Northern Cardinal Cardinalis cardinalis
Version: 2.0 — Published February 12, 2021
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Some individuals remain paired on breeding territories throughout the year (e.g., 100, 212). Among individuals that join winter flocks, some males may leave flock to claim territories and are later joined by females (293), or pairs may leave winter flocks together (280, 67). It is not known if this difference corresponds to whether these birds were mated in the previous breeding season. Courtship displays first reported in February in southern Ontario and West Virginia (293, 281), as early as January in southern Mississippi (JMJ). On basis of less clearly defined criteria, “pair formation” reported mid-January–early April in southern Indiana (67). Timing of pair formation, courtship initiation, and the beginning of nesting has not been compared between first-year breeders and older or previously paired birds. Upon divorce (separation of pairs with both mates surviving) or death, mates are replaced with non-mated individuals or neighboring individuals that have lost a mate themselves (SLH, SUL; see 269 for record of bigamy by a male after a neighboring individual died; also observed by SLH in Wisconsin). New pairs form during breeding season, or even in autumn (October) as result of death or divorce of mate (SLH, SUL, 278). Divorces reported within and between breeding seasons (28, SUL).
Jawor et al. (113) found that newly mated pairs mate assortatively by plumage and bill coloration, but not by face mask expression or crest length. Newly mated pairs did not mate assortatively by measures of condition and more ornamented pairs were not more successful in reproduction.
Begins late February to mid-April (278, 100, 62). In Tennessee, building begins “as soon as the thickets begin to turn green with early leaves” (280: 1); in Iowa, while there is still snow on the ground (277). The first nest may take 2–3 wk to build (280, JMJ, MSD, DPS); shorter building times reported for later nests (see Nest).
First Brood per Season
See Figure 1. First eggs laid in March or April. Generally later nesting at higher latitudes, but many exceptions. Earliest dates at which eggs have been found: Baja California, 22 March; Texas, 24 March; Florida, 30 March; Georgia, 19 April; Ontario, 13 April; and Michigan, 20 April; but 2 March was reported as early (possibly unreliable) egg date for New Jersey (62, 301). See Bent (62) for data from additional locations. Incubation lasts 11–13 d, nestling period 7–13 d, in first and later broods (see Eggs and Parental Care). First nests in a population seem fairly synchronized, which may be linked to environmental conditions (JMJ). Early-season nests are more consistently incubated by females than nests later in the season (measured as time on nest, and number and length of off-nest bouts, 99). Females with redder underwing ornamentation were found to produce their first nests earlier in the season (15). Males with redder breast coloration (76) and greater brightness (273) had mates that nested earlier in rural populations, but brightness was not related to earlier breeding in urban populations (273).
Second/Later Broods per Season
High rate of nest failure at all stages (43, and references therein) leads to desynchronized nesting of pairs living in same area. In southern Ontario, mean 5.5 d ± 1.4 SD (range 3–16, n = 84) between day of nest failure and day first egg laid in new nest (302); elsewhere, considerable individual variation exists in time taken to renest after failure (JMJ). When nests are successful, time to re-nesting varies with number of fledglings: Kinser (67) reported that when a single young fledged (n = 4), female started new nest 13–14 d after fledging, but that when > 1 fledgling survived (n = 6), female waited an average of 19.2 d after fledging to start the next nest. No latitudinal trend for last nesting dates; across range, latest dates for eggs in active nests tend to be in late August (293, 62), although autumn nests have been reported as “fairly common” in West Virginia, where an active nest with 3 eggs was found on 19 October (M. Brooks in 279). In Tennessee (100) and Wisconsin (SLH), last young fledge in late August or September. In Mississippi, recently fledged young observed at feeders in late October (JMJ). Drought or low temperatures may end nesting season early by reducing availability of insect prey used to feed young (280, 293). Nest predation rates tend to be high, ~70% of nests are depredated (43, 29, 30). Nest survival increases as the breeding season progresses, although per-nest fledgling production remains similar throughout the breeding season (54).
Although female alone builds nest, both adults may select site (243). Female visits various locations, fluffing feathers and turning; male follows, and both mates call and manipulate nesting material with bill (243); this behavior observed 5–16 d before construction of first nests in Indiana (67).
Constructed in thick tangles of vines or twigs, usually in shrubs or small trees. In southern Michigan, 53 species of shrubs and saplings were used (n = 334 nests); 21% were found in hawthorn (Crataegus), 19% dogwood (Cornus asperifolia, C. florida), 9% honeysuckle (Lonicera), 8% wild grape; conifers with nests included eastern redcedar (Juniperus virginiana), white spruce (Picea glauca), pines (Pinus spp.), eastern hemlock (Tsuga canadensis), and northern white-cedar (Thuja occidentalis) (W. P. Nickell in 288). In Ohio (n = 121 nests), 65% were located in honeysuckle or multiflora rose (Rosa multiflora), and 7% eastern redcedar (43). In Indiana (n = 140 nests), 34% were located in American elm (Ulmus americana), 21% hawthorn, 15% sugar maple (Acer saccharum), and 13% eastern redcedar, with remainder in wild grape, dogwood, black locust (Robinia pseudoacacia), honeysuckle, boxelder (Acer negundo), elderberry (Sambucus), and rose (Rosa) (67); Indiana nests also reported in privet (Ligustrum sp.), yew (Taxus sp.), English ivy (Hedera sp.), osage orange (Maclura pomifera), and crabapple (Pyrus sp.) (294). In south-central Wisconsin, nests primarily in honeysuckle shrubs and under leafy canopy of grapevines growing over shrubs or lower tree branches (SLH). In southeastern Arizona, in riparian habitats, Arizona sycamore (Platanus wrightii) and netleaf hackberry (Celtis reticulata) frequently chosen for nesting (194). In central Tennessee, nests in blackberry brier thickets and shrubs and small trees, often those covered with vines (303). In Mississippi, nests frequently in wild blueberry or honeysuckle shrubs, wisteria vines, and small trees, nest sites often heavily covered with leaves (JMJ). In central Ohio, occasionally nests in the spine clusters growing from the trunks of honey locust (Gleditsia triacanthos) (304).
Nests concealed in forks of twigs and small branches; nest height above ground 0.25–12 m (mean 1–2 m) (100, W. P. Nickell in 288, 305). In Indiana (n = 108), mean height 2 m (range 0.5–4.5) and nest height increased over the season (67), which is similar to the pattern observed in central Ohio (52). In Ohio, mean height 2.1 m ± 1.6 SD (range 0.7–12, n = 121) (43). In Wisconsin, most nests about 1.5 m above ground (SLH). In Mississippi, most nests about 1.5–2 m above ground (JMJ). Appears to respond to experience of success or failure in prior nesting attempt and perceived risk of nest predation by placing within-season renests in more concealed microsites (306).
Female does most building; male occasionally brings nesting material (280, 100, 288, 43). Female crushes twigs by chewing them with mandibles, then bends them around her body; turning in the nest while working, she pushes out with her feet to form the nest cup. Male feeds mate during nest-building (67). Construction reported in morning and mid-afternoon; trips reduced 50% when temperature > 25°C in afternoon (243, 67).
Structure and Composition Matter
Nest is not attached to substrate; it is wedged into position. Bowl-shaped structure is composed of 4 layers: rough outer material, leafy mat, grapevine bark, and grassy lining (67); may contain weed stems, pliable twigs, strips of bark, grasses, vines, rootlets, leaves, and pine needles (100). Paper and plastic common in outer cup (SLH, JMJ). One report of shed snakeskin being used (278).
In Indiana, mean nest measurements: height 67 mm ± 6.2 SD; inside depth 36 mm ± 4.3 SD; outside diameter 108 mm ± 4.8 SD; inside diameter 73 mm ± 4.3 SD; mean weight 17 g ± 3.5 SD (n = 50) (67). In Ohio (n = 41), mean dry weight 17.6 g ± 4.1 SD; highly variable in size and composition; largest nest was 6 times volume of smallest and heaviest was 3 times weight of lightest (R. Breitwisch and D. Szczepanik, unpublished data).
Nest typically concealed by foliage, even though nests built early in season may be more exposed because shrubs have not leafed out. Frequently uses sites deep in tangled thickets and briers (303, SUL, JMJ). Territories with successful nests have higher foliage density and patchiness at 2 m throughout territory than do territories with unsuccessful nests (50, 76). Nest concealment, height of nest, proximity to edge habitat, accessibility, choice of shrub species in which nests were constructed, and distance to human activity had no relationship to rates of predation on nests in southwestern Ohio (43), although in central Ohio populations, nesting in non-native shrubs was linked to increased nest predation (307, 52). Multiflora rose and Lonicera honeysuckle were the major non-native shrubs used for nesting in all three studies. Differences in outcomes may depend on seasonal effects, factors specific to the study sites including range of shrub sizes available, distribution of native and non-native vegetation, predators, and predation rates; or sample sizes.
Maintenance or Reuse of Nests, Alternate Nests
Rarely reuses nests (278), but presence of old nests may function as protection against predation. In Virginia, experimental sites with more empty cardinal nests added had lower removal rates of plastic artificial eggs in an adjacently placed cardinal nest: 90% for single nests, 60% in 3-nest groups, and 50% in 6-nest groups (n = 5 replicates of each condition) (308). Although nests themselves are rarely reused, specific nest sites on a territory have been reused after old nests fall apart (JMJ).
C. c. cardinalis: mean length × breadth: 24.88 mm (range 22.47–27.16) × 18.58 mm (range 17.04–19.66, n = 23 clutches, 71 eggs) (Western Foundation of Vertebrate Zoology). Six other subspecies measured were not significantly different.
Eggs can be distinguished from those of Brown-headed Cowbird (Molothrus ater) by size. In southern Ontario, for cardinal (n = 25), mean length 24.8 mm ± 1.1 SD, width 18.2 mm ± 0.6 SD; for cowbird (n = 20), mean length 21.7 mm ± 1.1 SD, width 16.5 mm ± 0.5 SD (293).
Eggs are significantly smaller in first clutches than in subsequent clutches, and egg size is inversely related to total clutch size (266).
In southern Ontario, mean 4.9 g (n = 16) (41).
From Bent (62): Ground color ranges from grayish white to buffy white to greenish white. Speckled or spotted with pale gray to medium brown marks. In most cases, spots are distributed over the entire shell, but tend to concentrate at larger end of egg. Speckling varies from sparse to thick, obscuring ground or forming blotches. Last egg in each clutch is always more lightly marked with spots and streaks than the others (67; D. Scott, personal communication). Abernathy and Peer (309) noted significant variation among eggs in reflectance in both the near ultraviolet and visual color spectrums. Reflectance in eggs varied in the near ultraviolet range peaking at ~300 nm, then decreased to a low at ~350 nm, and then rose through the visual range, with 4 successively higher peaks, the last and highest at ~700 nm.
Smooth, somewhat glossy.
Winters (268) found no differences in egg-yolk testosterone across eggs from first clutches of the breeding season with known laying order. However, egg-yolk carotenoid content varied with highest levels of carotenoids found in first laid eggs, and with lesser, and equal, amounts in second and third eggs. Carotenoids assessed were canthaxanthin and beta-carotein (268); other types likely occur and need assessment.
Clutches include 1–5 eggs; reported averages include: 2.78 eggs in southern Ontario (n = 254 clutches; 301); 3.31 eggs in Kansas (range 3–5, n = 25 clutches; 310); averages of 2.4 to 3.22 eggs across 9 study sites (311); 3 eggs in Tennessee (100); and 2 eggs in Iowa (277). Reported single-egg clutches may have suffered predation undetected by researchers. See Demography and Populations: Measures of Breeding Activity.
Begins 1–8 days after nest completion. According to Kinser (67), 1–8 d (mean 2.4, n = 25); according to Lemon (293), 1–5 d (mean 2.04, n = 23). Female lays 1 egg/d (100, 293, 67, 268), usually early in morning; mean of 69.7 min ± 13.2 SD after sunrise (n = 10 females, each contributing 1 oviposition record; 312); most times between 0450 and 1000 (177, 288, 67). Interval from nest completion to initiation of egg-laying shortens as breeding season progresses (67). Male guards female while she is fertile; see Behavior: Sexual Behavior.
No indication that females replace eggs lost to predation; when entire clutch is lost, builds new nest, and may even do so after partial clutch loss (JMJ). Up to 8–10 clutches may be initiated in a breeding season (67, 43, 99), although seldom are > 2–3 successful. See Demography and Populations: Measures of Breeding Activity.
Intraspecific egg-dumping appears to be rare. In Ohio (75), DNA-fingerprinting confirmed egg-dumping in two years: 2 of 48 nestlings in 1 of 20 nests in 1994, and 1 of 45 nestlings in 1 of 19 nests in 1995. In each case, male was identified as genetic father, but female attending nest was excluded as genetic mother. In a Mississippi population, during observations of egg laying and egg marking for laying order, no behavioral evidence of intraspecific brood parasitism was observed (268, 19).
Onset of Broodiness and Incubation in Relation to Laying
True incubation begins on day last egg is laid (100, 67), although female occasionally sleeps on nest after second of 3 eggs is laid (177). From Kinser (67), females (n = 7) remained on nest for average 15 min (range 7–22) during visit in which first or second eggs were laid in 3-egg nests. These females sat on nest for 3–6 periods averaging 38 min, mostly in afternoon, during first two days of egg-laying. They usually stayed on nest and initiated incubation after the third egg was laid.
Reported only in female; around 33 mm maximum diameter (313). Approximately oval, but precise shape and location not described. Assessment of females captured during breeding period found incubation patches on the lower half of the abdomen that were concealed by feathers from surrounding feather tracts (JMJ, MSD).
Lasts 11–13 d (314, 278, 100, 293, 67). Average 12.8 d ± 0.32 SD for 27 nests in southern Indiana, possibly slightly longer early in breeding season (67); average of 12.3 d for 16 nests in southern Ontario (41).
Roles and Attention to Eggs and Incubating Mate
Incubation apparently by female alone; males have been observed to sit on nests for short periods, though the extent of contact between the body and the eggs is unknown (62, 259). Male brings food to incubating female, either at or away from nest (100, 67, 272). Vocalizations may coordinate feeding visits by male (see Sounds and Vocal Behavior: Vocalizations). In southern Indiana, males fed incubating females about 3 times/h (combining feedings at and away from nest; no information given on number of pairs or hours of observation; 67). In an Ohio population, males fed females at a rate of 0.62 ± 0.40 feedings/h with a range of 0–1.4 feedings/h (n = 33 pairs); feeding rates were not impacted by day of incubation nor indicated by male ornamentation (272). In male removal experiments, incubating females did not abandon their nests when their mates disappeared; rate of nest destruction by predators was higher during incubation periods with male present, but lower during nestling periods with male present (294).
Incubation Rhythm; Duration of Attentive Periods
Few published data. During observations of 1 nest on day 7 of incubation (10 July, southern Indiana), female left nest a total of 21 times between 0510 and 2020, for periods averaging 9.4 min (range 2–15) and totaling 30% of daylight hours (67). Periods on nest averaged 35.2 min (range 2–112). Another female was reported to leave nest 11–12 times/d (315: 220, reporting data from W. E. Schantz; location and day of incubation not specified). In an Ohio population, females were observed on 5 consecutive days for 1 hour periods each day (days 3–7 of incubation); some females did not leave the nest during the hour of observation, while others left for up to 30 min, with up to 6 instances of leaving the nest/h (99). In a central Ohio population, females (n = 125) incubated for an average of 31 min ± 1.73 SE (range 0–60) over a 1-hour observation period when air temperatures were at least 10°C (296). Female ornamentation was not found to co-vary with incubation behavior (99).
Hardiness of Eggs Against Temperature Stress; Effect of Egg Neglect
Preliminary Events and Vocalizations
Bump appears on surface of egg, with no break in shell, approximately 12–16 hours before hatching (67). Vocalizations of hatching young, if any, not described.
Shell-Breaking and Emergence
Based on 278, 100, and 67. Most eggs hatch early in morning. Chick generally takes 12–24 hours to break through shell, although one report of 20 minutes from first break in shell until female carried shell away from hatched nestling. In 3-egg clutches, all 3 eggs usually hatch in same day. Second egg laid may hatch before first, and third before second.
Parental Assistance and Disposal of Eggshells
Based on 278, 100, and 67. Rarely, female assists in hatching, by pulling or even occasionally breaking shell away from nestling. Either parent may eat eggshells or carry them away; one female fed shells to newly hatched young.
Condition at Hatching
Altricial; naked except for sparse fine gray down along feather tracts. Eyes closed. Able to hold head up and open mouth. Skin transparent, giving chicks a yellowish coloration. Gape red-orange, with yellow edge in region where mandibles join (rictal flanges).
Young Brown-headed Cowbird nestlings remarkably similar, but down light buffy yellow to white; rictal flanges white in eastern subspecies (ater) and central subspecies (artemisiae), but yellow in at least some western obscurus (316).
Growth and Development
In southern Ontario, mean hatchling mass 3.5 g (n = 10) ( 41). Nestling mass follows sigmoid growth pattern in an Ohio population: mean nestling mass on day 1 (n = 6), 6.3 g ± 0.6 SD; day 2 (n = 10), 9.5 g ± 0.8 SD; day 4 (n = 15), 16.6 g ± 2.2 SD; day 6 (n = 17), 23.1 g ± 2.6 SD; day 8 (n = 8), 25.8 g ± 2.1 SD. Mean tarsus length: day 1 (n = 2), 11.06 mm ± 0.0 SD; day 2 (n = 2), 13.0 mm ± 1.4 SD; day 4 (n = 8), 17.9 mm ± 1.1 SD; day 6 (n = 10), 22.8 mm ± 1.4 SD; day 8 (n = 4), 24.9 mm ± 1.2 SD (42, SUL). Mass gain for days 1–6 is higher for nests with a single nestling than for nests with ≥ 2 nestlings (266).
Nestlings remain inactive until parent arrives with food, then stretch neck upward and gape. Nestlings do not compete for food other than by begging competitively when parent is present. Begging is loud by day 5; will beg if nest is disturbed. By day 8, alert, and handling may cause premature fledging (SUL, JMJ).
Nestling physiology unknown; on basis of decrease in brooding (see Parental Care: Brooding), chicks probably begin to regulate their body temperature on day 3.
Young are brooded exclusively by female throughout nestling period, for decreasing amounts of time as they get older. Brooding on day 0 (day of hatching), day 1, and day 2 may be almost continuous. Mean brooding duration for females in an Ohio population: day 3 (n = 17 nests), 29.0 min/h ± 14.7 SD; day 4 (n = 19), 21.9 min/h ± 20.3 SD; day 5 (n = 23), 14.2 min/h ± 18.5 SD; day 6 (n = 22), 3.1 min/h ± 7.1 SD; day 7 (n = 21), 6.8 min/h ± 16.6 SD; day 8 (n = 19), 5.3 min/h ± 11.8 SD (SUL).
In Indiana, shading nestlings from sun is infrequent, but female will shade during extreme high temperatures, standing over nest with wings slightly spread, maintaining position for 5–12 min (67); shading behavior also observed in late season nests in a Mississippi population (JMJ).
Commences soon after hatching. As during incubation, early in nestling life (first 2 days) male may bring food to female either at or away from nest (100, 67, 99), male feeds nestlings directly as they age. Published feeding rates range from 2 visits/h (294) to 4.7 visits/h (287); SLH observed at least 8 feeding visits (11:05–12:05) on day of hatching at a nest with 2 nestlings. In an Ohio population (28), feeding rates were higher for larger than for smaller broods; in 23 pairs, males fed nestlings at higher rates (2.3 visits/h) than did females (1.8 visits/h). Feeding rates increase as nestlings age (28, 15). Male proportion of feeding visits varied from 33% to 76%. In same Ohio population (29), males fed proportionately more as nestlings aged; mean 40% of feeding visits on day 3 and 60% on day 8. Feeding effort by mates can be correlated (272), with mating of good providers to good providers, although this is not true for all populations (30). Feeding visits/hour were positively correlated with brood size (n = 27 nests; 266). Filliater and Breitwisch (28) found that females with large broods have a lower per nestling feeding rate; however, this was not found by Jawor et al. (15) when using similar methods and the same population. There was no correlation between a male’s rate of bringing food to the incubating female during incubation, and his later rate of bringing food to the nest for nestlings during the nestling period (272). In a Mississippi population, testosterone levels were not found to co-vary with feeding rates (30) in males or females. Breitwisch et al. (269) recorded behavior of a bigamously mated male cardinal: the bigamous male fed nestlings at both nests at rates similar to a male caring for one set of nestlings (his summed feeding rate was therefore double that typical of a male caring for one set of nestlings).
Nestlings are fed primarily insects. Because cardinals transport food deep in their bills and only large items project beyond the margins, it is difficult to observe and identify food types being carried (see Diet and Foraging: Diet). Parents may occasionally feed by regurgitation (317; R. Breitwisch, personal communication; JMJ), but they usually bring in whole items that they manipulate in the bill before feeding them to nestlings (100, MSD, JMJ).
In Indiana, male removal experiments at nests from which Brown-headed Cowbird eggs were removed by the experimenter, showed no significant difference in nest failure between nests with the male present and nests with the male absent (294). In successional old field habitat with shrubby borders, of 34 nests with the male present, 82% failed, compared to 86% of 22 nests where the male had been removed. On an urban university campus, among 27 nests with the male present, 63% failed, compared to 80% of 5 nests where the male had been removed. Almost all failures were due to predation. Females increased feeding rates to compensate for their mate's absence. There was no brood reduction; average daily weight gain of nestlings was only slightly higher in 8 nests in successional habitat with males present, than in 7 nests with males absent; among campus nests, average daily weight gain of nestlings was significantly higher in 13 nests with the male present, than in 5 nests with male absent. Jawor and Breitwisch (272) found that male nestling provisioning rate did not covary with reproductive success in unmanipulated nests.
Nestlings defecate in the nest. Both parents remove fecal sacs after feeding nestlings, either ingesting them (until nestling day five) or carrying them from the nest. Female removes more fecal sacs than male (100, SUL). Tremble-Thrusting behavior also seen: Female thrusts her bill deep into nest cup with a trembling motion, only during brooding; may help rid nests of parasites (67; see Demography and Populations: Disease and Body Parasites).
One report of a juvenile bringing food to nestlings and to the adult female at the same nest, and carrying away “what seemed to be a dropping” (318: 50). Rare reports of 2 adult females incubating at the same nest, sometimes simultaneously while facing in opposite directions (315: 206, 319, 293, 320). In 2 such cases, eggs were known to hatch; at 1 nest, both females and a male fed the nestlings (320). In another case, in which no eggs hatched, the females had different mates, and the second female added her eggs and joined the first female on the nest 7 d after the first female had begun incubation (319).
Brood Parasitism by Other Species
Identity of Parasitic Species
Frequency of Occurrence, Seasonal or Geographic Variation
Comprehensive data limited to Ontario and Ohio. In southern Ontario (1955–1961), highest parasitism 30 April–2 July, when 71–100% of nests parasitized; mean number of Brown-headed Cowbird eggs per parasitized nest ranged from 1.0 to 3.3 (n = 187 parasitized nests, weekly means calculated 23 April–30 July; 38). An overlapping data set from May and June, 1960–1968, in southern Ontario showed 81% of 85 nests parasitized, and a mean of 1.8 cowbird eggs/nest (39). For 1955–1968 in same southern Ontario population, among 106 nests examined 24 April–2 July, the number of cowbird eggs present was: 0 eggs in 19 nests (18%), 1 egg in 37 nests (35%), 2 eggs in 24 nests (23%), 3 eggs in 14 nests (13%), > 3 eggs in 12 nests (11%); mean 2.1 eggs/nest (41).
In Ohio (1993–1995), Brown-headed Cowbird eggs were found in 55 of 115 nests (47.8%) examined 24 April–13 July; mean 1.3 eggs/parasitized nest ± 0.6 SD; highest percentage of nests (75%) parasitized in early May (42). Parasitic frequency and intensity were highest early in season in both southern Ontario and Ohio, perhaps because of availability of other hosts later in season; in addition, Northern Cardinal continues to breed after cowbirds have stopped laying (293). A study of a separate population in Ohio found seasonal and locational impacts on parasitism; early nests located away from habitat edges were less likely to be parasitized, whereas late nests located away from habitat edges were more likely to be parasitized (323). Across forested regions of Missouri, frequency of parasitism of Northern Cardinal nests declined from ~22% to ~10% over a 20-year period (1991–2010); statewide cowbird abundances also declined over this same time period (324).
Timing of Laying in Relation to Host's Laying
In southern Ontario, number of Brown-headed Cowbird eggs laid on successive days of Northern Cardinal laying (n = 142 eggs): prelaying (14%); day 1 (9%); day 2 (31%); day 3 (25%); day 4 (12%); day 5 (5%); from day 6 on (4%) (41).
Response to Parasitic Mother, Eggs, or Nestlings
In southern Ontario (39), nest attentiveness by Northern Cardinal may discourage laying by Brown-headed Cowbird. Percentage of nests 16 May–27 June with cardinal on or next to nest during census 0600–0759, just after the time when cowbirds usually lay eggs: day –1 (day before first cardinal egg laid; n = 17), 12%; day 1 (n = 31), 48%; day 2 (n = 33), 52%; day 3 (n = 25), 68%; days 4 and 5 (n = 30), 83%. During day –1 through day 2 (presumably before the onset of incubation), nest attentiveness was higher 0600–0759 than later in day, beyond the known laying time for cowbirds. Scott and Lemon (41) suggested that disappearance of cowbird eggs is more likely due to removal by other cowbirds than to removal by cardinal hosts. Nests rarely abandoned, even when cowbird lays before cardinal: 3 of 18 such nests were abandoned in southern Ontario (293, 41); cowbirds had also laid the first egg in the 2 parasitized nests (out of 55) that were abandoned in Ohio (42). Northern Cardinal occasionally buries cowbird eggs by adding new nesting material on top of them (41, 42). Observation in Ohio population of a female Northern Cardinal discovering a female cowbird at a nest where the cardinal had been incubating for at least two days; female cardinal did not attack female cowbird, but abandoned the nest immediately and was not observed on subsequent nest watches; a new nest for this female cardinal was found soon after (JMJ). Abernathy and Peer (309) altered ultraviolet reflectance by applying commercial sunscreen with 3% avobenzone to a small number of Brown-headed Cowbird eggs (n = 17) and Northern Cardinal eggs (n = 16) to determine adult cardinal response (either sex, ejection events not observed): neither cowbird nor cardinal eggs with reduced ultraviolet reflectance were rejected at a higher rate compared to eggs that were unmodified, suggesting that UV reflectance (or, in any case, the changes in UV reflectance caused by this avobenzone treatment) may not be impactful for cardinals recognizing cowbird parasitism or their own eggs in their nests.
Effects of Parasitism on Host
Loss of eggs from Northern Cardinal nests is associated with Brown-headed Cowbird parasitism. In Ohio during egg-laying period, 0.6 eggs lost/parasitized nest (n = 23 nests) versus 0.2 eggs lost/unparasitized nest (n = 18 nests); however, no significant difference in number of cardinal eggs at onset of incubation (2.4 eggs/parasitized nest ± 0.7 SD [n = 23 nests]; 2.7 eggs/unparasitized nest ± 0.6 SD [n = 18 nests]), or in number of cardinal nestlings hatched (2.1 nestlings/parasitized nest ± 0.7 SD [n = 28 nests]; 2.2 nestlings/unparasitized nest ± 0.8 SD [n = 21 nests]; 42); higher cardinal egg loss during egg-laying period in parasitized nests was partially counteracted by higher cardinal egg loss during incubation in unparasitized nests. Nestling cowbirds do not beg at higher rates than nestling cardinals and do not receive higher percentages of feedings (42). Aside from egg loss, nestling cowbirds do not appear to have a detrimental impact on cardinals during the nestling stage. Of 44 nests that fledged cowbirds in central Ohio, 39 also fledged cardinal young (from 2004–2007; D. Shustack and A. Rodewald, unpublished data).
Success of Parasite with This Host
Brown-headed Cowbird reproductive success in Northern Cardinal nests is very low. In southern Ontario (41), cowbird egg mortality was 85%, mostly because of predation of entire nest contents, removal of single cowbird eggs (probably by cowbirds or cardinals), or desertion of nests by cardinal after > 1 cardinal and/or cowbird egg had been removed. Reproductive success from laying to fledging (n = 148 eggs) was 5.4%. Cowbird nestling mortality was high for eggs that hatched after cardinals: 8 of 12 cowbird nestlings fledged when cowbird hatched before or with cardinal eggs, 1 of 9 cowbird nestlings fledged when hatched after cardinal eggs. Higher proportion of cowbirds fledged from cowbird-only broods (11 of 22 cowbird nestlings fledged) than from mixed broods (16 of 39). Body mass of cowbird nestlings “close to fledging” from cowbird-only broods was significantly greater (28.0 g ± 0.9 SD, n = 8 nestlings) than from mixed broods (24.8 g ± 1.4 SD, n = 8 nestlings). Cowbird nestling survival and fledgling survival were lower with 3 cardinal nestmates than with 1 or 2, suggesting one advantage gained by cowbirds that remove eggs from nests they parasitize.
Two instances observed (1 in Ohio, 1 in Indiana) of dead cowbird nestlings in cardinal nests that were known to have successfully fledged cardinals (JMJ). In one instance, adult cardinals were seen trying to induce the cowbird nestling to fledge (adults approaching nest with food in bill, but not delivering food to nestling cowbird), the cowbird nestling did not leave the nest and was later found dead in the nest.
Departure from Nest
Young depart nest at 7–13 d, though 9–10 d is most common when young are not disturbed (278, 100, 293, 62, 41). At fledging, young have small crest and very short tail; often they can fly, though only for short distances (100, 67, SLH, SUL, JMJ). Generally, depart nest in morning, less often in afternoon (278, 277, 67). Young leave on their own; parents may encourage young to depart by reducing rate of feeding at nest on morning of departure (67), offering food away from nest (277; JMJ), and/or giving chip calls to young (100, SUL). Young may or may not leave together; Kinser (67) reported 2 nests in which 3 young departed within 30 min of one another, but another 4 nests with approximately 20 hr between departure of first and last young.
Few data on growth of fledglings, which are difficult to find and catch. At day 10 after fledging, one brood had “distinct crests” and tails about 3.8 cm long; 3 days later, their tails had grown to 6.4 cm and they “approached the size of the female” (245: 11).
Association with Parents or Other Young
From Kinser (67), and others as noted: For first 11 days after fledging, young rarely move from branches on which they are perched; in one Indiana study, each fledgling was fed a mean of 8 times/hr (range 4–15, n = 60 hours of observation), with feedings usually in a series of trips in rapid succession. From about 12 to 20 days after fledging, young move around more, occasionally leaving parental territory, but still receiving almost all food from parents. After this, young continue to be fed at least occasionally until 25–56 days after fledging; last young of season receive food over longer period than earlier broods (315, 293). When just 1 young fledges, both parents feed it initially, but after ~12 days, female generally stops to start new nest (67). Prior to female's re-nesting, fledged brood may be divided among parents (280, 208); afterward, male feeds all young until next brood hatches (100), and occasionally for a couple of days longer (314). In southern Ontario, across breeding season, young are fed for average 32 d after fledging (n = 13 clutches; 293); in southern Indiana, for average 39.2 d after hatching (n = 16 clutches). Young may permanently leave parental territory by themselves, or they may be driven away.
Ability to Get Around, Feed, and Care for Self
Young fly well enough to evade capture by hand at or before 3 days after fledging (SUL, SLH), and “fly strongly” at 8 days after fledging (278). Daily survival rates increase substantially from 0.83 during first 3 days post fledging, to 0.97 or higher after day 3 (325). Young occasionally eat insects by themselves before they have been out of nest for 12 days (67); can attain independence from parental feeding 25–56 days after fledging. Using locations determined from radiotracking (n = 45 fledglings), fledglings selected locations with more vegetation cover than provided around nest sites or at random points. Fledglings were found lower in some substrates (e.g., 2.1 m ± 0.09 SD in honeysuckle [Lonicera] shrubs) compared to other substrates (5.2 m ± 0.20 SD) (325). Data from a subset (n = 21) of those radiomarked fledglings that survived at least 41 days showed that fledglings in more urban sites and locations with a greater amount of honeysuckle shrubs moved less far, compared to fledglings in rural sites and locations with less honeysuckle (210). Based on 95% minimum convex polygon analysis, fledglings had a natal range of 0.93 ha (0.13 SE), with fledglings from nests located farther from the forest edge having a larger natal range than fledglings from nests located closer to the habitat edge (210). See also Breeding: Immature Stage and Movement and Migrations: Dispersal and Site Fidelity for information on dispersal of young.
Ausprey and Rodewald (210) assessed home range of juvenile cardinals in relation to forest edge and presence of invasive Amur honeysuckle (Lonicera maackii) and found where honeysuckle cover was extensive, fledglings did not move far from the territories where they had hatched. Juveniles (up to 71 days post fledging) in more urbanized Ohio landscapes did not experience higher mortality rates compared to more rural landscapes (325). Thirteen of 20 radiotracked fledglings permanently departed the natal home range between 35 and 55 days post-fledgling; the remaining 7 fledglings did not permanently depart the home range during the 71-day observation period. Some fledglings made exploratory movements outside the natal home range during the fledgling period in advance of dispersal (210). See also Breeding: Fledgling Stage and Movement and Migrations: Dispersal and Site Fidelity for information on dispersal of young.
Immature birds may flock together. A flock of at least 18 hatch-year females, 11 hatch-year males, and 2 adult females were foraging on berries within 100-m-diameter area in Alabama 14–20 August (K. McGraw, personal communication).
Beak attains adult color 65–80 days after young hatch, although tip of upper mandible may remain dark for several months (100). Assessment of known age individuals in early spring and summer did not find first-year cardinals to be predictably different in ornamentation when compared to older individuals (113). See Appearance for information on plumages and molts.