Breeding

Pair Formation And Nest-Building

Arrives in Delaware and s. New Jersey by late Mar; New York Harbor by early Apr (Parsons 1994, 1995); Massachusetts by mid-Apr (KCP). Occupied breeding colony by mid-Apr in New Jersey (Burger 1978b; see Migration: nature of migration in the species, above). Nest construction begins with courtship and continues at least through incubation.

First/Only Brood Per Season

Figure 3 . Peak laying and hatching occurred in Delaware Bay 25–28 Apr and 17–21 May, respectively (Parsons 1995); mid-May in New Jersey (Burger 1978b). Mean hatch dates in New York Harbor 30 May–2 Jun (Parsons 1994). Mean hatch date (4 yr) on Cape Cod, MA, 14 Jun (KCP). Nested from Nov to Apr in Venezuela (de Visscher 1977). Incubation period 20–21 d.

Second/Later Brood(s) Per Season

Second brood not reported. Will renest if first attempt fails (Palmer 1962). May select new colony site for renesting (Ogden 1996).

Selection Process

Advertisement displays and nest-site selection are performed by males on stable sites within the defended nesting territory (see Behavior: sexual behavior, above). Males engage in slight to moderate nest-building prior to pair formation (Palmer 1962). Often nests are constructed primarily by females at one of these locations, which may include an old nest (Parsons 1985). Uses old nests as well as constructing new ones (TLM).

Microhabitat

Generally prefers isolated estuarine sites, including barrier and dredge spoil islands in East; estuarine, freshwater swamps, river bottomlands, and mangroves in s. U.S. and tropics; and inland lakes and rivers in w. U.S. (see Habitat: breeding range, above). Preferred nesting vegetation included Opuntia cactus in Texas (Burger 1979), privet (Ligustrum vulgare) in coastal New York (Burger and Gochfeld 1993), and a variety of other species from s. New Jersey to Boston Harbor including common reed (Phragmites communis); woody vines like blackberry (Rubus allegheniensis), greenbriar (Smilax spp.), and grape (Vitis spp.); shrubs like southern arrowwood (Viburnum dentatum), bayberry (Myrica pensylvanica), wax myrtle (Myrica cerifera), groundsel tree (Baccharis halimifolia), marsh elder (Iva frutescens), blueberries (Vaccinium spp.); and trees such as eastern red cedar (Juniperus virginiana), black cherry (Prunus serotina), sassafras (Sassafras albidum), American holly (Ilex opaca), gray birch (Betula populifolia), sweet gum (Liquidambar styraciflua), and black gum (Nyssa sylvatica; KCP, TLM).

Mean nest height and species diversity of larger wading birds were inversely related in 13 colonies in the Western Hemisphere, suggesting that nest height was subject to the Snowy Egret’s ability to defend sites (Burger and Trout 1979). Mean nest height was relatively lower in areas shared with Cattle Egrets in New Jersey (Burger 1978b). In 15 heronries from Argentina to New York, however, Burger (1979) found nest height to be closely correlated with vegetation height (r = 0.967). May prefer to nest near conspecifics rather than establish territories in vacant trees (Davis 1986).

In coastal n. Florida, studies of nest-site selection on a mangrove island found nest placement remaining the same with respect to distance from the shoreline (8 m; n = 71) as breeding season progressed (Maxwell and Kale 1977).

Site Characteristics

Characteristics of nest placement well-studied (McCrimmon 1978). Nest-site stability an important factor in explaining nest placement in 6 colonies (Beaver et al. 1980). Tree nests in s. New Jersey typically placed on branches away from trunk; those in woody vines or shrubs rest on top of vegetation (TLM). Mean nest height = 1.74 m (± 0.04 SE; n = 96 nests) in central Florida (Jenni 1969), 2.3 m (± 0.03 SE; n = 71 nests) in coastal Florida (Maxwell and Kale 1977), 3.18 m (± 0.77 SD; n = 32 nests) in S. Carolina (Post 1990), and 1.6 m (± 0.3 SE; n = 33 nests) in New York (Burger and Gochfeld 1993). In a mangrove colony in Florida, nested 1.67 m above ground (± 0.33 SD; n = 60 nests). Reported nesting height 3–5 m in mangroves in Netherlands Antilles (Voous 1983). Ground nesting reported in dense stands of common reed on Long Island and in s. New Jersey (Salzman 1985; TLM).

Distances between individual nests = 0.78 m (± 0.36 SD; n = 22 nests) in Florida (Girard and Taylor 1979), and 2.8 m (± 0.6 SE; n = 33 nests) in New York (Burger and Gochfeld 1993). Mean distance to nests of other species = 0.97 m (± 0.75 SD; n = 43 nests) in Florida (Girard and Taylor 1979) and 3.4 m (± 0.7 SE; n = 33 nests) in New York (Burger and Gochfeld 1993).

Construction Process

Female does most nest-building, which continues at least through incubation (Hancock and Kushlan 1984). Male supplies nesting material while female works sticks into nest (Palmer 1962). Nest-building often follows copulation (Hancock and Kushlan 1984). Nest-relief ceremony often accompanied by offering nest material. In central Florida colony, most twigs collected from the ground; some pruned from live shrubs, unlike other heron and egret species. Nest construction required an average of 4.4 d in central Florida (± 0.25 SE; n = 21 nests; Jenni 1969). Twigs and sticks also collected from the ground in s. New Jersey; stealing from other nests, both active and inactive, also suspected (TLM).

Structure And Composition Matter

Constructed of loosely woven twigs and small sticks. From records of the Western Foundation of Vertebrate Zoology (n = 39 nests), twigs, sticks, grass, tules, rushes, and Spanish moss (Tillandsia usneoides) used to line nests. Nest material reflected colony-site habitat.

Dimensions

Nest shape may be round or elliptical and typically flat/shallow in profile. In New Jersey, nests averaged 41 cm± 5.0 SD in width and 27.0 cm ± 6.5 SD in height (n = 20 nests; Burger 1978b).

Microclimate

Solar radiation (maximal potential solar load) at nests in Florida was 1.43 cal/cm²min (n = 178 nests; Ellis 1980).

Maintenance Or Reuse Of Nests, Alternate Nests

Known to use old nests (Burger 1978b, Davis 1986; see Nest site, above). Annual nest counts following the breeding season at Armacost Park, Avalon, NJ, indicate frequent use of old nests but detailed investigation not done (TLM).

Nonbreeding Nests

None reported.

Shape

Elliptical.

Size

Mean egg length and breadth in Massachusetts: 42.8 mm ± 1.4 SD and 32.0 mm ± 1.4 SD, respectively (n = 54 eggs, 15 clutches; Cannell and Harrington 1984). In the Netherlands Antilles: 42.6 mm × 23.2 mm, respectively (n = 37 eggs). In 3-egg clutches, egg length and volume of the third-laid egg is less than for first-laid egg (Custer and Frederick 1990).

Mass

Mean initial egg mass of 6 eggs (2 clutches) = 22.6 g ± 1.5 SD; 12% lost as water vapor during incubation. Mean daily rate of water loss in the nest was 121 mg ± 33 SD, lowest measured among 10 Ciconiiformes and Laridae (Vleck et al. 1983). Eggs appeared to be 8 mm smaller on average in each dimension in E. t. brewsteri (Bent 1926).

Color

Pale greenish blue.

Surface Texture

Smooth.

Eggshell Thickness

Mean shell thickness of 19 eggs (n = 19 clutches) collected in 1979 from Idaho was not different from pre-1947 thickness, but eggs with highest levels of DDE were 13.4% thinner than pre-1947 eggs (Findholt 1984). In Louisiana and Texas, 5.5% and 9.0% decreases in thickness, from pre-1947 to 1970 levels, respectively (Faber and Hickey 1973, King et al. 1978). Shell thickness and DDE concentration negatively correlated in San Francisco Bay (r = –0.69; p = 0.0270; Ohlendorf et al. 1988).

Clutch Size

Generally 3–5 eggs; occasionally 2–6. Slight trend toward smaller clutches in lower latitudes (Palmer 1962). Mean clutch size in central Florida was 3.9 eggs ± 0.07 SE (n = 102 clutches), although early nesters laid 4.1 eggs ± 0.05 SE (n = 89 clutches), late nesters 2.9 eggs ± 0.17 SE (n = 13 clutches; Jenni 1969). Mean clutch in a coastal Florida colony was 2.9 ± 0.06 (n = 77 clutches; Maxwell and Kale 1977). In s. Florida, mean annual clutch size in estuarine habitats over 4 yr ranged from 1.93 ± 0.8 SD (n = 14 nests) to 3.29 ± 0.7 SD (n = 14 nests); in freshwater sites over 2 yr: 2.67 ± 0.5 SD (n = 48 nests) to 3.57 ± 0.6 SD (n = 23 nests); in mar-ine habitats over 2 yr: 2.80 ± 0.5 SD (n = 5 nests) to 3.50 ± 1.4 SD (n = 10 nests; Frederick et al. 1992). In Idaho, typical clutch size 3–5 eggs (Palmer 1962).

Egg-Laying

In central Florida, eggs in 5-egg clutches laid at a mean interval of 1.9 d ± 0. 04 SE (n = 115 eggs; Jenni 1969); 2.1 d ± 0.04 SE (n = 57 nests) in coastal Florida (Maxwell and Kale 1977). Egg loss resulted in a total of 8 eggs laid in one nest in Florida (Jenni 1969). Mean interval between loss of clutch and first egg of replacement clutch 8.1 d 1.33 SE (n = 2 nests; Maxwell and Kale 1977).

Onset Of Broodiness And Incubation

In coastal Florida, effective incubation in 54% of nests began with the first egg; in 44% of nests with the second egg (Maxwell and Kale 1977). Similar findings in central Florida (Jenni 1969).

Incubation Patches

Not reported.

Incubation Period

Mean incubation period in Florida 22 d (± 0.12 SE; n = 39 nests; Jenni 1969), (± 0.17 SE; n = 29 nests; Maxwell and Kale 1977). Mean incubation period for first-laid egg 24.3 d ± 0.3 SE (n = 6 nests); second-laid egg 23.2 d ± 0.2 SE (n = 5 nests); third-laid egg 23.3 d ± 0.3 SE (n = 4 nests) in three-egg clutches in Texas (Custer et al. 1992).

Parental Behavior

Both sexes incubate; nest relief sometimes involves presentation of a stick by the relieving individual (Palmer 1962). Both sexes feed nestlings, initially by dropping food in nest, later by grasping beaks in a scissor-like fashion (Palmer 1962).

Hardiness Of Eggs Against Temperature Stress; Effect Of Egg Neglect

No information.

Preliminary Events And Vocalizations

No information.

Shell-Breaking And Emergence

In New York and Florida, mean hatching interval between first and second eggs 0.58 d ± 0.60 SD and 0.7 d ± 0.09 SE, between the second and third eggs 1.13 d ± 0.55 SD and 1.2 d ± 0.12 SE, and between the third and fourth eggs 1.21 ± 0.58 SD and 1.2 d ± 0.38 SE (Maxwell and Kale 1977, St. Clair Raye and Burger 1979), respectively.

Parental Assistance And Disposal Of Eggshells

Adults removed eggshells after hatching in a Florida colony (Jenni 1969).

Condition At Hatching

Semialtricial young described in detail by McVaugh (1975). Body length increases from 98.4 mm (hatchling) to 406.4 mm (34 d old). Hatchlings covered by white down except on wings; pinfeathers appear by 1 wk; by 2 wk Juvenal feathers and rectrices emerging. Egg tooth disappears after 2 wk. Leg and mandible color variable from yellow to grayish to black; tarsi always darker than toes. Mouth lining pink; iris generally pale gray. Body mass 20 g (n = 77; KCP).

Brain acetylcholinesterase increased with nestling age at a faster rate (0.58 µmoles acetylthiocholine iodide hydrolyzed/g brain tissue/min/d age) than Great Egret or Black-crowned Night-Heron nestlings; may be associated with greater nestling activity in Snowy Egrets compared to the other species (Custer and Ohlendorf 1989).

Growth And Development

Measurements summarized from McVaugh 1975 and Palmer 1962 . Vary according to individual nest, year, etc. (Erwin et al. 1996b). In a Virginia colony, the first chick to hatch typically gained 17.7 g/d compared to 14.1 g/d for third-hatched chicks (Erwin et al. 1996b).

Bill Length. Day 1: 11.9 mm; day 4: 15.9 mm; day 8: 25.4 mm; day 13: 33.3 mm; day 18: 38.1 mm; day 21: 50.1 mm; day 27: 54.0 mm; day 34: 57.2 mm. Adult male: 83.3 mm; adult female: 78.6 mm.

Wing Length. Day 1: 15.1 mm; day 4: 22.2 mm; day 8: 34.9 mm; day 13: 88.9 mm; day 18: 107.9 mm; day 21: 120.7 mm; day 27: 165.1 mm; day 34: 196.8 mm. Adult male: 259.9 mm; adult female: 251.2 mm.

Tarsus Length. Day 1: 16.6 mm; day 4: 25.4 mm; day 8: 36.5 mm; day 13: 50.8 mm; day 18: 60.3 mm; day 21: 60.3 mm; day 27: 63.5 mm; day 34: 79.4 mm. Adult male: 97.1 mm; adult female: 89.6 mm.

Body Length. Day 1: 98.4 mm; day 4: 139.7 mm; day 8: 196.9 mm; day 13: 250.8 mm; day 18: 317.5 mm; day 21: 330.2 mm; day 27: 361.8 mm; day 34: 406.4 mm.

Body Mass. Measurements from KCP: Day 1: 20 g; day 4: 42 g; day 8: 96 g; day 13: 178 g; day 18: 226 g; day 21: 268 g. Mass gain did not differ between A-, B- and C-chicks from 0 to 18 d in Texas (Custer and Peterson 1991) nor from 0 to 10 d in a New York colony; nesting success not related to brood size (St. Clair Raye and Burger 1979). Growth rates of forearm, tarsus, and culmen not different among A-, B-, and C-chicks 0–18 d in a Texas colony (Custer and Peterson 1991). A 2-yr Virginia study found mass gain in young depended on the effects of year, colony, and hatching order with C– and D–chicks having reduced rates of growth (Erwin et al. 1996b). Hatching order, but not year and colony, influenced culmen growth. Between 2 and 3 wk, Juvenal feathers on body and wings emerged and largely covered bird. Feathers emerged and covered head and neck between 3 and 4 wk (McVaugh 1975).

Reactions to intruders were age-specific in New York colony (St. Clair Raye and Burger 1979): nestlings 0–4 d old begged, 4–6-d-old nestlings reacted aggressively, 6–8-d-old nestlings crouched, nestlings 8–12 d old moved to nearby branches, and nestlings 11–16 d old escaped into underbrush. If nestlings malnourished, however, behavior reflected size rather than age. Chicks aged 11–15 d old spent greatest amount of time sleeping; those 34–40 d old spent least amount of time sleeping.

Chicks aged approximately 2 wk spent more time out of nest compared to younger chicks. Younger chicks returned to the nest in 20.4 min ± 9.9 SD on average (n = 20) after disturbance, whereas older chicks returned in 75.2 min ± 19.8 SD (n = 20). When a parent returned to the nest following disturbance, older chicks were first to return (St. Clair Raye and Burger 1979).

Brooding

Both parents brood continuously until young approximately 10 d old. From age 10 to 14 d old, nest attended by one parent approximately 50% of time. During storms, 2-wk-old young brooded continuously (Parsons 1985).

Feeding

Both parents feed young. Well-digested food regurgitated onto nest floor for hatchlings 1–5 d old. Older nestlings grasp parent’s bill in scissors grip to stimulate regurgitation directly into mouth. Asynchronous hatching produces feeding hierarchy dependent on nestling size. Feeding rates not reported but nestlings 5–10 d old spent 15% of time feeding whereas 21- to 25-d-old chicks spent only 6% of time feeding (St. Clair Raye and Burger 1979; see Food habits: diet, above).

Nest Sanitation

Nest sanitation activities limited to removal of eggshells from the nest by adults and defecation over the nest edge by both adults and prefledglings. Dead nestlings often trodden into nest structure.

Parental Carrying Of Young

Not reported.

Not reported.

Parasitized by Black-crowned Night-Herons in a Massachusetts colony and also in Virginia (M. Erwin pers. comm.). In one nest, a night-heron nestling survived approximately 3 wk with 4 Snowy Egret young before all died following a storm (Cannell and Harrington 1984). In Virginia,a young Black-crowned Night-Heron survived <1 wk. A Snowy Egret egg was hatched by Tricolored Herons and all 3 nestlings were fed and successfully fledged (McVaugh 1975). At 4 inland heronries in Texas, Snowy Egrets were parasitized by Great Egrets, Little Blue Herons, and Cattle Egrets (Telfair 1983).

Intraspecific egg-dumping not reported.

Departure From Nest

As early as 10 d of age, nestlings capable of leaving the nest when disturbed, but quickly return when disturbance passed. Older nestlings took longer to return to nests than younger nestlings (St. Clair Raye and Burger 1979). Radio-tagged fledglings remained in vicinity of colony for approximately 7–8 wk (Erwin et al. 1996a).

Survival rate of nestlings in Virginia colonies was 0.8–0.9 ± 0.04 SE (Erwin et al. 1996b). Dispersal began between 53.0 ± 3.7 and 56.3 ± 5.6 d after hatching (n = 42) in 1992 and 1993. Following dispersal, only 35–60% of fledglings survived another 6 wks.