Cassin's Sparrow

Peucaea cassinii



Welcome to the Birds of North America Online!

You are currently viewing one of the free species accounts available in our complimentary tour of Birds of North America. In this courtesy review, you can access all the life history articles and the multimedia galleries associated with this species.

For complete access to all species accounts, a subscription is required.

Subscribe Now

Already a subscriber? Sign In
Figure 2. Annual cycle of breeding, migration, and molt in se. Arizona.

For Cassin’s Sparrow populations in southeastern Arizona.

Cassin's Sparrow nest, Arizona.

Nest is on ground or in low shrub or grass clump, usually within 20 cm of ground. Specimen collected 12 mi N Sonoita, Pima County, Arizona. 1 August 1970. Ruler is 8 cm.; photographer Rene Corado.

Cassin's Sparrow clutch, Arizona.

Eggs are white, unspotted, and slightly glossy. Collected 12 mi N Sonoita, Pima Co., AZ. 1 Aug.; photographer Rene Corado.

Cassin's Sparrow nest, Arizona.

Full clutch of eggs. Santa Cruz Co., AZ; June.; photographer Rick and Nora Bowers.

Cassin's Sparrow chicks in nest.

Chicks are altricial and naked except for sparse, light-gray down on head and back, and pronounced yellow rictal flanges. Mouth lining is dark red with two parallel yellow lines on upper palate and two yellow spots on floor of mouth as feeding targets.

© Felipe Guerrero , Arizona , United States , 20 August 2017

Figure 2. Breeding circumstances vary annually and regionally as birds respond to local environmental conditions. In western portion of range (western Arizona, southwestern New Mexico), Cassin's Sparrow may breed only in abnormally wet years, whereas in the more mesic eastern portion of the breeding range, the species may be most obvious in relatively dry years. Thus, generalizations regarding when, where, and under what conditions Cassin's Sparrow usually breeds are difficult. Breeding biology has been well studied in only a few parts of range, and generalizations from one part of range may not be useful in other areas.


Pair Formation

Not described. In most of range, breeding pairs are first detected by singing of male, which may begin well after arrival on breeding grounds. In southeastern Arizona, male begins singing with onset of monsoon rains (usually in July). For example, at National Audubon Research Ranch in Sonoita Grasslands, Arizona, the first substantial monsoon rain (2.1 cm) in 1983 occurred on 8 July. Males were singing everywhere on the ranch on 9 July. Males were observed singing every 30–40 m along transects on 11 July 1983, totaling “several hundred” birds (RKB). Only one male was heard singing in this area on 26 June, 12 d before the rain began.

In central Texas, some males remain throughout winter, but a “conspicuous influx” of migrants arrives to claim territories in early March (29). Singing is common by mid March. First observation of females at end of March, with birds paired by third week of April (29). Schnase et al. (7) estimated the length of the “unmated period” (from first detection of males to first detection of females) in west-central Texas as an average of 27 d (range 14–35, n = 6). Dates of initiation of singing may be more accurate clue to arrival and initiation of breeding in northern part of range.


No record of actual time to build nest. One nest in New Mexico was found under construction on 18 July 1979 contained 4 eggs on 31 July 1979 (J. Haydock, personal communication). Nest found under construction at northern end of Baboquivari Mountains, western Arizona, on 16 April 1983 (D. Fischer, personal communication). Schnase et al. (7) reported that the average length of time between first detection of female on territory and laying of first egg was 14 d (range 10–19, n = 3).

First Brood of Season

Figure 4. Range of egg dates throughout range (from north to south; based on Hubbard [4], unless otherwise noted): Nebraska: 30 June (54); Kansas: May–June; Colorado: 2 nests 16 May and 14 June, young observed 30 June (119, 120); Oklahoma: 26 May–22 July; Texas: 1 March–1 August, with 52% of 85 clutches falling in May; New Mexico: 3 nests in late June and early July with fledglings on 2 July; Arizona: late July–early September (62), 4 nests with completed clutches found near Tucson 19–28 July (RKB); Chihuahua: juvenile collected on 21 June. In Rio Grande Delta, Texas, Cassin's Sparrow lays at earlier date than Botteri's Sparrow. In Amarillo, Texas, parents feeding young in nest 21 May–7 July, feeding fledglings 7 July–6 August (n = 5 observations; K. Seyffert, personal communication). Schnase (29) estimated time from egg-laying until fledgling for one pair was 21 d.

Second/Later Brood(s) per Season

No clear evidence that more than one brood is raised per year, but the long breeding season (3.75–5 mo) suggests that double-brooding is possible (29). Late nests (fledgling young in August and September in Texas or Oklahoma) may be second broods or renesting attempts after loss of initial nest. Three pairs renested following loss of nest earlier than mid June (29). Skylarking by male after fledging of first brood suggests that double-brooding is routinely attempted in Texas (7).

End of Breeding

Males cease territoriality and breeding activity in response to changes in day length (photorefractory response). Experimental studies involving hormonal treatments show that photorefractory response in male Cassin’s Sparrow is relative, and involves both changes in day length and plasma hormonal levels. Relative photorefractory response may develop to allow flexibility in breeding onset considering uncertainty of monsoon rains in late summer. Neuroendocrine mechanism involves decrease in releasable pool of GnRH-L hormone but not severe inhibition of GnRH-L synthesis as found in absolute photorefractory response (121).

Nest Site

Selection Process

Not described.


Nests are located on the ground or in a low shrub or grass clump, usually within 20 cm of ground. When placed on ground, the nest is not sunk below the ground surface in a scrape. Of 20 nests found in southeastern Arizona (RKB): 11 nests were in Desertbroom (Baccharis pteronioides), 5 were in Burroweed (Isocoma tenuisecta), 2 were in Sideoats Grama (Bouteloua curtipendula), and one each was located in exotic Lehmann Lovegrass (Eragrostis lehmanniana) and Weeping Lovegrass (E. curvula, var. conferta). Height of nests in shrubs was 9.65 cm ± 5.91 SD (range 0–20, n = 18; RKB). Wolf (3) claimed that all nests were placed on ground except for one nest in Arizona and in Tom Green County, Texas, where all of 10 nests were elevated (mean = 3.3 cm). However, Williams and LeSarrier (78) stated that, in literature, 50% of nests on ground, 50% above ground.

Other nest substrates include Sand Sagebrush in Wyoming (90); rabbitbrush (Chrysothamnus sp.) in Colorado (119); Christmas Cactus (Opuntia leptocaulis) and Adam's Needle (Yucca filamentosa) in Texas (78); Soapweed Yucca (Yucca glauca) in Nebraska (54); and Horehound (Marrubium vulgare) in Texas (29).

Site Characteristics

For nests in Tucson, Arizona (1983, RKB), dimensions of structure containing nest: mean height 74 cm (range 48–110, n = 17); mean circumference at base 97 cm (range 38–160, n = 17); mean circumference at widest point 300 cm (range 165–480, n = 15). Position of nest in support structure: 12 of 17 nests were in north to northeast portion of support structure, while 3 others were in northwest portion. One nest each was in east–southeast and west–southwest portions of the support structure. Nest generally faced open ground; mean distance from nest opening to next nearest grass clump or shrub was 3.9 m (range 1.1–14, n = 16). Supporting structure was live in 4 cases, and had both dead and live branches in 16 cases; no nests were found in completely dead shrubs or grass clumps. Seventeen nests were located on flat ground (slope = 0), one nest was located on a west-facing slope, and one on northeast-facing slope.

Each of 10 nests was shielded by vegetation on the south or southeast side of the nest, with an opening to the north or northwest sides (29).


Construction Process

Only female carries nest material and builds nest (7). Otherwise, construction process essentially undescribed.

Structure and Composition

Dry grass blades, weed stems, and vegetative fibers. Lined with finer grasses, rootlets, grass tops, and horsehair (78). Nest often supported by many grass or weed stems, relatively flimsy when removed from support structures (122, 29).


Mean dimensions of nests in Tucson, Arizona (1983, RKB): Inside width 70 mm (range 60–88, n = 18); rim thickness 15.0 mm (range 5–22, n = 18); and interior depth 56.9 mm (range 48–65, n = 16). Mean dimensions for 10 nests in west-central Texas (29): Inside width 5.9 cm ± 0.6 SD; inside depth 6.4 cm ± 1.0 SD; external width 10.7 cm ± 1.1 SD; and external depth 9.6 cm ± 1.4 SD. Of the 4 nests reported by Bailey (119), Williams and LeSarrier (78), and Dorn and Dorn (90): mean outside length 100 mm (n = 4); mean outside width 88.8 mm (n = 2); and height 8.75 cm (n = 1). No information on nest weight. For comparison of Botteri's Sparrow and Cassin's Sparrow nests and nest sites, see 6.


In west-central Texas, the average cup temperature of 5 abandoned nests ranged from 35 to 38°C on three clear days in mid June, suggesting that passive temperature regulation of young (not requiring brooding) was possible (7).

Maintenance or Reuse of Nests

No reuse of nests has been reported.

Nonbreeding Nests



Shape and Size

Nearly oval but somewhat elongated (78). Mean measurements (length × width) of 44 eggs: 19.0 mm × 14.6 mm (78).


Egg mass ranges from 1.0–1.5 g (RKB). Mean egg mass 1.6 g (range 1.2–1.8, n = 5) (29).


White, unspotted, slightly glossy.

Surface Texture

No information.

Eggshell Thickness

No information.


Schnase et al. (7) reported that the female lays one egg in the morning, beginning 2–3 d after completion of nest construction.


Onset of Broodiness and Incubation

No information.

Incubation Patch

One large patch on female.

Incubation Period

Little information. For 3 nests studied in southeastern Arizona, incubation periods were: ≥ 11 d, ≥ 11 d, and ≥ 9 d (RKB). Incubation period of one nest in Texas was 11 d (7). Incubation begins with penultimate egg.

Parental Behavior

Little information. A female flushed off anest in Colorado flew about 50 m and perched on weed. The female stayed in view while nest was examined, and did not show “particular uneasiness” (122). Female flushed from a nest in southeastern Arizona flew awkwardly, with noisy wingbeats, for a distance of 4–5 m, then ran along ground hopping over obstacles (RKB).

Hardiness of Eggs Against Temperature Stress

Little information, although Schnase et al. (7) estimated that in mid June in Texas, eggs could be kept warm by ambient temperatures without brooding by female.


No information about actual hatching events, emergence, or parental assistance during hatching. Little information on hatching success. A nest in Wyoming contained 3 young close to fledging, and one unhatched egg. No unhatched eggs were noted in 20 nests examined in southeastern Arizona (RKB).

Young Birds

Condition at Hatching

Young are altricial and naked except for sparse, light-gray down on head and back. Pronounced yellow rictal flanges. Mouth lining is dark red with 2 parallel yellow lines on upper palate and 2 yellow spots on floor of mouth as feeding targets (29). At hatching, tarsus length 3–5 mm, and body mass 1–2 g.

Growth and Development

From Schnase (29): Nestlings hold their heads upright and gape by day 2. By day 3, eyes are open and nestling produces high-pitched peeping sounds when disturbed. By days 6–7, flight feathers, coverts, and body and head feathers have broken from sheaths.

Nestling growth curves for body mass and tarsus length closely fit logistic growth models (6). Nestling Botteri's Sparrow and Cassin's Sparrow are similar in body mass during first days after hatching, but growth curves for Botteri's Sparrow reach a higher asymptote later in nestling period; thus Botteri's Sparrow young are heavier at fledging. Botteri's Sparrow has longer tarsi at hatching, and the difference in tarsus length increases as nestlings grow (6). Thus, at a given body weight, Botteri's Sparrow nestlings will have a longer tarsus, even though Cassin's Sparrow nestlings would be older than similar-sized (by mass) Botteri's Sparrow nestlings (6).

Nestling growth as estimated from figures 1 and 2 in Maurer (6): Tarsus length 4.5–8.0 mm by day 1; 5.0–12.5 mm by day 3; 11.0–16.0 mm by day 6; 13.0–15.5 mm by day 9. Body mass 2.0–2.5 g by day 1; 3.0–10.0 g by day 3; 11.0–12.5 g by day 6; and 11.0–12.5 g by day 9.

Parental Care


Female broods first 2–3 h after sunrise, then leaves nest unattended for long periods during day (7). See Nest. The female is known to brood the young at night until fledging (RKB).


Both parents feed young. Williams and LeSarrier (78) stated that female does majority of feeding, but both sexes fed equally at 3 nests in southeastern Arizona (RKB). At a nest in Midland, Texas, young were fed small moths and caterpillars up to 5 cm in length. Parents made 5 trips/h (78). Adults are cryptic in behavior and difficult to follow when bringing food to nest. Adult often lands on a perch 10–20 m from nest and survey surroundings before approaching with food; same perches used repeatedly.

Adult with food may walk final 10 m to nest (90, RKB). Johnson (107) observed at one nest that the male flew directly to nest with food, while female took a “more devious” route. Male forages with female during nestling period (7).

In southeastern Arizona (4–13 August 1983), young were fed grasshoppers, including the following species (K. Jepson-Innes, unpublished data): Psoloessa texana, P. delicatula, Helialula rufa, Eritetix simplex, Ageneotettix deorum, Amphitornus coloradus, Cordillacris crenulata, Parapomala wyomingensis, Syrbula montezuma, Aulocara femorata, and Opeia species. Parents at two nests delivered to young an average of 1.9 grasshoppers/10 min ± 0.59 SD (range 1.0–2.6, n = 8 observation periods). Observations covered 988 min, both evening and afternoon, 4–13 August 1983 (K. Jepson-Innes, personal communication; RKB). Delivery rates were slightly higher in morning (mean 2.0 grasshoppers/10 min [n = 4]) than in afternoon (mean 1.8 grasshoppers/10 min [n = 4]). Parents also delivered additional prey (numbers summed over same 8 observation periods, 4–13 August 1983): praying mantis (Mantodea, 2); caterpillar (Lepidoptera, 4); red ant (Hymenoptera, 1); other larvae (5); and cricket (Orthoptera, 1).

Nest Sanitation

Both parents remove fecal sacs. Parents occasionally eat a fecal sac at the nest, but more often fly off carrying fecal sac in bill (RKB).

Carrying of Young

No reports.

Cooperative Breeding

Not known to occur.

Brood Parasitism by Other Species

Identity of Parasitic Species

Brown-headed Cowbird, Molothrus ater; both ater and obscurus subspecies (123).

Frequency of Occurrence

Relatively uncommon. Ten records, including 9 by M. a. obscurus and one by M. a. ater were compiled by Friedmann (123). Additional reports include one nest with a cowbird egg in Colorado (120), while 3 of 12 nests were parasitized in 1983 in west-central Texas study (29). Eleven of 45 nests in Oklahoma over 3 years were parasitized; 2 parasitized nests produced sparrow fledglings; 3 nests produced cowbird chicks, but all 3 of those nests were depredated (124). None of 18 nests followed in southeastern Arizona were parasitized (RKB).

Timing of Laying

No information.

Response to Parasitic Mother, Eggs, or Nestlings

Little direct information. Two of 3 nests parasitized in a west-central Texas study were abandoned; researcher removed cowbird egg from third nest (29).

Success of Parasite with this Host


Fledgling Stage

Departure from the Nest

Young in 4 nests followed in southeastern Arizona fledged 7, 7, 8, and 9 days after hatching (RKB); several of these nests may have fledged prematurely due to observer presence. Schnase et al. (7) followed one nest that fledged naturally at day 9.


No quantified information. Fledglings capable of 10–15 m flights within 2 d of leaving nest. Flight strong by 8 d after leaving nest (7). Rectrices stub-tailed when fledged, appear fully grown 13–15 d after leaving the nest. Schnase (29) estimated adult proportions reached when young are 3 wk old.

All Cassin's Sparrows have fully pneumatized skull before first breeding season (3).

Association with Parents or Other Young

Female assumes primary care (7). Fledglings stay in dense vegetation for 7 d, exchange calls frequently with female parent. Male joins female in response to female Alarm Calls. Independent foraging by fledglings seen by 8 d after leaving nest (7). Young are completely independent in < 30 d (RKB).

Immature Stage

Little information. Some immatures can be identified when newly independent by broad streaks on breast. Immature may be less wary than adult, and may be observed on conspicuous perches (20).

Young may form independent flocks of juveniles of 10–20 individuals (29). Such flocks move through territories without provoking response from adult. Dorn and Dorn (90) observed “several adults and independent juveniles” in small loose flocks with Lark Bunting and Brewer's Sparrow, Chipping Sparrow, Clay-colored Sparrow, and Vesper Sparrow on 28 August 1993.

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.