Illinois Natural History Survey - University of Illinois

Snowy egret
Egretta thula

 

Taxonomy
Occurence in Illinois
Status
Habitat associations
Guilds
Food-habits
Environmental associations
Life history
Management practices
References


TAXONOMY

 

  • Phylum: Chordata
  • Class: Aves
  • Order: Ciconiiformes
  • Family: Ardeidae
  • Genus: Egretta
  • Species: Egretta thula
  • Authority: Molina

Comments on taxonomy:
Tribe:Ardeini. 2 subspecies:Egretta thula thula (Molina), found in Illinois, E.t. brewsteri (Thayer & Bangs), ave. larger, bill male 93.7 mm. wing 79.6, bill female 87.5 mm wing 264.9, found western regions of U.S. range.

 


OCCURENCE IN ILLINOIS

Lt. April-lt. August. Rare migrant and post-breeding wanderer. Rare local summer resident *18*. Recent breeding records: 1980: 2 nesting pairs, Pontoon Beach Colony, Madison Co.; 1981: 5 nests, Pontoon Beach Colony, Madison Co.; 1982: 3 Nests, Pontoon Beach Colony, Madison Co. *20*. Non-breeding snowy egrets appear widely over state esp. in lt. summer and fall with concentration in southern area of state *07*.

 


STATUS

Items in bold indicate applicable categories
Forest Service Categories: S = recommended for regional sensitive status, F = forest listed species, M = management indicator species

Federal Status:

Endangered Threatened Proposed for listing
Candidate for proposal Recovery plan approved Recovery plan received (USFWS)
Recovery plan in preparation Under notice of review Delisted
Migratory EPA indicator Forest Serv.- Shawnee species (F)

State Status:

Endangered Threatened Proposed

Other:

Game Furbearer Nongame protected
Sportfish Commercial Pest None of the above

Comments on status:
The snowy egret was hunted for its nuptial plumes and disappeared from Illinois in the late 19th century. Plume hunting was outlawed in the early 20th century which allowed populations to recover *04*. Reason for status: at present fewer than 50 pairs nest sporadically in or near the american bottoms region of Illinois, which is the first requirement for placement on the endangered species list: 1) low population numbers, 2) history of decline, 3) threatened habitat *01*.

 


HABITAT ASSOCIATIONS

Items in bold indicate applicable categories

General habitat:

Unknown Terrestrial Aquatic Riparian

USFS timber inventory forest size class:

Unknown Unstocked Seedling Sapling
Seedling/sapling Pole Mature Over mature

Land use and land cover:

Unknown   Urban Residential
Commercial
Industrial
Transportation, communication
Complex industrial/commercial
Mixed
Other
Agricultural Crop, pasture
Orchards, groves, nurseries
Feedlot
Other
Rangeland Herbaceous
Shrub and brush
Mixed
Forestland Deciduous
Evergreen
Mixed
Water Stream
Lake
Reservoir

Bay
Wetland Forest
Non-forest
Barren Salt flat
Beach
Sand
Rock
Mine
Transit
Mix

 


Forest cover types:

Cover typeStructural stageCanopy closureSeason
Oak-gum-cypress Young tree (1-9" dia.) Unknown Spring/summer
Oak-gum-cypress Mature (9" dia. & 100 yrs. old) Unknown Spring/summer
Elm-ash-cottonwood Young tree (1-9" dia.) Unknown Spring/summer    
Elm-ash-cottonwood Mature (9" dia. & 100 yrs. old) Unknown Spring/summer

Associated tree species:

  • Black willow
  • Sand-bar willow

National wetland inventory classifications:

SystemSubsystemClassSubclassWater regime modifiersWater chemistry
Lacustrine Littoral Emergent vegetation Persistent Unknown/unspecified Unknown/unspecified
Lacustrine Littoral Emergent vegetation Nonpersistent Unknown/unspecified Unknown/unspecified
Lacustrine Littoral Flat Mud Unknown/unspecified Unknown/unspecified
Lacustrine Littoral Scrub/shrub Deciduous Unknown/unspecified Unknown/unspecified
Palustrine   Emergent vegetation Persistent Unknown/unspecified Unknown/unspecified
Palustrine   Emergent vegetation Nonpersistent Unknown/unspecified Unknown/unspecified
Palustrine   Flat Mud Unknown/unspecified Unknown/unspecified
Palustrine   Forest Deciduous Unknown/unspecified Unknown/unspecified
Palustrine   Scrub/shrub Deciduous Unknown/unspecified Unknown/unspecified
Riverine Lower perennial Emergent vegetation Persistent Unknown/unspecified Unknown/unspecified
Riverine Lower perennial Emergent vegetation Nonpersistent Unknown/unspecified Unknown/unspecified

Comments on species-habitat associations:
Due to the lack of information on snowy egrets in Illinois and their reported close association with little blue herons, habitat descriptions are generalized between the two species *00*.

Important plant and animal association: Snowy egrets and Louisiana herons *01*. Snowy egrets are highly social, frequently associating with little blue and louisiana herons in their nesting and foraging habitats*01*, willow sp. and buttonbush stands are common nesting places *01,06*.

High value habitats

HabitatStructural stageSeason
Wetland Special habitat Spring
Wetland Special habitat Summer
Marsh Special habitat Spring
Marsh Special habitat Summer
Swamp Special habitat Spring
Swamp Special habitat Summer
Shrub swamp Special habitat Spring
Shrub swamp Special habitat Summer
Lake Michigan Special habitat Summer/fall
Reservoir Special habitat Summer/fall
River Special habitat Summer/fall
Marsh restoration Special habitat Summer/fall

Species-habitat interrelations: Due to the lack of habitat information of the snowy egret in Illinois, general and appropriate information has been reported from various southern studies. Also reported are its many similarities to the little blue heron *00*. Snowy egrets seem to prefer wetlands that afford a dense thicket of small trees or shrubs near water's edge for nesting *01,04,11,16*. Most foraging occurs in shallow waters *01,11*.


GUILDS

Feed-guilding:

HabitatStructural stageSeasonFeed-guilds
Unknown high value habitat Unknown Unknown Air- arthropods
Wetlands Special habitat All Water bottom-unconsolidated bottom, arthropods
Water bottom-unconsolidated bottom, invertebrates other than zooplankton or arthropods
Water bottom-unconsolidated bottom, fish
Water bottom-unconsolidated bottom, amphibians
Water bottom-unconsolidated bottom, reptiles
Water bottom-aquatic bed, arthropods
Water bottom-aquatic bed, invertebrates other than zooplankton or arthropods
Water bottom-aquatic bed, fish
Water bottom-aquatic bed, amphibians
Water bottom-aquatic bed, reptiles
Water column- arthropods
Water column- invertebrates other than zooplankton or arthropods
Water column- fish
Water column- amphibians
Water column- reptiles
Water surface- arthropods
Water surface- invertebrates other than zooplankton or arthropods
Water surface- fish
Water surface- amphibians
Water surface- reptiles

Comments on feed-guilding:
Snowy egrets forage primarily in wetland areas on small fishes, crustaceans, amphibians, reptiles and insects *04,05,06,07*. Have been reported to capture insects on wing *11*; take small mammals (especially microtus) *06*; accompany livestock (cattle, hogs) preying upon disturbed insects in dry fields *12*.

Breed-guilding:

HabitatStructural stageSeasonBreed-Guilds
Wetland Special habitat Spring/summer Shrub strata, canopy of broad-leaved deciduous shrubs
Shrub strata, canopy of needle-leaved deciduous shrubs
Shrub strata, canopy of broad-leaved evergreen shrubs
Shrub strata, canopy of needle-leaved evergreen shrubs
Shrub strata, grass and grasslike vegetation extending into shrub strata
Tree canopy, branches of broad-leaved deciduous trees
Tree canopy, branches of needle-leaved deciduous trees
Tree canopy, branches of broad-leaved evergreen trees
Tree canopy, branches of needle-leaved evergreen trees

Comments on breed-guilding:
It is reported copulation takes place in the nest or on a limb near it *08*. Snowy egrets may nest from ground -30 ft., ave. 5-10 ft. in dense thicket of vegetation usually bordering wetlands *01,04,06*.

 


FOOD-HABITS

Trophic level is CARNIVORE

Food itemLife stage/plant part
Invertebrates Unknown
Mollusca Unknown
Mollusca: Gastropoda (snails) Unknown
Arthropoda Unknown
Malacostraca (isopds, amphipods, crayfishes) See comments
Insecta Unknown
Orthoptera (grasshoppers, crickets, cockroaches) Adult
Hymenoptera (ants, wasps, bees) Adult
Osteichthyes (bony fishes) See comments
Amphibians See comments
Salientia (frogs, toads) Juvenile
Salientia (frogs, toads) Adult
Sauria (lizards, skinks, iguana) Unknown
Serpentes (snakes) See comments
Cricetidae (woodrats, mice, voles, lemmings, muskrats)( Unknown
Important:
Malacostraca (isopds, amphipods, crayfishes) See comments
Osteichthyes (bony fishes) See comments
Juvenile:
Osteichthyes (bony fishes) See comments
Salientia (frogs, toads) Juvenile
Adult:
Invertebrates Unknown
Mollusca Unknown
Mollusca: Gastropoda (snails) Unknown
Arthropoda Unknown
Malacostraca (isopds, amphipods, crayfishes) See comments
Insecta Unknown
Orthoptera (grasshoppers, crickets, cockroaches) Adult
Hymenoptera (ants, wasps, bees) Adult
Osteichthyes (bony fishes) See comments
Amphibians See comments
Salientia (frogs, toads) Juvenile
Salientia (frogs, toads) Adult
Sauria (lizards, skinks, iguana) Unknown
Serpentes (snakes) See comments
Cricetidae (woodrats, mice, voles, lemmings, muskrats)( Unknown

Comments on food habits: 
General: Snowy egrets feed primarily on small fishes, crayfishes, shrimps, frogs, lizards, snakes and insects. Feeds opportunistically according to prey abundance *08*, i.e. primarily shrimps where abundant, called "crayfish" bird in Louisiana. See feeding info. for building species.
Juvenile: Young fed by regurgitation mainly small fishes *16*. Tadpoles mentioned because very soft *11* when leave nest adopt adult food habits. See general food habits.
Adult: See general food habits.


ENVIRONMENTAL ASSOCIATIONS

General:

  • Air temperature:see comments
  • Biodegradable organics: clean waters that have not been polluted
  • Aquatic habitat: shallows with emergent vegetation (littoral zone)
  • Aquatic habitats: see comments
  • Ecotones: see comments
  • Canopy closure (%) of trees: see comments
  • Ground cover- shrub (%): see comments
  • Human associations: wildlife refuges/sanctuaries
  • Human associations: see comments

Limiting:

  • Biodegradable organics: clean waters that have not been polluted
  • Aquatic habitat: shallows with emergent vegetation (littoral zone)
  • Aquatic habitats: see comments
  • Human associations: see comments

Egg

  • Air temperature:see comments

Feeding juvenile:

  • Biodegradable organics: clean waters that have not been polluted
  • Aquatic habitat: shallows with emergent vegetation (littoral zone)
  • Aquatic habitats: see comments

Resting juvenile:

  • Aquatic habitats: see comments
  • Canopy closure (%) of trees: see comments
  • Ground cover- shrub (%): see comments

Feeding adult:

  • Biodegradable organics: clean waters that have not been polluted
  • Aquatic habitat: shallows with emergent vegetation (littoral zone)
  • Aquatic habitats: see comments

Resting adult:

  • Aquatic habitats: see comments
  • Canopy closure (%) of trees: see comments
  • Ground cover- shrub (%): see comments

Breeding adult:

  • Biodegradable organics: clean waters that have not been polluted
  • Aquatic habitat: shallows with emergent vegetation (littoral zone)
  • Aquatic habitats: see comments
  • Canopy closure (%) of trees: see comments
  • Ground cover- shrub (%): see comments

Comments on environmental associations:
General: A primary factor in the decline of snowy egrets today is the draining, developing or polluting of their essential wetlands *01*. The availability of foraging and nesting areas are essential to the continuence of the snowy egret as a breeding bird in Illinois.
Egg: Eggs left uncovered for long periods of time may be "cooked" by hot sun *11,16*.
Feeding juvenile: The availability of undisturbed and pollution free wetlands for foraging *01*.
Resting juvenile: Assume upon fledging that juveniles adopt roosting habits of adults.
Feeding adult: See feeding juvenile.
Resting adult: In association with other social herons in lowland thickets and forest *01,07*.
Breeding adult: Herons exhibit a direct intolerance of man. Nesting sites must be undisturbed *01*. Prefer thickets and dense stands of young trees near water but seem not to prefer any particular species to place its nest *01,16*.


LIFE HISTORY

Origin: Native *02,07,18*.

Physical description: Outwardly similar though male slightly larger *05,06*. Weight:12-13 oz.; length:22-26"; wingspread:38-45" *05,06, 19*. Plumage:spotless white; black bill; black legs, birght yellow feet *05,06,08,09,19*. Feet turn coral-orange color early in breed- ing season *11*. Nuptial plumes acquired jan. Molted in june. Only heron with "recurved" scapular plumes *05*. Little information is available on life history in Illinois. Generalities are gleaned from the literature and geographical locations are stated *00*.

Reproduction: In Florida both sexes arrive in early to mid April *05, 06* and are not usually seen in Illinois until mid to late April *07*. First signs of breeding appear 10 days-2 weeks after arrival *08,10*. Nesting usually begins in early May but may vary *08*, snowy egrets are highly social throughout the year and nest colonially, usually with other species of herons *01,05,06,07*. Males alone select a territory *06*. Advertising is conspicuous and extremely vocal *05,06*. In Florida, a male may spend 5 days in courting *10*. Pair formation takes place on the breeding territory after a series of individual and mutual displays (meyerriecks 1959). Snowy egrets exhibit seasonal monogamy but several observations of promiscuity were reported *14*. The pair-bond is maintained by a series of mutual displays and joint nest building *06*. Location of nest may be from ground level - 30 ft. In trees (mean=5-10 ft.) *05,06,12*. It is usually placed in trees or thickets near water, but no particular plant species preferred *16*. Snowy egrets are highly social nesters and are usually (always in Illinois *07*) associated with little blue herons *01,05,06,07*. In mixed colonies the snowy egret may share the same tree with other spp.; Or scatter their nests, interspersing them, but usually placing them lower on limbs or branches *06*. Building materials vary with habitat *08*. Probably little use of old nests exists, but nest site and materials from old nest may be used *06*. The nest is usually a loose affair of sticks and twigs built by both sexes *08*. The male brings sticks to female who does the actual construction *06*. At Lake Alice, Florida, nest completion took from 4-7 days *06,10*. Little or no preliminary ritual exists prior to copulation, which takes place in the nest or very near *06*. Average duration is approximately 10 sec. Eggs are layed: Fla. Jan.-July, usually Apr.-May; Texas Apr.-June; Utah Apr.-May. average clutch size 3-4 (1-6) *05,06,08*. Eggs are pale bluish-green and may be layed on alternate days or as in Florida slightly more than 2 days apart (2.1 +Or- 0.04) *06,13*. Incubation may begin with either the first or second egg (fla. 54% With 1st, 44% with 2nd) *06,16*. Both sexes incubate *04,05,06*. A relieving ritual is performed and may vary in intensity between pairs *06,14*. In early studies incubation was reported to last approximately 18 days but more recent work observed 20-24 days *05,06,08,13*. At hatching young are covered with hair like down and weigh approximately 16.7 gm. *06*. Replacement clutch will be layed if original destroyed *13*. Both sexes feed young *04,06*. Initially food is placed on edge of nest allowing young to grab and possibly develop accuracy with its bill *06,10*. Later young grab parents' bill to stimulate feeding, in typical heron fashion *06*. Young herons leave the nest at 20-26 days spending approximately 3 days learning to fly and procure food *04,05,10*. Breeding may begin at 1 yr. (more information is needed) *06*. Snowy egrets usually rear 1 brood per year *08*.

Behavior: Territories are selected by males alone and are used for hostile and sexual displays, copulation, and nesting *06*. No information exists on territory size, however, the initial size of the males territory is always larger than the subsequent area defended by the pair *06*. Palmer (1962) states a separate feeding territory may be defended *06*. Both sexes defend small area around nest from conspecifics and other species, especially other herons nesting in same colony *06*. Snowy egrets perform many ritualized behaviors as described in Meyerreicks 1960 *11*. Fighting is observed more frequently in snowy egrets than any other North American heron, though physical damage is rare *11*. Snowy egrets are migratory and limited to the western hemisphere *06*. It breeds and winters from central Chile and central Argentina north through South and Central America, the West Indies, and coastal areas of Mexico, and the Gulf and Atlantic coasts of the United States north to New Jersey *04,05,06*. Many individuals return to the same breeding grounds year after year *10,16*. Post-breeding dispersal is common and snowies have been sighted as far north as southern Canada *05,08*. In Illinois, fall populations are much greater than in spring, probably due to an influx from more southern breeding grounds *07*. This influx (post-breeding dispersal) probably begins in July and the number of birds remains relatively high most of August, depending on the availability of foraging sites *07*. Snowy egrets leave Illinois from late August - early September and are usually not seen after 12 September *07*. Foot-stirring, a foraging method, is particularly well developed in snowy egrets *05, 11,14*. The foot is used in a raking or stirring motion to poke and probe in shallow waters. The prey that are disturbed or "lured" to the yellow toes are quickly snapped up *14*.

Limiting factors: Data for limiting factors of snowy egrets is unavailable. In recent years, snowy egret populations have been estimated as approaching or even larger than their numbers prior to persecution *07*. Illinois probably never had a large breeding population of snowy egrets and current estimates suggest the total breeding population is probably less than 50 birds in a high year *07*. The availability of undisturbed nest sites and pollution free wetlands to forage in seem to be the greatest limiting factor to the snowy egret as a breeding bird in Illinois *01*. Predators in illinois seem few: racoons, mustelids, raptors, crows; where as in south, reptiles are a principal predator *03*. In georgia losses to the snowy egret were greatest during nesting stage and only 37% of all nests were successful in fledging at least one young *16*. In georgia, snowy egrets may suffer an annual mortality rate of approximately 52.4% (71.6% in their first year; 31.4% thereafter) *16*. No information on sex ratios is available but since snowy egrets exhibit seasonal monogamy one could assume approximatley 1:1. Much informaiton is needed for the snowy egret in Illinois.

 


MANAGEMENT PRACTICES

Beneficial:

  • Maintaining natural areas and nature preserves
  • Maintaining unique or special habitat features (wetlands, snags, caves, cliffs, talises, etc.
  • Preserving endangered species habitat
  • Preserving sensitive species habitat
  • Performing field survey prior to prescription
  • Controlling land use and human activities
  • Seasonal restriction of human use of habitats
  • Controlling pollution in aquatic habitats
  • Developing/maintaining lakes and ponds
  • Developing/maintaining wetlands
  • Developing/maintaining wetlands
  • Creating/maintaining wetlands from non-wetlands
  • Developing/maintaining mudflats
  • Protecting existing wetlands
  • Protecting existing wetlands
  • Restoration of wetlands (return flooded or drained areas to previous wetland conditions)
  • Developing/maintaining riparian habitat
  • Restricting human disturbance during migration, breeding, and nesting

Adverse:

  • Channelization
  • Dredging
  • Draining ponds/lakes
  • Draining wetlands
  • Strip mining
  • Applying pesticides
  • Clearcutting forests

Existing:

  • Performing field survey prior to prescription
  • Animal management practices other than those included in ifwis list (see comments)

Comments on management practices:
The protection of forage and nest sites from disturbance and human encroachment is critical to the survival of the snowy egret as a breeding bird in Illinois *01*. The snowy egret is protected by the state endangered species act upon its addition to the list in 1977. The snowy egret is also protected by the Migratory Bird Treaty Act of 1918 *21* and the Illinois Wildlife Code *22*.

 


REFERENCES

0. MALMBORG, PATTI L. ILL. NAT. HIST. SURV., 607 E. PEABODY DR., CHAMPAIGN, IL. 61820 (217)333-6846.

1. BOWLES, M. 1981. ENDANGERED AND THREATENED VERTEBRATE ANIMALS AND VASCULAR PLANTS OF ILLINOIS. ILLINOIS DEPT. OF CONS. P. 19.

2. 34TH SUPPLEMENT TO THE AMERICAN ORNITHOLOGIST'S UNION, CHECKLIST OF NORTH AMERICAN BIRDS. SUPPLEMENT TO AUK 99.

3. RYDER, R.A. 1978. BREEDING DISTRIBUTION, MOVEMENTS, & MORTALITY OF SNOWY EGRETS IN NORTH AMERICA. IN SPRUNT, A. IV, J.C. OGDEN & S. WINCKLER. WADING BIRDS. NAT. AUDUBON SOC. RES. REP. NO. 7:197- 205.

4. BENT, A.C., 1926. LIFE HISTORIES OF NORTH AMERICAN MARSH BIRDS. U.S. NAT. MUS. NO. 135. 490 PP. PP. 146-155.

5. TERRES, J.K. 1980. THE AUDUBON SOCIETY ENCYCLOPEDIA OF NORTH AMERICAN BIRDS. ALFRED A KNOPF. NEW YORK.

6. PALMER, R.S. 1962. HANDBOOK OF NORTH AMERICAN BIRDS. VOL. 1. YALE UNIV. PRESS. NEW HAVEN. PP. 456-463.

7. GRABER, J.W., R.R. GRABER, & E.L. KIRK. 1978. ILLINOIS BIRDS: CICONIIFORMES. ILLINOIS NAT. HIST. SURV. BIOL. NOTES NO. 97. 40 PP.

8. SPRUNT, A. & E.B. CHAMBERLAIN. 1970. SOUTH CAROLINA BIRD LIFE UNIV. OF S. CAROLINA PRESS, COLUMBIA. PP. 83-84.

9. STONE, W. 1937. BIRD STUDIES AT OLD CAPE MAY. DELAWARE VALLEY ORNITHOL. CLUB. PHILADELPHIA. PP. 124-126.

10. MCILHENNY, E.A. 1939. THE AUTOBIOGRAPHY OF AN EGRET. HASTINGS HOUSE. NEW YORK. 57 PP.

11. MEYERRIECKS, A. 1960. COMPARATIVE BREEDING BEHAVIOR OF FOUR SPECIES OF NORTH AMERICAN HERONS. THE CLUB. CAMBRIDGE. PP. 125-140.

12. BURLEIGH, T.D. 1958. GEORGIA BIRDS. UNIV. OF OKLAHOMA PRESS. NORMAN. PP. 102-104.

13. MAXWELL, G.R. II & H.W. KALE II. 1977. BREEDING BIOLOGY OF FIVE SPECIES OF HERONS IN COASTAL FLORIDA. AUK 94(4):689-700.

14. MEYERRIECKS, A.J. 1959. FOOT-STIRRING FEEDING BEHAVIOR IN HERONS. WILSON BULL. 71(2):153-158.

15. FORBUSH, E.H. 1929. BIRDS OF MASSACHUSETTS. VOL. I. NORWOOD PRESS, NORWOOD, MASS. P. 330.

16. TEAL, J.M. 1965. NESTING SUCCESS OF EGRETS AND HERONS IN GEORGIA. WILSON BULL. 77(3):257-263.

17. KELLER, C.E. 1966. STATUS OF THE CICONIIFORMES IN INDIANA, INDIANA AUDUBON QUART. VOL. 44. NO. 3. PP. 56-88.

18. BOHLEN, H.D. 1978. AN ANNOTATED CHECK-LIST OF THE BIRDS OF ILLINOIS. ILLINOIS STATE MUS., POP. SCI. SER., VOL. IX.

19. PETERSON, R.T. 1980. A FIELD GUIDE TO THE BIRDS. HOUGHTON MIFFLIN CO., BOSTON. P. 102.

20. KLEEN, V.M. FIELD NOTES, BREEDING SEASON. ILLINOIS AUDUBON BULL. NOS. 195 1980/81 P. 36, NO. 199 1981/82 P. 24, NO. 203 1982/ 83 P. 27.

 


 

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