Egretta caerulea is a medium sized,
long-necked wading bird of the Order Ciconiiformes (herons and storks). Both
sexes are similar in appearance, with deep blue-gray plumage, dull green legs,
and a black-tipped bill. Head coloration can become chestnut brown during the
HABITAT AND DISTRIBUTION
In the United States, E. caerulea occurs as far inland as Oklahoma.
Coastally, it ranges from New York to Florida. Its range also includes the Gulf
of Mexico, Central America and much of South America.
E. caerulea occurs throughout the Indian River Lagoon.
LIFE HISTORY AND POPULATION BIOLOGY
Age, Size, Lifespan
The little blue heron attains a height of 22 inches, with a wingspan of 41 inches.
E. caerulea can be common in areas throughout its range.
Like the great blue heron (Ardea
herodias), the little blue heron tends to form monospecific breeding
colonies that are often located at the fringes of a mixed heron colony. This
differs from most other medium sized wading birds such as the snowy egret (Egretta
thula) and the white ibis (Eudocimus albus) which breed in mixed
colonies (Maxwell and Kale 1997). Between 3 - 5 eggs are laid per clutch. One
brood is raised each year; however, should the first nest be destroyed, a
replacement clutch can be laid (Ehrlich et al. 1988). The nesting period for
this species as observed in Lake Okeechobee, Florida begins in mid-March and
April (Smith 1997).
Predation and disturbance rates determine nest
success in all wading bird species. Cold weather events are particularly
detrimental to nest success in many species. Additionally, in Florida, the
active management of water levels in wetland areas such as Lake Okeechobee may
also contribute to nest success (Smith and Collopy 1995). It has been suggested
that in order to enhance nest success and later fledgling success, water levels in managed wetlands should be maintained at low or receding levels throughout
the December to March nesting season. Low water levels help to concentrate prey
in a small area, thereby making it simpler for parent birds to feed nestlings.
It also contributes to the foraging success of fledglings (Smith and Collopy
Incubation time is approximately 20 - 23
days. As in all heron and egret chicks, hatching is asynchronous, and occurs
over several days. The first chick to hatch quickly gains experience at food
handling and aggressive interactions with siblings, so is often able to
outcompete its siblings. Thus, growth rates are unequal among nestmates. In one
California study, it was observed that as chicks age, predation gives way to
starvation as the primary cause of death (Alfaro and Russi 1989).
Young fledge after 42 - 49 days (Ehrlich et al. 1988).
E. caerulea is eurythermal. On the east coast, little blue herons overwinter from New Jersey south to the Gulf of Mexico and South America (Farrand
1988). However, they can be cold sensitive during the breeding season, with
spring cold events linked to nest failures at some sites (Smith and Collopy
The little blue heron feeds by keeping its bill close to the surface of the
water as it wades and peers around vegetation in search of prey. It apparently
utilizes this slow wading behavior as its only method of feeding (Willard 1977;
Kent 1987). Kent (1987) observed that less active feeding strategies such as
slow wading tended to have increased striking efficiencies, the percentage of
strikes that result in the capture and ingestion of prey. In the Kent (1987)
study, little blue herons had better foraging efficiency than either the snowy
egret or the tricolored heron. The tricolored heron was estimated to expend 1.5
times as much energy as the little blue heron in feeding, while the snowy egret
expended approximately 2 times as much energy as the little blue heron. However,
in terms of food intake per minute (g/min), the little blue heron falls between
the tricolored heron and the snowy egret. Overall then, the little blue heron
must forage approximately 0.6 times longer than the tricolored heron to obtain
its daily energy requirement, while the snowy egret must forage twice as long.
In a Puerto Rican study (Miranda and Collozo
1997), E. caerulea adults were observed to feed solely on fiddler crabs (Uca
spp). However, Smith (1997), in a study of wading birds in Lake Okeechobee and
the Florida Everglades, found that E. caerulea feeds primarily on
amphibians as well as on other crustaceans (i.e, shrimp, other crab species,
etc.). Fish, when taken, tend to be larger than those taken by wading birds of
When environmental conditions change and begin
to affect food supplies, the little blue heron responds by adjusting its diet to
include alternate prey types. This differs from some other species of wading
birds such as the snowy egret and tricolored heron which alter their feeding
strategies and foraging habitat in order to continue to encounter preferred prey
Food offered to nestlings includes as many as
30 different species. Grass shrimp appear to be the primary nestling food,
followed by mosquitofish, killifish, and the sailfin molly (Smith 1997).
Other medium sized wading birds such as
the snowy egret and tricolored heron and white ibis utilize similar habitats and
food resources, but there is some evidence to suggest that resource partitioning
among species minimizes direct competition (Smith 1997).
In a study conducted in the Indian River
Lagoon, around the vicinity of Vero Beach, Florida, Maxwell and Kale (1997)
found that E. caerulea nested exclusively in black mangrove trees at the
fringes of a mixed heron colony. In a Lake Okeechobee, Florida study by Smith
and Collopy (1995), it was observed that little blue herons prefer to nest in
lake or pond areas where spring water levels are low or receding. Reduced water
levels in lakes and ponds helps concentrate prey, thus increasing nest success
and the later foraging success of fledglings. Collopy and Smith (1995) have
suggested this choice of breeding habitat has direct applications to wetland
management around Lake Okeechobee. With the large numbers of wading birds
nesting in this area, it could be most beneficial to bird populations for
wetland managers to consider keeping lake levels low in the late winter or early
spring months of the nesting season.
E. caerulea shares forging habitat
with other wading birds of similar size such as the snowy egret and tricolored
heron. Breeding habitat is generally unshared, with little blue herons
initiating monospecific breeding colonies located along the fringe areas of
mixed heron colonies.
In Florida, listed as a species of species
of special concern (SSC). It is not federally listed as threatened or
Benefit in IRL
The environmental sensitivity of wading
birds, coupled with the relative ease of assessing their numbers, makes them
attractive as biological indicators of ecosystem health and habitat quality
(Custer and Osborn 1977; Powell and Powell 1986; Powell et al. 1989).
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Custer TW, Osborn RG. 1977. Wading birds as biological indicators 1975 colony survey. No 206: 1-28. US Fish and Wildlife Service.
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Smith JP. 1997. Nesting season food habits of 4 species of herons and egrets at Lake Okeechobee, Florida. Colonial Waterbirds 20: 198-220.
Smith JP, Collopy MW. 1995. Colony turnover, nest success and productivity, and causes of nest failure among wading birds (Ciconiiformes) at Lake Okeechobee, Florida (1989-1992). Archiv for Hydrobiologie, Adv Limnol 45: 287-316.
Willard DE. 1977. The feeding ecology and behavior of five species of herons in southeastern New Jersey. Condor 79: 462-470.