Breeding

Pair Formation; Nest-Building

Pair formation and nest-building occur almost simultaneously, or at least within several days of each other. Pairs form at the colony; courtship not noted elsewhere. Pairs form during Feb (extreme s. Florida; Stevenson and Anderson 1994) to late May farther north (Bent 1926).

First Brood Per Season

Figure 3 . Earliest laying dates are from extreme southern and coastal Florida, including Feb (Girard and Taylor 1979) and Dec (Bent 1926), but more commonly early to mid-Mar (Jenni 1969, Smith and Collopy 1995). Other early dates are 5 Apr in Texas (Oberholser 1974), 10 Apr in S. Carolina (Post and Gauthreaux 1989), 15 Apr in N. Carolina (McCrimmon 1978), 24 Apr in Maryland (Robbins and Blom 1996), and 8 May in Virginia (Kain 1987). Latest laying Jun, rarely Aug, in Florida (Bent 1926, Sprunt 1954), 23 Jun in Texas (Bent 1926), 5 Jun in Maryland (Robbins 1996), 20 Aug in Virginia (Kain 1987).

Mean laying date in coastal Everglades 31 Mar (Bancroft et al. 1994); in Atlantic coastal Florida, 87% of clutches completed between 22 Mar and 6 Apr (Maxwell and Kale 1977a). In Louisiana, laying peaks early Mar–early May (Bent 1926); in N. Carolina, 15 Apr–6 May (McCrimmon 1978).

On s. Yucatán Peninsula (Sian Ka’an Biosphere Reserve), Lopez-Ornat and Ramo (1992) found extreme egg dates of 2 Mar–23 Jun, with timing of breeding generally similar to that in se. U.S. In Colombia, late Jun (La Guajira; Hilty and Brown 1986). In Guyana, eggs laid Feb–Jun; timing of breeding variable and cued directly by onset of rainy season (Llowe-McConnell 1967, Haverschmidt and Mees 1994). In Trinidad, Feb–Aug (ffrench 1991).

Intervals between eggs variable: 2 d between first 2 eggs; 1-d intervals for later eggs (see Eggs, below).

Mean hatching date of first chick in Florida Everglades is 22 d from laying of first egg (Frederick and Collopy 1988).

Young reach independence from parents at 50–59 d of age (see also Fledgling stage, below).

Second/Later Broods Per Season

Second broods possible, but evidence can also be interpreted as nest failure followed by renesting (Bancroft and Jewell 1987).

Although typically nests in mixed-species colonies, may be found in small (2–100 nests) monospecific colonies (Smith 1994, Frederick 1995), and occasionally nests solitarily.

Selection Process

Male picks nest territory often before females appear at colony (Rodgers 1978a), and may establish nest site within territory before pair bond is initiated.

Site Characteristics

Nests in monospecific or multispecies colonies; in the latter, on edges, usually in denser vegetation than other species; likely to be in conspecific groups. Nests in dense, well-shaded shrubs and small trees between 0.15 and 3.7 m above ground or water. Nests preferentially in densest vegetation (1.5–2 m tall; Rodgers 1978a), and nesting seems to progress during breeding season from densest vegetation on periphery to sparsest in center of colony (Maxwell and Kale 1977a).

Uses wide variety of generally woody vegetation, including small oaks (Quercus spp.), red maples (Acer rubrum) and other wetland hardwoods, bald cypress (Taxodium distichum), Yucca sp., groundsel bush (Baccharis halimifolia), black mangrove, white mangrove (Laguncularia racemosa), buttonwood (Conocarpus erectus), red mangrove, willows (Salix sp.), wax myrtle (Myrica cerifera), buttonbush (Cephalanthus occidentalis), mesquite (Prosopis juliflora), huisache (Acacia farnesiana), prickly pear cactus (Opuntia); on salt marsh islands, flattened mats of needle rush (Juncus roemerianus). Nest heights vary between 0.14 and 4 m above ground, depending on vegetative structure, competition for nests, and mix of other nesting species (Bent 1926, Jenni 1969, Maxwell and Kale 1977a, Rodgers 1978a, Burger 1979, Girard and Taylor 1979, Post 1990).

In N. Carolina, nests generally below canopy in trees and shrubs; mean height of 2.03 m above ground (n = 39 nests; McCrimmon 1978). Mean nest tree diameter 6.2 cm; diameter of branch supporting nest 3.5 cm (n = 39 nests). Vegetative density above nest was high by comparison with other species. Mean distance to open space was 6.9 m and distance to colony edge was 15.8 m.

Of 28 nests in an inland n.-central Florida colony, 11% were in red maples, 29% in buttonbush, 39% in box elder (Acer negundo), and 4% in willow (Jenni 1969). In coastal Florida, Maxwell and Kale (1977a) reported 64% of nests in black mangrove, 28% in white mangrove, and 7% in red mangrove. In S. Carolina, nested farther out on limbs than do other species of herons, and nests tended to be on smaller, springier branches (Post 1990).

Construction Process

Male begins construction by forming loose platform of large twigs as foundation before pairing with female. Copulation seems to stimulate collection of twigs by males. Males usually collect twigs, females remain at nest site and work twigs into nest; Greeting Ceremony (see Behavior: agonistic behavior, above) frequent during exchanges of nest material. Female works twigs into nest structure using angled, sideways motion. Activity more likely in early morning and late afternoon (Jenni 1969). Between first copulation and laying of first eggs: 4–6 d. Jenni (1969) recorded 4–5 d for construction of 2 nests.

Structure And Composition Matter

Foundation is made of twigs about 1 cm in diameter and 30–60 cm long. After pair forms, construction is continued with twigs 0.5 cm in diameter and <30 cm long; no green material in nest (Rodgers 1977). In Louisiana, finishing material was fine twigs and cordgrass (Spartina) stems. Gathers most twigs from ground in immediate vicinity of nest (Jenni 1969), and often walks down angled branches and stems to ground during nest-building and incubation (Frederick and Collopy 1989a).

Dimensions

Total diameter <30 cm; slight depression in center (Portnoy 1977, Rodgers 1978a). No recognizable differences between nests of Snowy Egret, Tricolored Heron, and Little Blue Heron.

Microclimate

Generally shaded and below canopy, with little exposure to direct sun or aerial predators (McCrimmon 1978, Bjork 1986). No measurements of nest temperature or humidity available.

Maintenance Or Reuse Of Nests, Alternate Nests

Nests generally do not last between seasons, and are rebuilt annually, often appearing in same area of colony and same crotch of tree as in previous season. Abandoned nests may be reused within season. Failed nests and those skewed by accidents often provide foundation for new nests, sometimes producing a large, bulky structure.

Nonbreeding Nests

None recorded (Bent 1926, Sprunt 1954, Jenni 1969, Rodgers 1977, 1978a).

Shape

Ovate to oval; elliptical ovate or elliptical oval (Bent 1926, Sprunt 1954, Palmer 1962).

Size

Bent (1926) reported that 41 eggs from North America averaged 44.1 x 32.3 mm. In Florida Everglades, Frederick and Collopy (1988) found, in 1986, that 162 eggs from 49 clutches (all eggs in each clutch) averaged 44.44 mm ± 1.64 SD x 32.28 ± 1.12; in 1987, 605 eggs from 194 clutches averaged 44.63 ± 1.75 x 32.22 ± 0.96. In Texas, average size 43.9 x 32.3 mm (no n or SD given; Oberholser 1974). In Trinidad, 8 eggs averaged 40 x 30 mm (ffrench 1991), and in Suriname, 40.9–42.8 x 30.6–30.9 mm (Haverschmidt and Mees 1994).

Mean lipid content of 153 eggs from e. North America was 6.29% ± 0.11 SD (Ohlendorf et al. 1979), and of 5 eggs from Louisiana, 5.9% (Faber and Hickey 1973).

Mass

In Suriname, fresh eggs weighed 20.7–21.5 g (Haverschmidt and Mees 1994). No other egg masses available.

Color

Ground color is pale greenish blue, although descriptions vary. Variation includes pale Niagara green, lichen green, pale greenish blue, and blue with greenish cast (Bent 1926, McVaugh 1972).

Surface Texture

Smooth.

Eggshell Thickness

Pre-1947 (pre-DDT) mean was 0.240 mm ± 0.013 SD (n = 8); post-1947 (post-DDT), 0.236 ± 0.03 SD (n = 5); no significant differences between the 2 periods (Faber and Hickey 1973, Ohlendorf et al. 1979). This species does not appear to have been exposed to high enough levels of DDT to have experienced >4% eggshell thinning (Faber and Hickey 1973).

Clutch Size

Range 3–5 eggs; 3–4 the most common in North America (see Appendix 2). Bent (1926) cited 6 and 7 in rare cases, and Jenni (1969) found up to 9. In Florida, 3–4, with mean of 3.58 from museum sets (Stevenson and Anderson 1994). In Everglades, clutch size found to be significantly larger in freshwater habitat than in brackish or marine habitats, even when date of laying was controlled for (Frederick et al. 1992). In Maryland, 3–5 (Robbins and Blom 1996); in Delaware, 3.1–3.5 over 3-yr period (Wiese 1979). Early clutches may be larger; at Moore Creek, FL, early clutches averaged 3.1, late clutches 2.6 (Girard and Taylor 1979). Clutch size declines to 2–4 in Central America and Mexico (Howell and Webb 1995); 2–3 cited for Suriname (Haverschmidt and Mees 1994).

Egg-Laying

Generally begins after nest mostly completed, but material added to nest throughout egg-laying and incubation. During egg-laying, males guard nest, territory, and female—during courtship and early egg-laying, usually without breaks for feeding (Rodgers 1978a). In n.-central Florida, mean interegg interval of 1.7 d ± 0.10 SD (n = 40 intervals; Jenni 1969). First and second eggs laid on consecutive days about half the time, and on alternate days half the time; frequency of consecutive day intervals increases with successive eggs. In coastal Florida, eggs laid on average every 2.1 d ± 0.08 SD (n = 47); intervals are slightly less later in clutch (Maxwell and Kale 1977a).

Eggs are replaced continuously, up to 5 in a row, as they are removed by predators (Jenni 1969). Lays replacement clutch when primary clutch destroyed entirely, beginning 2–10 d (mean 5.3) after destruction (n = 8 nests; Maxwell and Kale 1977b).

Some evidence for low prevalence of intraspecific nest parasitism. Maxwell and Kale (1977a) noted a single egg present in a nest for 7 d, followed by 3 additional eggs; all eggs hatched. Other evidence includes several cases of egg additions during incubation in Everglades (PCF). Exceptionally large clutches reported by Bent (1926; 6 and 7 eggs) and Jenni (1969; up to 9) may be further evidence of egg-dumping. May lay eggs in nests of other species (see Brood parasitism, below).

Onset Of Broodiness And Incubation In Relation To Laying

Before uninterrupted incubation, adults may sit on eggs sporadically. Beginning of effective incubation is irregular, typically starting the day after second egg is laid, or the day the third egg is laid (Jenni 1969). In Florida, incubation began with laying of second egg (55% of nests) or first egg (21%; Maxwell and Kale 1977a).

Incubation Patch

No information.

Incubation Period

Laying of first egg to hatching of first egg computed as mean of 22 d ± 0.74 SD from Everglades data (n = 15 nests; Frederick and Collopy 1988). In n.-central Florida, mean of 23.8 d ± 0.19 SD (n = 10 nests) from laying of last egg to hatching of last egg (Jenni 1969); in coastal Florida, mean of 23.3 d ± 0.21 SD (n = 20 nests) from laying of first egg to hatching of first egg (Maxwell and Kale 1977b).

Parental Behavior

Both sexes incubate. One parent remains on nest almost continuously during incubation. Early-morning incubation is most intense; during late morning and afternoon, parents frequently stand up. Eggs may be turned regularly (Frederick and Collopy 1989b).

Periods of duty range from 1 to >14 h, most commonly 2–6 h (Rodgers 1978a). Incubation exchanges are frequently in midmorning, midafternoon, and early evening; rarely in early morning. No information on relative contributions of incubation times by males and females. Incubation exchanges include Greeting Ceremony (see Behavior: agonistic behavior, above), calling between mates, and presentations of twigs (Rodgers 1977).

Hardiness Of Eggs Against Temperature Stress; Effect Of Egg Neglect

As measured by thermistors inside similarly sized Cattle Egret eggs in direct sun, temperature increases to probable lethal limits in 30 min–1 h during the summer in Florida (PCF). No information on egg neglect, except that high hatching rates (see Hatching, below) are common in context of characteristically delayed incubation.

Preliminary Events And Vocalizations

Eggs show small pinpoint fractures and pip holes 24–30 h before hatching (PCF). Young emit high-pitched, peeping sound as they hatch, and adults often peer at eggs.

Shell-Breaking And Emergence

No information on time of day of hatching. Hatching generally takes 24–36 h, but little direct measurement. In Florida, clutches averaged 3.1 d (range 1–5, n = 76 nests) to complete hatching, independent of number of eggs in clutch (Maxwell and Kale 1977a). All chicks hatched on same day in some clutches. Time interval between hatching of successive eggs increased with laying order from 0.5 d for first and second eggs to 1.8 d for third and fourth eggs.

Parental Assistance And Disposal Of Eggshells

Parents drop eggshells over side of nest; no parental assistance with hatching noted, although parents frequently rise off eggs as they are hatching, and are attentive to calls of hatchlings (PCF).

In coastal Florida, 1.6% of eggs disappeared during incubation, and 1.0% of those that remained failed to hatch (Girard and Taylor 1979). In Florida Everglades, between 1.4 and 18% of eggs present at time of hatching failed to hatch (Frederick 1995; see Appendix 2).

Condition At Hatching

Semialtricial; wet, with downy feathers over much of body. Chicks can hold head up for brief periods and vocalize (peeping). Legs initially small and not functional for any type of locomotion. Mass at hatching unknown. At hatching, bill averaged 12.7–15.8 mm, wing 15.8 mm, total body length 101.6–107.9 mm (n = 65; McVaugh 1972). Top of head covered with long hairlike plumes, army brown to fawn, mixed with shorter gray down on head; back has long, soft, dark gray down; under neck, abdominal region, and femoral tract is coarse, scant, white down (McVaugh 1972).

Eyes partly open at hatching. Bill, feet, and naked skin light green to yellowish. Exposed skin flesh-colored under neck, deep flesh or fleshy gray in auricular region and nape, bright blue to bluish gray around eyes. Deep gray skin covers crown, and remaining body skin varies from fleshy gray to medium gray. Upper mandible fleshy gray to warm gray; black-tipped, with dark gray line only on cutting edge of upper mandible. Pale pink inside nostril; egg tooth present. Lower mandible flesh-colored with small dark tip. Mouth-lining yellow pink to pink. Eye deep-set in protruding dark gray eye-ring. Iris light gray to off-white; pupil black. Tarsus and toes pale bluish pink on top and flesh-colored underneath; varying intensity above. Toenails are pale ivory and hallux toenail darker (McVaugh 1972).

Capable of only short, jerky movements of head and upper body at hatching; within first day can move head toward parent and may be able to receive some well-digested food from parent’s bill.

Growth And Development

See McVaugh 1972 for detailed body measurements and descriptions of development.

Physical Ability. Just after hatching, nestling can hold head up and move in short, abrupt jerks; little or no reaction to humans at this stage. By 5 d, capable of movement in nest; calls frequently but not when handled by humans. By 11 d, young can climb from nest using bill, wings, and feet; sometimes perch on one side of nest; spend more time in nest than out of it; show fear when handled or approached by humans; call intermittently with harsh note. By 17 d, perch above or to one side of nest and return only to be fed; flee predators and humans by climbing; no call notes heard. At 24 d, young perch away from nest, usually in tops of bushes or trees all day and do not return to nest to be fed. Climb with wings and feet; call at approach by parent; some inter- and intraspecific quarreling and bill-jabbing. By 30 d, tend to perch in intraspecific groups; defend perch area. No call notes heard at this point.

Plumage. At 5 d, head covered with long brownish red down; brownish gray down on back; white down on femoral tract and sparse white down on abdomen. Juvenal feathers emerging; egg tooth still visible; iris gray to off-white; scales developing on tarsi and toes. By 11 d, some Juvenal feathers tipped with long white down, others emerging. Scales well formed on tarsi and toes. Upper mandible dark gray proximally. By 17 d, head covered with long faded white down; some dark gray down remains on back; reddish brown feathers just emerging from sheaths on upper half of neck; lower half well emerged. White underneck-stripe becoming defined. Primary and secondary feathers dark gray; tarsus and toes light gray green. By 24 d, head, neck and body covered with feathers, most of which retain long reddish down. Top of head and neck reddish or brownish red; mantle medium reddish gray; back medium gray; white feather stripe on front of neck well defined; underparts all white. Nails light-tipped and medium horn. By 30 d, some down left on head, otherwise covered by Juvenal feathers; primaries, secondaries, and rectrices medium gray; some pin-feathers on spinal tract. Iris off-white, pupil black, and eye-ring medium gray.

Molt into Juvenal plumage largely complete by 30 d (McVaugh 1972), though molt may continue after fledging (approximately 56 d). Molt into Basic I plumage gradual, through first fall and early winter. No information on ages when contour feathers appear on different tracts, or on sequence of molting among tracts.

Mass Increase. See Black et al. 1984; a near-exponential increase in mass to 17 d. After this, growth curve appears to be sigmoidal, with an apparent upper inflection point at 300–350 g, though data are lacking for latter part of pre-independence period (30–60 d).

Growth of Body Parts. As with other Egretta herons (Werschkul 1979), rapid initial growth of legs, bill, and especially feet, which probably aid in early climbing and movement. At 1 d of age, wing length 101.6–107.9 mm, tarsus 19.5–22.2 mm. The following are mean measurements. At 5 d, wing 31.8 mm, bill 20.6, tarsus 28.6, middle toe 31.8. At 11 d, wing 31.8 mm flattened, bill 30.2, middle toe 55.6, tarsus 39.7. At 17 d, wing 85.7 mm flattened, bill 42.9, middle toe 69.8, tarsus 60.3. At 30 d, wing 184.1 mm flattened, bill 69.8, middle toe 82.5, tarsus 88.9. (n = 65 nestlings; McVaugh 1972).

Control of Body Temperature. Thermoregulatory ability develops quickly; by approximately 14 d of age, almost completely able to survive without parental brooding.

Behavior. Food begging, forward threat, preening, and aggressive vocalizations well developed by 14 d.

Locomotion. Young can swim well for short distances by 14 d of age (Bent 1926); first flights at 25–30 d (Frederick et al. 1992). No information on learning process.

Brooding

Begins immediately upon hatching, waning to 12 d of age. No information on brooding rhythm.

Feeding

Chicks initially fed at 1–2 d of age; achieve complete independence from paren-tal feedings by 50–56 d of age. Both sexes feed young, though relative contributions are not documented.

Method of Feeding. For first 1–2 d, chicks feed by pecking at pile of food regurgitated by parent near chick’s head on floor of nest. By 2–3 d, chicks are strong enough to hold head up and take direct regurgitation from parent’s gape. After 1 wk, chicks begin grasping bill of parent, while adult extends mandibles downward with dorsal surface of upper mandible facing offspring. Chick grasps upper mandible and pulls downward; food more or less pours at an angle into chick’s open gape. After 2 wk of age, parents can no longer evade the constant begging and grasping of chicks, and they do not spend time on the nest except when actively regurgitating. After 4 wk, young approach adults near nest for feeding; both adult and young must flap wings to maintain balance. Between 4 and 6 wk, young pursue adults on short flights around colony and are usually fed away from nest, an activity that undoubtedly aids in development of flight abilities.

Food of Young. Initially semidigested liquid food regurgitated from parent in small amounts. After 5 d, mostly undigested small fish. Most reports in Appendix 1 are from boluses regurgitated from nestlings and young birds. Small killifishes and live-bearers are the most common prey items.

Rate of Feeding. Frederick and Powell (1994) estimated that 116,911 kJ are necessary for entire brood, over 55-d period. Four to 5 feedings/d up to 7–8 wk, at which point parental care ceases. Feeding trips at irregular times of day (Rodgers 1978a). No information on amount of food brought per trip. Food appears to be apportioned among young by scramble competition, dominated by older chicks; parents do not appear to intervene on behalf of youngest chicks.

Nest Sanitation

No obvious form of nest-cleaning; young defecate in nest. Nests are usually quite porous, and feces drip out of nest bottom or dry quickly on nest material. No fecal sacs; young defecate liquid or semiliquid feces directly into nest throughout nestling period.

Carrying Of Young

No reports, although congeneric Little Blue Heron capable of carrying eggs (Rodgers 1978b).

No indication of cooperative breeding in this species (Rodgers 1977, 1978a).

Identity Of Parasitic Species

In Florida Everglades, 1 case of Little Blue Heron hatching in Tricolored Heron nest, 1 possible case of Great Egret (Ardea albus) egg laid in or transported to a Tricolored Heron nest (PCF). In coastal Florida, 1 case of Snowy Egret chick in Tricolored Heron nest (not known if it hatched there; Maxwell and Kale 1977b). The Snowy Egret was 3–5 d younger than the hosts and was outcompeted for food and died by 6 d of age. One well-documented case of Tricolored Heron nestling being hatched and reared by Snowy Egret parents in Florida; the egg appeared following a violent dispute over nest ownership between neighboring Tricolored Heron and Snowy Egret pairs, during which original clutch of Snowy Egret was ejected by Tricolored Heron pair. The Tricolored Heron egg must have been laid during the short period before the Snowy Egret pair regained the nest (Morgan and Morgan 1995).

Response To Parasitic Mother, Eggs, Or Nestlings

Parents will feed and rear Snowy Egrets and Little Blue Herons; likewise Snowy Egrets will rear Tricolored Heron nestlings (McIlhenny 1934 in Rodgers 1978a, Morgan and Morgan 1995, PCF).

Effects Of Parasitism On Host

Probably small; on 2,113 nest-days (465 nests) observed during egg-laying and 12,289 nest-days (841 nests) during incubation, parasitism was found to occur at <0.1% of nests (PCF).

Success Of Parasite With This Host

Not measured.

Departure From Nest

By 17 d of age, young can perch at side of nest; by 21 d, usually perch above nest (McVaugh 1972, ffrench 1991, Frederick et al. 1993). By 24 d of age, young return to nest platform only to be fed. Between 24 and 60 d, young are fed in tops of trees by adults as young develop flight abilities. Age at independence from parental feedings and departure from colony were measured with radio-tagged chicks in Everglades: mean age 59.2 d ± 1.20 SD (n = 32; Frederick et al. 1993), and 51–56 d (n = 6; Bancroft and Jewell 1987).

With first instances of leaving nest, climbing abilities are well developed; no flight abilities; fully feathered, but many feathers still growing. At independence from adults, have full flight abilities; complete or nearly complete Juvenal plumage; foraging and perch defense behaviors well developed.

Parents often lead young around colony on long flights before feeding in final 2 wk of fledgling stage. This behavior suggests that young eventually follow foraging adults (possibly parents) from colony to foraging grounds on first flights away from colony.

Growth

No information on mass at time of independence, but plateau in mass for nestlings suggests adult body mass or slightly above (Black et al. 1984).

Association With Parents Or Other Young

At 3–4 wk of age, young often beg from nonparents but are rarely fed (Rodgers 1978a). No evidence of close association of young and parents or of broodmates following independence.

No information.