Demography and Populations

Age At First Breeding

Data lacking. Some breeding by 1-yr-olds suspected. Majority probably breed at 2 yr.

Clutch

See Breeding: eggs, above.

Annual And Lifetime Reproductive Success

No data for lifetime. Single brooded. In Delaware Bay, 1.6 young/nest that hatched ≥1 egg (n = 36 nests) survived to age 10 d (Parsons 1995). In central Florida colony, mean number of young hatched/nest 3.3 ± 0.10 SE (n = 91; Jenni 1969); 2.7 ± 0.08 SE (n = 77) in coastal Florida (Maxwell and Kale 1977). An estimated 3.2 chicks fledged/nesting female/yr required to maintain stable population in Idaho; actual prefledging (7–10 d posthatch) survival was 2.0–2.5 young/nesting attempt (Findholt 1984). In Florida Everglades, a mean of 2.8 young ± 0.8 SD/successful nest (nests that hatched ≥1 egg; n = 15) survived to 14 d (Frederick and Collopy 1989). In New York, successful nests produced 1.5 nestlings/nest surviving to age 14 d (St. Clair Raye and Burger 1979). In Texas, 91.3% of hatched eggs ultimately produced fledglings (Telfair 1979). In San Francisco Bay, mean prefledging (4–7 wk posthatch) brood size in successful nests was 2.07 young ± 0.73 SD (n = 14; Kelly et al. 1993).

Number Of Broods Normally Reared Per Season

One (Palmer 1962).

Proportion Of Total Females That Rear At Least One Brood To Nest-Leaving Or Independence

No data.

One banded individual recovered in Utah was 22 yr, 10 mo old (Jackson 1982). Mean annual mortality rate of adults throughout the U.S. 52.4%, estimated from band recoveries (n = 255; Ryder 1978). Mortality during first year 71.6%; during years 2–17, 31.4%. Calculated mortality rates have increased since mid-twentieth century by approximately 10% (Ryder 1978).

Diseases

No data.

Body Parasites

Three of 4 individuals collected at a Mississippi fish farm tested positive for the pathogenic fish bacterium Edwardsiella ictaluri (Taylor 1992). Infection by the endoparasitic nematode Eustrongylides ignotus determined reproductive success in Delaware Bay although severity of outbreak varied over several years; of 53 nestlings examined, 95% infected (Wiese 1978). Species subjected to nematode parasitism in Florida; 40.4% (n = 47 carcasses) of adults and nestlings found dead suffered from eustrongylidosis (Spalding 1990). At least 1 nestling infected with Eustrongylides spp. in 100%, 20%, and 10% of all nests in Texas, California, and Rhode Island, respectively (Franson and Custer 1994). Captive individual infected with trematode Apharyngostrigea simplex in Argentina.

In Idaho, missing and broken eggs were correlated with DDE concentration (Findholt 1984). Fenthion, which caused lethal cholinesterase de-pression, was implicated in 7 adult deaths in California (Zinkl et al. 1981). Approximately 20% of eggs failed to hatch and 28% of hatched chicks failed to survive 14 d in a Florida colony; mortality of offspring at time of hatching was approximately 15%; most nestling mortality was attributed to starvation (Jenni 1969, Erwin et al. 1996b). Starvation was also leading cause of death in chicks 8–10 d old in Delaware Bay (Parsons 1985). Similar patterns of mortality documented in one coastal Florida colony (Maxwell and Kale 1977) but were less in another (Girard and Taylor 1979). In Georgia, most nestling losses attributed to predators (Teal 1965).

Exposure

Nestlings in Massachusetts most vulnerable to inclement weather at about 1.3 wk of age (Parsons 1985). During average and poor weather years in a Massachusetts colony, species was inferior to Black-crowned Night-Heron in producing fledglings; in years of favorable weather, produced more young than Black-crowned Night-Heron (Parsons 1985). Drought suspected in colony failure in Alabama (Dusi and Dusi 1968).

Predation

See Behavior: predation, above. In Delaware Bay (1993), predation most prevalent cause of death in nestlings 0–7 d old (72% of 39 nestlings; Parsons 1985). Nestlings 1–5 d old most likely to be eaten by predators in a New York colony. Gray rat snakes, Fish Crows, and Barred Owls were main causes of predation in mixed-species Alabama colony (Dusi and Dusi 1968). Nestlings 7–11 d old more likely to starve and accidents most likely to claim 11–13 d-old-nestlings (St. Clair Raye and Burger 1979). Suspected cause of egg predation in Virginia largely Fish Crows (M. Erwin pers. comm.). One radio-tagged chick consumed by a Black-crowned Night-Heron in the same colony (M. Erwin pers. comm.).

Competition With Other Species

Few inter- or intraspecific aggressive encounters observed among individuals in mixed-species foraging aggregations in s. New Jersey (TLM). In areas shared with Cattle Egrets, Snowy Egrets hatched only 68% of eggs laid compared to 88% in the absence of Cattle Egrets; may be the heron most seriously affected by increases in Cattle Egret numbers (Burger 1978b). Numbers may have declined at Salton Sea, CA, because of competition for nest sites with Cattle Egrets (Garrett and Dunn 1981).

Importance of nest competitors in determining reproductive success is equivocal.

Initial Dispersal From Natal Site

Within 2 wk of fledging from a Virginia colony, approximately 50% of 39 radio-tagged immatures was relocated at least once within 10 km of the colony, usually on wetlands of Chincoteague National Wildlife Refuge (Erwin et al. 1996b). In S. Carolina, individuals fledged along coast wander inland after breeding season (Belser and Post 1987). Three birds banded as nestlings on Long Island, NY, were recovered as subadults in the West Indies 2,400–3,200 km from natal site (Davis 1968). Radio-tagged and banded fledglings dispersed generally north of breeding sites, sometimes as far as 300 km (Ryder 1978, Erwin et al. 1996a). Birds fledged on Texas coast tend to disperse northward into e. Texas (Telfair and Swepston 1985), and individuals banded as nestlings in Mississippi were recovered in Arkansas (James and Neal 1986).

Fidelity To Breeding Site And Winter Home Range

No information.

Dispersal From Breeding Site Or Colony

No information.

Home Range

Evidence suggests repeated visits to specific foraging sites during breeding season (Custer and Osborn 1978a). Foraging flights averaged 2.8 km from breeding colonies at Lake Okeechobee, FL; reported to be less than half that typical of individuals in the Florida Everglades (Smith 1995). High water levels and artificial interruptions in normal water-level trends caused longer foraging flights (Smith 1995).

Numbers

Of breeding adults from Maine to Georgia, about 37,000 in 1975 (Ogden 1978) but dropped to 26,800 by 1977 (Spendelow and Patton 1988). Similarly, peninsular Florida populations decreased from 13,600 adults in late 1950s to 8,000 adults by mid-1970s (Ogden 1978). A statewide survey of Florida in 1974–1975 revealed 10,300 adults nesting in 23 colonies (Frohring et al. 1988). Atlantic coast surveys indicated presence in 85 colonies (all coastal states Florida to Maine) in mid-1970s (Custer et al. 1980). Inland surveys in 1970s–1980s documented nesting in Wyoming (40 adults; Findholt and Berner 1988) and Wisconsin (2 adults; Spendelow and Patton 1988; see Distribution: the Americas, above). Atlantic coast surveys were to be repeated in 1994–1996.

Trends

Breeding populations subject to considerable flux since mid-twentieth century. Explosive recolonization of mid-Atlantic coast and colonization of the ne. U.S. tempered with population declines since 1980s; e.g., Appledore I., ME, breeding population declined from 200 to 250 pairs in 1978–1979 to approximately 50 pairs in 1988 (Foss 1994). During this period, Massachusetts population dropped 31% from 800 to 550 pairs but increased and expanded by 1993 (Veit and Petersen 1993). In the late 1980s to early 1990s, New York Harbor increased 50% from 200 to 300 pairs; New Jersey declined 50% from 1,300 to 650 (D. Jenkins pers. comm.); Delaware Bay declined 60% from 2,500 to 1,000 pairs; Rehoboth Bay, DE, increased 400% from 100 to 500 pairs. Total loss in mid-Atlantic in mid-1970s to mid-1990s about 39% or 1,900 pairs (KCP). Some evidence that Virginia populations have declined from about 1,500 adults in the mid-1970s to only 595 in the late 1980s (Williams et al. 1990). In S. Carolina, population remained relatively stable from 1988 to 1996 at 3,500 pairs (Dodd and Murphy 1996). Texas population appears stable at approximately 1,200 pairs (n = 18 colonies; Green 1992).

Southern California population declining around Salton Sea, may be due to pollution and competition with Cattle Egrets (Garrett and Dunn 1981, Small 1994; see Conservation and management: effects of human activity, below).

Showed impressive capacity to expand into recently vacated and entirely new coastal regions after persecution from plume hunters stopped around the turn of the twentieth century. Information available at the end of the century suggests nesting sites, while protected from direct human intrusion in most cases, are not safe from human commensals (raccoons, feral cats, etc.) unless located on islands. Therefore, numerous historical nesting sites located on coastal spits and peninsulas increasingly abandoned in favor of more completely isolated sites on islands. Populations may be limited by availability of suitable island nesting sites within feasible commuting distance (<10 km) to adequate foraging wetlands.

Quality of foraging habitats lowering reproduction rate, wetland degradation from chemical contamination (Parsons 1994), and nutrient enrichment (Spalding et al. 1993) put species at risk because of diet specificity.