lower than those of sympatric Rufous-winged Sparrow, but similar levels to sympatric Botteri’s Sparrow and Rufous-crowned Sparrow (40). Measurements of plumage hue, saturation and brightness were not consistently related to levels of parasite prevalence in this species or congeners (40).

Causes of Mortality

Little information on causes of mortality (see Behavior: Predation). There was little evidence of winter mortality among banded birds in southeastern Arizona grasslands (80).


No information on dispersal behavior or distances traveled by either young or adults. Fidelity to breeding range can be low—few birds banded at study sites in southern Arizona returned in subsequent seasons (RKB). Few studies of fidelity to breeding territories from center of range. Using song characteristics, Schnase (29) documented return of several males to previously occupied territories. At Davis Mountain State Park in western Texas, 32 Cassin's Sparrows were banded in fall 1992–1997 (most were captured in September). No new individuals were captured in the following spring (March–May), but 6 fall-banded birds were recaptured, implying site fidelity within a single overwintering period (K. Bryan, personal communication).

Population Status


Using data from the North American Breeding Bird Survey (BBS), the mean annual population for the Cassin's Sparrow was estimated at 9,700,000 individuals in the United States for the period between 2005 and 2014 (129).

In much of its breeding range, Cassin's Sparrow populations vary dramatically from year to year. As a result, the best estimates of population density are provided by long-term censuses presented with both means and measures of annual variation. Such estimates are unavailable, however. Published densities are usually estimated either as the number of territories or singing males per unit area, or the number of singing males along transects (often roadsides surveyed by car). In Davis Mountains, western Texas: 17 singing males along a 24-km roadway through treeless grassy plain, south-facing slope. In Midland, Texas: 3 whole territories and parts of 4 other territories on a 20.8-ha plot; an 8-ha plot had only one pair which moved over the whole plot (78). Nest densities in Conservation Reserve Program fields in Southern Highlands, Texas, averaged 1.7 nests/ha ± 1.78 SE (n = 32; nests/ha is presumably equal to pairs/ha) in several field types, all dominated by Blue Grama (125). Maxwell National Wildlife Refuge, New Mexico: lower densities on ungrazed refuge lands compared to grazed lands off refuge (130). On 100-ha area in west-central Texas, Schnase (29) estimated an average of 11 pairs/40.4 ha over a 2-year study. Local spring concentrations of > 500 singing males/km2 near Coolidge, Arizona, during March 1978, outside of the normal winter/spring range (K. Kaufman in Witzman [110]).


Analysis of data (1968–2015) from the BBS indicated a negative long-term population trend for the central U.S. (–0.69%/yr, n = 259, 95% C.I. –2.3 to 0.4), and for the U.S. as a whole (–0.75%/yr, n = 333, 95% C.I. –2.3 to 0.3), but decreases were not significant for time period (131). Nonetheless, over a 45-yr period (1970–2014), BBS data indicated that the U.S. population has declined by an estimated 43% (129), illustrating that a statistically insignificant long-term decline can amount to a large change in population size. More recently (2005–2015), BBS data results indicated a significant decrease in the western U.S. (–5.8%/yr, n = 74, 95% C.I. –10.2 to –1.1) and the Chihuahuan Desert (–3.3%, n = 47, 95% C.I. –10.9 to –1.5). There were significant annual decreases in the Oaks and Prairies (–3.3%, n = 36) and Edwards Plateau (–4.7%, n = 17) physiographic regions from 1966 to 2015, although sample sizes were small. No significant trends (positive or negative) were evident at the state level for 1968–2015 or 2005–2015.

Population Regulation

Poorly understood. Populations fluctuate erratically at the edges of the Cassin's Sparrow range. Since it is not even known where or if some populations move between seasons, it is difficult to know the factors to which the birds are responding. One consistent theme is that the Cassin's Sparrow responds to annual variation in rainfall. In southwestern portions of range (southeastern Arizona, southwestern New Mexico), breeding populations and reproductive success are positively associated with summer rainfall. In more mesic portions of range such as southeastern Texas, however, breeding success decreases with increasing rainfall (132, 133). Summer rains in the southwestern U.S. and Texas are erratic, so Cassin's Sparrow occupancy can vary dramatically from year to year. Near Amarillo, Texas, Cassin's Sparrow is normally common at Buffalo Lake National Wildlife Refuge. However, no individuals were recorded in 1996, a year of severe drought. In 1997, the wettest year on record locally, no singing males were heard through mid May, 3 weeks after normal singing period (K. Seyffert, personal communication).

Population response to rainfall is presumably tied to changes in vegetation structure. Cassin's Sparrow is associated with sparse grasslands with light to moderate shrub cover. In normally mesic habitats, increased rainfall can lead to dense growth of grasses beyond the density normally occupied by this species, perhaps lowering habitat quality. In arid habitats, increased rainfall can lead to growth of grasses and annual forbs and to increased insect foods, to make an area more suitable than normal. Grasshoppers, perhaps the preferred food, show similar preference for intermediate grassland structure (134). No tests of population regulatory factors have been made; however, exclosure experiments suggested that insectivorous birds in southern Arizona can reduce populations of grasshoppers on common weed species (105)

In southeastern Arizona grasslands, insectivorous birds (including Cassin's Sparrow) limited the population size of grasshoppers, but did not mediate competition between grasshopper species or reduce grasshopper impacts on vegetation; thus, the sparrow community did not act as a keystone predator (104). At the same site in winter, Cassin's Sparrow abundance was greater in an ungrazed area following a wet summer, presumably because of increased vegetative cover and seed production (67).

Recommended Citation

Dunning, J. B., Jr., R. K. Bowers Jr., S. J. Suter, and C. E. Bock (2018). Cassin's Sparrow (Peucaea cassinii), version 2.0. In The Birds of North America (P. G. Rodewald, Editor). Cornell Lab of Ornithology, Ithaca, NY, USA.