Illinois Natural History Survey - University of Illinois

Great Blue Heron
Ardea herodias

 

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: Ardea
  • Species: Ardea Herodias
  • Authority: Linnaeus

Comments on taxonomy:
Tribe: Ardeini. According to the Palmer's Map (1962), the morthern half of Illinois is inhabited by A.h. herodias and the southern half by A.h. wardi *05*. Bent(L926) reported A.h. wardi being sighted in southeastern Illinois (Mount Carmel) *16*. Other names: Blue Crane, Big Cranky, Treganza's Heron, Gray Crane, Long John, Poor Joe *04*.

 


OCCURENCE IN ILLINOIS

Early March - late November.
Common migrant and locally common summer resident along major rivers of the state. Uncommon migrant in remainder of state. Winter resident in south, occasional winter resident in central and rare winter resident in northern Illinois *01*.

1982-83 breeding season *21*:

  • Rend lake - 200 nests
  • Clear lake - 170 nests
  • Volo - 110 yng 2 July, 71 yng 7 July
  • Otter I - 70 nests
  • New Boston - 60 nests
  • Little Black Slough - 45 nests
  • Union Co. conserv. area - 14 nests
  • Lake Renwick - 22 yng
  • Marshal Co. conserv. area - 50 nests

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

State Status:

Endangered Threatened Proposed

Other:

Game Furbearer Nongame protected
Sportfish Commercial Pest None of the above

Comments on Status:
During breeding season, nesting great blues are now found primarily on major rivers. Great blue herons away from colonies may be found in all parts of the state in almost any month. It is now eivdent that this species is experiencing a decline in Illinois. 25 colonies censused each year from 1974-76 indicate a 39% decline with a progressive loss of 12-18% per year (nesting birds). Causes cannot be determined without detailed studies *03*. The great blue heron is considered migratory and protected under the Migratory Bird Treaty Act of 1918 *23*. Also, A. herodias is protected under the Illinois Wildlife Code of 1972 *24*.


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
Northern white cedar Mature
(9" dia. & 100 yrs. old)
all
(0-100%)
spring/summer
Oak-hickory Mature
(9" dia. & 100 yrs. old)
all
(0-100%)
spring/summer
Oak-gum-cypress Mature
(9" dia. & 100 yrs. old)
all
(0-100%)
spring/summer
Elm-ash-cottonwood Mature
(9" dia. & 100 yrs. old)
all
(0-100%)
spring/summer

Associated tree species:

  • Cottonwood
  • Silver maple
  • Sycamore

National wetland inventory classifications:

SystemSubsystemClassSubclassWater regime modifiersWater chemistry
Lacustrine Littoral Emergent vegetation Persistent Intermittently exposed/
Permanent nontidal
Freshwater
Lacustrine Littoral Emergent vegetation Non-persistent Intermittently exposed/
Permanent nontidal
Freshwater
Palustrine   Unknown Unknown Intermittently exposed/
Permanent nontidal
Freshwater
Palustrine   Emergent vegetation Persistent Intermittently exposed/
Permanent nontidal
Freshwater
Palustrine   Emergent vegetation Non-persistent Intermittently exposed/
Permanent nontidal
Freshwater
Palustrine   Forest Dead trees Intermittently exposed/
Permanent nontidal
Freshwater
Palustrine   Forest Deciduous Intermittently exposed/
Permanent nontidal
Freshwater
Palustrine   Forest Evergreen Intermittently exposed/
Permanent nontidal
Freshwater
Riverine Lower perennial Emergent vegetation Persistent Intermittently exposed/
Permanent nontidal
Freshwater
Riverine Lower perennial Emergent vegetation Non-persistent Intermittently exposed/
Permanent nontidal
Freshwater
Riverine Lower perennial Flat Mud Intermittently exposed/
Permanent nontidal
Freshwater
Riverine   Unknown Unknown Intermittently exposed/
Permanent nontidal
Freshwater

Comments on species-habitat associations:
In Illinois, great blue herons almost invariably nest in bottomland forest habitat and usually within extensive tracts and not usually at the edge *03*. Nesting trees are usually typical floodplain species (cottonwood, sycamore, silver maple, etc.) *03*. Most nesting colonies are found on major rivers of Illinois, but birds away from colonies may be found almost anywhere *03*.

Important plant and animal association: No comments

High value habitats

HabitatStructural stageSeason
Forest land Mature
(9" dia. & 100 yrs. old)
Fall
Forest land Mature
(9" dia. & 100 yrs. old)
Spring/summer
Water Not applicable
(HVAL-HAB cover)
All
Wetland Special habitat All
Floodplain forest Mature
(9" dia. & 100 yrs. old)
Fall
Floodplain forest Mature
(9" dia. & 100 yrs. old)
Spring/summer
Wet floodplain forest Mature
(9" dia. & 100 yrs. old)
Fall
Wet floodplain forest Mature
(9" dia. & 100 yrs. old)
Spring/summer
Wet prairie Special habitat All
Marsh Special habitat Fall
Marsh Special habitat Spring/summer
Swamp Special habitat Fall
Swamp Special habitat Spring/summer
Shrub swamp Special habitat Fall
Shrub swamp Special habitat Spring/summer
Lakes and ponds Not applicable
(HVAL-HAB cover)
All
Large river Not applicable
(HVAL-HAB cover)
All

Species-habitat interrelations: See comments for species-habitat associations. When nesting, size of trees appear an important factor. This species usually nests in the largest tree available *03*.

 


GUILDS

Feed-guilding:

HabitatStructural stageSeasonFeed-guilds
Wet prairie Special habitat All Terrestrial surface-Arthropods
Terrestrial surface-Invertebrates other than arthropods
Terrestrial surface-Amphibians
Terrestrial surface-Reptiles
Terrestrial surface-Birds
Terrestrial surface-Large mammals (>1 kg)
Wetland 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-Unconsolidated bottom, birds
Water bottom-Unconsolidated bottom, mammals
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 bottom-Aquatic bed, birds
Water bottom-Aquatic bed, mammals
Water column-Arthropods
Water column-Invertebrates other than zooplankton or arthropods
Water column-Fish
Water column-Amphibians
Water column-Reptiles
Water column-Birds
Wetland All Summer/fall Water column-Mammals
Water surface-Arthropods
Water surface-Invertebrates other than zooplankton or arthropods
Water surface-Fish
Water surface-Amphibians
Water surface-Reptiles
Water surface-Birds
Water surface-Mammals
Wetland Special habitat All Terrestrial surface-Arthropods
Terrestrial surface-Invertebrates other than arthropods
Terrestrial surface-Amphibians
Terrestrial surface-Reptiles
Terrestrial surface-Birds
Terrestrial surface-Large mammals (>1 kg)

Comments on feed-guilding:
The great blue heron feeds in wetland situations, shallow waters, but also forages in open meadows and fields *05,16*.

Breed-guilding:

HabitatStructural stageSeasonBreed-Guilds
Floodplain forest All Summer/fall Tree canopy, large branches of live broad-leaved deciduous trees
Tree canopy, large branches of live needle-leaved deciduous trees
Tree canopy, large branches of live broad-leaved evergreen trees
Tree canopy, large branches of live needle-leaved evergreen trees
Tree canopy, large branches of dead broad-leaved deciduous trees
Tree canopy, large branches of dead needle-leaved deciduous trees
Tree canopy, large branches of dead broad-leaved evergreen trees
Tree canopy, large branches of dead needle-leaved evergreen trees
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

Comments on breed-guilding:
Copulation takes place in the nest or very near to it *03,05,09,14*. Nests are typically placed in the tallest trees available, but will nest in low shrubs *04,16*.

 


FOOD-HABITS

Trophic level is CARNIVORE.

Food itemLife stage/plant part
Invertebrates Unknown
Annelida: hirudinea (leeches) Unknown
Malacostraca (isopods, amphipods, crayfishes) Unknown
Insecta Unknown
Odonata (dragonflies, damselfiles) Unknown
Orthoptera (grasshoppers, crickets, cockroaches) Unknown
Osteichthyes (bony fishes) Unknown
Semionotiformes (gars) Juvenile
Amiiformes (bowfin) Juvenile
Anguilliformes (American eel) Unknown
Clupeformes (herrings) See comments
Clupeformes (herrings) Unknown
Salmoniformes (trouts, salmons, smelts, pikes) Unknown
Cypriniformes (carps, minnow, loaches) See comments
Cypriniformes (carps, minnow, loaches) Unknown
Siluriformes (catfishes) Unknown
Perciformes (basses, sunfishes, perches, sculpins) See comments
Perciformes (basses, sunfishes, perches, sculpins) Unknown
Amphibians Unknown
Caudata (salamanders, newts, mudpuppies, sires, hellbenders) Unknown
Salientia (frogs, toads) See comments
Salientia (frogs, toads) Unknown
Reptiles Unknown
Serpentes (snakes) Unknown
Mammals Unknown
Soricidae (shrews) Unknown
Leporidae (rabbits, hares) Unknown
Sciuridae (squirrels, chipmunks, marmots, prairie dogs) Unknown
Geomydae (pocket gophers) Unknown
Cricetidae (woodrats, mice, voles, lemmings, muskrats) Unknown
Muridae (Norway rat, house mouse) Unknown
Rallidae (rails, coots) Unknown
Important:
Clupeformes (herrings) See comments
Cypriniformes (carps, minnow, loaches) See comments
Perciformes (basses, sunfishes, perches, sculpins) See comments
Juvenile:
Clupeformes (herrings) Unknown
Cypriniformes (carps, minnow, loaches) Unknown
Perciformes (basses, sunfishes, perches, sculpins) Unknown
Adult:
Invertebrates Unknown
Annelida: hirudinea (leeches) Unknown
Malacostraca (isopods, amphipods, crayfishes) Unknown
Insecta Unknown
Odonata (dragonflies, damselfiles) Unknown
Orthoptera (grasshoppers, crickets, cockroaches) Unknown
Osteichthyes (bony fishes) Unknown
Semionotiformes (gars) Juvenile
Amiiformes (bowfin) Juvenile
Anguilliformes (American eel) Unknown
Clupeformes (herrings) Unknown
Salmoniformes (trouts, salmons, smelts, pikes) Unknown
Cypriniformes (carps, minnow, loaches) Unknown
Siluriformes (catfishes) Unknown
Perciformes (basses, sunfishes, perches, sculpins) Unknown
Amphibians Unknown
Caudata (salamanders, newts, mudpuppies, sires, hellbenders) Unknown
Salientia (frogs, toads) Juvenile
Salientia (frogs, toads) Adult
Reptiles Unknown
Serpentes (snakes) Unknown
Mammals Unknown
Soricidae (shrews) Unknown
Leporidae (rabbits, hares) Unknown
Sciuridae (squirrels, chipmunks, marmots, prairie dogs) Unknown
Geomydae (pocket gophers) Unknown
Cricetidae (woodrats, mice, voles, lemmings, muskrats) Unknown
Muridae (Norway rat, house mouse) Unknown
Rallidae (rails, coots) Unknown

Comments on food habits: 
General: In Illinois, gizzard shad and carp compromise >50% of a young grest blue heron's diet with over 80% being of gizzard shad, carp, buffalo and sunfishes *03* (this may not reflect samer prooprtions in adult diet). Size of prey varies from a few centimeters to >14 inches *15*. It is suggested this species will feed on anything it can swallow *13* and accepts whatever is most easily available *16*.
Juvenile: Fish are important in the diet of young birds *03,16*. Particular species depend on location and availability. For Illinois, gizzard shad, carp, buffalo and sunfish seem important *03*. The food of juveniles resembles that of adults. Size increases with age of young *03*.
Adult: Adult great blue herons seem opportunistic. Depending on foraging territory held, location of feeding areas and availability, individuals may consume a wide variety of food items *13,16*.

 


ENVIRONMENTAL ASSOCIATIONS

General:

  • Biodegradable organics: Clean waters that have not been polluted
  • Aquatic habitat: Shallows with emergent vegetation (littoral zone)
  • Water level: See comments
  • Flood plain: See comments
  • Aquatic habitats:
    • Island inhabitant
    • Embayments
    • Sloughs, bayous
    • Ditches
    • Prairie potholes
    • Riffles
    • Swamp
    • See comments
    • Marsh
    • Backwaters
  • Ecotones: Woodland/water
  • Grassland: See comments
  • Meadows: See comments
  • Shrubs: See comments
  • Coniferous forest: See comments
  • Hardwood forest: See comments
  • Overstem trees, ave. height: See comments
  • Overstem trees, ave. DBH: See comments
  • Size of continuous forested land: See comments
  • Vegetation successional stage: Climax forest
  • Human associations: Wildlife refuges/sanctuaries
  • Unknown

Limiting:

  • Biodegradable organics: Clean waters that have not been polluted
  • Flood plain: See comments
  • Aquatic habitats: See comments
  • Size of continuous forested land: See comments

Egg

  • Unknown

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:

  • Flood plain: See comments
  • Coniferous forest: See comments
  • Hardwood forest: See comments
  • Size of continuous forested land: 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:

  • Flood plain: See comments
  • Coniferous forest: See comments
  • Hardwood forest: See comments
  • Size of continuous forested land: See comments

Breeding adult:

  • Biodegradable organics: Clean waters that have not been polluted
  • Flood plain: See comments
  • Aquatic habitats: See comments
  • Overstem trees, ave. height: See comments
  • Overstem trees, ave. DBH: See comments
  • Size of continuous forested land: See comments

Comments on environmental associations:
General: Great blue herons frequent many wetland situations, meadows, fields, etc., but almost invariably nest in flood plain forests *03*. Great blue herons respond unfavorably to pollution, habitat destruction and human disturbance. Great blue herons require large tracts of floodplain forest in which to nest and the availability of undisturbed, unpolluted wetlands in which to forage *03,18,19*. Both habitats are essential. It is suggested that the great blue heron (and other species) has a particular association with the natural floodplain sequence in which lagoons are filled by spring floods on major streams, dry back as summer progresses, and concentrate fish populations as the flood requirements of nestlings reach their peak *03*.
Feeding juvenile: Upon fledging, juveniles adopt adult feeding habits and share same requirements. This species seems opportunistic and depending on habitat characteristics, forage on many food items *13,16*. Fish apparently are important in the diet of nestlings, therefore, unpolluted, undisturbed wetland situations must be available to adults *03,18,19*.
Resting juvenile: Juveniles roost in branches of tress near nest site, usually in floodplain forest or in trees outside of breeding season *04,LL*. Nests are usually placed in the largest trees available, but may be in shrubs or on ground *05*.
Feeding adult: Adults seem to feed opportunistically and take advantage of the availability of particuilar food items *13,16*. Fish apparently are their principal food item. Therefore, unpolluted, undisturbed wetland situations are essential *03,16,18*.
Resting adult: Adults perch in trees and during breeding season perch on branches near nest (if not incubating) *see card *7485* *03*.
Breeding adult: The great blue heron perfers to nest in trees and selects the tallest trees available *03,16*. This species requires relatively undisturbed fishing as well as nesting sites, therefore, in Illinois most larger heronries are located within extensive tracts of bottomland forest *03*.

 


LIFE HISTORY

Origin: Native *01*

Physical description: Height to 4 ft. tall. 42-52 inches long, wingspread to 7 ft. Weight 5-8 lbs. (males average larger). Tall long-legged, long-necked heron. Appears grey-blue except for white feathers around head and neck. Head and most of crown white in adults with sides of crown down to eyes black. Usually 2 occipital plumes to approx. 9 inches cinnamon on neck. Dagger-like bill *03,05,22*.

Reproduction: Most breeding data from Illiniois was taken at Crab Orchard Lake. The great blue heron appears in Illinois in late Feb. with most of the breeding population returning after 12 March and into April *03*. Upon arrival from winter range they proceed almost immediately to their nesting colonies *03,05*. In the Florida Bay area, the observance of dancing ground behavior is the first sign of breeding activity *05*. Apparently the male selects a territory which preferably contains an old nest *O5,14*. The territory is used for hostile and sexual displays, copulation and nesting *05*. The male begins to display, attracting females, but repelling them. Eventually the male allows 1 female onto the nest *14*. Copulation can occur anytime after the female is accepted onto the nest and is repeated irregularly until eggs are layed *14*. Copulation occurs nearly always on nest or nearby, duration 12-15 seconds *03,05,09,l4*. Precopulatory displays have been observed but may also occur with little or no display *03,05*. Mutual displays during nest building and later phases help maintain pair bond *05*. At the Sabula colony in Illinois, both membres brought sticks to the nest *03*. Elsewhere it is reported that the male gathers the sticks and give them to the female who adds them to the old nest or constructs a new nest *05,14*. Twig passing involves ritualized display *11*. The male may add some material to nest prior to pair formation. The nest is a stick structure ranging from flimsy to sturdy depending on when constructed and how many years it has been reused *03,05*. Nest site depends on the habitat. In Illinois this species almost invariably nests in bottomland forest habitat *03*. When nesting in forested areas, typically nest in tops of tallest trees available, 21m (14-29) nest height mean, but there are many exceptions *03,05,16*. Nest construction took 3 days in Mich. but is unknown for Illinois *O5*. Time elapsed between arrival and the onset of laying was nearly 1 a month at Crab Orchard Lake *03*. Laying season in ME. (lt. April), Mich. (lt. March), Calif. (m. March), Fla. (Nov.-April) and 25 March-17 May for Illinois *03,04,05,09*. Incubation is reported to begin with first egg, 1st or 2nd egg or not with first but definitely before last egg *03,05,09,16*. Duration is approximately 28 days (25-29) and performed by both sexes *03,05,09,14,16*. Eggs are pale blue green (64.5 x 47.6 mm) and the most common number is 4 (3-9) *03,04,05,16*. In Calif. the most likely interval between eggs is 2 days. Hatching time from 1st egg to last was 5-8 days *09*. The incubating bird sometimes rolled eggs, in Calif. timing was variable, Terres (1980) reports on the average of 1/2 hrs. *04, 09*. Newly hatched chicks are covered with pearl grey down *11, 16*. The first food observed in Illinois were very small fish (approx. 5 cm) which were regurgitated several at a time into the nest *03*. Bent (1926) reports young are first fed soft regurgitated food directly into mouth and later more solid food (whole fish) was regurgitated into the nest *16*. In California all ages were fed by dropping food into the nest *09*. By the end of their 3rd week young grab parents' bill in typical heron fashion to stimulate regurgitation *09*. New hatchlings were brooded constantly for about 1 week aftyer hatching and by approx. 25 days parents just return to feed them *03,09,14*. After hatching parents' only contact is at nest relief *14*. At 3 wks. young stand erect in nest, approx. 5 weeks begin to walk on limbs of nest tree and fly short distances at 7 wks. *03*. At 5 weeks young birds weigh approx. 4 lbs. *O5*. In Calif. nestlings abandoned nest between 64 and 91 days (mean=81) *09*. The parents' bond may weaken or disintegrate entirely by fledging and independence of young *14*. Great blue herons are single brooded and will lay replacement clutches *O5*. It is generally thought that breeding occurs in 2nd or 3rd year *O5,11,16*. Pratt (1973) reports 2 attempts of first year birds breeding with older birds. Neither attempt was successful *12*. Merrit (L983) suggest young great blue herons "practice" in their 1st and 2nd years *11*. Gross estimates on productivity for Illinois are approx. 2.3 yng/nest in norhtern and central Illinois and 2.5 yng/nest in southern Illinois *03*. In northern Wisc. 2-3 yng were produced per nest *15*. In Oregon 2.43 yng were produced per nest *18*.

Behavior: The great blue heron has both migratory and resident populations in North America. Most of the breeding population in Illinois (if not all) is migratory, appearing in lt. Feb. with peak numbers arriving after 12 March *03*. This species nests colonially and also singly. Great blues perfer to nest in extensive tract of bottomland forest and measurements for 28 of the largest extant (or recently) colinies in Illinois is approx. 103-1969 ha (mean=608 ha) *03*. In Oregon the mean area of 7 heronries was 36.8 ha (1-114) *18*. In Oregon, 24 of 31 heronries were located within 100m of known feeding areas *18*. In Minn. feeding territories ranged from 13.7-34.1 km from nesting colonies *07*. There is a rough correlation between the nesting heron population in Ilinois and the amount of surface water available (r=0.592) and perhaps backwaters, characteristic of the major rivers in Illinois, would be better correlated *03*. Great blue herons are territorial in both breeding and non-breeding seasons. Males choose and defend breeding territories upon arrival on breeding areas *05,14*. It is suggested the area defended by the male decreases up to the time of pair formation, but more information is needed. In Florida, the size of a territory depended on the habitat and stage of reproductive cycle *05*. After pair formation, the male and female share in territorial defense which is almost exclusively directed against other great blue herons or great egrets *05*. In non-breeding season, this species is known to defend feeding territories *05,07,17*. Lengths of actively defened shoreline in Minn. ranged from 0.60-1.37 km (mean=0.98) *07*. In Oregon (resident population), some feeding territories were maintained year after year, up to 3 years of the study *17*. Home range sizes are unavailable, but great blue herons were seen foraging near and also 10 km away from colony sites *03*. Post-breeding dispersal is common in the great blue heron. Palmer (L962) reports dispersal occurs in all compass directions, beginning after young can fly *05*. In Illinois, dispersal occurs with a trend toward the north in lt. July and August, with some birds lingering in the north until lt. in Oct. *03*. Southward migration occurs in Sept. and Oct., with most of the popultaion through Illinois by the end of Oct., though some individuals may linger well into Dec. *03*. Peak fall numbers in S. Illinois occur from 1 Aug.-20 Sept. and in north and central Illinoid from 16 Aug.-20 Sept., ration of spring to fall numbers for the entire state is 1:3.05 (1967-1970) *03*. Great blue herons feed at night as well as during the day *04,09,16*. Its usual hunting method is to stand motionless in shallow water and wait until prey comes within striking distance. This species is very wary but is highly adaptable, fishing in suburban ponds, around fishing docks and even in back yards *05*. This species is also known to feed in fields far from water *04,05*. Here, meals are made of insects and small mammals. Great blues usually forage in a habitat in which they hold a territory and food items depend on the territory held (terrestrial-aquatic) *07*. Great blue herons are very wary of humans and usually try to nest in remote and inaccessible area *16*. Shortly after their arrival in spring, this species is very alert to the presence of man *05*.

Limiting factors: Adult great blue herons seem to have no natural predators because very few would attack such a large bird *16*. Great damage, however, is done to their eggs and nestlings by crown, ravens, all raptors, probably gulls and racoons. This species' gravest enemy is man. The great blue heron population is experiencing a progressive loss of 12-18% per year (known up to 1978) *03*. Causes cannot be determined without detailed studies but contributing factors are suggested. Agriculture, through deforestation of large areas, draining of wetland areas and application of pesticides has decreased both foraging and nesting habitat, which is probably the most critical limiting factor to this species *03,18*. Cutting of heronry sites has been recorded in Marshall, Tazewell, Massac, and Union counties *03*. Logging of extensive tracts of timber decreases the protective factor from outside disturbance and wind storms *03*. In Illinois, banding recoveries are instructive in showing that this species seeks isolation from humans. Humans flock to waterways during the summer when young herons need the most food. Together with poaching and vandalism, human pressure may already exceed what some Illinois populations can tolerate *03*. If we are to conserve the remnant nesting population of great blue herons in Illinois, colony sites and fishing areas must be located and protected, even to the point of eliminating human traffic during the breeding season and migration *03*.

Population parameters: The great blue heron is perhaps the most widely distributed of all herons and breeds throughout much of North America *03,16*. This species continues to maintain its numbers throughout its range except locally where heronries are abandoned because of habitat destruction *03*. In Illinois, breeding populations are now confined to only the major rivers of the state *03*. From banded birds, the average age at death is approx. 2 years for Illinois. Survival is poorest in the first 6 months of life, when mortality is 60%. Great blues experience a total mortality of 64% for their first year *03*. This is explained as a cost of inexperience and lack of wariness toward humans. After the first year, mortality then drops to an average of 24% per year for Illinois *03*. Figures given by Owen (1959-60) for all Canada and U.S. are 71% mortality in the first year after which the average annual mortality decreases to 29% per year *06*. Bayer (1981) has shown that great blue herons in refuges have greater longevity than those in the wild and depending on their proportion in your sample (more birds in refuges west of 100 degrees longitude than east of 100 degrees) longevity calculations will vary *10*. Owen (1959-60) reports life expectancy after leaving the nest is approx. 1.5 years, but once an individual has reached the beginning of his second year, expectancy of further life is 2.9 years *06*. The survival rate (productivity) calculated by Owen (1959-60) assuming reproduction begins in 2nd year, would have to be 2.8 great blue heron young per nest to sustain a popultaion. The best productivity estimated for Illinois is 2.5 young per nest, which implies a loss of 3% per year (gross estimates in north and central: Illinois 2.3/nest, southern Illinois: 2.5/nest) *03,06*. In 1947 a heronry at Rockford produced 3.0/nest *03*. No information is available on sex ratios and the best possible age ratio for Illinois is 1 adult:1.25 juveniles (based on 2.5 young/nest) *03*. The oldest bird recorded was 21 years old *06*. The oldest bird recorded in Illinois was 14 yrs. 3 mos *03*.

 


MANAGEMENT PRACTICES

Beneficial:

  • Maintaining undisturbed/undeveloped areas
  • Maintaining natural areas and nature preserves
  • Maintaining unique or special habitat features (wetlands, snags, caves, cliffs, talises, etc.)
  • Preserving sensitive species habitat
  • Performing special survey prior to prescription
  • Performing field survey prior to prescription
  • Controlling land use and human activities
  • Seasonal restriction of human use of habitats
  • Controlling pollution
  • Controlling sedimentation
  • Controllind pollution in aquatic habitats
  • Creating artificial islands of rafts
  • Maintaining streams
  • Developing/maintaining lakes and ponds
  • Creating/maintaining islands with permanent impoundments
  • Developing/maintaining wetlands
  • Creating/maintaining wetlands from non-wetlands
  • Developing/maintaining mudflats
  • Maintaining bogs
  • Protecting existing wetlands
  • Restoration of wetlands (return flooded or drained areas to previous wetland conditions)
  • Developing/maintaining riparian habitat
  • Maintaining forests
  • Restricting human disturbance during migration, breeding, and nesting
  • Maintaining large trees for denning, nesting, or roosting
  • Developing islands for waterfowl

Adverse:

  • Recreational development
  • Channelization
  • Navigational improvements such as channelization and locks and dams
  • Dredging
  • Draining ponds/lakes
  • Draining wetlands
  • Applying pesticide on agricultural land
  • Strip mining
  • Applying pesticides
  • Cutting and deforestation
  • Clearcutting forests
  • Removal of old trees

Comments on management practices:
If we are to conserve the remnant nesting population of great blue herons in Illinois, their colony sites and fishing areas must be protected *03*. It is first important to locate major foraging are as for each colony *03*. These areas must be protected from human encroachment, disturbances and pollution *03*. Sanctuaries are the best method for habitat protection *19*. Dredging and channelization cause waters to become murky and disrupt the natural floodplain sequence in certain areas, decreasing prime foraging ans nesting habitat. Great blues also require undisturbed nesting sites *03*. Forestry practices of cutting the largest trees selects against the great blue heron *03*. The break-up of extensive tracts of timber may reduce concealment and protection from high winds which, because of the heron's great weight, destroys many nests and contents *03*. In Illinois agriculture, through complete deforestation of large areas, draining of heron foraging areas and application of persistent pesticides has destroyed essential habitat *03*. Great blue herons are susceptible to hyrdocarbon pollution *03,18*. During breeding season, herons are very sensitive to disturbance *18*. It maybe beneficial to regenerate riparian (floodplain) forest habitat and preserve other riparian areas for alternate use *18*. Also, sites should be protected permanently, not only when birds are present *18*. Poaching and ruthless killing should be stringently controlled.

 


REFERENCES

0. Malmborg, Patti L., INHS

1. Bohlen, H.D. 1978. An Annotated Checklist of the Birds of Illinois. IL State Museum., Pop. Sci. ser. vol. IX. pp 17-18.

2. Bowles, M. 1981. Endangered and Threatened Vertebrate Animals and Vascular Plants of Illinois. IL Dept. of Conserv. pg. 35.

3. Graber, J.W., R.R. Graber and E.L. Kirk. 1978. Illinois Birds: Ciconiiformes, Biological Notes no. 109. INHS. pp. 5-20.

4. Terres, J.K. 1980. The Audubon Society Encyclopedia of North American Birds. Alfred A. Knopf. p. 499.

5. Palmer, R.S. 1962. Handbook of North American Birds. Vol. I. Yale University Press. New Haven. pp. 391-403.

6. Owen, D.F. 1959. Mortality of the Grest Blue Heron as Shown By Banding Recoveries. AUK 76:464-470.

7. Peifer, R.W. 1979. Great Blue Herons Foraging for Small Mammals. Wilson Bull. 91(4):630-631.

8. Willard, D.E. 1977. The Feeding Ecology and Behavior of Five Species of Herons in Southeastern New Jersey. Condor 79:462-470.

9. Pratt, H.M. 1970. Breeding Biology of Great Blue Herons and Common Egrets in Central California. Condor 72:407-416.

10. Bayer, R.D. 1981. Regional Variation of Great Blue Heron Longevity. J. Field Orinthol. 52(3):210-213.

11. Merrit, M.A. 1983. Ontogeny of Behavior in the Great Blue Heron (Ardea heroidas). MS.S thesis, Ohio State University. 119 pp.

12. Pratt, H.M. 1973. Breedgin Attempts by Juvenile Great Blue Herons. AUK 90:897-899.

13. Dennis, C.J. 1971. Observations on the Feeding Behavior of the Great Blue Heron. Passenger Pigeon 33(2):166-172.

14. Mock, D.W. 1976. Pair-formation Displays of the Great Blue Heron. Wilson Bull. 88(2):185-230.

15. Kirkpatrick, C.M. 1940. Some Foods of the Young Great Blue Herons. Amer. Midl. Natur. 24:594-601.

16. Bent, A.C. 1926. Life Histories of North American Marsh Birds. U.S. Nat'l Mus. Bull. No. 135. pp. 101-131.

17. Bayer, R.D. 1978. Aspects of an Oregon Estuarine Great Blue Heron Population. pp.213-217 in Wading Birds (Eds.) A, Sprunt, J. Ogden and S. Winckler Res. Rept. No. 7. National Audubon Society, NY.

18. English, S.M. 1978. Distribution and Ecology of Great Blue Heron Colonies on the WIliamette River, Oregon. pp. 235-244 in Wading Birds (Eds.) A, Sprunt, J. Ogden and S. Winckler Res. Rept. No. 7. National Audubon Society, NY.

19. Anderson, J.M. 1978. Protection and Management of Wading Birds. pp. 99-103 in Wading Birds (Eds.) A, Sprunt, J. Ogden and S. Winckler Res. Rept. No. 7. National Audubon Society, NY.

20. 34th Supplement to the Maerican Orinthologist's Union's Check-list of North American Birds. Supplement to AUK vol. 99.

21. Kleen, V. 1982/83. Field Notes: Breeding Season. Illinois Audubon Bulletin #203. Illinois Audubon Society, Wayne. pg. 27.

22. Peterson, R.T. 1980. A Field Guide to the Birds. Houghton Mifflin Co., Boston. pg. 100.

23. U.S. Fish and Wildlife Service. 1983. Code of Federal Regulations. Title 50. Wildlife and Fisheries. Chapter 1. pp. 11-18. 50CFR10.13. List of Migratory Birds. Special Publ. Federal Register. General Services Admin. October 1.

24. Illinois Department of Conservation. 1980. Conservation Laws. Ch. 61. Wildlife. Art. II. Par. 2.2. Reprinted from Illinois Revised Statutes, 1979. West Publ. Co., St. Paul. MN. 123 pp.

 


 

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