Breeding

Pair Formation

Occurs soon after return to colony (RTP).

Nest-Building

Nest-building immediately follows pair formation and may serve to strengthen new pair bond. Nesting attempts initiated almost any month in s. Florida, with 2 primary pulses: Nov–Feb or Feb–May; along peninsular coasts, primarily Feb–Jun, but some young fledged as late as Oct (Paul 1991, 1996; Stevenson and Anderson 1994, RTP). In Texas, nesting primarily Mar–Jun (Oberholser 1974, Paul 1991). In Caribbean and Bahamas, not studied, but most nesting probably Nov–May (e.g., Spaans 1974, Voous 1983).

First/Only Brood Per Season

Figure 4 . Florida: Most clutches begin Feb or Mar, as early as Nov, as late as May (Paul 1991), peaks mid-Apr (Scott 1889); at Cowpens Key, s. Florida, completed clutch 25 Feb, with young 17 Apr (Palmer 1962). First eggs in s. Texas 9 Apr (Palmer 1962), peak egg-laying 15 Mar–10 Apr (McMurry 1971). At Sain Ka’an Biosphere Reserve, Quintana Roo, Mexico, extreme dates observed for eggs 3 Dec–6 Jun (Lopez-Ornat and Ramo 1992). One brood/yr; some renesting likely following failure.

Second Brood Per Season

Not known to occur. Renesting probably occurs after failure of first attempt, particularly if failure occurs during egg-laying or incubation.

Selection Process

Not studied in detail, but probably similar to other day herons, where male chooses nest territory before pairing (see Mock 1976). Nest may be placed at male’s display site (ground nests) or under canopy beneath male’s display perch within territory (tree nests). In Texas, new pairs forming after other birds are incubating walk irregularly through colony and appear to choose site together.

Microhabitat

Nests on ground or in vegetation or trees up to >10 m above ground. Usually nests in mixed-species heron colonies, occasionally in small monospecific groups or even singly. In Texas colonies on coastal islands, nests built in low vegetation (bisbirinda, Spanish dagger, and prickly-pear cactus; or sea oxeye, sea purslane, goldenrod, ragweed) or on bare sand (Cahn 1923, Bent 1924, Bancroft 1927, RTP). In Florida, nests in trees, typically selects secure fork 1–2 m below canopy in red or black mangroves or, less often, in Brazilian pepper; frequently nests over water, above interior lagoon of mangrove key or over creek or pocket where mangroves from both sides converge (Paul 1996). Height of nests in trees varies from 2 to >10 m, depending in part on size of the tree. May build on old nests of Double-crested Cormorant (Bancroft 1927). Colonies in Baja California nest on the ground on Isla San Luís or at 1–2 m in glass-wort (Sarcornia sp.) at Scammons Lagoon (= Laguna Ojo de Liebre; Bancroft 1927).

“By the middle of April, they construct their nests, which they place for the most part on the south-western sides of the mangroves immediately bordering the keys, never on the trees at a distance from the water, and rarely very close together. Some are placed on the top branches, others a foot or two [about 0.5 m] above the highest tide-mark; many of them are annually repaired, perhaps all that stand the winter gales. The nest, which is quite flat, is large for the size of the bird, and is formed of dry sticks, interspersed with grass and leaves” (Audubon 1843: 142).

Construction Process

Little information. Sticks may be obtained from old or deserted nests (Cahn 1923).

Structure And Composition Matter

Nest well made from sticks and lined with forbs and grasses.

Dimensions

For 3 ground nests, outside diameter range 20–26 in. (51–66 cm), depth 8–10 in. (20–25 cm), inside diameter range 10–12 in. (25–30 cm), depth 3–4 in. (8–10 cm; Bent 1926).

Microclimate

No information other than nest often totally exposed (see Nest site, above).

Maintenance Or Reuse Of Nests

Nests may be repaired and reused from year to year (Audubon 1843).

Nonbreeding Nests

No information.

Shape

Ovate to elliptical ovate (Bent 1926); near elliptical (between elliptical and short subelliptical; Palmer 1962).

Size

Mean (mm) for 42 eggs: 51.0 (range 46.5–55.6) × 37.6 (range 36.0–41.7; Bent 1926). For 20 eggs (1 egg each from separate clutches), 50.23 ± 2.65 SD × 36.31 ± 1.72 SD (Palmer 1962).

Mass

No information.

Color

Pale bluish green (deep lichen green to pale Niagara green or pale olivine; Bent 1926).

Surface Texture

Smooth, not glossy (Bent 1926).

Eggshell Thickness

Texas, pre-1943 sample, 0.270 mm ± 0.014 SD (n = 47); 1970 sample, 0.267 mm ± 0.022 SD (n = 54; King et al. 1978). Eggshells of 1970 sample 1% thinner than pre-1943 sample; subsample from Green I., TX (n = 28; near discharge of Rio Grande), significantly thinner than sample (n = 17) from Aransas Bay, TX, and 6.3% thinner than a pre-1943 sample (n = 47; King et al. 1978, RTP).

Clutch Size

Usually 3 or 4, very rarely to 7 (Bent 1926). In Texas, 3.12 eggs ± 0.57 SD (n = 57; McMurry 1971); in Florida, 2.75 eggs (n = 81; Paul 1996, RTP).

Egg-Laying

No information.

Onset Of Broodiness And Incubation

No information.

Incubation Patch

No information.

Incubation Period

Estimated at 29–30 d (range 21–36; McMurry 1971). For nests with known dates of laying and hatching of last egg, estimated 26 d (RTP).

Parental Behavior

Incubation by both sexes; role of each sex unknown (Palmer 1962).

Hardiness Of Eggs Against Temperature Stress; Effect Of Egg Neglect

No information.

No information.

Condition At Hatching

Semiprecocial and nidicolous.

Growth And Development

“The young while yet naked are of a dark colour, there being only a few scanty tufts of long soft down on the head and other parts; but when the feathers begin to sprout they become white. Being abundantly and carefully fed, at first by regurgitation, they grow fast, and soon become noisy. When about a month old, they are fed less frequently, and the fish is merely dropt before them, or into their open throats; soon after they sit upright on the nest, with their legs extended forward, or crawl about on the branches, as all other Herons are wont to do. They are now sensible of danger, and when a boat is heard coming towards them they hide among the branches, making towards the interior of the keys, where it is extremely difficult to follow them. On one occasion, when I was desirous of procuring some of them alive, to take to Charleston, it took more than an hour to catch eight or nine of them, for they moved so fast and stealthily through the mangroves, always making for the closest and most tangled parts, that a man was obliged to keep his eyes constantly on a single individual, which it was very difficult to do, on account of the number of birds crossing each other in every direction. They do not fly until they are six or seven weeks old, and even then do not venture beyond the island on which they have been reared” (Audubon 1843: 142). Little additional information. Young hiss and jab at intruders (Cahn 1923).

Brooding

Young brooded or guarded at nest until about 3 wk old (RTP). During heat of the day, adults may stand in nest “. . . with wings extended and drooping like a canopy over the hatching eggs or squirming young” (Cahn 1923: 477).

Feeding

No information.

Nest Sanitation

No information.

Not known to occur.

Not known to occur.

Departure From Nest

Young leave nest at about 4–5 wk but remain close to nest (RTP).

Growth

No information once young leave nest.

Association With Parents Or Other Young

No information.

Ability To Get Around, Feed, And Care For Self

Capable of flight at about 6.5–7 wk but continue to be fed by adults an additional 2–4 wk (Paul 1996, RTP).

No information.